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/I {WB 8 SS 1 FS} D
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/SM {WB 13 SS /FN Fp D 0 FS} D
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/SY {WB -1 SS -1 FS} D
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/ES {WB /SL SL 1 sub NN D /CF 0 D /FN FO SL get D SZ SL get FR SL get FS ()Ec}D
/FZ {3 sub 1.2 E exp GS mul E WB TL /C1 C1 ( Cp ) join D /SL SL 1 add D 0 FS} D
/Ef {WB TL ()ES /C1 C1 ( Cp ) join D} D
/BZ {dup /Bf E D FZ}D
/Sc {dup -1 ne Cf and{/CL CL 1 add D dup 0 eq{pop [0 0 0]}if
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/eM {/C1 C1 ( k2 ) join D}d
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/k2 {gsave 3 LW -9 CP E pop Ts 0.2 mul sub M -9 YC L stroke grestore /mF f D}d
/Ac {/AC E D WB}d
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/Es {ES /Io Io 1 sub NN D /Yo OV Io get D SO} D
/SB {/N2 0 D 0 1 NI{/N E D{IX N2 get 0 lt{/N2 N2 1 add D}{exit}ie}loop
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 {/L1 E D ma YA gt{/YA ma D}if mb YB gt{/YB mb D}if}ie /TB f D
 OU{CP E pop YS sub LE neg lt Fl not and PB not and{NP /YA ma D /YB mb D}if
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 ty 4 eq{X ST cvs ( ) join Y ST cvs join ( ) join E join}if C1 E join
 ( DI ) join FP 2 eq FP 1 eq AF and or{( FM ) join}if
 ( Il Cp ) apa /C1 E D /EN f D}if /HM t D /T f D} D
/DI {II /Xc CP /Yc E D D /YN YW neg D /HM t D /CI 0 D /K2 IX K get D gsave
 TY 4 eq{OX X IS mul add OY FY add YS sub Y IS mul sub}
 {/FY YS D CP MB sub 2 copy /OY E D /OX E D}ie
 translate K2 0 ge{/DP AZ K2 get D /BV BM K2 get D XS YS scale /N 0 D XW YW DP
 [XW 0 0 YN 0 YW] {IP} FC K2 get 1 eq{image}{f 3 colorimage}ie}
 {EX}ie grestore XS 0 R /Ms t D} D
/FM {gsave 0 Sg CP MB sub translate XS neg 0 M 0 YS RL XS 0 RL 0 YS neg RL
 XS neg 0 RL stroke grestore} D
/NA {/AT E D /AL AL 1 add D AV AL AT put} D
/OA {AL 0 gt{/AL AL 1 sub D /AT AV AL get D}if} D
/D1 {/BR {CP E pop E BN Mb{CP E pop eq{0 YI R}if}{pop}ie} D
 /Sn {OU{C1 E ST cvs join ( Ld ) join /C1 E D}{pop}ie} D} D
/D1 {/BR {BN} D /Sn {OU {C1 E ST cvs join ( Ld ) join /C1 E D} {pop} ie} D} D
/TC {/TF t D /ML 0 D HN{SW pop dup ML gt{/ML E D}{pop}ie}forall NP /RM RM not D
 RC /OU Tc D Ep /PN 0 D Ms not TP and{Ip}if /W IW ML sub Ts sub D
 /A0 0 D TH{/BR {( ) join BT} D /Sn {pop} D /Au () D}if} D
/TN {0 eq{E EA PF HF or not XR and{HN E get Xr}{pop}ie}
 {OU{Tn 0 ge{() BN}if /Tn E D}{pop}ie WB}ie} D
/NT {OU LB not and Tn 0 ge and{PL 0 eq{Ms not{CS CF FS}if CP dup
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/Ld {/DN E D HN DN Pn put [/View [/XYZ -4 Fl{PS}{CP YA add US E pop}ie null]
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/C {ND 1 eq{1 sub}if TI mul /XO E D NL Nf not{pop()}if 0 3 -1 roll 1 A} D
/OP {BP not{NP}if PN 2 mod 0 eq{/Ms t D NP}if}D
/Ep {Xp PN 2 mod 0 eq and OU and{/Pn (-) D showpage /PM 1 D LA}if}D
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/Rd [0 [1 1 0][2 1 0][3 1 0][2 1 1][1 1 1][2 2 1][3 3 1][4 4 1][2 1 2]] D
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 c 96 le m 0 gt and{c 32 le {/i 0 D /d 77 D /l 100 D /m m j 1000 mul sub D
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   n 0 gt {/x Rd n get D x 0 get -1 1 {pop p i d c add put /i i 1 add D}for
   p i x 1 get sub Dg x 2 get j add get c add put}if /l l 10 idiv D
  }for p 0 i GI}
  {/i ST length 1 sub D m {1 sub dup 0 ge{dup 26 mod c add 1 add
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 {m p cvs}ie} D
/US {matrix currentmatrix matrix defaultmatrix matrix invertmatrix
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/Tl {/Rn E D Xc CP pop ne{
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/Il {/Rn E D [/Rect [Xc Yc GB Xc XS add Yc YS add GB] /Subtype /Link
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 {/Action [/Subtype /URI /URI Rn] Cd}ie /ANN pdfmark} D
/XP {[{/Z Bz 2 div D Z 0 R Z Z RL Z neg Z RL Z neg Z neg RL Z Z neg RL
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/O {BN()Sm BX} D
/O {BN()0 Sm BX} D
/BX {/Bt E D Bt 2 lt{/Ch E D CS 0.8 mul}{11 mul}ie W XO sub MR sub
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 ( ) Pd /PF f D Bt 2 lt{YA CS .8 mul lt{/YA CS .8 mul D}if}
 {YB 5 lt{/YB 5 D}if YA 21 lt{/YA 21 D}if}ie /CI 0 D} D
/Bx {dup 2 eq{E /Bz E D}{E /cH E D /Bz CS .8 mul D}ie
 OU {gsave 0 Sg XP E get exec stroke grestore}{pop}ie Bz 0 R /Ms t D}D
/SD {FD 4 mul Dy add DZ NF newpath 0 0 M DX t charpath pathbbox
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/Pt {/tp t D Tp{NP /Pn (TP) D 0 Tt neg R Th BN NP Ep ET RC ZF}if /tp f D} D
/RC {/AI 0 D /LG 0 D /BC 0 D /UI 0 D /PF f D /Cc 0 D /cC 0 D /Dc 10 array D
 /NR [0 1 9{pop 0}for] D /La Ds D /AR 10 array D /TR 10 array D /AV 30 array D
 SI /AL -1 D /AT A0 D AT NA /OV 9 array D /Yo 0 D /Co 0 D /Io 0 D /Hy f D
 /Ph f D /CL -1 D Ct Sc}D
/ZF {/FR [0 1 30{pop 0}for] D /SZ [0 1 30{pop 0}for] D /FO [0 1 30{pop 0}for] D
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/QO [[(\234)(\233)(\253\240)(\232)(\273)(\253)][(')(`)(\253\240)(\231)(\273)(\253)]] D
/QC [[(\234)(\234)(\240\273)(\233)(\253)(\273)][(')(')(\240\273)(`)(\253)(\273)]] D
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/Cb Db D
/Ct Dt D
/Cl Dl D
[/Creator (html2ps version 1.0 beta5) /Author () /Keywords () /Subject ()
 /Title (The XPA Help Facility) /DOCINFO pdfmark
/ND 22 D
/HN [(1) (1) (1) (3) (5) (8) (10) (14) (15) (16) (15) (16) (17) (19) (22) (25)
(26) (29) (30) (30) (31) (32) (32) (33) (34) (34) (35) (37) (38) (46) (46)
(39) (40) (42) (43) (44) (47) (48) (50) (51) (55) (61) (63) (75) (76) (77)
(80) (1) (1) (1) (2) (1) (??) (??) (1) (1) (1) (2) (3) (3) (3) (3) (4) (5)
(5) (5) (5) (7) (8) (8) (8) (8) (9) (10) (10) (10) (10) (10) (11) (12) (13)
(14) (14) (14) (14) (14) (15) (15) (15) (16) (16) (17) (18) (19) (19) (19)
(19) (20) (21) (22) (22) (22) (24) (25) (25) (33) (25) (25) (25) (25) (26)
(29) (30) (30) (31) (32) (32) (33) (33) (34) (34) (35) (36) (37) (37) (37)
(37) (37) (38) (38) (38) (38) (38) (38) (39) (40) (42) (43) (44) (46) (46)
(47) (48) (49) (50) (50) (50) (50) (50) (51) (53) (51) (51) (51) (51) (51)
(52) (53) (54) (55) (55) (55) (55) (60) (61) (61) (61) (61) (62) (63) (63)
(63) (63) (63) (63) (64) (64) (64) (65) (65) (66) (67) (67) (67) (68) (68)
(68) (68) (69) (69) (69) (70) (70) (70) (70) (70) (71) (71) (71) (71) (72)
(72) (73) (73) (73) (74) (74) (74) (74) (75) (75) (75) (75) (75) (76) (76)
(76) (76) (76) (77) (77) (77) (77) (79) (80) (80) (80) (80) (80)] D
/h0 [()(Table of Contents)] D
/h1 [(0.1\240\240)(XPA: Public Access to Data and Algorithms)] D
/h2 [(0.2\240\240)(Summary)] D
/h3 [(0.3\240\240)(Description)] D
/h4 [(0.3.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h5 [(0.4\240\240)(XPAIntro: Introduction to the XPA Messaging System)] D
/h6 [(0.5\240\240)(Summary)] D
/h7 [(0.6\240\240)(Description)] D
/h8 [(0.6.0.0.1\240\240)(Last updated: March 10, 2007)] D
/h9 [(0.7\240\240)(XPATemplate: Access Point Names and Templates)] D
/h10 [(0.8\240\240)(Summary)] D
/h11 [(0.9\240\240)(Description)] D
/h12 [(0.9.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h13 [(0.10\240\240)(XPACommon: Getting Common Information About Access Points)] D
/h14 [(0.11\240\240)(Summary)] D
/h15 [(0.12\240\240)(Description)] D
/h16 [(0.12.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h17 [(0.13\240\240)(XPAMethod: XPA Communication Methods)] D
/h18 [(0.14\240\240)(Summary)] D
/h19 [(0.15\240\240)(Description)] D
/h20 [(0.15.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h21 [(0.16\240\240)(XPAInet: XPA Communication Between Hosts)] D
/h22 [(0.17\240\240)(Summary)] D
/h23 [(0.18\240\240)(Description)] D
/h24 [(0.19\240\240)(Manual Registration)] D
/h25 [(0.20\240\240)(Remote Registration)] D
/h26 [(0.21\240\240)(XPANS Proxy Registration)] D
/h27 [(0.21.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h28 [(0.22\240\240)(XPAUsers: Distinguishing Users)] D
/h29 [(0.23\240\240)(Summary)] D
/h30 [(0.24\240\240)(Description)] D
/h31 [(0.24.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h32 [(0.25\240\240)(XPA Programs)] D
/h33 [(0.26\240\240)(Summary)] D
/h34 [(0.27\240\240)(xpaset: send data to one or more XPA servers)] D
/h35 [(0.28\240\240)(xpaget: retrieve data from one or more XPA servers)] D
/h36 [(0.29\240\240)(xpainfo: send short message to one or more XPA servers)] D
/h37 [(0.30\240\240)(xpaaccess: see if template matches registered XPA access points)] D
/h38 [(0.30.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h39 [(0.31\240\240)(xpamb: the XPA Message Bus)] D
/h40 [(0.32\240\240)(Summary)] D
/h41 [(0.33\240\240)(Description)] D
/h42 [(0.34\240\240)(Options)] D
/h43 [(0.34.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h44 [(0.35\240\240)(xpans: the XPA Name Server)] D
/h45 [(0.36\240\240)(Summary)] D
/h46 [(0.36.0.0.1\240\240)(Last updated: January 24, 2005)] D
/h47 [(0.37\240\240)(XPAServer: The XPA Server-side Programming Interface)] D
/h48 [(0.38\240\240)(Summary)] D
/h49 [(0.39\240\240)(Introduction to XPA Server Programming)] D
/h50 [(0.40\240\240)(Introduction)] D
/h51 [(0.41\240\240)(XPANew: create a new XPA access point)] D
/h52 [(0.42\240\240)(XPACmdNew: create a new XPA public access point for commands)] D
/h53 [(0.43\240\240)(XPACmdAdd: add a command to an XPA command public access point)] D
/h54 [(0.44\240\240)(XPACmdDel: remove a command from an XPA command public access point)] D
/h55 [(0.45\240\240)(XPAInfoNew: define an XPA info public access point)] D
/h56 [(0.46\240\240)(XPAFree: remove an XPA public access point)] D
/h57 [(0.47\240\240)(XPAMainLoop: optional main loop for XPA)] D
/h58 [(0.48\240\240)(XPAPoll: execute existing XPA requests)] D
/h59 [(0.49\240\240)(XPAAtExit: install exit handler)] D
/h60 [(0.50\240\240)(XPACleanup: release reserved XPA memory)] D
/h61 [(0.51\240\240)(XPA Server Callback Macros)] D
/h62 [(0.52\240\240)(XPA Race Conditions)] D
/h63 [(0.52.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h64 [(0.53\240\240)(Xpaoom: What happens when XPA runs out of memory?)] D
/h65 [(0.54\240\240)(Summary)] D
/h66 [(0.55\240\240)(Description)] D
/h67 [(0.55.0.0.1\240\240)(Last updated: April 7, 2009)] D
/h68 [(0.56\240\240)(XPAClient: The XPA Client-side Programming Interface)] D
/h69 [(0.57\240\240)(Summary)] D
/h70 [(0.58\240\240)(Introduction to XPA Client Programming)] D
/h71 [(0.59\240\240)(Introduction)] D
/h72 [(0.60\240\240)(XPAGet: retrieve data from one or more XPA servers)] D
/h73 [(0.61\240\240)(XPASet: send data to one or more XPA servers)] D
/h74 [(0.62\240\240)(XPAInfo: send short message to one or more XPA servers)] D
/h75 [(0.63\240\240)(XPAGetFd: retrieve data from one or more XPA servers and write to files)] D
/h76 [(0.64\240\240)(XPASetFd: send data from stdin to one or more XPA servers)] D
/h77 [(0.65\240\240)(XPAOpen: allocate a persistent client handle)] D
/h78 [(0.66\240\240)(XPAClose: close a persistent XPA client handle)] D
/h79 [(0.67\240\240)(XPANSLookup: lookup registered XPA access points)] D
/h80 [(0.68\240\240)(XPAAccess: return XPA access points matching template \(XPA 2.1 and above\))] D
/h81 [(0.68.0.0.1\240\240)(Last updated: March 10, 2007)] D
/h82 [(0.69\240\240)(XPAXt: the XPA Interface to Xt \(X Windows\))] D
/h83 [(0.70\240\240)(Summary)] D
/h84 [(0.71\240\240)(Description)] D
/h85 [(0.71.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h86 [(0.72\240\240)(XPATcl: the XPA Interface to the Tcl/Tk Environment)] D
/h87 [(0.73\240\240)(Summary)] D
/h88 [(0.74\240\240)(Server Routines)] D
/h89 [(0.75\240\240)(Client Routines)] D
/h90 [(0.76\240\240)(Description)] D
/h91 [(0.77\240\240)(XPANew)] D
/h92 [(0.78\240\240)(XPARec)] D
/h93 [(0.78.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h94 [(0.79\240\240)(XPAEnv: Environment Variables for XPA Messaging)] D
/h95 [(0.80\240\240)(Summary)] D
/h96 [(0.81\240\240)(Description)] D
/h97 [(0.81.0.0.1\240\240)(Last updated: December 23, 2009)] D
/h98 [(0.82\240\240)(XPAAcl: Access Control for XPA Messaging)] D
/h99 [(0.83\240\240)(Summary)] D
/h100 [(0.84\240\240)(Description)] D
/h101 [(0.84.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h102 [(0.85\240\240)(XPA ChangeLog)] D
/h103 [(0.86\240\240)(Public Release 2.1.15 \(July 23, 2013\))] D
/h104 [(0.87\240\240)(Public Release 2.1.14 \(June 7, 2012\))] D
/h105 [(0.88\240\240)(Public Release 2.1.13 \(April 14, 2011\))] D
/h106 [(0.89\240\240)(Public Release 2.1.12 \(January 26, 2010\))] D
/h107 [(0.90\240\240)(Public Release 2.1.11 \(December 7, 2009\))] D
/h108 [(0.91\240\240)(Public Release 2.1.10 \(September 1, 2009\))] D
/h109 [(0.92\240\240)(Internal Release 2.1.9)] D
/h110 [(0.93\240\240)(Public Release 2.1.8 \(1 November 2007\))] D
/h111 [(0.94\240\240)(Patch Release 2.1.7b[1,2] \(Feb 22, 2006; March 8, 2007\))] D
/h112 [(0.95\240\240)(Patch Release 2.1.6 \(4 May 2005\))] D
/h113 [(0.96\240\240)(Patch Release 2.1.5 \(12 January 2004\))] D
/h114 [(0.97\240\240)(Patch Release 2.1.4 \(24 March 2003\))] D
/h115 [(0.98\240\240)(Patch Release 2.1.3 \(26 September 2002\))] D
/h116 [(0.99\240\240)(Patch Release 2.1.2 \(18 July 2002\))] D
/h117 [(0.100\240\240)(Patch Release 2.1.1 \(20 June 2002\))] D
/h118 [(0.101\240\240)(Public Release 2.1.0 \(22 April 2002\))] D
/h119 [(0.102\240\240)(Pre-Release 2.1.0e \(2 April 2002\))] D
/h120 [(0.103\240\240)(Pre-Release 2.1.0e \(1 April 2002\))] D
/h121 [(0.104\240\240)(Pre-Release 2.1.0e \(25 March 2002\))] D
/h122 [(0.105\240\240)(Pre-Release 2.1.0e \(19 March 2002\))] D
/h123 [(0.106\240\240)(Pre-Release 2.1.0e \(14 February 2002\))] D
/h124 [(0.107\240\240)(Pre-Release 2.1.0e \(11 February 2002\))] D
/h125 [(0.108\240\240)(Beta Release 2.1.0b10 \(31 January 2002\))] D
/h126 [(0.109\240\240)(Beta Release 2.1.0b9 \(26 January 2002\))] D
/h127 [(0.110\240\240)(Beta Release 2.1.0b8 \(4 January 2002\))] D
/h128 [(0.111\240\240)(Beta Release 2.1.0b7 \(21 December 2001\))] D
/h129 [(0.112\240\240)(Beta Release 2.1.0b6 \(29 October 2001\))] D
/h130 [(0.113\240\240)(Beta Release 2.1.0b5 \(22 October 2001\))] D
/h131 [(0.114\240\240)(Beta Release 2.1.0b4 \(24 September 2001\))] D
/h132 [(0.115\240\240)(Beta Release 2.1.0b3 \(6 September 2001\))] D
/h133 [(0.116\240\240)(Beta Release 2.1.0b2 \(17 August 2001\))] D
/h134 [(0.117\240\240)(Beta Release 2.1.0b1 \(6 August 2001\))] D
/h135 [(0.118\240\240)(Patch Release 2.0.5 \(10 November 2000\))] D
/h136 [(0.119\240\240)(Patch Release 2.0.4 \(20 September 2000\))] D
/h137 [(0.120\240\240)(Patch Release 2.0.3 \(15 June 2000\))] D
/h138 [(0.121\240\240)(Patch Release 2.0.2 \(9 September 1999\))] D
/h139 [(0.122\240\240)(Patch Release 2.0.1 \(6 August 1999\))] D
/h140 [(0.123\240\240)(Public Release 2.0 \(27 May 1999\))] D
/h141 [(0.123.0.0.1\240\240)(Last updated: 22 April 2002)] D
/h142 [(0.124\240\240)(XPACode: Where to Find Example/Test Code)] D
/h143 [(0.125\240\240)(Summary)] D
/h144 [(0.126\240\240)(Description)] D
/h145 [(0.126.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h146 [(0.127\240\240)(XPA Changes: Changes For Users from XPA 1.0 and 2.0)] D
/h147 [(0.128\240\240)(Summary)] D
/h148 [(0.129\240\240)(Description)] D
/h149 [(0.129.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h150 [(0.130\240\240)(XPAConvert: Converting the XPA API to 2.0)] D
/h151 [(0.131\240\240)(Summary)] D
/h152 [(0.132\240\240)(Description)] D
/h153 [(0.132.0.0.1\240\240)(Last updated: September 10, 2003)] D
/h154 [(0.133\240\240)(XPAName: What does XPA stand for?)] D
/h155 [(0.134\240\240)(Summary)] D
/h156 [(0.135\240\240)(Description)] D
/h157 [(0.135.0.0.1\240\240)(Last updated: September 10, 2003)] D
/Hr [-47 47 48 49 -50 -50 50 -54 54 55 56 -57 -57 57 -59 59 60 61 -62 -62
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ZF /FN Fp D Ps 0 FS /WC Wf{( )}{<A1A1>}ie SW pop D
ET RC ZF
/Df f D
/R1 (http://hea-www.harvard.edu/RD/xpa/changelog.html) D
/Ba f D /BO 0 D Bs
/UR (help.html) D
/Ti (The XPA Help Facility) D
/Au () D
/Df f D
/ME [()] D
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/Ba f D /BO 0 D Bs
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/Ti (The XPA Help Facility) D
/Au () D
/Df f D
/ME [()] D
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NP RC ZF
()1 Sl()WB 0 Sn(


)0 2 0 H(XPA:)WB 47 Sn()WB 1 Sn( Public Access to Data and Algorithms)EA()EH(


)0 2 1 H(Summary)WB 48 Sn()EH(
This document is the Table of Contents for XPA.


)0 2 2 H(Description)WB 49 Sn()EH(
)0 P(The XPA messaging system provides seamless communication between many
kinds of Unix programs, including X programs and Tcl/Tk programs.  It
also provides an easy way for users to communicate with XPA-enabled
programs by executing XPA client commands in the shell or by utilizing
such commands in scripts.  Because XPA works both at the programming
level and the shell level, it is a powerful tool for unifying any
analysis environment: users and programmers have great flexibility in
choosing the best level or levels at which to access XPA services, and
client access can be extended or modified easily at any time.

)0 P(A program becomes an XPA-enabled server by defining named points of
public access through which data and commands can be exchanged with
other client programs \201and users\202.  Using standard TCP sockets as a
transport mechanism, XPA supports both single-point and broadcast
messaging to and from these servers.  It supports direct communication
between clients and servers, or indirect communication via an
intermediate message bus emulation program. Host-based access control
is implemented, as is as the ability to communicate with XPA servers
across a network.

)0 P(XPA implements a layered interface that is designed to be useful both
to software developers and to users.  The interface consists of a
library of XPA client and server routines for use in C/C++ programs and
a suite of high-level user programs built on top of these libraries.
Using the XPA library, access points can be added to Tcl/Tk programs,
Xt programs, or to Unix programs that use the XPA event loop or any
event loop based on select\201\202.  Client access subroutines can be added
to any Tcl/Tk, Xt, or Unix program. Client access also is supported at
the command line via a suite of high-level programs.

)0 P(Choose from the following topics:

)UL( 
)-1 LI()0 2 1 A(Introduction to XPA)2 1 TN TL()Ec /AF f D(

)-1 LI()0 3 1 A(Access Point Names and Templates)3 1 TN TL()Ec /AF f D(

)-1 LI()0 4 1 A(Getting Common Information About Access Points)4 1 TN TL()Ec /AF f D(

)-1 LI()0 5 1 A(Communication Methods)5 1 TN TL()Ec /AF f D(

)-1 LI()0 6 1 A(Communication Between Hosts)6 1 TN TL()Ec /AF f D(

)-1 LI()0 7 1 A(Distinguishing Users)7 1 TN TL()Ec /AF f D(


)-1 LI()0 8 1 A(XPA User Programs)8 1 TN TL()Ec /AF f D(
)UL()-1 LI()0 9 1 A(xpaget: get data and info)9 1 TN TL()Ec /AF f D(

)-1 LI()0 10 1 A(xpaset: send data and info)10 1 TN TL()Ec /AF f D(

)-1 LI()0 11 1 A(xpainfo: send info alert)11 1 TN TL()Ec /AF f D(

)-1 LI()0 12 1 A(xpaaccess: get access point info)12 1 TN TL()Ec /AF f D(

)-1 LI()0 13 1 A(xpamb: message bus emulation)13 1 TN TL()Ec /AF f D(

)-1 LI()0 14 1 A(xpans: the XPA name server)14 1 TN TL()Ec /AF f D(
)LU(

)-1 LI()0 15 1 A(XPA Server Routines)15 1 TN TL()Ec /AF f D(
)UL()-1 LI()0 16 1 A(XPANew: define a new access point)16 1 TN TL()Ec /AF f D(

)-1 LI()0 17 1 A(XPACmdNew: define a new command access point)17 1 TN TL()Ec /AF f D(

)-1 LI()0 18 1 A(XPACmdAdd: add a command)18 1 TN TL()Ec /AF f D(

)-1 LI()0 19 1 A(XPACmdDel: delete a command)19 1 TN TL()Ec /AF f D(

)-1 LI()0 20 1 A(XPAInfoNew: define an info access point)20 1 TN TL()Ec /AF f D(

)-1 LI()0 21 1 A(XPAFree: free an access point)21 1 TN TL()Ec /AF f D(

)-1 LI()0 22 1 A(XPAMainLoop: event loop for select server)22 1 TN TL()Ec /AF f D(

)-1 LI()0 23 1 A(XPAPoll: poll for XPA events)23 1 TN TL()Ec /AF f D(

)-1 LI()0 24 1 A(XPACleanup: release reserved XPA memory)24 1 TN TL()Ec /AF f D(

)-1 LI()0 25 1 A(XPA Server Macros: accessing structure internals)25 1 TN TL()Ec /AF f D(

)-1 LI()0 26 1 A(XPA Race Conditions: how to avoid them)26 1 TN TL()Ec /AF f D(

)-1 LI()0 27 1 A(XPA Out of Memory \201OOM\202 errors)27 1 TN TL()Ec /AF f D(
)LU(

)-1 LI()0 28 1 A(XPA Client Routines)28 1 TN TL()Ec /AF f D(
)UL()-1 LI()0 29 1 A(XPAOpen: open a persistent client connection)29 1 TN TL()Ec /AF f D(

)-1 LI()0 30 1 A(XPAClose: close persistent client connection)30 1 TN TL()Ec /AF f D(

)-1 LI()0 31 1 A(XPAGet: get data)31 1 TN TL()Ec /AF f D(

)-1 LI()0 32 1 A(XPASet: send data or commands)32 1 TN TL()Ec /AF f D(

)-1 LI()0 33 1 A(XPAInfo: send an info alert)33 1 TN TL()Ec /AF f D(

)-1 LI()0 34 1 A(XPAGetFd: get data and write to an fd)34 1 TN TL()Ec /AF f D(

)-1 LI()0 35 1 A(XPASetFd: read data from and fd and send)35 1 TN TL()Ec /AF f D(

)-1 LI()0 36 1 A(XPANSLookup: look up an access point)36 1 TN TL()Ec /AF f D(

)-1 LI()0 37 1 A(XPAAccess: get access info)37 1 TN TL()Ec /AF f D(

)-1 LI()0 38 1 A(The XPA/Xt Interface: Xt interface to XPA)38 1 TN TL()Ec /AF f D(

)-1 LI()0 39 1 A(The XPA/Tcl Interface: Tcl interface to XPA)39 1 TN TL()Ec /AF f D(
)LU(

)-1 LI( Tailoring the XPA Environment
)UL()-1 LI()0 40 1 A(Environment Variables)40 1 TN TL()Ec /AF f D(

)-1 LI()0 41 1 A(Access Control)41 1 TN TL()Ec /AF f D(
)LU(

)-1 LI( Miscellaneous
)UL(
)-1 LI()0 42 1 A(XPA ChangeLog)42 1 TN TL()Ec /AF f D(

)-1 LI()0 43 1 A(Where to Find Example/Test Code)43 1 TN TL()Ec /AF f D(
)-1 LI()0 44 1 A(User Changes Between XPA 1.0 and 2.0)44 1 TN TL()Ec /AF f D(
)-1 LI()0 45 1 A(API Changes Between XPA 1.0 and 2.0)45 1 TN TL()Ec /AF f D(
)-1 LI()0 46 1 A(What Does XPA Stand For, Anyway?)46 1 TN TL()Ec /AF f D()LU(
)LU( 



)0 5 3 H(Last)WB 50 Sn( updated: September 10, 2003)EH(
)WB NL NP Ep ET /Tc f D
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (intro.html) D
/Ti (Introduction to XPA) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 2 Sn(


)0 2 4 H(XPAIntro:)WB 54 Sn()WB 51 Sn( Introduction to the XPA Messaging System)EA()EH(


)0 2 5 H(Summary)WB 55 Sn()EH(
)0 P(A brief introduction to the XPA messaging system, which provides
seamless communication between all kinds of Unix event-driven
programs, including X programs, Tcl/Tk programs, and Perl programs.


)0 2 6 H(Description)WB 56 Sn()EH(
)0 P(The XPA messaging system provides seamless communication between all
kinds of Unix programs, including X programs, Tcl/Tk programs, and
Perl programs.  It also provides an easy way for users to communicate
with these XPA-enabled programs by executing XPA client commands in
the shell or by utilizing such commands in scripts.  Because XPA works
both at the programming level and the shell level, it is a powerful
tool for unifying any analysis environment: users and programmers have
great flexibility in choosing the best level or levels at which to
access XPA services, and client access can be extended or modified
easily at any time.

)0 P(A program becomes an XPA-enabled server by defining named points of
public access through which data and commands can be exchanged with
other client programs \201and users\202.  Using standard TCP sockets as
a transport mechanism, XPA supports both single-point and broadcast
messaging to and from these servers.  It supports direct communication
between clients and servers, or indirect communication via an
intermediate message bus emulation program. Host-based access control
is implemented, as is as the ability to communicate with XPA servers
across a network.

)0 P(XPA implements a layered interface that is designed to be useful both
to software developers and to users.  The interface consists of a
library of XPA client and server routines for use in programs and a
suite of high-level user programs built on top of these libraries.
Using the XPA library, access points can be added to
)0 52 1 A(Tcl/Tk)52 0 TN TL()Ec /AF f D(
programs, 
)0 53 1 A(Xt)53 0 TN TL()Ec /AF f D(
programs, or to Unix programs that use the XPA event loop or any
event loop based on select\201\202.  Client access subroutines can be added
to any Tcl/Tk or Unix program. Client access also is supported at the
command line via a suite of high-level programs. 

)0 P(The major components of the XPA layered interface are:
)UL()-1 LI(A set of XPA server routines, centered on 
)0 16 1 A(XPANew\201\202,)16 0 TN TL()Ec /AF f D(
which are used by XPA server programs to tag public access points with
string identifiers and to register send and receive callbacks for
these access points.

)-1 LI(A set of XPA client routines, centered on the 
)0 32 1 A(XPASet\201\202)32 0 TN TL()Ec /AF f D(
and
)0 31 1 A(XPAGet\201\202,)31 0 TN TL()Ec /AF f D(
which are used by external client applications to exchange data and
commands with an XPA server.

)-1 LI(High-level programs, centered on
)0 10 1 A(xpaset)10 0 TN TL()Ec /AF f D(
and
)0 9 1 A(xpaget,)9 0 TN TL()Ec /AF f D(
which allow data
and information to be exchanged with XPA server programs from the
command line and from scripts.  These programs have the command syntax:
) 2 35 PR(  [data] | xpaset  [qualifiers ...]
           xpaget  [qualifiers ...])RP(
)-1 LI(An XPA name server program, 
)0 14 1 A(xpans,)14 0 TN TL()Ec /AF f D(
through which XPA access point names are
registered by servers and distributed to clients.)LU(

)0 P(Defining an XPA access point is easy: a server application calls
)0 16 1 A(XPANew\201\202,)16 0 TN TL()Ec /AF f D(
)0 17 1 A(XPACmdNew\201\202,)17 0 TN TL()Ec /AF f D(
or the experimental
)0 20 1 A(XPAInfoNew\201\202)20 0 TN TL()Ec /AF f D(
routine to
create a named public access point.  An XPA service can specify "send"
and "receive" callback procedures \201or an "info" procedure in the case
of XPAInfoNew\201\202\202 to be executed by the program when an external
process either sends data or commands to this access point or requests
data or information from this access point.  Either of the callbacks
can be omitted, so that a particular access point can be specified as
read-only, read-write, or write-only.  Application-specific client
data can be associated with these callbacks.  Having defined one or
more public access points in this way, an XPA server program enters
its usual event loop \201or uses the standard XPA event loop\202.

)0 P(Clients communicate with these XPA public access points
using programs such as
)0 9 1 A(xpaget)9 0 TN TL()Ec /AF f D(,
)0 10 1 A(xpaset)10 0 TN TL()Ec /AF f D(, and
)0 11 1 A(xpainfo)11 0 TN TL()Ec /AF f D(
\201at the command line\202,
or routines such as
)0 31 1 A(XPAGet\201\202,)31 0 TN TL()Ec /AF f D(
)0 32 1 A(XPASet\201\202,)32 0 TN TL()Ec /AF f D(
and
)0 33 1 A(XPAInfo\201\202)33 0 TN TL()Ec /AF f D(
within a program.  Both methods require specification of the name of
the access point.  The xpaget program returns data or other
information from an XPA server to its standard output, while the
xpaset program sends data or commands from its standard input to an
XPA application. The corresponding API routines set/get data to/from
memory, returning error messages and other info as needed.  If a
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
is used to specify the access point name \201e.g., "ds9*"\202, then
communication will take place with all servers matching that template.

)0 P(Please note that XPA currently is not thread-safe. All XPA calls must be
in the same thread.





)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 7 H(Last)WB 57 Sn( updated: March 10, 2007)EH(

)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (template.html) D
/Ti (Access Point Names and Templates) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 3 Sn(


)0 2 8 H(XPATemplate:)WB 59 Sn()WB 58 Sn( Access Point Names and Templates)EA()EH(

)0 2 9 H(Summary)WB 60 Sn()EH(
)0 P(XPA access points are composed of two parts: a general class and a
specific name.  Both parts accept template characters so that you
can send/retrieve data to/from multiple servers at one time.


)0 2 10 H(Description)WB 61 Sn()EH(
)0 P(When XPA servers call
)0 16 1 A(XPANew\201\202,)16 0 TN TL()Ec /AF f D(
or
)0 17 1 A(XPACmdNew\201\202)17 0 TN TL()Ec /AF f D(
to define XPA access points, they specify a string identifier composed of a
class and a name. When clients communicate with XPA access points,
they specify which access points to communicate with using
an identifier of the form:
) 1 12 PR(  class:name)RP(
All registered XPA access points that match the specified identifier
will be available for communication \201subject to access control rules,
etc.\202

)0 P(As of XPA 2.1.5, the length of both the class and name designations are
limited to 1024 characters.

)0 P(The XPA class:name identifier actually is a template: it accepts wild
cards in its syntax, so a single specifier can match more than one XPA
access point.  \201Note that the class is optional and defaults to "*".\202
The allowed syntax for clients to specify the class:name template is
of the form shown below. \201Note that "*" is used to denote a generic
wild card, but other wild cards characters are supported, as described
below\202.
) 7 46 PR(  template      explanation
  --------      -----------
  class:name    exact match of class and name
  name          match any class with this name
  *:name        match any class with this name
  class:*       match any name of this class
  *:*           match any access point)RP(
)0 P(In general, the following wild-cards can be applied to class and name:
) 5 58 PR(  wildcard      explanation
  --------      -----------
  ?             match any character, but there must be one
  *             match anything, or nothing
  [...]         match an inclusive set)RP(
)0 P(Although the class:name template normally is used to refer to XPA
access points, these also can be specified using their individual
socket identifiers.  For inet sockets, the socket identifier is
)BD(ip:port)ES(, where ip can be the DNS-registered name,
the ASCII IP number \201e.g. 123.45.67.890\202 or the hex IP number
\201e.g. 838f3a60\202. For unix sockets, the identifier is the )BD(socket file
name)ES(.  These socket identifiers are displayed as the fourth argument
in the xpans display of registered access points.  For example,
consider the ds9 program started using inet sockets. The xpans name
server will register something like this:
) 2 40 PR(  csh> xpaget xpans
  DS9 ds9 gs saord.harvard.edu:3236 eric)RP(
You can access ds9 using ip:3236 in any of the three forms:
) 8 37 PR(  csh> xpaget saord:3236 file
  /home/eric/data/snr.ev

  csh> xpaget 123.45.67.890:3236 file
  /home/eric/data/snr.ev

  csh> xpaget 838f3a60:3236 file
  /home/eric/data/snr.ev)RP(
In the case of unix  sockets, the socket identifier is a file:
) 5 41 PR(  csh> xpaget xpans
  DS9 ds9 gs /tmp/.xpa/DS9_ds9.2631 eric

  csh> xpaget /tmp/.xpa/DS9_ds9.2631 file
  /home/eric/data/snr.ev)RP(
This feature can be useful in distinguishing between multiple
instances of a program that all have the same class:name designation.





)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 11 H(Last)WB 62 Sn( updated: September 10, 2003)EH(

)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (info.html) D
/Ti (Getting Common Information About Access Points) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 4 Sn(


)0 2 12 H(XPACommon:)WB 64 Sn()WB 63 Sn( Getting Common Information About Access Points)EA()EH(


)0 2 13 H(Summary)WB 65 Sn()EH(
)0 P(There are various kinds of generic information you can retrieve about
an XPA access point by using the xpaget command.


)0 2 14 H(Description)WB 66 Sn()EH(
)0 P(You can find out which XPA access points have been registered with
the currently running 
)0 14 1 A(XPA name server)14 0 TN TL()Ec /AF f D(
by executing the
)0 9 1 A(xpaget)9 0 TN TL()Ec /AF f D(
command to retrieve info from the XPA name server:
) 1 14 PR(  xpaget xpans)RP(
If, for example, the
)0 43 1 A(stest)43 0 TN TL()Ec /AF f D( test server program
is running, the following XPA access points will be returned \201the specifics
of the returned info will vary for different machines and users\202:
) 4 33 PR(  XPA xpa gs 838e2f67:1262 eric
  XPA xpa1 gs 838e2f67:1266 eric
  XPA c_xpa gs 838e2f67:1267 eric
  XPA i_xpa i 838e2f67:1268 eric)RP(
Note that access to this information is subject to the usual
)0 41 1 A(XPA Access Control)41 0 TN TL()Ec /AF f D( restrictions.

)0 P(Each XPA access point supports a number of reserved sub-commands that provide
access to different kinds of information, e.g. the access control for
that access point.  These sub-commands can be executed by using
)0 10 1 A(xpaset)10 0 TN TL()Ec /AF f D(
or
)0 9 1 A(xpaget)9 0 TN TL()Ec /AF f D(
at the command line, or
)0 31 1 A(XPAGet\201\202)31 0 TN TL()Ec /AF f D(
or
)0 32 1 A(XPASet\201\202)32 0 TN TL()Ec /AF f D(
in programs, e.g:
) 5 30 PR(  xpaget ds9 -acl
  xpaget ds9 -help
  xpaget ds9 env FOO

  xpaset -p ds9 env FOO foofoo)RP(
With the exception of )BD(-help)ES( and )BD(-version)ES(, reserved
sub-commands are available only on the machine on which the XPA server
itself is running.

The following reserved sub-commands are defined for all access points:
)0 DL(
)0 P()0 DT()BD(-acl)ES( get \201set\202 the access control list [options: host type acl, for set]
)DD( 
The 'xpaset' option allows you to add a new acl for a given host, or change
the acl for an existing host. See
)0 41 1 A(XPA Access Control)41 0 TN TL()Ec /AF f D(
for more information.
This access point is available only on the server machine.

)0 P()0 DT()BD(-env)ES( get \201set\202 an environment variable [options: name \201value, for set\202]
)DD(The 'xpaget' option will return the value of the named environment
variable.  The 'xpaset' option will set the value of the names
variable to the specified value.
This access point is available only on the server machine.
\201Please be advised that we have had problems setting environment
variables in static Tcl/Tk programs such as ds9 running under Linux.\202

)0 P()0 DT( )BD(-clipboard)ES( set\201get\202 information on a named clipboard
)DD( Clients can store ASCII state information on any number of named
clipboards. Clipboards of the same name created by clients on
different machines are kept separate.  The syntax for creating a
clipboard is:
) 2 65 PR(  [data] | xpaset [server] -clipboard add|append [clipboard_name]
  xpaset -p [server] -clipboard delete [clipboard_name])RP(
Use "add" to create a new clipboard or replace the contents of an existing
one. Use "append" to append to an existing clipboard.
)0 P(Information on a named clipboard is retrieved using:
) 1 45 PR(  xpaget [server] -clipboard [clipboard_name])RP(
)0 P()0 DT()BD(-exec)ES( set: execute commands from buffer [options: none]
)DD(If -exec is specified in the paramlist of an 'xpaset' call, then further
sub-commands will be retrieved from the data buffer.

)0 P()0 DT()BD(-help)ES( get: return help string for this XPA or sub-command [options: name \201for sub-commands\202]
)DD(Each XPA access point and each XPA sub-command can have a help string
associated with it that is specified when the access point is defined.
The -help option will return this help string.  For XPA access points
that contain user-defined sub-commands, you can get the help string
for a particular sub-command by specifying its name, or else get the
help strings for all sub-commands if not name is specified.

)0 P()0 DT()BD(-ltimeout)ES( get \201set\202 the long timeout value [options: seconds|reset]
)DD(The 'xpaget' option will return the value of the long timeout \201in seconds\202.
The 'xpaset' option will set the value of the long timeout. If "reset" is
specified, then the timeout value will be reset to the default value.

)0 P()0 DT()BD(-nsconnect)ES( set: re-establish name server connection to all XPA's [options: none]
)DD(If the 
)0 14 1 A(XPA Name Server \201xpans\202)14 0 TN TL()Ec /AF f D(
process has terminated unexpectedly and then re-started, this
sub-command can be used to re-establish the connection.  You use it by
sending the command to the [name:port] or [file] of the access point
instead of to the XPA name \201since the latter requires the xpans
connection!\202:
) 1 36 PR(  xpaset -p 838e2f67:1268 -nsconnect)RP(
See )0 14 1 A(xpans)14 0 TN TL()Ec /AF f D( for more information.

)0 P()0 DT()BD(-nsdisconnect)ES( set: break name server connection to all XPA's [options: none]
)DD(This sub-command will terminate the connection to the
)0 14 1 A(XPA Name Server \201xpans\202)14 0 TN TL()Ec /AF f D(, thereby making
all access points inaccessible except through their underlying [name:port]
or [file] identifiers.  I forget why we added it, it seems pretty useless.

)0 P()0 DT()BD(-stimeout)ES( get \201set\202 the short timeout value [options: seconds|reset]
)DD(The 'xpaget' option will return the value of the short timeout \201in seconds\202.
The 'xpaset' option will set the value of the short timeout. If "reset" is
specified, then the timeout value will be reset to the default value.

)0 P()0 DT()BD(-remote)ES( set: register xpa with remote server [options: host[:port] [acl]] [-proxy]
)DD(This sub-command will register the XPA access point with the XPA name
server \201xpans\202 on the specified host \201which must already be running\202.
The specified host also is given access control to the access point,
using the specified acl or the default acl of "+" \201meaning the remote
host can xpaset, xpaget, xpainfo or xpaaccess\202. If the acl is
specified as "-", then the access point is unregistered. 
See )0 6 1 A(Communication Between Machines)6 0 TN TL()Ec /AF f D(
for more information on how this sub-command is used.

)0 P()0 DT()BD(-version)ES( get: return XPA version string [options: none]
)DD(The version refers to the version of XPA used to define this access point
\201currently something like 2.0\202.
)LD(

)0 P(You can add your own reserved commands to all XPA access points by using the
)0 18 1 A(XPACmdAdd\201\202)18 0 TN TL()Ec /AF f D(
routine, passing the XPA handle returned by )EM(XPA XPAGetReserved\201void\202)ES(
as the first argument. Note again that these will only be available on the
machine where the XPA service is running.





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)0 2 16 H(XPAMethod:)WB 69 Sn()WB 68 Sn( )EA(XPA Communication Methods)EH(


)0 2 17 H(Summary)WB 70 Sn()EH(
)0 P(XPA supports both inet and unix \201local\202 socket communication.


)0 2 18 H(Description)WB 71 Sn()EH(
)0 P(XPA uses sockets for communication between processes. It supports
three methods of socket communication: inet, localhost, and unix. In
general, the same method should be employed for all XPA processes in a
session and the global environment variable XPA_METHOD should be used
to set up the desired method. By default, the preferred method is
"inet", which is appropriate for most users. You can set up a
different method by typing something like:
) 3 70 PR(  setenv XPA_METHOD local              # unix csh
  XPA_METHOD=local; export XPA_METHOD  # unix sh, bash, windows/cygwin
  set XPA_METHOD=localhost             # dos/windows)RP(
The options for XPA_METHOD are: )BD(inet)ES(, )BD(unix)ES( \201or
)BD(local)ES(\202, and )BD(localhost)ES(. On Unix machines, this
environment setup command can be placed in your shell init file
\201.cshrc, .profile, .bashrc, etc.\202 On Windows platforms, it can be
placed in your AUTOEXEC.BAT file \201I think!\202.

)0 P(By default, )BD(inet)ES( sockets are used by XPA. These are the standard
Internet sockets that are used by programs such as Netscape,
ftp. etc. Inet sockets utilize the IP address of the given machine and
a \201usually random\202 port number to communicate between processes on the
same machine or between different machines on the Internet. \201Note that
XPA has an )0 41 1 A(Access Control)41 0 TN TL()Ec /AF f D( mechanism to
prevent unauthorized access of XPA access points by other computers on
the Net\202. For users connected to the Internet, this usually is the
appropriate communication method. For more information about setting
up XPA communication between machines, see
)0 6 1 A(Communication Between Machines)6 0 TN TL()Ec /AF f D(.

)0 P(In you are using XPA on a machine without an Internet connection, then
inet sockets are not appropriate. In fact, an XPA process often will
hang for many seconds while waiting for a response from the Domain
Name Service \201DNS\202 when using inet sockets. Instead of inet sockets,
users on Unix platforms can also use )BD(unix)ES( sockets \201also known
as local sockets\202. These sockets are based on the local file system
and do not make use of the DNS. They generally are considered to be
faster than inet sockets, but they are not implemented under
Windows. Use local sockets as a first resort if you are on a Unix
machine that is not connected to the Internet.

)0 P(Users not connected to the Internet also can use )BD(localhost)ES(
sockets. These are also inet-type sockets but the IP address used for
the local machine is the )BD(localhost)ES( address, 0x7F000001, instead
of the real IP of the machine. Depending on how sockets are set up for
a given platform, communication with the DNS usually is not required in
this case \201though of course, XPA cannot interact with other machines\202.
The localhost method will generally work on both Unix and Windows
platforms, but whether the DNS is required or not is subject to
individual configurations.

)0 P(A final warning/reminder: if your XPA-enabled server hangs at startup
time and your XPA_METHOD is )BD(inet)ES(, the problem probably is
related to an incorrect Internet configuration. This can be confirmed
by using the )BD(unix)ES( method or \201usually\202 the )BD(localhost)ES(
method. You can use these alternate methods if other hosts do not need
access to the XPA server.





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)0 2 20 H(XPAInet:)WB 74 Sn()WB 73 Sn( XPA Communication Between Hosts)EA()EH(


)0 2 21 H(Summary)WB 75 Sn()EH(
XPA uses standard inet sockets to support communication between two or
more host computers.


)0 2 22 H(Description)WB 76 Sn()EH(
)0 P(When the )0 5 1 A(Communication Method)5 0 TN TL()Ec /AF f D( is set to
)BD(inet)ES( \201as it is by default\202, XPA can be used to communicate
between different computers on the Internet.  INET sockets utilize the
IP address of the given machine and a \201usually random\202 port number to
communicate between processes on the same machine or between different
machines on the Internet.  These standard Internet sockets are also
used by programs such as Netscape, ftp. etc.

)0 P(XPA supports a host-based )0 41 1 A(Access Control)41 0 TN TL()Ec /AF f D( mechanism
to prevent unauthorized access of XPA access points by other computers
on the Net.  By default, only the machine on which the XPA server is
running can access XPA services. Therefore, setting up communication
between a local XPA server machine and a remote client machine
requires a two-part registration process:

)UL()-1 LI( the XPA service on the local machine must be made known to the 
remote machine
)-1 LI( the remote machine must be given permission to access the local
XPA service)LU(

Three methods by which this remote registration can be accomplished
are described below.

)0 2 23 H(Manual)WB 77 Sn( Registration)EH(

The first method is the most basic and does not require the remote
client to have xpans running.  To use it, the local server simply
gives a remote client machine access to one or more XPA access points
using xpaset and the )BD(-acl)ES( sub-command. For example,
consider the XPA test program "stest" running on a local machine.  By
default the access control for the access point named "xpa" is
restricted to that machine:
) 3 25 PR(  [sh]$ xpaget xpa -acl
  *:* 123.456.78.910 gisa
  *:* localhost gisa)RP(
Using xpaset and the )BD(-acl)ES( sub-command, a remote client
machine can be given permission to perform xpaget, xpaset, xpaaccess,
or xpainfo operations.  For example, to allow the xpaget operation, the
following command can be issued on the local machine:
) 1 45 PR(  [sh]$ xpaset -p xpa -acl "remote_machine g")RP(
This results in the following access permissions on the local machine:
) 4 26 PR(  [sh]$ xpaget xpa -acl
  XPA:xpa 234.567.89.012 g
  *:* 123.456.78.910 gisa
  *:* localhost gisa)RP(

The remote client can now use the local server's xpans name server to
establish communication with the local XPA service. This can be done
on a call-by-call basis using the )BD(-i)ES( switch on xpaset, xpaget, etc:
) 6 43 PR(  [sh]$ xpaget -i "local_machine:12345" xpa
  class: XPA
  name: xpa
  method: 88877766:2778
  sendian: little
  cendian: big)RP(
Alternatively, the XPA_NSINET variable on the remote machine can be
set to point directly to xpans on the local machine, removing
the need to override this value each time an XPA program is run:
) 7 42 PR(  [csh]$ setenv XPA_NSINET 'karapet:$port'
  [csh]$ xpaget xpa
  class: XPA
  name: xpa
  method: 88877766:2778
  sendian: little
  cendian: big)RP(
Here, '$port' means to use the default XPA name service port \20114285\202.
not a port environment variable.

)0 P(Access permission for remote client machines can be stored in a file
on the local machine pointed to by the )BD(XPA_ACLFILE)ES( environment
variable or using the )BD(XPA_DEFACL)ES( environment variable. See )0 41 1 A(XPA Access Control)41 0 TN TL()Ec /AF f D( for more information.

)0 2 24 H(Remote)WB 78 Sn( Registration)EH(

If xpans is running on the remote client machine, then a local xpaset
command can be used with the )BD(-remote)ES( sub-command to
register the local XPA service in the remote name service, while at
the same time giving the remote machine permission to access the local
service.  For example, assume again that "stest" is running on the
local machine and that xpans is also running on the remote machine.
To register access of this local xpa on the remote machine, use 
the xpaset and the )BD(-remote)ES( sub-command:
) 1 56 PR(  [sh]$ ./xpaset -p xpa -remote 'remote_machine:$port' +)RP(
To register the local xpa access point on the remote machine with xpaget
access only, execute:
) 1 56 PR(  [sh]$ ./xpaset -p xpa -remote 'remote_machine:$port' g)RP(
Once the remote registration command is executed, the remote client
machine will have an entry such as the following in its own xpans name
service:
) 2 31 PR(  [csh]$ xpaget xpans
  XPA xpa gs 88877766:2839 eric)RP(
The xpa access point can now be utilized on the remote machine without
further setup:
) 6 23 PR(  [csh]$ xpaget xpa
  class: XPA
  name: xpa
  method: 838e2f68:2839
  sendian: little
  cendian: big)RP(
To unregister remote access from the local machine, use the same
command but with a '-' argument:
) 1 54 PR(  [sh]$ xpaset -p xpa -remote 'remote_machine:$port' -)RP(
The benefit of using remote registration is that communication with
remote access points can be mixed with that of other access points
on the remote machine.  Using )0 3 1 A(Access Point
Names and Templates)3 0 TN TL()Ec /AF f D(, one XPA command can be used to send or
receive messages to the remote and local services.

)0 2 25 H(XPANS)WB 79 Sn( Proxy Registration)EH(

The two methods described above are useful when the local and remote
machines are able to communicate freely to one another. This would be
the case on most Local Area Networks \201LANs\202 where all machines are
behind the same firewall and there is no port blocking between
machines on the same LAN.  The situation is more complicated when the
XPA server is behind a firewall, where outgoing connections are
allowed, but incoming port blocking is implemented to prevent machines
outside the firewall from connecting to machines inside the
firewall. Such incoming port blocking will prevent xpaset and xpaget
from connecting to an XPA server inside a firewall.

)0 P(To allow locally fire-walled XPA services to register with remote
machines, we have implemented a proxy service within the xpans name
server. To register remote proxy service, xpaset and the
)BD(-remote)ES( sub-command is again used, but with an additional
)BD(-proxy)ES( argument added to the end of the command:
) 1 63 PR(  [sh]$ ./xpaset -p xpa -remote 'remote_machine:$port' g -proxy)RP(
Once a remote proxy registration command is executed, the remote
machine will have an entry such as the following in its own xpans name
service:
) 2 32 PR(  [csh]$ xpaget xpans
  XPA xpa gs @88877766:2839 eric)RP(
The '@' sign in the name service entry indicates that xpans proxy
processing is being used for this access point. Other than that, from
the user's point of view, there is no difference in how this XPA
access point is contacted using XPA programs \201xpaset, xpaget, etc.\202 or
libraries:
) 6 23 PR(  [csh]$ xpaget xpa
  class: XPA
  name: xpa
  method: 88877766:3053
  sendian: little
  cendian: big)RP(
)0 P(Of course, the underlying processing of the XPA requests is very much
different when xpans proxy is involved. Instead of an XPA program such
contacting the XPA service directly, it contacts the local xpans.
Acting as a proxy server, xpans communicates with the XPA service
using the command channel established at registration time. Commands
\201including establishing a new data channel\202 are sent between xpans and
the XPA service to set up a new message transfer, and then data is fed
to/from the xpa request, through xpans, from/to the XPA service. In
this way, it can be arranged so that connections between the
fire-walled XPA service and the remote client are always initiated by
the XPA service itself. Thus, incoming connections that would be
blocked by the firewall are avoided. Note that there is a performance
penalty for using the xpans/proxy service.  Aside from extra overhead
to set up proxy communication, all data must be sent through the
intermediate proxy process.

)0 P(The xpans proxy scheme requires that the remote client allow the local
XPA server machine to connect to the remote xpans/proxy server. If the
remote client machine also is behind a port-blocking firewall, such
connections will be disallowed. In this case, the only solution is to
open up some ports on the remote client machine to allow incoming
connections to xpans/proxy. Two ports must be opened \201for command and
data channel connections\202. By default, these two ports are 14285 and
14287. The port numbers can be changed using the )BD(XPA_NSINET)ES(
environment variable. This variable takes the form:
) 1 49 PR(  setenv XPA_NSINET machine:port1[,port2[,port3]])RP(
where port1 is the main connecting port, port2 is the XPA access port,
and port3 is the secondary data connecting port. The second and third
ports are optional and default to port1+1 and port1+2, respectively.
It is port1 and port3 that must be left open for incoming connections.

)0 P(For example, to change the port assignments so that xpans listens
for registration commands on port 12345 and data commands on port 28573:
) 1 32 PR(  setenv XPA_NSINET myhost:12345)RP(
Alternatively, all three ports can be assigned explicitly:
) 1 43 PR(  setenv XPA_NSINET remote:12345,3000,12346)RP(
In this case 12345 and 12346 should be open for incoming connections.
The XPA access port \201which need not be open to the outside
world\202 is set to 3000.

)0 P(Finally, note that we currently have no mechanism to cope with
Internet proxy servers \201such as SOCKS servers\202. If an XPA service is
running on a machine that cannot connect directly to outside machines,
but goes through a proxy server instead, there currently is no way to
register that XPA service with a remote machine.  We hope to implement
support for SOCKS proxy in a future release.





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)0 2 27 H(XPAUsers:)WB 82 Sn()WB 81 Sn( Distinguishing Users)EA()EH(


)0 2 28 H(Summary)WB 83 Sn()EH(
)0 P(XPA normally distinguishes between users on a given host, but it is possible
to send data to access points belonging to other users.


)0 2 29 H(Description)WB 84 Sn()EH(
)0 P(A single XPA name service typically serves all users on a given
machine.  Two users can register the same XPA access points on the
same machine without conflict, because the user's username is
registered with each access point and, by default, programs such as
xpaget and xpaset only process access points of the appropriate user.
For example:
) 4 32 PR(  XPA xpa1 gs 838e2f67:1262 eric
  XPA xpa2 gs 838e2f67:1266 eric
  XPA xpa1 gs 838e2f67:2523 john
  XPA xpa2 gs 838e2f67:2527 john)RP(
Here the users "eric" and "john" both have registered the access
points xpa1 and xpa2. When either "john" or "eric" retrieves
information from xpa1, they will process only the access point
registered in their user name.

)0 P(If you want to access another user's XPA access points on a single
machine, use the -u [user] option on xpaset, xpaget, etc. For example,
if eric executes:
) 1 21 PR(  xpaget -u john xpa1)RP(
he will access John's xpa1 access point.Use "*" to access all users
on a given machine:
) 1 20 PR(  xpaget -u "*" xpa1)RP(
Note that the )0 40 1 A(XPA Environment Variable)40 0 TN TL()Ec /AF f D(
XPA_NSUSERS can be used to specify the default list of users to
process:
) 1 32 PR(  setenv XPA_NSUSERS "eric,john")RP(
will cause access points from both "eric" and "john" to be processed
by default.





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)0 2 31 H(XPA)WB 86 Sn( Programs)EH(

)0 2 32 H(Summary)WB 87 Sn()EH(

)0 P(Use the XPA programs to send/receive data to/from XPA servers from the
command line or from scripts.

)0 P() 7 116 PR(  <data> | xpaset  [-h] [-i nsinet] [-m method] [-n] [-p] [-s] [-t sval,lval] [-u users] [-v] <template> [paramlist]

  xpaget  [-h] [-i nsinet] [-m method] [-s] [-t sval,lval] [-u users] <template> [paramlist]
        
  xpainfo [-h] [-i nsinet] [-m method] [-n] [-s] [-t sval,lval] [-u users] <template> [paramlist]

  xpaaccess [-c] [-h] [-i nsinet] [-m method] [-n] [-u users] [-v|-V] <template> [type])RP(




)0 2 33 H(xpaset:)WB 88 Sn()WB 10 Sn( send data to one or more XPA servers)EA()EH(


)BD() 1 124 PR(<data> | xpaset  [-h] [-i nsinet] [-m method] [-n] [-p] [-s] [-t sval,lval] [-u users] [-v] <template|host:port> [paramlist])RP()ES(


)0 P() 10 79 PR(  -h            print help message
  -i            access XPA point on different machine \201override XPA_NSINET\202
  -m            override XPA_METHOD environment variable
  -n            don't wait for the status message after server completes
  -p            don't read \201or send\202 buf data from stdin
  -s            enter server mode
  -t [s,l]      set short and long timeouts \201override XPA_[SHORT,LONG]_TIMEOUT\202
  -u [users]    XPA points can be from specified users \201override XPA_NSUSERS\202
  -v            verify message to stdout
  --version     display version and exit)RP(


)0 P(Data read from stdin will be sent to access points matching the 
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
or host:port.
A set of qualifying parameters can be appended.
)0 P(Normally, xpaset reads data input from stdin until EOF and sends those
data to the XPA target, along with parameters entered on the command
line. For example to send a FITS file to the ds9 image display:
) 1 32 PR(  cat foo.fits | xpaset ds9 fits)RP(
)0 P(Sometimes, however, it is desirable to send only parameters to an XPA
access point, without sending data. For such cases, use the -p switch to
indicate that there is no data being send to stdin. For example, to
change the colormap used by the ds9 image display program, use:
) 1 30 PR(  csh> xpaset -p ds9 cmap Heat)RP(
Of course, this also can be accomplished by sending EOF to stdin in
any of the usual ways:
) 4 43 PR(  csh> echo "" | xpaset ds9 cmap Heat
  csh> xpaget ds9 cmap Heat < /dev/null
  csh> xpaset ds9 cmap Heat
  ^D                    # Ctl-D signals EOF)RP(
)0 P(The -s switch puts xpaset into server mode, in which commands and data
can be sent to access points without having to run xpaset multiple times.
\201Its not clear if this buys you much!\202 The syntax for sending commands
in server mode is:
)0 P() 8 24 PR(  csh> xpaset -s
  xpaset ds9 colormap I8
  ^D
  xpaset ds9 regions
  circle 200 300 40
  circle 300 400 50
  ^D
etc.)RP(
After the  required "xpaset" command is specified, optional ASCII data
can be appended \201as in the region example\202.  A single data/command set is
delimited by ^D. Note that typing ^D when a command is expected terminates
the program.
)0 P(NB: server mode only works from the terminal and only ASCII data can be
sent in this way.
)0 P()BD(Examples:)ES(
) 2 40 PR(  csh> xpaset ds9 file < foo.fits
  csh> echo "stop" | xpaset myhost:12345)RP(




)0 2 34 H(xpaget:)WB 89 Sn()WB 9 Sn( retrieve data from one or more XPA servers)EA()EH(


)BD() 1 99 PR(xpaget [-h] [-i nsinet] [-m method] [-s] [-t sval,lval] [-u users] <template|host:port> [paramlist])RP()ES(


)0 P() 8 79 PR(  -h            print help message
  -i            access XPA point on different machine \201override XPA_NSINET\202
  -m            override XPA_METHOD environment variable
  -n            don't wait for the status message after server completes
  -s            enter server mode
  -t [s,l]      set short and long timeouts \201override XPA_[SHORT,LONG]_TIMEOUT\202
  -u [users]    XPA points can be from specified users \201override XPA_NSUSERS\202
  --version     display version and exit)RP(


)0 P(Data will be retrieved from access points matching the 
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
or host:port.
A set of qualifying parameters can be appended.
)0 P()BD(Examples:)ES(
) 2 38 PR(  csh> xpaget ds9 images
  csh> xpaget myhost.harvard.edu:12345)RP(




)0 2 35 H(xpainfo:)WB 90 Sn()WB 11 Sn( send short message to one or more XPA servers)EA()EH(


)BD() 1 105 PR(xpainfo [-h] [-i nsinet] [-m method] [-n] [-s] [-t sval,lval] [-u users] <template|host:port> [paramlist])RP()ES(


)0 P() 8 79 PR(  -h            print help message
  -i            access XPA point on different machine \201override XPA_NSINET\202
  -m            override XPA_METHOD environment variable
  -n            don't wait for the status message after server completes
  -s            enter server mode
  -t [s,l]      set short and long timeouts \201override XPA_[SHORT,LONG]_TIMEOUT\202
  -u [users]    XPA points can be from specified users \201override XPA_NSUSERS\202
  --version     display version and exit)RP(


)0 P(Info will be sent to access points matching the
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
or host:port.
A set of qualifying parameters can be appended.
)0 P()BD(Examples:)ES(
) 1 30 PR(  csh> xpainfo IMAGE ds9 image)RP(




)0 2 36 H(xpaaccess:)WB 91 Sn()WB 12 Sn( see if template matches registered XPA access points)EA()EH(


)BD() 1 95 PR(xpaaccess [-c] [-h] [-i nsinet] [-m method] [-n] [-t sval,lval] [-u users] -v <template> [type])RP()ES(


)0 P() 10 79 PR(  -c            contact each access point individually
  -h            print help message
  -i            access XPA point on different machine \201override XPA_NSINET\202
  -m            override XPA_METHOD environment variable
  -n            return number of matches instead of "yes" or "no"
  -t [s,l]      set short and long timeouts \201override XPA_[SHORT,LONG]_TIMEOUT\202
  -u [users]    XPA points can be from specified users \201override XPA_NSUSERS\202
  -v            print info about each successful access point
  -V            print info or error about each access point
  --version     display version and exit)RP(


)0 P(xpaaccess returns "yes" to stdout \201with a return error code if 1\202 if there are
existing XPA access points that match the 
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
\201and optional access type: g,i,s\202. Otherwise, it returns "no" \201with a
return error code of 0\202.  If -n is specified, the number of matches is
returned instead \201both to stdout and in the returned error code\202. If
-v is specified, each access point is displayed to stdout instead of
the number of matches.

)0 P(By default, xpaaccess simply contacts the xpans name server to find
the list of registered access points that match the specified
template. It also checks to make sure the specified types are
supported by that access point. This is the fastest way to determine
available access points. However, an access point might registered but
not yet available, if, for example, the server program has not entered
its event loop to process XPA requests. To find access points that are
guaranteed to be available for processing, use the -c \201contact\202
switch.  With this switch, xpaaccess contacts each matching XPA server
\201rather than the name server\202 to make sure the registered access point
really is ready for processing. In this mode, if an access point is
registered but not available, xpaaccess will pause for a period of
time equal to the XPA_LONG_TIMEOUT, in order to give the server a
chance to ready itself. By default, this timeout is 30 seconds. You
can shorten the time of delay using the -t "short,long" switch. For
example, to shorten the delay time to 2 seconds, use:
) 1 27 PR(  xpaaccess -c -t "2,2" ds9)RP(
The first argument is the short delay value, and is ignored in this
operation. The second is the long delay timeout.

)0 P(Note also that the default xpaaccess method \201no -c switch\202 does not
check access control \201acls\202 but rather only checks whether the access
point is both registered with the xpans name server and provides the
specified type of access. In other words, the default xpaaccess could
return 'yes' when you might not actually have access. This mode also
always returns 'yes' for the xpans name server itself, regardless of
whether the name server is active. The -c \201contact\202 switch, which
contacts the access point directly, can and does check the access
control \201only for servers using version 2.1 and above\202 and also
returns the real status of xpans.











)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 37 H(Last)WB 92 Sn( updated: September 10, 2003)EH(
)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (xpamb.html) D
/Ti (The XPA Message Bus \201xpamb\202) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 13 Sn(


)0 2 38 H(xpamb:)WB 94 Sn()WB 93 Sn( the XPA Message Bus)EA()EH(


)0 2 39 H(Summary)WB 95 Sn()EH(
)0 P(The xpamb program can act as a "classical" message bus interface
between clients and servers. A client can send a data request to
the message bus, which then interfaces with multiple servers and
returns the data back to the client.


)0 2 40 H(Description)WB 96 Sn()EH(
)0 P(A "classical" message bus \201such as ToolTalk\202 consists of servers and
clients, along with a mediating program that transfers data between
different processes. XPA takes a slightly different approach in that
communication between clients and servers is direct.  This generally
is the correct technique when there is only one connection \201or even a
small number of connections\202, but can become inefficient for the
serving program if a large amount of data is being transferred to many
clients. For example, if a real-time data acquisition program is
broadcasting a FITS image to several clients, it would need to
transmit that image to each client individually.  This might interfere
with its own processing cycles.  The preferable mechanism would be to
pass the image off to an intermediate program that can then broadcast
the data to the several clients.
)0 P(The )BD(xpamb)ES( program can alleviate such problems by functioning
as a message bus in cases where such an intermediary process is
wanted.  It pre-defines a single access point named
)BD(XPAMB:xpamb)ES( to which data can be sent for re-broadcast. You
also can tell )BD(xpamb)ES( to save the data, and associate with that
data a new access point, so that it can be retrieved later on.

)0 P(All interaction with )BD(xpamb)ES( is performed through
)BD(xpaset)ES( and )BD(xpaget)ES( \201or the corresponding API
routines, )BD(XPASet\201\202)ES( and )BD(XPAGet\201\202)ES(\202 to the
)BD(XPAMB:xpamb)ES( access point. That is, )BD(xpamb)ES( is just
another XPA-enabled program that responds to requests from
clients. The paramlist is used to specify the targets to which
the data will be for re-broadcast, as well as the re-broadcast paramlist:
) 1 69 PR(  data | xpaset xpamb [switches] broadcast-target broadcast-paramlist)RP(
Optional switches are used to store data, and manipulate stored data,
and are described below.

)0 P(In its simplest form, you can, for example, send a FITS image to xpamb for
broadcasting to all ds9 image simply by executing:
) 1 51 PR(  cat foo.fits | xpaset xpamb "DS9:*" fits foo.fits)RP(
Since )BD(DS9)ES( is the class name for the ds9 image display
program, this will result in the FITS image being re-sent to all fits
access points for all active image display programs.

)0 P(You can send stored data and new data to the same set of access points at
the same time.  The stored data always is send first, followed by the new
data:
) 1 62 PR(  cat foo2.fits | xpaset xpamb -send foo "DS9:*" fits foo.fits)RP(
will first send the foo.fits file, and then the foo2.fits file to all
access points of class )BD(DS9)ES(.  Notice that in this example,
the foo2.fits file is not stored, but it could be stored by using the
)BD(-store [name])ES( switch on the command line.

)0 P(The )BD(xpaget)ES( command can be used to retrieve a data from XPA
access points or from a stored data buffer, or retrieve information
about a stored data buffer.  If no arguments are given:
) 1 14 PR(  xpaget xpamb)RP(
then information about all currently stored data buffers is returned. This
information includes the data and time at which the data was stored, the
size in bytes of the data, and the supplied info string.

)0 P(If arguments are specified, they will be in the form:
) 1 49 PR(  xpaget xpamb [-info] [-data] [name [paramlist]])RP(
If the optional )BD(-info)ES( and/or )BD(-data)ES( switches are specified, then
information and/or data will be returned for the named data buffer
following the switches. You can use either or both of these switches
in a single command. For example, if the -info switch is used:
) 1 24 PR(  xpaget xpamb -info foo)RP(
then the info about that stored data buffer will be returned.
If the -data is used with a specific name:
) 1 24 PR(  xpaget xpamb -data foo)RP(
then the stored data itself will be returned. If both are used:
) 1 30 PR(  xpaget xpamb -info -data foo)RP(
then the info will be returned, followed by the data. Note that it is an
error to specify one of these switches without a data buffer name and that
the paramlist will be ignored.

)0 P(If neither the )BD(-info)ES( or )BD(-data)ES( switch is specified, then
the name refers to an XPA access point \201with an optional paramlist
following\202.
For example:
) 1 23 PR(  xpaget xpamb ds9 file)RP(
is equivalent to:
) 1 17 PR(  xpaget ds9 file)RP(


)0 2 41 H(Options)WB 97 Sn()EH(
)0 P(For xpaset, several optional switches are used to save data and
manipulate the stored data:
)0 DL(
)0 P()0 DT()BD(-data [name])ES(
)DD( Add the supplied data buffer to a pool of stored data buffers,
using the specified name as a unique identifier for later retrieval.
An error occurs if the name already exists \201use either )BD(replace)ES(
or )BD(del)ES( to rectify this\202. The )BD(-add)ES( switch is supported
for backwards compatibility with xpa 2.0.

)0 P()0 DT()BD(-replace [name])ES(
)DD( Replace previously existing stored data having the same unique name
with new data. This essentially is a combination of the )BD(del)ES(
and )BD(data)ES( commands.

)0 P()0 DT()BD(-info ["'info string'"])ES(
)DD( When adding a data buffer, you can specify an informational
string to be stored with that data.  This string will be returned
by xpaget:
) 1 24 PR(  xpaget xpamb foo -info)RP(
\201along with other information such as the date/time of storage and the size of
the data buffer\202 if the -info switch is specified. If the info string contains
spaces, you must enclose it in )BD(two)ES( sets of quotes:
) 1 65 PR(  cat foo | xpaset xpamb -store foo -info "'this is info on foo'")RP(
The first set of quotes is removed by the shell while the second is used to
delineate the info string.

)0 P()0 DT()BD(-send [name])ES(
)DD( Broadcast the stored data buffer to the named template.

)0 P()0 DT()BD(-del [name])ES(
)DD( Delete the named data buffer and free all allocated space.)LD(

)0 P(Switches can be used in any combination that makes sense. For example:
) 1 75 PR(  cat foo.fits | xpaset xpamb -store foo -info "FITS" "DS9:*" fits foo.fits)RP(
will broadcast the foo.fits image to all access points of class
)BD(DS9)ES(.  In addition, the foo.fits file will be stored under the
name of )BD(foo)ES( for later manipulation such as:
) 1 49 PR(  xpaset -p xpamb -send foo "DS9:*" fits foo.fits)RP(
will re-broadcast the foo.fits image to all access points of class "DS9".





)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 42 H(Last)WB 98 Sn( updated: September 10, 2003)EH(
)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (xpans.html) D
/Ti (The XPA Name Server \201xpans\202) D
/Au () D
/Df f D
/ME [()] D

0 BO R
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)0 2 43 H(xpans:)WB 100 Sn()WB 99 Sn( the XPA Name Server)EA()EH(


)0 2 44 H(Summary)WB 101 Sn()EH(
) 1 70 PR(  xpans [-h] [-e] [-k sec] [-p port] [-l log] [-s security log] [-P n])RP(


)0 P() 8 71 PR(  -h            print help message
  -e            exit when there are no more XPA connections
  -k            send keepalive messages every n sec
  -l            log data base entries to specified file
  -p            listen for connections on specified port
  -s            log security info for each connection to specified file      
  -P            accept proxy requests \201P=1\202 using separate thread \201P=2\202
  --version     display version and exit)RP(


)0 P(The xpans name server is an XPA-enabled program that is used to
manage the names and ports of XPA access points. It is started
automatically when an XPA access point is registered. You can access
the name server using xpaget to get a list of registered access points.
)0 P(The )EM(xpans)ES( name server provides a crucial link between XPA
clients and servers.  When an XPA server defines an access point using
XPANew\201\202, XPACmdNew\201\202, or XPAInfoNew\201\202, the name of the access point
is registered in the name service, along with connection information.
The name server then matches class:name templates passed to it by XPA
clients with these registered entries, so that the clients can
communicate with the appropriate servers.

)0 P(The socket connection between an XPA-enabled program and
)EM(xpans)ES( is kept open until the former exits \201or explicitly
closes the connection\202. Apparently, some Internet equipment \201e.g. DSL
modems\202 can cause such a connection to time-out after a period of
inactivity. To prevent this from happening, you can use the )EM(-k
[sec])ES( switch to send a short keep-alive message to each open
connection after the specified time delay. \201Note that this
application level use of keep-alive is necessary only if you are
serving XPA-enabled clients over the Internet and have to deal with
long-term connections involving DSL or similar equipment.  XPA uses
the ordinary socket-level keep-alive, which works for all other cases.\202
)BD(NB \20112/2/2009\202: Out-of-band \201URG\202 TCP data, used by xpans
keep-alive, is changed by some Cisco routers into in-band data.
Encountering such a router will break the keep-alive function and may
break your XPA server as well. Proceed with caution!)ES(

)0 P(The )EM(xpans)ES( program will be started automatically \201assuming it
can be found in the user's path\202 when the first XPA access point is
registered.  It therefore need not be started explicitly.  However,
when started automatically, the )EM(-e)ES( switch is used, so that
the name server will exit when there are no more XPA access points
registered. If you wish to keep the name server running continually,
simply start it manually without the )EM(-e)ES( switch.

)0 P(The name server will keep a log of registered access points if the
)EM(-l [log])ES( switch is used on the command line \201this is the
case for automatic start-up\202.  The log contains enough name and connection
information to allow you to re-register all XPA access points in case
the name server process is terminated prematurely. For example, after
the ds9 access point is registered,the log will contain the entry:
) 1 35 PR(  add 838e2f67:1863 ds9 ds9 gs eric)RP(
If )EM(xpans)ES( is terminated but ds9 still is running, you
can re-register both access points for the ds9 process by running:
) 1 36 PR(  xpaset -p 838e2f67:1863 -nsconnect)RP(
Notice that the ip:port specifier is used with )EM(xpaset)ES( to bypass
the need for contacting the name server \201which does not have the name
registered yet!\202

)0 P(The name server will keep a log of security information if the )EM(-s
[security log])ES( switch is used on the command line. For each
accepted connection, \201including connections via the )EM(xpaget)ES(
command\202, information will be logged about the host issuing the
command and the parameters passed into the program. This is most
useful when )EM(xpans)ES( is accepting connections from untrusted
machines.

)0 P(When an XPA access point is removed by a server using )EM(XPAFree\201\202)ES(,
the access information is removed from the name server.  If an
XPA-enabled process is terminated, all names registered by that process
will be removed automatically.  The log file is always updated to
reflect the currently registered access points.

)0 P(The name server itself has an XPA access point names )EM(xpans)ES(
registered through which you can find out information about currently
registered access points \201assuming you have access to the name server;
see )0 41 1 A(XPA Access Control)41 0 TN TL()Ec /AF f D( for more information\202.
For each registered access point, the following information is returned:
) 5 80 PR(  class         # class of the access point
  name          # name of the access point
  access        # allowed access \201g=xpaget,s=xpaset,i=xpainfo\202
  id            # socket access method \201host:port for inet, file for local/unix\202
  user          # user name of access point owner)RP(

)0 P(For example, to display all currently registered access points, simply execute:
) 1 14 PR(  xpaget xpans)RP(
Continuing the example of ds9 above, this will return:
) 1 31 PR(  DS9 ds9 gs 838e2f67:1863 eric)RP(
If the same program has been started with different XPA access names,
you can look up only names matching a specified template. For example,
assume that ds9 has been started up using:
) 3 25 PR(  ds9 &
  ds9 -title ds9-1-eric &
  ds9 -title ds9-2-eric &)RP(
To lookup all ds9 access points which end in ".eric" and which can
be accessed using )EM(xpaset)ES(, use:
) 1 35 PR(  xpaget xpans "DS9:*.eric" "s" "*")RP(
This will return:
) 2 39 PR(  DS9 ds9-2-eric gs 838e29d3:42102 eric
  DS9 ds9-1-eric gs 838e29d3:42105 eric)RP(
The third argument "*" requests all access points from all users.
You also can specify a specific user name and only access points
registered by that user will be returned.

)0 P(The name server uses the )EM(XPA_METHOD)ES( environment variable
to determine whether it should listen for requests on INET or LOCAL
sockets.  Since XPA access points also use this environment variable,
the choice of socket method will be consistent.  Note that, when INET
sockets are used, a local server can be accessed from remote machines
if the )EM(XPA_NSINET)ES( environment variable is set to point to
the local machine.  See
)0 40 1 A(XPA Environment Variables)40 0 TN TL()Ec /AF f D(
for more information.

)0 P(An experimental feature of xpans is its ability to act as a proxy to
XPA servers behind firewalls that want to communicate with external
processes.  The basic idea is the following: an XPA server \201call it
"foo"\202 on host1, possibly behind a firewall, makes a remote connection
to a proxy-enabled xpans program on host2 \201specifying host2's XPA method\202.
For example:
) 1 59 PR(  xpaset -p foo -remote 'host2:28571' + -proxy   # on host1)RP( 
When this is done, host2 can use xpaset, xpaget, and xpainfo calls to
communicate with the XPA server foo. All command communication is
performed via the xpans socket connection between foo on host1 and
xpans on host2 \201which was initiated by foo from inside the firewall\202.
Data communication is similarly performed using a socket connection
initiated on host1 \201usually with a port value two greater than the
port value of the main xpans socket connection\202. An xpaset or xpaget
call on host2 contacts xpans, which performs an XPASet\201\202 or XPAGet\201\202
call to foo, passing commands and data back and forth between the two
programs.

)0 P(By default, proxy connections are not allowed by xpans. If the -P switch is
specified with a value of 1, proxy connection are allowed, but all proxy
communication is performed in the same thread as xpans processing. If
a value of 2 is specified, the proxy processing is performed in a
separate thread \201assuming pthreads are supported on your system\202.
Because xpa callback processing of any type can take a long time and
therefore can interfere with normal xpans processing, threaded proxy
connections \201-P 2\202 are recommended.  When using proxy connections, it
might also be useful to set the XPA_IOCALLSXPA environment variable, so
that multiple proxy requests can be handled at the same time, instead of
serially.

)0 P(Note that this proxy interface to xpans is experimental. It is used
to provide remote data analysis capabilities on the Chandra-Ed system
using ds9.  \201See http://chandra-ed.cfa.harvard.edu and
http://hea-www.harvard.edu/saord/ds9 for more details\202. As always, please
contact us if you have problems or questions.





)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 45 H(Last)WB 102 Sn( updated: January 24, 2005)EH(
)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
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/Ba f D /BO 0 D Bs
/UR (server.html) D
/Ti (XPA Server API) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 15 Sn(


)0 2 46 H(XPAServer:)WB 106 Sn()WB 103 Sn( The XPA Server-side Programming Interface)EA()EH(


)0 2 47 H(Summary)WB 107 Sn()EH(
A description of the XPA server-side programming interface.


)0 2 48 H(Introduction)WB 108 Sn()WB 104 Sn( to XPA Server Programming)EH()EA(
)0 P(Creating an XPA server is easy: you generally only need to call the
XPANew\201\202 subroutine to define a named XPA access point and set up the
send and receive callback routines.  You then enter an event loop such
as XPAMainLoop\201\202 to field XPA requests.
) 27 66 PR(  #include <xpa.h>

  XPA )0 16 1 A(XPANew)16 0 TN TL()Ec /AF f D(\201char *class, char *name, char *help,
      int \201*send_callback\202\201\202, void *send_data, char *send_mode,
      int \201*rec_callback\202\201\202,  void *rec_data,  char *rec_mode\202;

  XPA )0 17 1 A(XPACmdNew)17 0 TN TL()Ec /AF f D(\201char *class, char *name\202;

  XPACmd )0 18 1 A(XPACmdAdd)18 0 TN TL()Ec /AF f D(\201XPA xpa,
         char *name, char *help,
         int \201*send_callback\202\201\202, void *send_data, char *send_mode,
         int \201*rec_callback\202\201\202,  void *rec_data,  char *rec_mode\202;

  void )0 19 1 A(XPACmdDel)19 0 TN TL()Ec /AF f D(\201XPA xpa, XPACmd cmd\202;

  XPA )0 20 1 A(XPAInfoNew)20 0 TN TL()Ec /AF f D(\201char *class, char *name,
      int \201*info_callback\202\201\202, void *info_data, char *info_mode\202;

  int )0 21 1 A(XPAFree)21 0 TN TL()Ec /AF f D(\201XPA xpa\202;

  void )0 22 1 A(XPAMainLoop)22 0 TN TL()Ec /AF f D(\201void\202;

  int )0 23 1 A(XPAPoll)23 0 TN TL()Ec /AF f D(\201int msec, int maxreq\202;

  void )0 105 1 A(XPAAtExit)105 0 TN TL()Ec /AF f D(\201void\202;

  void )0 24 1 A(XPACleanup)24 0 TN TL()Ec /AF f D(\201void\202;)RP(

)0 2 49 H(Introduction)WB 109 Sn()EH(

To use the XPA application programming interface, a software developer
generally will include the xpa.h definitions file:
) 1 18 PR(  #include <xpa.h>)RP(
in the software module that defines or accesses an XPA access point, and
then will link against the libxpa.a library:
) 1 27 PR(  gcc -o foo foo.c libxpa.a)RP(
XPA has been compiled using both C and C++ compilers.

)0 P(A server program generally defines an XPA access point by calling the
XPANew\201\202 routine and specifies "send" and/or "receive" callback
procedures to be executed by the program when an external process
either sends data or commands to this access point or requests data or
information from this access point. A program also can define several
sub-commands for a single access point by calling XPACmdNew\201\202 and
XPACmdAdd\201\202 instead.  Having defined one or more public access points
in this way, an XPA server program enters its usual event loop \201or
uses the standard XPA event loop\202.




)0 2 50 H(XPANew:)WB 110 Sn()WB 16 Sn( create a new XPA access point)EA()EH(


)BD() 7 49 PR(  #include <xpa.h>

  XPA XPANew\201char *class, char *name, char *help,
             int \201*send_callback\202\201\202,
             void *send_data, char *send_mode,
             int \201*rec_callback\202\201\202,
             void *rec_data,  char *rec_mode\202;)RP()ES(


)0 P(Create a new XPA public access point with the class:name
identifier )0 3 1 A(template)3 0 TN TL()Ec /AF f D(
and enter this access point into the XPA name server, so that it
can be accessed by external processes. XPANew\201\202 returns an XPA struct.
Note that the length of the class and name designations must be less
than or equal to 1024 characters each.

)0 P(The XPA name server daemon, xpans, will be started automatically if it
is not running already \201assuming it can be found in the path\202.  The
program's ip address and listening port are specified by the
environment variable XPA_NSINET, which takes the form :.  If
no such environment variable exists, then xpans is started on the
current machine listening on port 14285.  It also uses 14286 as a
known port for its public access point \201so that routines do not have
to go to the name server to find the name server ip and port!\202
As of XPA 2.1.1, version information is exchanged between the xpans
process and the new access point. If the access point uses an XPA
major/minor version newer than xpans, a warning is issued by both processes,
since mixing of new servers and old xpa programs \201xpaset, xpaget,
xpans, etc.\202 is not likely to work. You can turn off the warning
message by setting the XPA_VERSIONCHECK environment variable to "false".

)0 P(The help string is meant to be returned by a request from xpaget:
) 1 25 PR(  xpaget class:name -help)RP(
)0 P(A send_callback and/or a receive_callback can be specified; at
least one of them must be specified.

)0 P(A send_callback can be specified that will be executed in response to
an external request from the xpaget program, the XPAGet\201\202 routine, or
XPAGetFd\201\202 routine. This callback is used to send data to the
requesting client.

)0 P(The calling sequence for send_callback\201\202 is:
) 7 53 PR(  int send_callback\201void *send_data, void *call_data,
    char *paramlist, char **buf, size_t *len\202
  {
    XPA xpa = \201XPA\202call_data;
    ...
    return\201stat\202;
  })RP(
)0 P(The send_mode string is of the form: "key1=value1,key2=value2,..."
The following keywords are recognized:
) 4 81 PR(  key           value           default         explanation
  ------        --------        --------        -----------
  acl           true/false      true            enable access control
  freebuf       true/false      true            free buf after callback completes)RP(
)0 P(The call_data should be recast to the XPA struct as shown.  In
addition, client-specific data can be passed to the callback in
send_data.

)0 P(The paramlist will be supplied by the client as qualifying parameters
for the callback.  There are two ways in which the send_callback\201\202
routine can send data back to the client:

)0 P(1. The send_callback\201\202 routine can fill in a buffer and pass back a
pointer to this buffer. An integer len also is returned to specify the
number of bytes of data in buf.  XPA will send this buffer to the
client after the callback is complete.

)0 P(2. The send_callback can send data directly to the client by writing
to the fd pointed by the macro:
) 1 17 PR(  xpa_datafd\201xpa\202)RP(
)0 P(Note that this fd is of the kind returned by socket\201\202 or open\201\202.

)0 P(If a buf has been allocated by a standard malloc routine, filled, and
returned to XPA, then freebuf generally is set so that the buffer will
be freed automatically when the callback is completed and data has
been sent to the client.  If a static buf is returned, freebuf should
be set to false to avoid a system error when freeing static storage.
Note that default value for freebuf implies that the callback will
allocate a buffer rather than use static storage.

)0 P(On the other hand, if buf is dynamically allocated using a method
other than a standard malloc/calloc/realloc routine \201e.g. using Perl's
memory allocation and garbage collection scheme\202, then it is necessary
to tell XPA how to free the allocated buffer. To do this, use the
XPASetFree\201\202 routine within your callback:
) 1 69 PR(  void XPASetFree\201XPA xpa, void \201*myfree\202\201void *\202, void *myfree_ptr\202;)RP(
The first argument is the usual XPA handle. The second argument is the
special routine to call to free your allocated memory. The third
argument is an optional pointer.  If not NULL, the specified free
routine is called with that pointer as its sole argument. If NULL, the
free routine is called with the standard buf pointer as its sole
argument. This is useful in cases where there is a mapping between the
buffer pointer and the actual allocated memory location, and the
special routine is expecting to be passed the former.

)0 P(If, while the callback performs its processing, an error occurs that
should be communicated to the client, then the routine XPAError should be
called:
) 1 29 PR(  XPAError\201XPA xpa, char *s\202;)RP(
)0 P(where s is an arbitrary error message.  The returned error message
string will be of the form:
) 1 42 PR(  XPA$ERROR   [error] \201class:name ip:port\202)RP(
)0 P(If the callback wants to send a specific acknowledgment message back
to the client, the routine XPAMessage can be called:
) 1 31 PR(  XPAMessage\201XPA xpa, char *s\202;)RP(
)0 P(where s is an arbitrary error message.  The returned error message
string will be of the form:
) 1 44 PR(  XPA$MESSAGE [message] \201class:name ip:port\202)RP(
)0 P(Otherwise, a standard acknowledgment is sent back to the client
after the callback is completed.

)0 P(The callback routine should return 0 if no error occurs, or -1 to
signal an error.

)0 P(A receive_callback can be specified that will be executed in response
to an external request from the xpaset program, or the XPASet \201or
XPASetFd\201\202\202 routine. This callback is used to process data received
from an external process.

)0 P(The calling sequence for receive_callback is:
) 7 59 PR(  int receive_callback\201void *receive_data, void *call_data,
    char *paramlist, char *buf, size_t len\202
  {
    XPA xpa = \201XPA\202call_data;
    ...
    return\201stat\202;
  })RP(
)0 P(The mode string is of the form: "key1=value1,key2=value2,..."
The following keywords are recognized:
) 6 92 PR(  key           value           default         explanation
  ------        --------        --------        -----------
  acl           true/false      true            enable access control
  buf           true/false      true            server expects data bytes from client
  fillbuf       true/false      true            read data into buf before executing callback
  freebuf       true/false      true            free buf after callback completes)RP(
)0 P(The call_data should be recast to the XPA struct as shown.  In
addition, client-specific data can be passed to the callback in
receive_data.

)0 P(The paramlist will be supplied by the client. In addition, if the
receive_mode keywords buf and fillbuf are true, then on entry into the
receive_callback\201\202 routine, buf will contain the data sent by the
client. If buf is true but fillbuf is false, it becomes the callback's
responsibility to retrieve the data from the client, using the data fd
pointed to by the macro xpa_datafd\201xpa\202.  If freebuf is true, then buf
will be freed when the callback is complete.

)0 P(If, while the callback is performing its processing, an error occurs
that should be communicated to the client, then the routine XPAError
can be called:
) 1 29 PR(  XPAError\201XPA xpa, char *s\202;)RP(
)0 P(where s is an arbitrary error message.

)0 P(The callback routine should return 0 if no error occurs, or -1 to
signal an error.




)0 2 51 H(XPACmdNew:)WB 111 Sn()WB 17 Sn( create a new XPA public access point for commands)EA()EH(


)BD() 3 41 PR(  #include <xpa.h>

  XPA XPACmdNew\201char *class, char *name\202;)RP()ES(


)0 P(Create a new XPA public access point for commands that will share a
common identifier class:name. Enter this access point into the XPA
name server, so that it can be accessed by external processes.
XPACmdNew\201\202 returns an XPA struct.

)0 P(It often is more convenient to have one public access point that can
manage a number of commands, rather than having individual access
points for each command. For example, it is easier to command the
ds9 image display using:
) 3 35 PR(  echo "colormap I8"   | xpaset ds9
  echo "scale log"     | xpaset ds9
  echo "file foo.fits" | xpaset ds9)RP(
)0 P(then to use:
) 3 39 PR(  echo "I8"       | xpaset ds9_colormap
  echo "log"      | xpaset ds9_scale
  echo "foo.fits" | xpaset ds9_file)RP(
)0 P(In the first case, the commands remain the same regardless of the
target XPA name.  In the second case, the command names must change
for each instance of ds9.  That is, if a second instance of ds9
called DS9 were running, it would be commanded either as:
) 3 35 PR(  echo "colormap I8"   | xpaset DS9
  echo "scale log"     | xpaset DS9
  echo "file foo.fits" | xpaset DS9)RP(
)0 P(or as:
) 3 39 PR(  echo "I8"       | xpaset DS9_colormap
  echo "log"      | xpaset DS9_scale
  echo "foo.fits" | xpaset DS9_file)RP(
)0 P(Thus, in cases where a program is going to manage many commands, it
generally is easier to define them as commands associated with the
XPACmdNew\201\202 routine, rather than as separate access points using
XPANew\201\202.

)0 P(When XPACmdNew\201\202 is called, only the class:name identifier is
specified.  Each sub-command is subsequently defined using the
XPACmdAdd\201\202 routine.




)0 2 52 H(XPACmdAdd:)WB 112 Sn()WB 18 Sn( add a command to an XPA command public access point)EA()EH(


)BD() 7 52 PR(  #include <xpa.h>

  XPACmd XPACmdAdd\201XPA xpa, char *name, char *help,
                   int \201*send_callback\202\201\202,
                   void *send_data, char *send_mode,
                   int \201*rec_callback\202\201\202,
                   void *rec_data,  char *rec_mode\202;)RP()ES(


)0 P(Add a command to an XPA command access point. The XPA argument specifies the
XPA struct returned by a call to XPANewCmd\201\202. The name argument is the
name of the command. The other arguments function identically to the
arguments in the XPANew\201\202 command, i.e., the send_callback and rec_callback
routines have identical calling sequences to their XPANew\201\202 counterparts,
with the exceptions noted below.

)0 P(When help is requested for a command access point using:
) 1 22 PR(  xpaget -h class:name)RP(
)0 P(all of the command help strings are listed.  To get help for a given
command, use:
) 1 26 PR(  xpaget -h class:name cmd)RP(
)0 P(Also, the acl keyword in the send_mode and receive_mode strings is
global to the access point, not local to the command.  Thus, the value
for the acl mode should be the same in all send_mode \201or receive_mode\202
strings for each command in a command access point. \201The acl for
send_mode need not be the same as the acl for receive_mode, though\202.




)0 2 53 H(XPACmdDel:)WB 113 Sn()WB 19 Sn( remove a command from an XPA command public access point)EA()EH(


)BD() 3 38 PR(  #include <xpa.h>

  void XPACmdDel\201XPA xpa, XPACmd cmd\202;)RP()ES(


)0 P(This routine removes a command from the list of available commands in
a given XPA.  That command will no longer be available for processing.




)0 2 54 H(XPAInfoNew:)WB 114 Sn()WB 20 Sn( define an XPA info public access point)EA()EH(


)BD() 5 51 PR(  #include <xpa.h>

  XPA XPAInfoNew\201char *class, char *name,
                 int \201*info_callback\202\201\202,
                 void *info_data, char *info_mode\202;)RP()ES(


)0 P([NB: this is an experimental interface, new to XPA 2.0, whose value
and best use is evolving.]

)0 P(A program can register interest in receiving a short message about a
particular topic from any other process that cares to send such a
message.  Neither has to be an XPA server.  For example, if a user
starts to work with a new image file called new.fits, she might
wish to alert interested programs about this new file by sending a
short message using xpainfo:
) 1 34 PR(  xpainfo IMAGEFILE /data/new.fits)RP(

)0 P(In this example, each process that has used the XPAInfoNew\201\202 call to
register interest in messages associated with the identifier IMAGEFILE
will have its info_callback\201\202 executed with the following calling
sequence:
) 4 64 PR(  int info_cb\201void *info_data, void *call_data, char *paramlist\202
  {
    XPA xpa = \201XPA\202call_data;
  })RP(
)0 P(The arguments passed to this routine are equivalent to those sent in
the send_callback\201\202 routine.  The main difference is that there is no
buf sent to the info callback: this mechanism is meant for short
announcement of messages of interest to many clients.

)0 P(The mode string is of the form: "key1=value1,key2=value2,..."
The following keywords are recognized:
) 3 69 PR(  key           value           default         explanation
  ------        --------        --------        -----------
  acl           true/false      true            enable access control)RP(
)0 P(Because no buf is passed to this callback, the usual buf-related keywords
are not applicable here.

)0 P(The information sent in the parameter list is arbitrary.  However, we
envision sending information such as file names or XPA access points
from which to collect more data.  Note that the xpainfo program and
the XPAInfo\201\202 routine that cause the info_callback to execute do not
wait for the callback to complete before returning.




)0 2 55 H(XPAFree:)WB 115 Sn()WB 21 Sn( remove an XPA public access point)EA()EH(


) 3 23 PR()BD(  #include <xpa.h>

  int XPAFree\201XPA xpa\202;)ES()RP(


)0 P(Remove the specified XPA public access point from the name server and
free all associated storage.  Note that removal from the name server
happens automatically when the process terminates, so this call is not
generally needed.  It is used when public access points are being
defined temporarily and then destroyed when no longer needed.  For
example, ds9 temporarily creates a public access point when it
loads a new image for display and destroys it when the image is
unloaded.




)0 2 56 H(XPAMainLoop:)WB 116 Sn()WB 22 Sn( optional main loop for XPA)EA()EH(


)BD() 3 21 PR(  #include <xpa.h>

  void XPAMainLoop\201\202;)RP()ES(


)0 P(Once XPA access points have been defined, a program must enter an
event loop to watch for requests from external programs. This can be
done in a variety of ways, depending on whether the event loop is
processing events other than XPA events.  In cases where there are no
non-XPA events to be processed, the program can simply call the
XPAMainLoop\201\202 event loop.  This loop is implemented essentially as
follows \201error checking is simplified in this example\202:
) 8 62 PR(  FD_ZERO\201&readfds\202;
  while\201 XPAAddSelect\201NULL, &readfds\202 \202{
    if\201 sgot = select\201swidth, &readfds, NULL, NULL, NULL\202 >0 \202
      XPAProcessSelect\201&readfds, 0\202;
    else
      break;
    FD_ZERO\201&readfds\202;
  })RP(
)0 P(The XPAAddSelect\201\202 routine sets up the select\201\202 readfds variable so
that select\201\202 will wait for I/O on all the active XPA channels.  It
returns the number of XPAs that are active; the loop will end when
there are no active XPAs. The standard select\201\202 routine is called to
wait for an external I/O request.  Since no timeout struct is passed
in argument 5, the select\201\202 call hangs until there is an external
request.  When an external I/O request is made, the XPAProcessSelect\201\202
routine is executed to process the pending requests.  In this routine,
the maxreq value determines how many requests will be processed: if
maxreq <=0, then all currently pending requests will be processed.
Otherwise, up to maxreq requests will be processed.  \201The most usual
values for maxreq is 0 to process all requests.\202

)0 P(If a program has its own Unix select\201\202 loop, then XPA access points can
be added to it by using a variation of the standard XPAMainLoop:
) 7 39 PR(  XPAAddSelect\201xpa, &readfds\202;
  [app-specific ...]
  if\201 select\201width, &readfds, ...\202 \202{
    XPAProcessSelect\201&readfds, maxreq\202;
    [app-specific ...]
    FD_ZERO\201&readfds\202;
  })RP(
)0 P(XPAAddSelect\201\202 is called before select\201\202 to add the access points.
If the first argument is NULL, then all active XPA access points
are added. Otherwise only the specified access point is added.
After select\201\202 is called, the XPAProcessSelect\201\202 routine can be called
to process XPA requests.  Once again, the maxreq value determines how
many requests will be processed: if maxreq <=0, then all currently
pending requests will be processed.  Otherwise, up to maxreq requests
will be processed.

)0 P(XPA access points can be added to
)0 38 1 A(Xt event loops)38 0 TN TL()Ec /AF f D( \201using XtAppMainLoop\201\202\202
and
)0 39 1 A(Tcl/Tk event loops)39 0 TN TL()Ec /AF f D( \201using vwait and the Tk loop\202.
When using XPA with these event loops, you only need to call:
) 1 44 PR(int XPAXtAddInput\201XtAppContext app, XPA xpa\202)RP(
or
) 1 29 PR(  int XPATclAddInput\201XPA xpa\202)RP(
respectively before entering the loop.




)0 2 57 H(XPAPoll:)WB 117 Sn()WB 23 Sn( execute existing XPA requests)EA()EH(


)BD() 3 36 PR(  #include <xpa.h>

  int XPAPoll\201int msec, int maxreq\202;)RP()ES(


)0 P(It is sometimes desirable to implement a polling loop, i.e., where one
checks for and processes XPA requests without blocking.  For this
situation, use the XPAPoll\201\202 routine:
) 1 32 PR(  XPAPoll\201int msec, int maxreq\202;)RP(
)0 P(The XPAPoll\201\202 routine will perform XPAAddSelect\201\202 and select\201\202, but with a
timeout specified in millisecs by the msec argument. If one or more
XPA requests are made before the timeout expires, the XPAProcessSelect\201\202
routine is called to process those requests. The maxreq value determines
how many requests will be processed: if maxreq < 0, then no events are
processed, but instead, the return value indicates the number of events
that are pending.  If maxreq == 0, then all currently pending requests
will be processed.  Otherwise, up to maxreq requests will be processed.
\201The most usual values for maxreq are 0 to process all requests and 1
to process one request\202.




)0 2 58 H(XPAAtExit:)WB 118 Sn()WB 105 Sn( install exit handler)EA()EH(


) 3 23 PR()BD(  #include <xpa.h>

  void XPAAtExit\201void\202;)ES()RP(


)0 P(XPAAtExit\201\202 will install an exit handler using atexit\201\202 to run XPAFree on all
XPA access points. This might be useful in cases where Unix sockets are being
used: if an explicit call to XPAFree\201\202 is not made by the program, the Unix
socket file will not be deleted immediately without an atexit handler. \201NB: this
call should not be made in a Tcl/Tk application. Accessing the Tcl native file
system after Tcl has shut down all file systems causes the Tcl/Tl program to
crash\202.




)0 2 59 H(XPACleanup:)WB 119 Sn()WB 24 Sn( release reserved XPA memory)EA()EH(


) 3 24 PR()BD(  #include <xpa.h>

  void XPACleanup\201void\202;)ES()RP(


)0 P(When XPA is initialized, it allocates a small amount of memory for the
access control list, temp directory path, and reserved commands. This
memory is found by valgrind to be "still reachable", meaning that "your
program didn't free some memory it could have". Calling the
XPACleanup\201\202 routine before exiting the program will free this memory
and make valgrind happy.




)0 2 60 H(XPA)WB 120 Sn()WB 25 Sn( Server Callback Macros)EA()EH(


)BD() 4 57 PR(  #include <xpa.h>

  xpa_class, xpa_name, xpa_method, xpa_cmdfd, xpa_datafd,
  xpa_sendian, xpa_cendian)RP()ES(


)0 P(Server routines have  access to information about the XPA being called via
the following macros \201each of which takes the xpa handle as an argument\202:
) 9 66 PR(  macro                 explanation
  ------                -----------
  xpa_class             class of this xpa
  xpa_name              name of this xpa
  xpa_method            method string \201inet or local connect info\202
  xpa_cmdfd             fd of command socket
  xpa_datafd            fd of data socket
  xpa_sendian           endian-ness of server \201"little" or "big"\202
  xpa_cendian           endian-ness of client \201"little" or "big")RP(
)0 P(The argument to these macros is the call_data pointer that is passed
to the server procedure.  This pointer should be type case to XPA
in the server routine:
) 1 27 PR(  XPA xpa = \201XPA\202call_data;)RP(

)0 P(The most important of these macros is xpa_datafd\201\202.  A server routine
that sets "fillbuf=false" in receive_mode or send_mode can use this
macro to perform I/O directly to/from the client, rather than using
buf.

)0 P(The xpa_cendian and xpa_sendian macros can be used together to determine
if the data transferred from the client is byte swapped with respect
to the server. Values for these macros are: "little", "big", or "?".
In order to do a proper conversion, you still need to know the format
of the data \201i.e., byte swapping is dependent on the size of the data
element being converted\202.




)0 2 61 H(XPA)WB 121 Sn()WB 26 Sn( Race Conditions)EA()EH(


Potential XPA race conditions and how to avoid them.


)0 P(Currently, there is only one known circumstance in which XPA can get
\201temporarily\202 deadlocked in a race condition: if two or more XPA
servers send messages to one another using an XPA client routine such
as XPASet\201\202, they can deadlock while each waits for the other server
to respond.  \201This can happen if the servers call XPAPoll\201\202 with a
time limit, and send messages in between the polling call.\202  The
reason this happens is that both client routines send a string to the
other server to establish the handshake and then wait for the server
response. Since each client is waiting for a response, neither is able
to enter its event-handling loop and respond to the other's
request. This deadlock will continue until one of the timeout periods
expire, at which point an error condition will be triggered and the
timed-out server will return to its event loop.

)0 P(Starting with version 2.1.6, this rare race condition can be
avoided by setting the XPA_IOCALLSXPA environment variable for servers
that will make client calls. Setting this variable causes all XPA
socket IO calls to process outstanding XPA requests whenever the
primary socket is not ready for IO. This means that a server making a
client call will \201recursively\202 process incoming server requests while
waiting for client completion. It also means that a server callback
routine can handle incoming XPA messages if it makes its own XPA call.
The semi-public routine oldvalue=XPAIOCallsXPA\201newvalue\202 can be used
to turn this behavior off and on temporarily. Passing a 0 will turn
off IO processing, 1 will turn it back on. The old value is returned
by the call.

)0 P(By default, the XPA_IOCALLSXPA option is turned off, because we judge
that the added code complication and overhead involved will not be
justified by the amount of its use.  Moreover, processing XPA requests
within socket IO can lead to non-intuitive results, since incoming
server requests will not necessarily be processed to completion in the
order in which they are received.

)0 P(Aside from setting XPA_IOCALLSXPA, the simplest way to avoid this race
condition is to multi-process: when you want to send a client message,
simply start a separate process to call the client routine, so that
the server is not stopped. It probably is fastest and easiest to use
fork\201\202 and then have the child call the client routine and exit. But
you also can use either the system\201\202 or popen\201\202 routine to start one
of the command line programs and do the same thing. Alternatively, you
can use XPA's internal launch\201\202 routine instead of system\201\202. Based on
fork\201\202 and exec\201\202, this routine is more secure than system\201\202 because
it does not call /bin/sh.

)0 P(Starting with version 2.1.5, you also can send an XPAInfo\201\202 message with
the mode string "ack=false". This will cause the client to send a message
to the server and then exit without waiting for any return message from
the server. This UDP-like behavior will avoid the server deadlock when
sending short XPAInfo messages.



























)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 62 H(Last)WB 122 Sn( updated: September 10, 2003)EH(
)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (oom.html) D
/Ti (Out of Memory) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 27 Sn(


)0 2 63 H(Xpaoom:)WB 124 Sn()WB 123 Sn( What happens when XPA runs out of memory?)EA()EH(


)0 2 64 H(Summary)WB 125 Sn()EH(
)0 P(When XPA can't allocate memory, it exits. You can arrange to have it call
longjmp\201\202 instead.


)0 2 65 H(Description)WB 126 Sn()EH(
)0 P(When an XPA server or client cannot allocate memory, it will attempt to
output an error message and then exit. If this is not satisfactory \201e.g.,
perhaps your program is interactive and can recover from OOM errors\202, you
can tell XPA to call longjmp\201\202 to go to a recovery branch. To pass the 
requisite jmp_buf variable to XPA, make the following call:
) 1 24 PR(  XPASaveJmp\201void *env\202;)RP(
The value of env is the address of a jmp_buf variable that was previously 
passed to setjmp\201\202. For example:
) 9 62 PR(  jmp_buf env;
  ...
  if\201 setjmp\201jmp_buf\202 != 0 \202{
    /* out of memory -- take corrective action, if possible */
  } else {
    /* save env for XPA */
    XPASaveJmp\201\201void *\202&jmp_buf\202;
  }
  // enter main loop ...)RP(





)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 66 H(Last)WB 127 Sn( updated: April 7, 2009)EH(

)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (client.html) D
/Ti (XPA Client API) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 28 Sn(


)0 2 67 H(XPAClient:)WB 130 Sn()WB 128 Sn( The XPA Client-side Programming Interface)EA()EH(


)0 2 68 H(Summary)WB 131 Sn()EH(
A description of the XPA client-side programming interface.


)0 2 69 H(Introduction)WB 132 Sn()WB 129 Sn( to XPA Client Programming)EH()EA(
)0 P(Sending/receiving data to/from an XPA access point is easy: you
generally only need to call the XPAGet\201\202 or XPASet\201\202 subroutines.
) 33 71 PR(  #include <xpa.h>

  int )0 31 1 A(XPAGet)31 0 TN TL()Ec /AF f D(\201XPA xpa,
      char *template, char *paramlist, char *mode,
      char **bufs, size_t *lens, char **names, char **messages, int n\202;

  int )0 32 1 A(XPASet)32 0 TN TL()Ec /AF f D(\201XPA xpa,
      char *template, char *paramlist, char *mode,
      char *buf, size_t len, char **names, char **messages, int n\202;

  int )0 33 1 A(XPAInfo)33 0 TN TL()Ec /AF f D(\201XPA xpa,
      char *template, char *paramlist, char *mode,
      char **names, char **messages, int n\202;

  int )0 37 1 A(XPAAccess)37 0 TN TL()Ec /AF f D(\201XPA xpa,
      char *template, char *paramlist, char *mode,
      char **names, char **messages, int n\202;

  int )0 34 1 A(XPAGetFd)34 0 TN TL()Ec /AF f D(\201XPA xpa,
      char *template, char *paramlist, char *mode,
      int *fds, char **names, char **messages, int n\202;

  int )0 35 1 A(XPASetFd)35 0 TN TL()Ec /AF f D(\201XPA xpa,
      char *template, char *paramlist, char *mode,
      int fd, char **names, char **messages, int n\202;

  XPA )0 29 1 A(XPAOpen)29 0 TN TL()Ec /AF f D(\201char *mode\202;

  void )0 30 1 A(XPAClose)30 0 TN TL()Ec /AF f D(\201XPA xpa\202;

  int )0 36 1 A(XPANSLookup)36 0 TN TL()Ec /AF f D(\201XPA xpa,)WR(
      char *template, char *type,
      char ***classes, char ***names, char ***methods, char ***infos\202;)RP(

)0 2 70 H(Introduction)WB 133 Sn()EH(

To use the XPA application programming interface, a software developer
generally will include the xpa.h definitions file:
) 1 18 PR(  #include <xpa.h>)RP(
in the software module that defines or accesses an XPA access point and
then will link against the libxpa.a library:
) 1 27 PR(  gcc -o foo foo.c libxpa.a)RP(
XPA has been compiled using both C and C++ compilers.
)0 P(Client communication with XPA public access points generally is
accomplished using XPAGet\201\202 or XPASet\201\202 within a program \201or xpaget
and xpaset at the command line\202.  Both routines require specification
of the name of the access point.  If a )0 3 1 A(template)3 0 TN TL()Ec /AF f D(
is used to specify the access point name \201e.g., "ds9*"\202, then
communication will take place with all servers matching that template.




)0 2 71 H(XPAGet:)WB 134 Sn()WB 31 Sn( retrieve data from one or more XPA servers)EA()EH(


)BD() 6 70 PR(  #include <xpa.h>

  int XPAGet\201XPA xpa,
             char *template, char *paramlist, char *mode,
             char **bufs, size_t *lens, char **names, char **messages,
             int n\202;)RP()ES(


)0 P(Retrieve data from one or more XPA servers whose class:name identifier
matches the specified template.

)0 P(A 
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
of the form "class1:name1" is sent to the
XPA name server, which returns a list of at most n matching XPA
servers.  A connection is established with each of these servers and
the paramlist string is passed to the server as the data transfer
request is initiated. If an XPA struct is passed to the call, then the
persistent connections are updated as described above. Otherwise,
temporary connections are made to the servers \201which will be closed
when the call completes\202.

)0 P(The XPAGet\201\202 routine then retrieves data from at most n XPA servers,
places these data into n allocated buffers and places the buffer
pointers in the bufs array. The length of each buffer is stored in the
lens array. A string containing the class:name and ip:port is stored
in the name array.  If a given server returned an error or the server
callback sends a message back to the client, then the message will be
stored in the associated element of the messages array.  NB: if
specified, the name and messages arrays must be of size n or greater.

)0 P(The returned message string will be of the form:
) 1 46 PR(  XPA$ERROR error-message \201class:name ip:port\202)RP(
or
) 1 42 PR(  XPA$MESSAGE message \201class:name ip:port\202)RP(
)0 P(Note that when there is an error stored in an messages entry, the
corresponding bufs and lens entry may or may not be NULL and 0
\201respectively\202, depending on the particularities of the server.

)0 P(The return value will contain the actual number of servers that were
processed.  This value thus will hold the number of valid entries in
the bufs, lens, names, and messages arrays, and can be used to loop
through these arrays.  In names and/or messages is NULL, no information is
passed back in that array.

)0 P(The bufs, names, and messages arrays should be freed upon completion \201if
they are not NULL\202;

)0 P(The mode string is of the form: "key1=value1,key2=value2,..."
The following keywords are recognized:
) 4 115 PR(  key           value           default         explanation
  ------        --------        --------        -----------
  ack           true/false      true            if false, don't wait for ack from server \201after callback completes\202
  doxpa         true/false      true            client processes xpa requests)RP(
)0 P(The ack keyword is not very useful, since the server completes the callback
in order to return the data anyway.  It is here for completion \201and perhaps
for future usefulness\202.

)0 P(Normally, an XPA client will process incoming XPA server requests
while awaiting the completion of the client request.  Setting this
variable to "false" will prevent XPA server requests from being
processed by the client.
        
)0 P()BD(Example:)ES(
) 25 70 PR(  #include <xpa.h>

  #define NXPA 10
  int  i, got;
  size_t  lens[NXPA];
  char *bufs[NXPA];
  char *names[NXPA];
  char *messages[NXPA];
  got = XPAGet\201NULL, "ds9", "file", NULL, bufs, lens, names, messages,
  NXPA\202;
  for\201i=0; i<got; i++\202{
    if\201 messages[i] == NULL \202{
      /* process buf contents */
      ProcessImage\201bufs[i], ...\202;
      free\201bufs[i]\202;
    }
    else{
      /* error processing */
      fprintf\201stderr, "ERROR: %s \201%s\202\200n", messages[i], names[i]\202;
    }
    if\201 names[i] \202
      free\201names[i]\202;
    if\201 messages[i] \202
      free\201messages[i]\202;
  })RP(




)0 2 72 H(XPASet:)WB 135 Sn()WB 32 Sn( send data to one or more XPA servers)EA()EH(


)BD() 6 66 PR(  #include <xpa.h>

  int XPASet\201XPA xpa,
             char *template, char *paramlist, char *mode,
             char *buf, size_t len, char **names, char **messages,
             int n\202;)RP()ES(


)0 P(Send data to one or more XPA servers whose class:name identifier
matches the specified template.

)0 P(A 
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
of the form "class1:name1" is sent to the
XPA name server, which returns a list of at most n matching XPA
servers.  A connection is established with each of these servers and
the paramlist string is passed to the server as the data transfer
request is initiated. If an XPA struct is passed to the call, the
persistent connections are updated as described above. Otherwise,
temporary connections are made to the servers \201which will be closed
when the call completes\202.

)0 P(The XPASet\201\202 routine transfers data from buf to the XPA servers.
The length of buf \201in bytes\202 should be placed in the len variable.

)0 P(A string containing the class:name and ip:port of each of these server
is returned in the name array.  If a given server returned an error or
the server callback sends a message back to the client, then the
message will be stored in the associated element of the messages
array. NB: if specified, the name and messages arrays must be of size
n or greater.

)0 P(The returned message string will be of the form:

) 1 42 PR(  XPA$ERROR   [error] \201class:name ip:port\202)RP(
or
) 1 44 PR(  XPA$MESSAGE [message] \201class:name ip:port\202)RP(
)0 P(The return value will contain the actual number of servers that were
processed.  This value thus will hold the number of valid entries in
the names and messages arrays, and can be used to loop through these
arrays.  In names and/or messages is NULL, no information is passed back
in that particular array.

)0 P(The mode string is of the form: "key1=value1,key2=value2,..."
The following keywords are recognized:
) 5 115 PR(  key           value           default         explanation
  ------        --------        --------        -----------
  ack           true/false      true            if false, don't wait for ack from server \201after callback completes\202
  verify        true/false      false           send buf from XPASet[Fd] to stdout
  doxpa         true/false      true            client processes xpa requests)RP(
)0 P(The ack keyword is useful in cases where one does not want to wait for
the server to complete, e.g. if a lot of processing needs to be done
by the server on the passed data or when the success of the server
operation is not relevant to the client.

)0 P(Normally, an XPA client will process incoming XPA server requests
while awaiting the completion of the client request.  Setting this
variable to "false" will prevent XPA server requests from being
processed by the client.
        
)0 P()BD(Example:)ES(
) 21 75 PR(  #include <xpa.h>

  #define NXPA 10
  int  i, got;
  size_t  len;
  char *buf;
  char *names[NXPA];
  char *messages[NXPA];
  ...
  [fill buf with data and set len to the length, in bytes, of the data]
  ...
  /* send data to all access points */
  got = XPASet\201NULL, "ds9", "fits", NULL, buf, len, names, messages, NXPA\202;
  /* error processing */
  for\201i=0; i<got; i++\202{
    if\201 messages[i] \202{
      fprintf\201stderr, "ERROR: %s \201%s\202\200n", messages[i], names[i]\202;
    }
    if\201 names[i] \202    free\201names[i]\202;
    if\201 messages[i] \202 free\201messages[i]\202;
  })RP(
        



)0 2 73 H(XPAInfo:)WB 136 Sn()WB 33 Sn( send short message to one or more XPA servers)EA()EH(


)BD() 5 58 PR(  #include <xpa.h>

  int XPAInfo\201XPA xpa,
              char *template, char *paramlist, char *mode,
              char **names, char **messages, int n\202;)RP()ES(


)0 P(Send a short paramlist message to one or more XPA servers whose
class:name identifier matches the specified
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(.

)0 P(A
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
of the form "class1:name1" is sent to the
XPA name server, which returns a list of at most n matching XPA
servers.  A connection is established with each of these servers and
the paramlist string is passed to the server as the data transfer
request is initiated. If an XPA struct is passed to the call, then the
persistent connections are updated as described above. Otherwise,
temporary connections are made to the servers \201which will be closed
when the call completes\202.

)0 P(The XPAInfo\201\202 routine does not send data from a buf to the XPA
servers. Only the paramlist is sent.  The semantics of the paramlist
is not formalized, but at a minimum is should tell the server how to
get more information.  For example, it might contain the class:name
of the XPA access point from which the server \201acting as a client\202
can obtain more info using XPAGet.

)0 P(A string containing the class:name and ip:port of each server is
returned in the name array.  If a given server returned an error or
the server callback sends a message back to the client, then the
message will be stored in the associated element of the messages
array.  The returned message string will be of the form:
) 1 48 PR(  XPA$ERROR   error-message \201class:name ip:port\202)RP(
or
) 1 46 PR(  XPA$MESSAGE message     \201class:name ip:port\202)RP(
)0 P(The return value will contain the actual number of servers that were
processed.  This value thus will hold the number of valid entries in
the names and messages arrays, and can be used to loop through these
arrays.  In names and/or messages is NULL, no information is passed back
in that array.

)0 P(The following keywords are recognized:
) 3 88 PR(  key           value           default         explanation
  ------        --------        --------        -----------
  ack           true/false      true            if false, don't wait for ack from server)RP(
)0 P(When ack is false, XPAInfo\201\202 will not wait for an error return from the XPA
server. This means, in effect, that XPAInfo will send its paramlist string
to the XPA server and then exit: no information will be sent from the server
to the client. This UDP-like behavior is essential to avoid race
conditions in cases where XPA servers are sending info messages to
other servers. If two servers try to send each other an info message
at the same time and then wait for an ack, a race condition will result and
one or both will time out.

)0 P()BD(Example:)ES(
) 1 65 PR(  \201void\202XPAInfo\201NULL, "IMAGE", "ds9 image", NULL, NULL, NULL, 0\202;)RP(
        



)0 2 74 H(XPAGetFd:)WB 137 Sn()WB 34 Sn( retrieve data from one or more XPA servers and write to files)EA()EH(


)BD() 5 63 PR(  #include <xpa.h>

  int XPAGetFd\201XPA xpa,
               char *template, char *paramlist, char *mode,
               int *fds, char **names, char **messages, int n\202;)RP()ES(


)0 P(Retrieve data from one or more XPA servers whose class:name identifier
matches the specified
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
and write it to files associated with
one or more standard I/O fds \201i.e, handles returned by open\201\202\202.

)0 P(A 
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
of the form "class1:name1" is sent to the
XPA name server, which returns a list of at most ABS\201n\202 matching XPA
servers.  A connection is established with each of these servers and
the paramlist string is passed to the server as the data transfer
request is initiated. If an XPA struct is passed to the call, then the
persistent connections are updated as described above. Otherwise,
temporary connections are made to the servers \201which will be closed
when the call completes\202.

)0 P(The XPAGetFd\201\202 routine then retrieves data from the XPA servers,
and write these data to the fds associated with one or more fds
\201i.e., results from open\202. Is n is positive, then there will be n fds
and the data from each server will be sent to a separate fd. If n is
negative, then there is only 1 fd and all data is sent to this single
fd. \201The latter is how xpaget is implemented.\202

)0 P(A string containing the class:name and ip:port is stored in the name
array.  If a given server returned an error or the server callback
sends a message back to the client, then the message will be stored in
the associated element of the messages array.  NB: if specified, the
name and messages arrays must be of size n or greater.

)0 P(The returned message string will be of the form:
) 1 48 PR(  XPA$ERROR   error-message \201class:name ip:port\202)RP(
or
) 1 46 PR(  XPA$MESSAGE message     \201class:name ip:port\202)RP(
)0 P(Note that when there is an error stored in an messages entry, the
corresponding bufs and lens entry may or may not be NULL and 0
\201respectively\202, depending on the particularities of the server.

)0 P(The return value will contain the actual number of servers that were
processed.  This value thus will hold the number of valid entries in
the bufs, lens, names, and messages arrays, and can be used to loop
through these arrays.  In names and/or messages is NULL, no information is
passed back in that array.

)0 P(The mode string is of the form: "key1=value1,key2=value2,..."
The following keywords are recognized:
) 3 115 PR(  key           value           default         explanation
  ------        --------        --------        -----------
  ack           true/false      true            if false, don't wait for ack from server \201after callback completes\202)RP(
)0 P(The ack keyword is not very useful, since the server completes the callback
in order to return the data anyway.  It is here for completion \201and perhaps
for future usefulness\202.
        
)0 P()BD(Example:)ES(
) 19 72 PR(  #include <xpa.h>
  #define NXPA 10
  int  i, got;
  int fds[NXPA];
  char *names[NXPA];
  char *messages[NXPA];
  for\201i=0; i<NXPA; i++\202
    fds[i] = open\201...\202;
  got = XPAGetFd\201NULL, "ds9", "file", NULL, fds, names, messages, NXPA\202;
  for\201i=0; i<got; i++\202{
    if\201 messages[i] != NULL \202{
      /* error processing */
      fprintf\201stderr, "ERROR: %s \201%s\202\200n", messages[i], names[i]\202;
    }
    if\201 names[i] \202
      free\201names[i]\202;
    if\201 messages[i] \202
      free\201messages[i]\202;
  })RP(




)0 2 75 H(XPASetFd:)WB 138 Sn()WB 35 Sn( send data from stdin to one or more XPA servers)EA()EH(

)ES(
) 5 60 PR(  #include <xpa.h>

  int XPASetFd\201XPA xpa,
               char *template, char *paramlist, char *mode,
               int fd, char **names, char **messages, int n\202)RP()ES(


)0 P(Read data from a standard I/O fd and send it to one or more XPA
servers whose class:name identifier matches the specified
)0 3 1 A(template.

)0 P(A
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
of the form "class1:name1" is sent to the
XPA name server, which returns a list of at most n matching XPA
servers.  A connection is established with each of these servers and
the paramlist string is passed to the server as the data transfer
request is initiated. If an XPA struct is passed to the call, then the
persistent connections are updated as described above. Otherwise,
temporary connections are made to the servers \201which will be closed
when the call completes\202.

)0 P(The XPASetFd\201\202 routine then reads bytes from the specified fd
until EOF and sends these bytes to the XPA servers.  
The final parameter n specifies the maximum number of servers to contact.
A string containing the class:name and ip:port of each server is returned in
the name array.  If a given server returned an error, then the error
message will be stored in the associated element of the messages array.
NB: if specified, the name and messages arrays must be of size n or greater.

)0 P(The return value will contain the actual number of servers that were
processed.  This value thus will hold the number of valid entries in
the names and messages arrays, and can be used to loop through these
arrays.  In names and/or messages is NULL, no information is passed back
in that array.

)0 P(The mode string is of the form: "key1=value1,key2=value2,..."
The following keywords are recognized:
) 4 115 PR(  key           value           default         explanation
  ------        --------        --------        -----------
  ack           true/false      true            if false, don't wait for ack from server \201after callback completes\202
  verify        true/false      false           send buf from XPASet[Fd] to stdout)RP(
)0 P(The ack keyword is useful in cases where one does not want to wait for
the server to complete, e.g. is a lot of processing needs to be done
on the passed data or when the success of the server operation is not
relevant to the client.

)0 P()BD(Example:)ES(
) 19 71 PR(  #include <xpa.h>

  #define NXPA 10
  int  i, got;
  int fd;
  char *names[NXPA];
  char *messages[NXPA];
  fd = open\201...\202;
  got = XPASetFd\201NULL, "ds9", "fits", NULL, fd, names, messages, NXPA\202;
  for\201i=0; i<got; i++\202{
    if\201 messages[i] != NULL \202{
      /* error processing */
      fprintf\201stderr, "ERROR: %s \201%s\202\200n", messages[i], names[i]\202;
    }
    if\201 names[i] \202
      free\201names[i]\202;
    if\201 messages[i] \202
      free\201messages[i]\202;
  })RP(




)0 2 76 H(XPAOpen:)WB 139 Sn()WB 29 Sn( allocate a persistent client handle)3 0 TN TL()Ec /AF f D()EH(


)BD() 3 26 PR(  #include <xpa.h>

  XPA XPAOpen\201char *mode\202;)RP()ES(


)0 P(XPAOpen\201\202 allocates a persistent XPA struct that can be used with
calls to XPAGet\201\202, XPASet\201\202, XPAInfo\201\202, XPAGetFd\201\202, and
XPASetFd\201\202. Persistence means that a connection to an XPA server is
not closed when one of the above calls is completed but will be
re-used on successive calls. Using XPAOpen\201\202 therefore saves the time
it takes to connect to a server, which could be significant with slow
connections or if there will be a large number of exchanges with a
given access point.  The mode argument currently is ignored \201"reserved
for future use"\202.

)0 P(An XPA struct is returned if XPAOpen\201\202 was successful; otherwise NULL
is returned. This returned struct can be passed as the first argument
to XPAGet\201\202, etc.  Those calls will update the list of active XPA
connections.  Already connected servers \201from a previous call\202 are
left connected and new servers also will be connected.  Old servers
\201from a previous call\202 that are no longer needed are disconnected.
The connected servers will remain connected when the next call to
XPAGet\201\202 is made and connections are once again updated.

)0 P()BD(Example:)ES(
) 4 22 PR( #include <xpa.h>

  XPA xpa;
  xpa = XPAOpen\201NULL\202;)RP(




)0 2 77 H(XPAClose:)WB 140 Sn()WB 30 Sn( close a persistent XPA client handle)EA()EH(


)BD() 3 25 PR(  #include <xpa.h>

  void XPAClose\201XPA xpa\202;)RP()ES(


)0 P(XPAClose closes the persistent connections associated with this XPA struct
and frees all allocated space. It also closes the open sockets connections
to all XPA servers that were opened using this handle.

)0 P()BD(Example:)ES(
) 4 18 PR(  #include <xpa.h>

  XPA xpa;
  XPAClose\201xpa\202;)RP(




)0 2 78 H(XPANSLookup:)WB 141 Sn()WB 36 Sn( lookup registered XPA access points)EA()EH(


)BD() 6 49 PR(  #include <xpa.h>

  int XPANSLookup\201XPA xpa,
                  char *template, char type,
                  char ***classes, char ***names,
                  char ***methods, char ***infos\202)RP()ES(


)0 P(XPA routines act on a class:name identifier in such a way
that all access points that match the identifier are processed.  It is
sometimes desirable to choose specific access points from the
candidates that match the
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(.  In order to do this, the
XPANSLookup routine can be called to return a list of matches, so that
specific class:name instances can then be fed to XPAGet\201\202, XPASet\201\202, etc.

)0 P( The first argument is an optional XPA struct. If non-NULL, the
existing name server connection associated with the specified xpa is
used to query the xpans name server for matching templates. Otherwise,
a new \201temporary\202 connection is established with the name server.

)0 P(The second argument to XPANSLookup is the class:name 
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
to match.

)0 P(The third argument for XPANSLookup\201\202 is the type of access and can be
any combination of:
) 5 62 PR(  type          explanation
  ------        -----------
  g             xpaget calls can be made on this access point
  s             xpaset calls can be made on this access point
  i             xpainfo calls can be made on this access point)RP(
)0 P(The call typically specifies only one of these at a time.

)0 P(The final arguments are pointers to arrays that will be filled
in and returned by the name server. The name server will allocate and
return arrays filled with the classes, names, and methods of all XPA
access points that match the )0 3 1 A(template)3 0 TN TL()Ec /AF f D(
and have the specified type. Also returned are info strings, which
generally are used internally by the client routines. These can be
ignored \201but the strings must be freed\202.  The function returns the
number of matches. The returned value can be used to loop through the
matches:

)BD(Example:)ES(
) 24 73 PR(  #include <xpa.h>

  char **classes;
  char **names;
  char **methods;
  char **infos;
  int i, n;
  n = XPANSLookup\201NULL, "foo*", "g", &classes, &names, &methods, &infos\202;
  for\201i=0; i<n; i++\202{
    [more specific checks on possibilities ...]
    [perhaps a call to XPAGet for those that pass, etc. ...]
    /* don't forget to free alloc'ed strings when done */
    free\201classes[i]\202;
    free\201names[i]\202;
    free\201methods[i]\202;
    free\201infos[i]\202;
  }
  /* free up arrays alloc'ed by names server */
  if\201 n > 0 \202{
    free\201classes\202;
    free\201names\202;
    free\201methods\202;
    free\201infos\202;
  })RP(
)0 P(The specified 
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
also can be a host:port specification, for example:
) 1 14 PR(  myhost:12345)RP(
)0 P(In this case, no connection is made to the name server. Instead, the
call will return one entry such that the ip array contains the ip for
the specified host and the port array contains the port.  The class
and name entries are set to the character "?", since the class and
name of the access point are not known. 




)0 2 79 H(XPAAccess:)WB 142 Sn()WB 37 Sn( return XPA access points matching
template \201XPA 2.1 and above\202)EA()EH(


)BD() 5 60 PR(  #include <xpa.h>

  int XPAAccess\201XPA xpa,
                char *template, char *paramlist, char *mode,
                char **names, char **messages, int n\202;)RP()ES(


)0 P(The XPAAccess routine returns the public access points that match the
specified second argument )0 3 1 A(template)3 0 TN TL()Ec /AF f D( and
have the specified access type.

)0 P(A
)0 3 1 A(template)3 0 TN TL()Ec /AF f D(
of the form "class1:name1" is sent to the
XPA name server, which returns a list of at most n matching XPA
servers.  A connection is established with each of these servers and
the paramlist string is passed to the server as the data transfer
request is initiated. If an XPA struct is passed to the call, then the
persistent connections are updated as described above. Otherwise,
temporary connections are made to the servers \201which will be closed
when the call completes\202.

)0 P(The XPAAccess\201\202 routine retrieves names from at most n XPA servers
that match the specified template and that were checked for access
using the specified mode.  The return string contains both the
class:name and ip:port.  If a given server returned an error or the
server callback sends a message back to the client, then the message
will be stored in the associated element of the messages array.
NB: if specified, the name and messages arrays must be of size n or greater.

)0 P(The returned message string will be of the form:
) 1 46 PR(  XPA$ERROR error-message \201class:name ip:port\202)RP(
)0 P(Note that names of matching registered access points are always
returned but may not be valid; it is not sufficient to assume that the
returned number of access points is the number of valid access points.
Rather, it is essential to check the messages array for error
messages.  Any string in the messages array is an error message and
indicated that the associated access point is not available.

)0 P(For example, assume that a server registers a number of access points
but delays entering its event loop. If a call to XPAAccess\201\202 is made
before the event loop is entered, the call will timeout \201after waiting
for the long timeout period\202 and return an error of the form:
) 1 65 PR(  XPA$ERROR: timeout waiting for server authentication \201XPA:xpa1\202)RP(
The error means that the XPA access point has been registered but is
not yet available \201because events are not being processed\202. When the
server finally enters its event loop, subsequent calls to XPAAccess\201\202
will return successfully.

)0 P(NB: This routine only works with XPA servers built with XPA 2.1.x and later.
Servers with older versions of XPA will return the error message:

  XPA$ERROR invalid xpa command in initialization string

If you get this error message, then the old server actually is ready
for access, since it got to the point of fielding the query! The
xpaaccess program, for example, ignores this message in order to work
properly with older servers.

)0 P(The third argument for XPAAccess\201\202 is the type of access and can be
any combination of:
) 5 62 PR(  type          explanation
  ------        -----------
  g             xpaget calls can be made on this access point
  s             xpaset calls can be made on this access point
  i             xpainfo calls can be made on this access point)RP(
)0 P(The mode string argument is of the form: "key1=value1,key2=value2,..."
The following keywords are recognized:
) 3 115 PR(  key           value           default         explanation
  ------        --------        --------        -----------
  ack           true/false      true            if false, don't wait for ack from server \201after callback completes\202)RP(
)0 P(The ack keyword is not very useful, since the server completes the callback
in order to return the data anyway.  It is here for completion \201and perhaps
for future usefulness\202.























)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 80 H(Last)WB 143 Sn( updated: March 10, 2007)EH(

)WB NL
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/Ba f D /BO 0 D Bs
/UR (xt.html) D
/Ti (XPA/Xt Interface) D
/Au () D
/Df f D
/ME [()] D

0 BO R
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)0 2 81 H(XPAXt:)WB 145 Sn()WB 144 Sn( the XPA Interface to Xt \201X Windows\202)EA()EH(


)0 2 82 H(Summary)WB 146 Sn()EH(
Describes how XPA access points can be added to X Toolkit \201Xt\202 programs.


)0 2 83 H(Description)WB 147 Sn()EH(
)0 P(XPA supports Xt programs: you can call XPANew\201\202, XPACmdNew\201\202, or
XPAInfoNew\201\202 within any C routine to add XPA server callbacks to an Xt
program.  Since an Xt program has its own event loop call \201i.e.,
XtAppMainLoop\201\202\202, it therefore does not need or want to use the XPA
even loop.  Thus, in order to add XPA access points to the standard Xt
event loop, the following routine should be called before entering the
loop:
) 1 46 PR(  int XPAXtAddInput\201XtAppContext app, XPA xpa\202)RP(
)0 P(The XPAAddAddInput\201\202 routine will add XPA access points to the Xt event
loop by making calls to the standard XtAppAddInput\201\202 routine. \201If the
XtAppContext argument is NULL, then the alternate XtAddInput\201\202 routine
is used instead.\202  If the xpa argument is NULL, then all active XPA
access points are added to the loop.  If xpa is not NULL, then only
the specified access point is added.  The latter type of call is used
to add new access points from within a callback, after the program has
entered the XtAppMainLoop\201\202 even loop.





)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 84 H(Last)WB 148 Sn( updated: September 10, 2003)EH(
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DS
/Ba f D /BO 0 D Bs
/UR (tcl.html) D
/Ti (XPA/Tcl Interface) D
/Au () D
/Df f D
/ME [()] D

0 BO R
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)0 2 85 H(XPATcl:)WB 151 Sn()WB 149 Sn( the XPA Interface to the Tcl/Tk Environment)EA()EH(


)0 2 86 H(Summary)WB 152 Sn()EH(

)0 P(Tcl/Tk programs can act as XPA clients and/or servers using the Tcl
interface to XPA that is contained in the libtclxpa.so shared object.

)0 2 87 H(Server)WB 153 Sn( Routines)EH(

) 11 70 PR(  set xpa [xpanew class name help sproc sdata smode rproc rdata rmode]
  xpafree xpa
  set xpa [xpanew class name help iproc idata imode]
  set xpa [xpacmdnew class name]
  xpacmdadd xpa name help sproc sdata smode rproc rdata rmode
  xpacmddel xpa cmd
  set val [xparec xpa option]
    options: name, class, method, cmdfd, datafd, cmdchan, datachan
  xpasetbuf xpa buf len
  xpaerror xpa message
  xpamessage xpa message)RP(

)0 2 88 H(Client)WB 154 Sn( Routines)EH(
 
) 11 69 PR(  set xpa [xpaopen mode]
  xpaclose xpa
  set got [xpaget xpa template paramlist mode bufs lens names errs n]
  set got [xpaget xpa template paramlist mode chans names errs n]
  set got [xpaset xpa template paramlist mode buf len names errs n]
  set got [xpasetfd xpa template paramlist mode chan names errs n]
  set got [xpainfo xpa template paramlist mode names errs n]
  # NB: 2.1 calling sequence change
  # set got [xpaaccess template type] \2012.0.5\202
  set got [xpaaccess xpa template paramlist mode names errs n]
  set got [xpanslookup template type classes names methods])RP(


)0 2 89 H(Description)WB 155 Sn()EH(
)0 P(You can call XPANew\201\202, XPACmdNew\201\202, or XPAInfoNew\201\202 within a C
routine to add C-based XPA server callbacks to a TCL/Tk program that
uses a Tcl/Tk event loop \201either vwait\201\202 or the Tk event loop\202;
Such a program does not need or want to use the XPA event loop.
Therefore, in order to add XPA access points to the Tcl/Tk loop, the
following routine should be called beforehand:
) 1 30 PR(  int XPATclAddInput\201XPA xpa\202;)RP(
)0 P(Normally, the xpa argument is NULL, meaning that all current XPA
access points are registered with the event loop.  However, if a
single XPA access point is to be added \201i.e., after the event loop is
started\202 then the handle of that XPA access point can be passed to
this routine.

)0 P(The significance of the XPA/TCL interface goes beyond the support for
using XPA inside C code. The interface allows you to write XPA
servers and to make calls to the XPA client interface within the Tcl
environment using the Tcl language directly. The XPA/Tcl
interface can be loaded using the following package command:
) 1 28 PR(  package require tclxpa 2.0)RP(
Alternatively, you can load the shared object \201called libtclxpa.so \202 directly:
) 1 30 PR(  load .../libtclxpa.so tclxpa)RP(
)0 P(Once the tclxpa package is loaded, you can use Tcl versions of XPA
routines to define XPA servers or make client XPA calls.  The
interface for these routines is designed to match the Unix XPA
interface as nearly as possible.  Please refer to
)0 15 1 A(XPA Servers)15 0 TN TL()Ec /AF f D(
and
)0 28 1 A(XPA Clients)28 0 TN TL()Ec /AF f D(
for general information about these routines.  

)0 P(The file test.tcl in the XPA source directory gives examples for using the 
XPA/Tcl interface.

)0 P(The following notes describe the minor differences between the interfaces.

)0 2 90 H(XPANew)WB 156 Sn()WB 150 Sn()EA()EH(
) 1 70 PR()BD(  set xpa [xpanew class name help sproc sdata smode rproc rdata rmode])ES()RP(
)0 P(rproc and sproc routines are routines.  The calling sequence of the
rproc routine is identical to its C counterpart:
) 1 59 PR(  proc rec_cb { xpa client_data paramlist buf len } { ... })RP(
)0 P(The sproc routine, however is slightly different from its C counterpart
because of the difficulty of passing data back from the callback to C:
) 1 51 PR(  proc sendcb { xpa client_data paramlist } { ... })RP(
)0 P(Note that the C-based server's char **buf and int *len arguments are
missing from the Tcl callback. This is because we did not know how to
fill buf with data and pass it back to the C routines for communication
with the client.  Instead, the Tcl server callback uses the following
routine to set buf and len:
) 1 23 PR(  xpasetbuf xpa buf len)RP(
where:
) 5 79 PR(  arg           explanation
  ------        -----------
  xpa           the first argument of the server callback
  buf           the data to be returned to the client
  len           data length in bytes, \201if absent, use length of the buf object\202)RP(
)0 P(When this routine is called, a copy of buf is saved for transmission to
the client.

)0 P(The fact that buf is duplicated means that TCL server writers might wish to
perform the I/O directly within the callback, rather than have XPA do it
automatically at the end of the routine.  To do this, set:
) 1 15 PR(  fillbuf=false)RP(
)0 P(in the xpanew smode and then perform I/O through the Tcl channel
obtained from:
) 1 34 PR(  set dchan [xparec $xpa datachan])RP(
)0 P(where:
) 5 79 PR(  arg           explanation
  ------        -----------
  xpa           the first argument of the server callback
  datachan      literal string "datachan" that returns the data channel
  len           data length in bytes, \201if absent, use length of the buf object\202)RP(
)0 P()BD(NB: datachan and cmdchan are not available under Windows. It is
necessary to use the "raw" equivalents: datafd and cmdfd.)ES(

)0 P(The same considerations apply to the rproc for receive servers: a copy
of the incoming data is generated to pass to the receive callback. This
copy again can be avoided by using "fillbuf=false" in the rmode and then
reading the incoming data from datachan.

)0 P(The send and receive callback routines can use the xpaerror and xpamessage
routines to send errors and messages back to the client.  If you also
want tcl itself to field an error condition, use the standard return call:
) 1 56 PR(  return ?-code c? ?-errorinfo i? ?-errorcode ec? string)RP(
)0 P(See the Tcl man page for more info.

)0 2 91 H(XPARec)WB 157 Sn()WB 150 Sn()EA()EH(
)0 P(The Tcl xparec procedure supplies server routines with access to information 
that is available via macros in the C interface:
) 1 31 PR(  set val [xparec xpa <option>])RP(
)0 P(where option is: name, class, method, cmdfd, datafd, cmdchan,
datachan.  Note that two additional identifiers, cmdchan and datachan,
have been added to to provide Tcl channels corresponding to datafd and
cmdfd.  \201These latter might still be retrieved in Tcl and passed back
to a C routines.\202  An additional option called "version" can be used to
determine the XPA version used to build the Tcl interface. Note that
the standard options require a valid XPA handle, but "version" does
not \201since it simply reports the value of the XPA_VERSION definition
in the XPA source include file\202.

)0 P()BD(NB: datachan and cmdchan are not available under Windows. It is
necessary to use the "raw" equivalents: datafd and cmdfd.)ES(
) 12 58 PR(  macro         explanation
  ------        -----------
  class         class of this xpa
  name          name of this xpa
  method        method string \201inet or local connect info\202
  cmdchan       Tcl channel of command socket
  datachan      Tcl channel of data socket
  cmdfd         fd of command socket
  datafd        fd of data socket
  sendian       endian-ness of server \201"little" or "big"\202
  cendian       endian-ness of client \201"little" or "big"
  version       XPA version used to build this code)RP(

)0 P(Under Windows, the Tcl event handler cannot automatically sense when an
XPA socket is ready for IO \201i.e. Tcl_CreateFileHandler\201\202 is not available
under Windows\202. The Windows Tcl event handler therefore must be awakened
occasionally for check for XPA events. This is done using the standard
Tcl_SetMaxBlockTime\201\202 call. The time parameter is defined in tclloop.c
and is currently set to 1000 microseconds \2011/1000 of a second\202. 

)0 P(The version option can be used to differentiate between source code versions.
It was created to support legacy Tcl code that needs to maintain the 2.0.5
calling sequence for xpaaccess. You can use a version test such as:
) 12 44 PR(  if [catch { xparec "" version } version] {
    puts "pre-2.1.0e"
  } else {
    puts [split $version .]
  }
) 7 32 PR(



)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 92 H(Last)WB 158 Sn( updated: September 10, 2003)EH(
)WB NL
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DS
/Ba f D /BO 0 D Bs
/UR (env.html) D
/Ti (The XPA Environment) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 40 Sn(


)0 2 93 H(XPAEnv:)WB 160 Sn()WB 159 Sn( Environment Variables for XPA Messaging)EA()EH(


)0 2 94 H(Summary)WB 161 Sn()EH(
Describes the environment variables which can be used to tailor the overall
XPA environment.


)0 2 95 H(Description)WB 162 Sn()EH(
)0 P(The following environment variables are supported by XPA:
)0 DL()0 P()0 DT()BD(XPA_ACL)ES(
)DD( If )EM(XPA_ACL)ES( is )EM(true)ES(, then 
host-based )0 41 1 A(XPA Access Control)41 0 TN TL()Ec /AF f D(
is turned on and only specified machines can access specified access
points.  If )EM(false)ES(, then access control is turned off and any
machine can access point. The default is turn turn access control on.

)0 P()0 DT()BD(XPA_ACLFILE)ES(
)DD( If
)0 41 1 A(XPA Access Control)41 0 TN TL()Ec /AF f D(
is turned on, this variable specifies the name of the file containing
access control information for all access points started by this user.
The default file name is: )EM($HOME/acls.xpa)ES(.

)0 P()0 DT()BD(XPA_CONNECT_TIMEOUT)ES(
)DD( When an XPA server first starts up, it immediately tries to
connect to the XPA name server program \201xpans\202 on the host specified by
the )EM(XPA_NSINET)ES( variable. \201If this connection fails on the
local host, and if xpans can be found in the path, then the name
server is started automatically.\202  Unfortunately, a mis-configured
network can cause this connect attempt to hang for many seconds while
the connect\201\202 system call times out. Therefore, an alarm is started
to interrupt the connect\201\202 call and prevent a long hang.  The initial
value of the alarm timeout is 10 seconds, but can be changed by setting
this environment variable. If you want to disable the alarm and allow
the initial connect\201\202 to time out, set the value of this variable to
0. Normally, users would not change this variable at all.

)0 P()0 DT()BD(XPA_CLIENT_DOXPA)ES(
)DD( Normally, an XPA client \201xpaget, xpaset, etc.\202 will process incoming
XPA server requests while awaiting the completion of the client request.
Setting this variable to "false" will prevent XPA server requests from
being processed by the client.

)0 P()0 DT()BD(XPA_DEFACL)ES(
)DD( If
)0 41 1 A(XPA Access Control)41 0 TN TL()Ec /AF f D(
is turned on, this variable specifies the default access control
condition for all access points, if the )EM(XPA_ACLFILE)ES( file does
not exist.  The default acl is: )EM($host:* $host +)ES(, meaning that
all processes on the host machine have full access to all access points.

)0 P()0 DT()BD(XPA_HOST)ES(
)DD(For the INET socket method, XPA utilizes the canonical hostname \201as
returned by the gethostname\201\202 routine\202 to construct the IP part of the
method id. Under some circumstances, this might not be a correct choice
of name and IP. For example, if an XPA server is started on a machine
running VPN, you might want to use the VPN name and IP instead of the
canonical host name, so that other machines in the VPN network can
access the server. In this case, you can set the XPA_HOST to be
the VPN name \201if resolvable\202 or, more easily, the VPN IP.

)0 P()0 DT()BD(XPA_IOCALLSXPA)ES(
)DD( 
Setting this variable causes all XPA socket IO calls to process
outstanding XPA requests whenever the primary socket is not ready for
IO. This means that a server making a client call will \201recursively\202
process incoming server requests while waiting for client completion.
This inter-IO XPA processing avoids a rare
)0 26 1 A(XPA Race Condition)26 0 TN TL()Ec /AF f D(: two or more
XPA servers sending messages to one another using an XPA client
routine such as XPASet\201\202 can deadlock while each waits for the other
server to respond. This can happen, for example, if the servers call
XPAPoll\201\202 with a time limit, and send messages in between the polling call.

)0 P(By default, this option is turned off, because we judge that the added
code complication and overhead involved will not be justified by the
amount of its use.  Moreover, processing XPA requests within socket IO
can lead to non-intuitive results, since incoming server requests will
not necessarily be processed to completion in the order in which they
are received.

)0 P()0 DT()BD(XPA_LOGNAME)ES(
)DD(XPA preferentially uses the de facto standard environment variable
LOGNAME to determine the username when registering an access point in
the name server. If this environment variable has been used for
something other than the actual user name \201such as a log file name\202,
unexpected results can ensue. In such cases, use the XPA_LOGNAME
variable to set the user name. \201If neither exists, then getpwuid\201geteuid\201\202\202
is used as a last resort\202.

)0 P()0 DT()BD(XPA_LONG_TIMEOUT)ES(
)DD( XPA is designed to allow data to be sent from one process to
another over a long period of time \201i.e., a program that generates
image data sends that data to an image display, but slowly\202 but it
also seeks to prevent hangs. This is done by supporting 2 timeout
periods: a )EM(short)ES( timeout for protocol communication
and a )EM(long)ES( for data communication.
)0 P(The )EM(XPA_LONG_TIMEOUT)ES( variable controls the )EM(long)ES(
timeout and is used to prevent hangs in cases where communication
between the client and server that is )EM(not)ES( controlled by the
XPA interface itself. Transfer of data between client and server, or a
client's wait for a status message after completion of the server
callback, are two examples of this sort of communication. By default,
the )EM(long)ES( timeout is set to 180 seconds.
Setting the value to -1 will disable )EM(long)ES( timeouts and allow
an infinite amount of time.

)0 P()0 DT()BD(XPA_MAXHOSTS)ES(
)DD( The maximum number of access points that the programs 
)EM(xpaset)ES(, )EM(xpaget)ES(, and )EM(xpainfo)ES( will
communicate with at one time. The default is 64, meaning, for
example, that the )EM(xpaset)ES( program will not send a message
to more than 100 access points at one time and )EM(xpaget)ES( will
not retrieve from more than 100 access points at one time.

)0 P()0 DT()BD(XPA_METHOD)ES(
)DD(Determines the socket connection method used by this session of XPA.
The choices are: )EM(inet)ES( \201to use INET or Internet-based
sockets\202, )EM(localhost)ES( \201to use the machines localhost inet
socket\202, or )EM(local \201unix\202)ES( \201to use UNIX sockets\202. The default
is )EM(INET)ES(.  Using the )EM(inet)ES( method will allow access
from other machines \201subject to access controls\202 but using
)EM(localhost)ES( or )EM(local)ES( will not. Localhost is most useful
for private access and when the machine in question is not connected
to the Internet. The unix method also can be used for private access
and non-Internet connections \201Unix platforms only\202.
)0 P(Once defined, the first registration of an XPA access point will
ensure that an instance of the
)0 14 1 A(XPA Name Server \201xpans\202)14 0 TN TL()Ec /AF f D(
is running that handles that connection method. All new access points
will use the new connection method but existing access points will use
the original method.

)0 P()0 DT()BD(XPA_NSINET)ES(
)DD( For the )EM(inet)ES( method of socket connection, this variable
specifies the host and port on which the 
)0 14 1 A(XPA Name Server \201xpans\202)14 0 TN TL()Ec /AF f D(
is listens for new access points. The default is )EM($host:$port)ES(,
meaning that the default XPA port \20114285\202 on the current machine
\201as returned by gethostname\201\202\202 is used. If several machines were all
accessing the same XPA access points, you would use this variable to
specify that they all use the same name server to find out about these
access points.  For example, a value of )EM(myhost:$port)ES( would
mean that the xpans name server is running on myhost and uses the
default port 12345.  All machines would then get the XPA access points
registered with that name server, subject to access controls.
)0 P(The port used by xpans to register its XPA access point normally is
taken to be one greater than the port on which it receives new access
points from XPA servers. You can specify a specific access point port
using the syntax machine:port1,port2, i.e., the access point port is
specified after the comma.  For example, $host:12345,23456 will listen
for new access ports on 12345 and will accept XPA commands on 23456.

)0 P()0 DT()BD(XPA_NSREGISTER)ES(
)DD(This boolean variable specifies whether a server registers its XPA
access point with the specified xpans name server. The default is
)EM(true)ES(.  If set to )EM(false)ES(, the access point still is
set up but it is not registered with xpans and therefore cannot be
accessed by name. \201It can be accessed by method, if the latter is
known.\202 Note that an access point can be registered later on \201using
-remote or -proxy, for example\202. This variable mainly is useful in
cases where the Internet configuration is broken \201so that registration
causes a DNS hang\202 but you still wish to and can use the server with a
remote xpans \201e.g., ds9's Virtual Observatory capability\202.

)0 P()0 DT()BD(XPA_NSUNIX)ES(
)DD( For the )EM(local)ES( method of socket connection, this variable
specifies the name of the Unix file that will be used to access the
)0 14 1 A(XPA Name Server \201xpans\202)14 0 TN TL()Ec /AF f D(. The default is
)EM(xpans_unix)ES(. This variable is not usually needed. Note that
is the )EM(local)ES( socket method is used, then remote machines will
not be able to access the xpans name server or the registered XPA access
points.

)0 P()0 DT()BD(XPA_NSUSERS)ES(
)DD(This variable specifies whether other users' access points will be
returned by the
)0 14 1 A(XPA Name Server \201xpans\202)14 0 TN TL()Ec /AF f D( for use by
)EM(xpaget)ES(, )EM(xpaset)ES(, etc.
Generally speaking, it is sufficient to run one xpans name server per
machine and register the access points for all users with that xpans.
This means, for example, that if you request information from
ds9 by running:
) 1 21 PR(  xpaget ds9 colormap)RP(
you might get information from your own ds9 as well as
from another user running ds9 on the same machine.  The
)EM(XPA_NSUSERS)ES( variable controls whether you want such access 
to the access points of other users.
By default, only your own access points are returned, so
that, in the example above, you would only get the colormap information
from the ds9 you registered. If, however, you had set the value of the
)EM(XPA_NSUSERS)ES( variable to )EM(eric,fred)ES(, then you would be
able to communicate with both eric and fred's access points. Note that
this variable can be overridden using the )EM(-u)ES( switch on the
)EM(xpaget)ES(, )EM(xpaset)ES(, and )EM(xpainfo)ES( programs.

)0 P()0 DT()BD(XPA_PORT)ES(
)DD( 
A semi-colon delimited list of user specified ports to use for specific
XPA access points. The format is each specification is:
) 1 28 PR(class:template port1[ port2])RP(
where )BD(port1)ES( is the main \201command\202 port for the access point and
)BD(port2)ES( is the \201secondary\202 data port. If port2 is not specified,
it defaults to a value of 0 \201meaning the system assigns the port\202.

)0 P(Specification of specific ports is useful, for example, when a machine
outside a firewall needs to communicate with a machine inside a
firewall. In such a case, the firewall should be configured to allow
socket connections to both the command and data port from the outside
machine, and the inside XPA program should be started up with the
outside machine in its ACL list. Then, when the inside program is
started with specified ports, outside XPA programs can use
"machine:port" to contact the inside access points, instead of the
access point names. That is, the machine outside the firewall does not
need access to the XPA name server:
) 2 62 PR(export XPA_PORT="DS9:ds9 12345 12346"   # on machine "inside"
cat foo.fits | xpaset inside:12345 fits # on machine "outside")RP(
Note that 2 ports are required for full XPA communication and
therefore 2 ports should be specified to go through a firewall.  The
second port assignment is not important if you simply are assigning
the command port in order to communicate commands with a known
port \201e.g., to bypass the xpans name server\202. If only one \201command\202
port is specified, the system will negotiate a random data port and
everything will work properly.

)0 P(This support is somewhat experimental. If you run into problems, please
let us know.

)0 P()0 DT()BD(XPA_PORTFILE)ES(
)DD( 
A list of user-specified port to use for specific xpa access points.
The format of the file is:
) 1 28 PR(class:template port1 [port2])RP(
where )BD(port1)ES( is the main port for the access point and
)BD(port2)ES( is the data port. If port2 is not specified, it defaults
to a value of 0 \201meaning the system assigns the port\202.  See
)BD(XPA_PORT)ES( above for an explanation of user-specified ports.

)0 P()0 DT()BD(XPA_SHORT_TIMEOUT)ES(
)DD( XPA is designed to allow data to be sent from one process to
another over a long period of time \201i.e., a program that generates
image data sends that data to an image display, but slowly\202 but it
also seeks to prevent hangs. This is done by supporting 2 timeout
periods: a )EM(short)ES( timeout for protocol communication
and a )EM(long)ES( for data communication.
)0 P(The )EM(XPA_SHORT_TIMEOUT)ES( variable
controls the )EM(short)ES( timeout and is used to prevent hangs
in cases where the XPA protocol requires internal communication between
the client and server that is controlled by the XPA interface
itself. Authentication is an example of this sort of communication,
as is the establishment of a data channel between the two processes.
The default value for the )EM(short)ES( is 30 seconds \201which is
a pretty long time, actually\202. Setting the value to -1 will disable
)EM(short)ES( timeouts and allow an infinite amount of time.

)0 P()0 DT()BD(XPA_SIGUSR1)ES(
)DD( If the value of this variable is )EM(true)ES(, then XPA will
catch SIGUSR1 signals when performing an I/O operation in order to
curtail that operation. This facility allows users to send a SIGUSR1
signal to an XPA server if a client is hanging up the server by
sending or receiving data too slowly \201timeouts also can be used -- see
above\202. When enabled in this way, the SIGUSR1 signal is ignored at all other
times, so that its safe to send the signal at any time.  If the
variable is set to )EM(false)ES(, then SIGUSR1 is not used at
all. Turning off SIGUSR1 would be desired in cases there the program
uses SIGUSR1 for some other reason and does not want XPA interfering.
The default is to use the signal.

)0 P()0 DT()BD(XPA_TIMESTAMP_ERRORS)ES(
)DD( If )EM(XPA_TIMESTAMP_ERRORS)ES( is )EM(true)ES(, then error
messages will include a date/time string.  This can be useful when
XPA errors are being saved in an error log \201e.g. Web/CGI use\202. The
default is false.)LD(

)0 P()0 DT()BD(XPA_TMPDIR)ES(
)DD( This variable specifies the directory into which XPA logs, Unix
socket files \201when )EM(XPA_METHOD)ES( is )EM(local)ES(\202, etc. are
stored. The default is )EM(/tmp/.xpa)ES(.

)0 P()0 DT()BD(XPA_VERBOSITY)ES(
)DD( Specify the verbosity level of error messages. If the value is
set to )EM(0)ES(, )EM(false)ES(, or )EM(off)ES(, then no error
messages are printed to stderr.  If the value is )EM(1)ES(, then
important XPA error messages will be output.  If the value is
set to )EM(2)ES(, XPA warnings about out-of-sync messages will also
be output.  These latter almost always can be ignored.

)0 P()0 DT()BD(XPA_VERSIONCHECK)ES(
)DD( Specify whether a new access point should check its major and minor XPA
version number against the version used by the xpans name server at
registration time. The default is )EM(true)ES(. When checking is
performed, a warning is issued if the server major version is found to
be greater than the xpans version. Note that the check is performed
both by the XPA server and by the xpans process and warnings will be
issued by each.  Also, instead of the values of )EM(true)ES( or
)EM(false)ES(, you can give this variable an integer value n. In this
case, each version checking process \201i.e., the XPA-enabled server or
xpans\202 will print out a maximum of n warning messages \201after which
version warnings are silently swallowed\202.
)0 P(In general, it is a bad idea to run an XPA-enabled server program
using a version of XPA newer than the basic xpaset, xpaget, xpaaccess,
xpans programs. This sort of mismatch usually will not work due to
protocol changes.





)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 96 H(Last)WB 163 Sn( updated: December 23, 2009)EH(

)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (acl.html) D
/Ti (XPA Access Control) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 41 Sn(


)0 2 97 H(XPAAcl:)WB 165 Sn()WB 164 Sn( Access Control for XPA Messaging)EA()EH(


)0 2 98 H(Summary)WB 166 Sn()EH(
)0 P(XPA supports host-based access control for each XPA access point.  You
can enable/disable access control using the XPA_ACL environment
variable. You can specify access to specific XPA access points for
specific machines using the XPA_DEFACL and XPA_ACLFILE environment
variables. By default, an XPA access point is accessible only to
processes running on the same machine \201same as X Windows\202.


)0 2 99 H(Description)WB 167 Sn()EH(
)0 P(When INET sockets are in use \201the default, as specified by the
)EM(XPA_METHOD)ES( environment variable\202, XPA supports a host-based
access control mechanism for individual access points. This mean that
access can be specified for get, set, or info operations for each
access point on a machine by machine basis.  For LOCAL sockets, access
is restricted \201by definition\202 to the host machine.

)0 P(XPA access control is enabled by default, but can be turned off by
setting the )EM(XPA_ACL)ES( environment variable to )EM(false)ES(.
In this case, any process can access any XPA server.

)0 P(Assuming that access control is turned on, the ACL for an individual
XPA access point is set up when that access point is registered
\201although it can be changed later on; see below\202. This can be done in
one of two ways:

Firstly, the )EM(XPA_ACLFILE)ES( environment variable can defined to
point to a file of access controls for individual access points. The format
of this file is:
) 1 18 PR( class:name ip acl)RP(
The first argument is a template that specifies the class:name of the
access point covered by this ACL. See
)0 3 1 A(XPA Access Points and Templates)3 0 TN TL()Ec /AF f D(
for more information about xpa templates.

)0 P(The second argument is the IP address \201in human-readable format\202 of
the machine which is being given access.  This argument can be
)EM(*)ES( to match all IP addresses.  It also can be )EM($host)ES(
to match the IP address of the current host.

)0 P(The third argument is a string combination of )EM(s)ES(, )EM(g)ES(,
or )EM(i)ES( to allow )EM(xpaset)ES(, )EM(xpaget)ES(, or
)EM(xpainfo)ES( access respectively.  The ACL argument can be
)EM(+)ES( to give )EM(sgi)ES( access or it can be )EM(-)ES( to turn
off all access.

)0 P(For example,
) 3 21 PR(  *:xpa1  somehost sg
  *:xpa1  myhost +
  * * g)RP(
will allow processes on the machine somehost to make xpaget and xpaset calls,
allow processes on myhost to make any call, and allow all other hosts to
make xpaget \201but not xpaset\202 calls.

Secondly, if the )EM(XPA_ACLFILE)ES( does not exist, then a single
default value for all access points can be specified using the
)EM(XPA_DEFACL)ES( environment variable.  The default value for this
variable is:
) 1 34 PR(  #define XPA_DEFACL "*:* $host +")RP(
meaning that all access points are fully accessible to all processes
on the current host. Thus, in the absence of any ACL environment variables,
processes on the current host have full access to all access points
created on that host. This parallels the X11 xhost mechanism.

)0 P(Access to an individual XPA access point can be changed using the -acl
parameter for that access point.  For example:
) 1 34 PR(  xpaset -p xpa1 -acl "somehost -")RP(
will turn off all access control for somehost to the xpa1 access point, while:
) 1 38 PR(  xpaset -p XPA:xpa1 -acl "beberly gs")RP(
will give beberly xpaget and xpaset access to the access point whose
class is XPA and whose name is xpa1.
)0 P(Similarly, the current ACL for a given access point can be retrieved using:
) 1 18 PR(  xpaget xpa1 -acl)RP(
Of course, you must have xpaget access to this XPA access point to
retrieve its ACL.

)0 P(Note that the XPA access points registered in the )EM(xpans)ES(
program also behave according to the ACL rules.  That is, you cannot
use xpaget to view the access points registered with xpans unless
you have the proper ACL.

)0 P(Note also when a client request is made to an XPA server, the access
control is checked when the initial connection is established.  This
access in effect at this time remains in effect so long as the client
connection is maintained, regardless of whether the access fro that
XPA is changed later on.

)0 P(We recognize that host-based access control is only relatively secure
and will consider more stringent security \201e.g., private key\202 in the
future if the community requires such support.





)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 100 H(Last)WB 168 Sn( updated: September 10, 2003)EH(

)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (changelog.html) D
/Ti (XPA ChangeLog) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 42 Sn(
)0 2 101 H(XPA)WB 169 Sn( ChangeLog)EH(

)0 P(This ChangeLog covers the XPA 2 implementation. It will be updated
as we continue to develop and improve XPA.  The up-to-date version can be 
found )R1 2 A(here)EA(.

)0 2 102 H()WB 170 Sn( Public Release 2.1.15 \201July 23, 2013\202)EH(
)UL()0 P()-1 LI( Added support for large data transfers
)0 P()-1 LI( XPAGet and XPASet now pass size_t instead of int for lengths
)0 P()-1 LI( Send and receive callbacks now pass size_t instead of int for lengths
)0 P()-1 LI( Port to mingw \201Windows\202)LU(


)0 2 103 H()WB 171 Sn( Public Release 2.1.14 \201June 7, 2012\202)EH(
)UL()0 P()-1 LI( Fixed several memory leaks in the Tcl wrappers \201tcl.c\202.
)0 P()-1 LI( Use Tcl stubs library for linking shared Tcl, if available.)LU(

)0 2 104 H()WB 172 Sn( Public Release 2.1.13 \201April 14, 2011\202)EH(
)UL()0 P()-1 LI( An atexit handler is no longer installed automatically \201it crashes
Tcl 8.5.8 applications\202. Call XPAAtExit\201void\202 to install the handler.
)0 P()-1 LI( Removed permission checking from Find\201\202 on cygwin systems. This was broken
by Windows 7.
)0 P()-1 LI( Removed addition of -no-cpp-precomp flag from gcc 4.2 and beyond \201Mac\202.)LU(

)0 2 105 H()WB 173 Sn( Public Release 2.1.12 \201January 26, 2010\202)EH(
)UL()0 P()-1 LI( Added XPA_HOST environment variable to allow users to specify
the hostname \201and hence, ip\202 component of the INET method id. This is
useful, for example, if you want to register an access point using a
VPN-generated IP instead of the canonical IP.
)0 P()-1 LI( Fix typo in Tcl binding to xpainfo causing a crash after 2 invocations.)LU(

)0 2 106 H()WB 174 Sn( Public Release 2.1.11 \201December 7, 2009\202)EH(
)UL()0 P()-1 LI( Generalized XPANSKeepAlive\201\202 to send messages to xpans, proxy xpans, or
both. The default is to send just to proxies \201e.g. chandra-ed\202.
)0 P()-1 LI( Changed XPANSKeepAlive\201\202 to send an in-band new-line char to
xpans, changed xpans to handle an in-band new-line as a keep-alive
message. Necessitated by Cisco routers that clear the URG flag in
a TCP packet, breaking OOB data transfer for the whole Internet, as
well as the OOB-based keep-alive implemented in xpans.
)0 P()-1 LI( In xpans, print warning when the keep-alive option switch is used.
)0 P()-1 LI( Port to mingw \201thanks to B.Schoenhammer\202
)0 P()-1 LI( Change OOB character sent by xpans keepalive to a space, trying to working around cisco routers that force OOB data into the inbound stream.
)0 P()-1 LI( fix gcc fprintf warning in xpans.c)LU(

)0 2 107 H()WB 175 Sn( Public Release 2.1.10 \201September 1, 2009\202)EH(
)UL()0 P()-1 LI( Update mklib and configure.ac to support 64-bit builds on Macs.
)0 P()-1 LI( Fixed bug in XPAAccess\201\202 in which the returned names could have an extra
\201bogus\202 character when the target is an explicit ip:port or local socket file.
)0 P()-1 LI( Add setjmp/longjmp support to xalloc.
)0 P()-1 LI( Add XPASaveJmp\201void *env\202 as a high-level interface to xalloc_savejmp\201\202;)LU(

)0 2 108 H()WB 176 Sn( Internal Release 2.1.9)EH(
)UL()0 P()-1 LI( Fixed a bug that prevented an access point starting with a number
from being recognized peoperly. NB: a pure number still signifies a
port on the current machine. Also num:num signifies ip:port, where ip
can be a pure hex value or the canonical form vvv.xxx.yyy.zzz.
)0 P()-1 LI( Modified internal Launch\201\202 routine to use posix_spawn\201\202, if necessary.
This is required for OS X 10.5 \201leopard\202, which frowns upon use of fork\201\202
and exec\201\202. Also modified zprocess routines to use Launch\201\202.
)0 P()-1 LI( Added XPASetFree\201xpa, void \201*myfree\202\201void *\202\202 routine to allow callbacks
to specify a free routine other than malloc free \201e.g. Perl garbage collection\202.
)0 P()-1 LI( XPACmdAdd\201\202 now checks to ensure that it was passed an XPA struct created
by XPACmdNew\201\202.
)0 P()-1 LI( Change launch.h to xlaunch.h to avoid conflict with OS X.)LU(

)0 2 109 H()WB 177 Sn( Public Release 2.1.8 \2011 November 2007\202)EH(
)UL()0 P()-1 LI( A public release to complete current XPA development work.)LU(

)0 2 110 H()WB 178 Sn( Patch Release 2.1.7b[1,2] \201Feb 22, 2006; March 8, 2007\202)EH(
)UL(
)0 P()-1 LI( Added a convenience null to the end of the buffers returned by XPAGet.

)0 P()-1 LI( Added code to avoid calling atexit routine if a fork'ed child
calls exit\201\202 instead of _exit\201\202.

)0 P()-1 LI( Added XPA_CLIENT_DOXPA environment variable to turn off client
processing of xpa server requests.

)0 P()-1 LI( Added --version to xpaset, xpaget, xpainfo, xpaaccess, xpans to
display XPA version and exit.

)0 P()-1 LI( Added support for integrating XPA into a Gtk loop.

)0 P()-1 LI( xpaaccess now returns its answer in the error code as well as to stdout
\201without the -n switch, it returns 1 for a match, with the -n switch,
the number of matches is returned\202.

)0 P()-1 LI( Fixed bug which prevented xpans from being started up automatically
by an xpa server if its pathname contained a space character.

)0 P()-1 LI( Fixed bug in MINGW port of xpans in which an XPA server that
terminated via an interrupt was not being properly removed from the
list of registered access points.

)0 P()-1 LI( Added XPA_LOGNAME to override LOGNAME when registering username

)0 P()-1 LI( Upgraded swish-e indexing code to 2.4.5.
)LU(

)0 2 111 H()WB 179 Sn( Patch Release 2.1.6 \2014 May 2005\202)EH(
)UL(
)0 P()-1 LI( Added -P switch to xpans to enable experimental proxy support
\201default is disabled\202.  An argument of 1 processes proxy requests in
the same thread as xpans requests, while an argument of 2 processes
proxy requests in a separate thread. \201The latter is recommended to
avoid xpans timeouts, since xpa callback processing can take a long
time.\202

)0 P( 
)-1 LI( Added ability to build shared libraries \201done automatically with
configure --enable-shared\202 with compilers other than gcc.

)0 P()-1 LI( Made yet another attempt to build shared libraries under OS X.

)0 P()-1 LI( Fixed a server bug in Tcl support under Windows \201introduced early
in 2.1.6\202 which caused an occasional SEGV.

)0 P()-1 LI( Fixed race condition in cases where 2 or more servers makes client calls
to one another.

)0 P()-1 LI( Fixed bug in the XPA handler routine in which an access point was
turned off if an error occurred in that routine \201as opposed to the
user-defined callback routine\202.

)0 P()-1 LI( Fixed race condition when "ack=false" flag \201or -n\202 is used with XPASet\201\202
\201or xpaset\202.

)0 P()-1 LI( Added defensive code to XPA handler to ensure that the passed XPA record
is valid.

)0 P()-1 LI( Tcl/XPA servers such as ds9 were not turning off select\201\202 on the
xpa channels inside an xpa callback, as required. This is now fixed.

)0 P()-1 LI( Added timestamps to most server and client error messages if the
XPA_TIMESTAMP_ERRORS variable is set. This is useful when XPA errors are
being logged in an error log \201e.g. Web/CGI use\202.

)0 P()-1 LI( Generated PostScript and PDF versions of the help pages.

)0 P()-1 LI( Moved OPTIONS section before \201often-lengthy\202 DESCRIPTION section in
man pages.

)0 P()-1 LI( All memory allocation now performs error checking on the result.

)0 P()-1 LI( Removed some compiler warnings that surfaced when using gcc -O2.
 
)0 P()-1 LI( Updated configure.ac to better support Tcl in Panther with Apple
Frameworks.
)LU(

)0 2 112 H()WB 180 Sn( Patch Release 2.1.5 \20112 January 2004\202)EH(
)UL(
)0 P()-1 LI( Fixed bug in XPAPoll\201\202. Erroneously, no requests were being
processed when maxreq==0. Now, all pending events are processed, as
per the documentation.

)0 P()-1 LI( Added ack=false to XPAInfo\201\202 \201and corresponding -n to xpainfo\202
so that client does not wait for a response from the server. This is
essential in cases where XPA servers wish to send info messages to
one another without causing a race condition.

)0 P()-1 LI( Generated man pages from the html pages. These are installed
automatically at build time.

)0 P()-1 LI( The xpans program with Unix sockets now uses a lock file to signal
that it is running, in order to avoid a potential \201but rare\202 race
condition at startup.

)0 P()-1 LI( Code that calls Unix-type bind\201\202 now manipulate umask\201\202 to ensure that
all users have write permissions to the socket file \201OS X apparently uses
these permissions while previous platforms ignore them\202.

)0 P()-1 LI( Configure now checks for socklen_t type \201OS X does not define it\202.

)0 P( 
)-1 LI( Added an atexit function to run XPAFree. The aim here is to delete Unix
socket files on exiting.

)0 P()-1 LI( Under Windows, the Tcl event-handling code now blocks for 1/1000 of a
second instead of not blocking at all \201which inadvertently used 100% of cpu\202.

)0 P()-1 LI( Upgraded Tcl/Tk support to 8.4.

)0 P()-1 LI( Made another round of checks was made through all instances of
strcat, strcpy, etc. to look for potential buffer overflows.  Changed
all instances of sprintf\201\202 to snprintf\201\202.

)0 P()-1 LI( Class and name designators are now limited to 1024 characters, for
no particular reason.

)0 P()-1 LI( The obsolete $SAORD_BIN variable was being added to the path when
searching for xpans. This is no longer the case.

)0 P()-1 LI( Fixed non-ANSI compiler errors in both xpa.c and xpans.c.

)0 P()-1 LI( Fixed minor problems to support compilation with g++.

)0 P()-1 LI( Ported to Intel icc and gcc 3.3 compilers.

)0 P()-1 LI( Upgraded autoconf to 2.57. Included in this upgrade is a change that
makes gcc the default compiler \201use "configure CC=cc" to change this\202.
Also, by default, the Tcl shared object is no longer automatically built
if the Tcl libraries are used. Use the --enable-tclshlib switch in 
configure to enable this feature.

)0 P()-1 LI(  Changed license from public domain to GNU GPL.
)LU(

)0 2 113 H()WB 181 Sn( Patch Release 2.1.4 \20124 March 2003\202)EH(
)UL(
)0 P()-1 LI( Made inet method unique, even when hosts are behind a firewall using
the same ports \201on different local machines\202.

)0 P()-1 LI( The initial connection from an xpa server to a local xpans now is
controlled by a timeout \201default 5 sec, controlled by XPA_CONNECT_TIMEOUT
variable\202. This should prevent a hang on connect\201\202 if the network
is not set up correctly.

)0 P()-1 LI( Fixed rare race condition when an XPA server callback performed its own
XPAGet or XPASet call to another XPA server.

)0 P()-1 LI( Use POSIX O_NONBLOCK for non-blocking I/O in fcntl call if it
exists, instead of O_NDELAY.
)LU(

)0 2 114 H()WB 182 Sn( Patch Release 2.1.3 \20126 September 2002\202)EH(
)UL(
)0 P()-1 LI( Added -k [sec] switch to xpans to support sending one-byte keepalive
messages from xpans to registered xpa servers.

)0 P()-1 LI( Added XPANSKeepAlive routine \201and Tcl equivalent\202 to allow
xpa servers to send a one-byte keepalive message to xpans.
)LU(

)0 2 115 H()WB 183 Sn( Patch Release 2.1.2 \20118 July 2002\202)EH(
)UL(
)0 P()-1 LI( The "-help" reserved command now also displays the XPA version, if
no explicit sub-commands are specified.

)0 P()-1 LI( Change internal state of xpans proxy to save ip:port value of a
server behind a NAT firewall. This is required to give some hope of
distinguishing multiple instances of ds9 running behind NAT.
)LU(

)0 2 116 H()WB 184 Sn( Patch Release 2.1.1 \20120 June 2002\202)EH(
)UL(
)0 P()-1 LI( Added a version check between xpans and an access point,
performed when it gets registered by an XPA server.  If the server
has a version greater than the xpans version, a warning is issued by
both programs.

)0 P()-1 LI( Added a boolean XPA_NSREGISTER environment variable to allow an
XPA server to skip xpans registration. The default is to register with
the name server.  If set to "false", the access point still is set up
but it is not registered with an xpans. It can be registered later on
\201using -remote or -proxy, for example\202.

)0 P()-1 LI( Fixed bug in which xpans was still listening on any interface when
XPA_METHOD was localhost \201instead of just listening on localhost\202.
)LU(

)0 2 117 H()WB 185 Sn( Public Release 2.1.0 \20122 April 2002\202)EH(

)0 P(New features include:

)UL()0 P()-1 LI( Support for proxy access to XPA servers \201e.g. ds9\202 situated
behind a firewall \201useful for NVO-type applications\202.

)0 P()-1 LI( Improved support for allowing remote machines access rights to the
XPA access points \201useful for NVO-type applications\202.

)0 P()-1 LI( Ability for XPAAccess\201\202 routine and xpaaccess program to contact XPA
 directly.

)0 P()-1 LI( Support for a clipboard access point that allows clients to store ASCII
state information in an XPA-enabled server.

)0 P()-1 LI( Improved support for Windows platform, as well as new support for Mac OSX.)LU(

)0 2 118 H()WB 186 Sn( Pre-Release 2.1.0e \2012 April 2002\202)EH(
)UL(
)0 P()-1 LI( Removed the environment variable generated by each XPA access
point \201of the form XPA_name=method\202. The putenv\201\202 call was causing ds9
to crash under both Linux and LinuxPPC during a socket operation. We
suspect a bug in putenv but cannot prove it and this feature is not
essential, so ...
)LU(

)0 2 119 H()WB 187 Sn( Pre-Release 2.1.0e \2011 April 2002\202)EH(
)UL(
)0 P()-1 LI( Fixed an uninitialized variable in xpamb which prevented it from
working at all on some systems.

)0 P()-1 LI( Changed xpamb switch from "-add" to "-data" \201to store named data\202.

)0 P()-1 LI( Changed how xpamb works with xpaget so that xpamb can return data
from XPA access points as well as from stored data. \201Previous versions
only returned stored data.\202 Now, you can retrieve stored data
explicitly using the -info and/or -data switches. For example:
) 1 24 PR(  xpaget xpamb -info foo)RP(
will return info about the previously stored data named foo. If
neither switch is present, then the name is assumed to be an XPA access
point.)LU(

)0 2 120 H()WB 188 Sn( Pre-Release 2.1.0e \20125 March 2002\202)EH(
)UL(
)0 P()-1 LI( Changed symbol for default port from "*" to "$port" to avoid
a syntactical conflict between class:* and machine:* when processing an
XPA access point class:name specification. Thus, the default inet
method now is '$host:$port' instead of '$host:*'.
)LU(

)0 2 121 H()WB 189 Sn( Pre-Release 2.1.0e \20119 March 2002\202)EH(
)UL(
)0 P()-1 LI( Removed timeout check when reading data \201in clients using xpaget
and servers filling the data buffer\202. We have more and more cases
where we need to wait a long time to retrieve data \201e.g., slow
networks or receiving data being compressed on the fly\202.

)0 P()-1 LI( Moved call to sigaction\201SIGCHLD,...\202 out of XPAOpen\201\202, so that it
is only executed when needed by XPAGet\201\202/XPASet\201\202 routines called from
within xpans/proxy. But then changed logic to use a double fork\201\202 instead
of sigaction\201\202 to prevent zombies \201Stevens Adv. Programming p 202\202.

)0 P()-1 LI( Each XPA access point now generates an environment variable of the
form XPA_name=method so that children can communicate with the parent access
point more easily.

)0 P()-1 LI( Added version option to Tcl xparec:
) 5 44 PR(  if [catch { xparec "" version } version] {
    puts "pre-2.1.0e"
  } else {
    puts [split $version .]
  })RP(
to help differentiate between XPA versions within Tcl code.
)LU(

)0 2 122 H()WB 190 Sn( Pre-Release 2.1.0e \20114 February 2002\202)EH(
)UL()0 P()-1 LI( Fixed client handling of out-of-sync messages.)LU(

)0 2 123 H()WB 191 Sn( Pre-Release 2.1.0e \20111 February 2002\202)EH(
)UL(
)0 P()-1 LI( Fixed client.c/xopen\201\202 so that it does not open an extra socket.

)0 P()-1 LI( Fixed xpainfo/xopen\201\202 to prevent client from hanging waiting for ack.

)0 P( 
)-1 LI( Modified stest to generate xpaaccess points xpa, xpa1, c_xpa, and
i_xpa \201or more generally, , 1, c_, i\202 to allow
more flexible testing of templates. Also added -a for testing XPAAccess\201\202.
)LU(

)0 2 124 H()WB 192 Sn( Beta Release 2.1.0b10 \20131 January 2002\202)EH(
)UL(
)0 P()-1 LI( Added support for Mac OSX/Darwin to configure file.
)LU(

)0 2 125 H()WB 193 Sn( Beta Release 2.1.0b9 \20126 January 2002\202)EH(
)UL(
)0 P()-1 LI( Fixed bug in client library that caused XPAAccess\201\202 call to hang.
)LU(

)0 2 126 H()WB 194 Sn( Beta Release 2.1.0b8 \2014 January 2002\202)EH(
)UL(
)0 P()-1 LI( Made modifications to Makefile.in to make releases easier.

)0 P()-1 LI( Added instructions to Makefile.in so that xpa.h will always have
correct #defines for XPA_VERSION, XPA_MAJOR_VERSION, XPA_MINOR_VERSION,
and XPA_PATCH_LEVEL.
)LU(

)0 2 127 H()WB 195 Sn( Beta Release 2.1.0b7 \20121 December 2001\202)EH(
)UL(
)0 P()-1 LI( Added -proxy switch to -remote sub-command to allow remote access
through a firewall, using xpans as a proxy server. The support for proxy
processing required a change to the client/server protocol. This means
that new xpa servers will not work with old xpa clients \201although new
xpa clients will work with old xpa servers\202. For details about proxy
firewall support, see http://hea-www.harvard.edu/RD/xpa/inet.html.

)0 P()-1 LI( Fixed Tcl support for XPA under Windows/Cygwin by re-writing
the code used to add XPA to the Tcl event loop. This fix makes ds9
support for XPA much more stable under Windows.

)0 P()-1 LI( Added the shutdown\201\202 call to XPA under Cygwin/Windows before
closing send\201\202 sockets. It appears that a Cygwin recv\201\202 socket call
does not always sense when the other end closes the socket using
close\201\202. This measure must be considered a hack, since the actual
problem was never resolved.

)0 P()-1 LI( Added code to protect accept\201\202 and select\201\202 calls from interrupts.

)0 P()-1 LI( Extended syntax of the environment variable XPA_NSINET to:
) 1 43 PR(  setenv XPA_NSINET host:port[,port[,port]])RP(
to allow specification of the XPA access point port for xpans,
as well as the proxy data port.

)0 P()-1 LI( Modified xpans log file so that it contains the xpaset commands
required to reconnect with xpa servers.

)0 P()-1 LI( xpans now deletes its Unix socket files.
)LU(

)0 2 128 H()WB 196 Sn( Beta Release 2.1.0b6 \20129 October 2001\202)EH(
)UL(
)0 P()-1 LI( Implemented a reserve public access point named -clipboard so
that clients can store ASCII state information on any number of named
clipboards. Clipboards of the same name created by clients on
different machines are kept separate.  The syntax for creating a
clipboard is:
) 3 65 PR(  [data] | xpaset [server] -clipboard add|append [clipboard_name]
  xpaset -p [server] -clipboard delete [clipboard_name]
  xpaget [server] -clipboard [clipboard_name])RP(
Use "add" to create a new clipboard or replace the contents of an existing
one. Use "append" to append to an existing clipboard.
)LU(

)0 2 129 H()WB 197 Sn( Beta Release 2.1.0b5 \20122 October 2001\202)EH(
)UL(
)0 P()-1 LI( Use FD_SETSIZE instead of getdtablesize\201\202 to determine how many files
to check during select\201\202;

)0 P()-1 LI( Under Cygwin, the launch\201\202 routine now uses the Cygwin spawnvp\201\202
instead of fork\201\202/exec\201\202 where possible \201i.e., if no stdfiles are
being redirected\202. This is recommended by Cygwin's \201skimpy\202 on-line
documentation and seems to fix the problems ds9 had when starting xpans
automatically.

)0 P()-1 LI( Added error check to select\201\202 call in xpans.
)LU(

)0 2 130 H()WB 198 Sn( Beta Release 2.1.0b4 \20124 September 2001\202)EH(
)UL(
)0 P()-1 LI( The launch\201\202 now can return an error code if the execv\201\202 system
call fails \201something system\201\202 does not do\202.

)0 P()-1 LI( INET socket calls between xpa clients and servers now will use
localhost if they are on the same machine. This protects against
Linux systems where the hostname is hardwired \201wrongly\202 in a DHCP
environment.
)LU(

)0 2 131 H()WB 199 Sn( Beta Release 2.1.0b3 \2016 September 2001\202)EH(
)UL(
)0 P()-1 LI( Modified xpans so that, in the case of a firewall, it tries to
correct the specified ip:port by matching against the ip found in
the socket packet at accept\201\202 time.

)0 P()-1 LI( Replaced system\201\202 call used to start xpans automatically with
a special launch\201\202 call, which performs execvp\201\202 directly without going
through sh. \201launch\201\202 works under DOS and has fewer security problems.\202

)0 P()-1 LI( Fixed bug in xpans in which its xpa port was always being set to 14286.
)LU(

)0 2 132 H()WB 200 Sn( Beta Release 2.1.0b2 \20117 August 2001\202)EH(
)UL(
)0 P()-1 LI(Added support for -remote command, which registers the access
point in the XPA name server of the specified remote server, and gives
the remote server access rights to the access point. This is used, for
example, to give data servers xpa access to ds9 so that data can be
sent to ds9 as a result of a CGI-based Web query.

)0 P()-1 LI(Reserved commands \201except "-help" and "-version"\202 now can only be
executed on the machine on which the xpa service is running \201not
through -remote servers\202.

)0 P()-1 LI(Fixed bug in xpans in which a bad telnet command could hang the program.

)0 P()-1 LI(Added -s [security file] to xpans to allow logging of all external
connections.
)LU(

)0 2 133 H()WB 201 Sn( Beta Release 2.1.0b1 \2016 August 2001\202)EH(
)UL()0 P()-1 LI( The xpaaccess client program and XPAAccess\201\202 client subroutine
were modified so that an access-type query can directly contact the
xpa servers matching the requested xpa template, instead of just
querying the name server for registered access points. This avoid the
race condition in which an access point is registered but is not yet
available, perhaps because the server has not yet entered its event
loop.  Note that the calling sequence of the XPAAccess\201\202 routine was
changed to return all matching access points and their availability
status \201instead of just returning the number of registered access
points\202. Because of this, we are calling this a minor release instead
of a patch.

)0 P()-1 LI( Added support for XPA_PORT and XPA_PORTFILE environment variables
to allow specification of the port to be used by the command channel
\201and data channel, if an optional second port is specified\202 for a given
access point.

)0 P()-1 LI( Added -m switch to xpaget, xpaset, xpainfo, xpaaccess to allow
override of the XPA_METHOD environment variable.

)0 P()-1 LI( Changed the default name of the ACL file from xpa.acl to acls.xpa.

)0 P()-1 LI( Fixed bug in which it was not possible to send a "set ACL"
command to an XPA server which did not have a receive callback \201i.e.,
did not allow xpaset\202. The xpans program is one such server. It now is
possible to set the ACL on xpans.

)0 P()-1 LI( We have discovered that Tcl support for datachan and cmdchan is
broken under Windows due to an unexplained incompatibility between
Cygwin sockets and Win32 sockets. We therefore have removed datachan
and cmdchan from the Windows/Tcl support until further notice.

)0 P()-1 LI( Extended the behavior of the XPA_DEFACL environment variable so that
it can support more than one acl, using a list of semi-colon delimited
controls such as: setenv XPA_DEFACL '*:* $host +; *:foo1 otherhost +'.

)0 P()-1 LI( Fixed bug in which the class:name specifier "*:*" was erroneously
trying to access the xpans name server, instead of accessing all
access points.

)0 P()-1 LI( Support TMPDIR and TMP environment variables as well as XPA_TMPDIR.
)LU(

)0 2 134 H()WB 202 Sn( Patch Release 2.0.5 \20110 November 2000\202)EH(
)UL()0 P()-1 LI( Added support for Tcl on Windows where there is no select\201\202-based
event loop \201i.e., where there is no Tcl_CreateFileHandler call in Tcl\202
)0 P()-1 LI( Minor fixes in Makefile for installing on Windows
)0 P()-1 LI( Minor compiler fixes from gcc -Wall.)LU(

)0 2 135 H()WB 203 Sn( Patch Release 2.0.4 \20120 September 2000\202 )EH(
)UL()0 P()-1 LI( Removed extraneous include of varargs.h from find.c.
)0 P()-1 LI( Ported to SGI C compiler, which caught lots of unused variables, etc.
)0 P()-1 LI( Ported to Cygwin/Windows, which required that we change socket read\201\202
and write\201\202 calls to recv\201\202 and send\201\202 respectively. Also had to ensure that
we only did socket I/O on sockets \201no fileio\202.)LU(

)0 2 136 H()WB 204 Sn( Patch Release 2.0.3 \20115 June 2000\202 )EH(
)UL( 
)0 P()-1 LI( Fixed the client XPASet\201\202 and XPASetFd\201\202 calls to handle the specified
max number of connections \201they were ignoring this argument, leading to
memory overwrites\202.
)0 P()-1 LI( Fixed Makefile.in so that CFLAGS and LDFLAGS are not hard-wired values.
)0 P()-1 LI( Fixed word.h to load malloc.h and stdlib.h only if they exist.
)0 P()-1 LI( Documentation fixes to programs.html \201in xpaaccess\202 and client.html
\201XPANSLookup\202.
)0 P()-1 LI( Added explicit typecast to strlen\201\202 argument to MAX #define in
XPAClientStart \201strlen\201\202 is unsigned in Linux, which can break MAX\202.
)0 P()-1 LI( Removed bogus Imakefile from directory.
)0 P()-1 LI( Changed directory name to include patch level \201i.e., xpa-2.0.3\202.)LU(

)0 2 137 H()WB 205 Sn( Patch Release 2.0.2 \2019 September 1999\202)EH(
)UL( 
)0 P()-1 LI( Fixed server mode \201-s\202 in the xpaset program by properly cleaning up
the input buffers \201sending commands and data in server mode was broken\202.)LU(

)0 2 138 H()WB 206 Sn( Patch Release 2.0.1 \2016 August 1999\202)EH(
)UL( 
)0 P()-1 LI( Fixed the Tcl binding code \201tcl.c\202 for 64-bit machines \201Dec Alpha\202
\201erroneously used %x instead of %p when converting pointers to ASCII\202.
)0 P()-1 LI( Got rid of a few compiler warnings on 64-bit machines \201a few are
unavoidable since we must cast int to void * and back when passing around
client data\202.)LU(

)0 2 139 H()WB 207 Sn( Public Release 2.0 \20127 May 1999\202)EH(
)UL( 
)0 P()-1 LI( "a new day with no mistakes ... yet")LU(

)2 1 1 HR()0 P()0 0 1 A(Index to the XPA Help Pages)0 0 TN TL()Ec /AF f D(

)2 1 1 HR()0 5 140 H(Last)WB 208 Sn( updated: 22 April 2002)EH(
)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (examples.html) D
/Ti (Where to Find Example/Test Code) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 43 Sn(


)0 2 141 H(XPACode:)WB 210 Sn()WB 209 Sn( Where to Find Example/Test Code)EA()EH(


)0 2 142 H(Summary)WB 211 Sn()EH(
)0 P(The XPA source code directory contains two test programs,
)EM(stest.c)ES(, and )EM(ctest.c)ES( that can serve as
examples for writing XPA servers and clients, respectively.
They also can be used to test various features of XPA.


)0 2 143 H(Description)WB 212 Sn()EH(
)0 P(To build the XPA test programs, execute:
) 1 11 PR(   make All)RP(
in the XPA source directory to generate the )EM(stest)ES( and
)EM(ctest)ES( programs.  \201NB: this should work on all platforms,
although we have had problems with unresolved externals on one
Sun/Solaris machine, for reasons still unknown.\202
)0 P(The stest program can be executed with no arguments to start
an XPA server that contains the access points: xpa, xpa1,
c_xpa \201containing sub-commands cmd1 and cmd2\202, and i_xpa.
You then can use xpaset and xpaget to interact with these access points:
) 4 57 PR(  cat xpa.c | xpaset xpa      # send to xpa
  cat xpa.c | xpaset "xpa*"   # send to xpa and xpa1
  xpaget xpa                  # receive from xpa
  xpaget xpa*                 # receive from xpa and xpa1)RP(
etc. You also can use ctest to do the same thing, or to iterate:
) 4 66 PR(  ctest -s -l 100 xpa        # send to xpa 100 times
  ctest -s -l 100 "xpa*"     # send to xpa and xpa1 100 times
  ctest -g -l 100 xpa        # receive from xpa 100 times
  ctest -g -l 100 "xpa*"     # receive from xpa and xpa1 100 times)RP(
More options are available: see the stest.c and ctest.c code itself, which
were used extensively to debug XPA.

)0 P(The file test.tcl in the XPA source directory gives examples for using the 
)0 39 1 A(XPATcl)39 0 TN TL()Ec /AF f D(Interface.





)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 144 H(Last)WB 213 Sn( updated: September 10, 2003)EH(
)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (changes.html) D
/Ti (Changes For Users from XPA 1.0 and 2.0) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 44 Sn(


)0 2 145 H(XPA)WB 215 Sn()WB 214 Sn( Changes: Changes For Users from XPA 1.0 and 2.0)EA()EH(


)0 2 146 H(Summary)WB 216 Sn()EH(
)0 P(This document describes changes that will affect users who migrate
from XPA 1.0 to XPA 2.0.


)0 2 147 H(Description)WB 217 Sn()EH(
)0 P(There have been a few changes that affect users who upgrade XPA
from version 1.0 to version 2.0.  These changes are detailed below.
)UL()0 P()-1 LI(XPA commands no longer have a resolver routine \201this is open to
negotiations, but we decided the idea was dumb\202.  For the SAOtng
program, this means that you must explicitly specify the access
point, i.e.,:
) 1 35 PR(  cat foo.fits | xpaset SAOtng fits)RP(

)0 P(instead of:
) 1 30 PR(  cat foo.fits | xpaset SAOtng)RP(
)0 P()-1 LI(By default, xpaset, xpaget, etc. now wait for the server callback to
complete; i.e., the old -W is implied \201and the switch is ignored\202.
This allows support for better error handling.  If you want xpaset, etc.
to return before the callback is complete, use -n switch:
) 1 41 PR(  echo "file foo.fits" | xpaset -n SAOtng)RP(
)0 P()-1 LI(The old -w switch in xpaset and xpaget is no longer necessary \201and is
ignored\202, since you can have more than one process communicating with
an xpa access point at one time.

)0 P()-1 LI(The new -p switch on xpaset means you need not read from stdout:
) 2 30 PR(              
  xpaset -p SAOtng colormap I8)RP(
)0 P(will send the paramlist to the SAOtng callback without reading from stdin.
)LU(





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)0 5 148 H(Last)WB 218 Sn( updated: September 10, 2003)EH(
)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (convert.html) D
/Ti (Converting the XPA API to 2.0) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 45 Sn(


)0 2 149 H(XPAConvert:)WB 220 Sn()WB 219 Sn( Converting the XPA API to 2.0)EA()EH(


)0 2 150 H(Summary)WB 221 Sn()EH(
)0 P(This document describes tips for converting from xpa 1.0 \201Xt-based
xpa\202 to xpa 2.0 \201socket-based xpa\202.


)0 2 151 H(Description)WB 222 Sn()EH(
)0 P(The following are tips for converting from xpa 1.0 \201Xt-based xpa\202 to
xpa 2.0 \201socket-based xpa\202. The changes are straight-forward and
almost can be done automatically \201we used editor macros for most of
the conversion\202.
)UL()0 P()-1 LI(The existence of the cpp XPA_VERSION directive to distinguish between 1.0
\201where it is not defined\202 and 2.0 \201where it is defined\202.

)0 P()-1 LI(Remove the first widget argument from all send and receive server
callbacks.  Also change first 2 arguments from XtPointer to void
*. For example:
) 16 74 PR(#ifdef XPA_VERSION
static void XPAReceiveFile\201client_data, call_data, paramlist, buf, len\202
     void *client_data;
     void *call_data;
     char *paramlist;
     char *buf;
     int len;
#else
static void XPAReceiveFile\201w, client_data, call_data, paramlist, buf, len\202
     Widget w;
     XtPointer client_data;
     XtPointer call_data;
     char *paramlist;
     char *buf;
     int len;
#endif)RP(
)0 P()-1 LI(Server callbacks should be declared as returning int instead
of void. They now should return 0 for no errors, -1 for error.

)0 P()-1 LI( The mode flags have changed when defining XPA server callbacks.
The old )EM(S)ES( flag \201save buffer\202 is replaced by )EM(freebuf=false)ES(.
The old )EM(E)ES( flag \201empty buffer is OK\202 is no longer used \201it
was an artifact of the X implementation\202.

)0 P()-1 LI(Change NewXPACommand\201\202 to XPAcmdNew\201\202, with the new calling sequence:
) 1 52 PR(  xpa = NewXPACommand\201toplevel, NULL, prefix, NULL\202;)RP(
is changed to:
) 1 32 PR(  xpa = XPACmdNew\201xclass, name\202;)RP(
)0 P()-1 LI(Change the AddXPACommand\201\202 subroutine name to XPACmdAdd \201with the same
calling sequence\202:
) 3 53 PR(  AddXPACommand\201xpa, "file",
    "\200tdisplay a new file\200n\200t\200t  requires: filename",
    NULL, NULL, NULL, XPAReceiveFile, text, NULL\202;)RP(
is changed to:
) 3 53 PR(  XPACmdAdd\201xpa, "file",
    "\200tdisplay a new file\200n\200t\200t  requires: filename",
    NULL, NULL, NULL, XPAReceiveFile, text, NULL\202;)RP(
)0 P()-1 LI(The XPAXtAppInput\201\202 routine should be called just before XtAppMainLoop\201\202
to add xpa fds to the Xt event loop:
) 5 35 PR(  /* add the xpas to the Xt loop */
  XPAXtAddInput\201app, NULL\202;

  /* process events */
  XtAppMainLoop\201app\202;)RP(
)0 P()-1 LI(Change NewXPA\201\202 to XPANew\201\202 and call XPAXtAddInput\201\202 if the XtAppMainLoop
routine already has been entered:
) 4 71 PR(  xpa = NewXPA\201saotng->xim->toplevel, prefix, xparoot,
               "FITS data or image filename\200n\200t\200t  options: file type",
               XPASendData, new, NULL,
               XPAReceiveData, new, "SE"\202;)RP(
is changed to:
) 6 74 PR(  sprintf\201tbuf, "%s.%s", prefix, xparoot\202;
  xpa = XPANew\201"SAOTNG", tbuf,
               "FITS data or image filename\200n\200t\200t  options: file type",
               XPASendData, new, NULL,
               XPAReceiveData, new, "SE"\202;
  XPAXtAddInput\201XtWidgetToApplicationContext\201saotng->xim->toplevel\202, xpa\202;)RP(
)0 P()-1 LI(Change XPAInternalReceiveCommand\201\202 to XPACmdInternalReceive\201\202
remove first argument in the calling sequence\202:
) 3 61 PR(  XPAInternalReceiveCommand\201im->saotng->xim->toplevel,
                            im->saotng, im->saotng->commands,
                            "zoom reset", NULL, 0\202;)RP(
is changed to:
) 2 57 PR(  XPACmdInternalReceive\201im->saotng, im->saotng->commands,
                        "zoom reset", NULL, 0\202;)RP(
)0 P()-1 LI(Change DestroyXPA to XPAFree:
) 1 26 PR(  DestroyXPA\201im->dataxpa\202;)RP(
is changed to:
) 1 23 PR(  XPAFree\201im->dataxpa\202;)RP()LU(





)0 P()0 0 1 A(Go to XPA Help Index)0 0 TN TL()Ec /AF f D(

)0 5 152 H(Last)WB 223 Sn( updated: September 10, 2003)EH(

)WB NL
/Cb Db D /Ct [16#00 16#00 16#00] D /Cl [16#00 16#00 16#00] D /CL -1 D Ct Sc
DS
/Ba f D /BO 0 D Bs
/UR (name.html) D
/Ti (What does XPA stand for?) D
/Au () D
/Df f D
/ME [()] D

0 BO R
()1 Sl()WB 46 Sn(


)0 2 153 H(XPAName:)WB 225 Sn()WB 224 Sn( What does XPA stand for?)EA()EH(


)0 2 154 H(Summary)WB 226 Sn()EH(
)0 P(What does XPA stand for? Who knows anymore!


)0 2 155 H(Description)WB 227 Sn()EH(
)0 P(What does XPA stand for? Dunno! The XPA messaging system originally
was built on top of the X Window System and XPA was the mnemonic for
)EM(X Public Access)ES(, to emphasize that we were providing public
access to previously private data and algorithms in Xt programs.  Now
that XPA no longer is tied to X, it can be argued that we ought to
change the name \201how about )EM(SPAM: simple public access mechanism)ES(\202, but XPA is in wide-spread use in the astronomical community of
its birth, and the name has taken on a life of its own. If anyone can
think of what XPA now means, please let us know.

)0 P(If you think this is bad, consider the MMT Telescope on Mount Hopkins,
Arizona. When first installed twenty years ago, it featured an array
of six 72-inch diameter mirrors. from which came its name: the
)EM(Multiple Mirror Telescope)ES(.  In spring of 1999, these mirrors
were replaced by a single 21 and 1/2 -foot diameter primary mirror,
the largest single-piece glass reflector on the North American
continent. And now MMT stands for ... MMT!





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)0 5 156 H(Last)WB 228 Sn( updated: September 10, 2003)EH(

)WB NL
/TE t D NP TU PM 0 eq and{/Pn () D showpage}if end restore