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Always turn off hyphenation; it makes +.\" way too many mistakes in technical documents. +.if n .ad l +.nh +.SH "NAME" +\&\fBxpans: the \s-1XPA\s0 Name Server\fR +.SH "SYNOPSIS" +.IX Header "SYNOPSIS" +.Vb 1 +\& xpans [\-h] [\-e] [\-k sec] [\-p port] [\-l log] [\-s security log] [\-P n] +.Ve +.SH "OPTIONS" +.IX Header "OPTIONS" +.Vb 8 +\& \-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 (P=1) using separate thread (P=2) +\& \-\-version display version and exit +.Ve +.SH "DESCRIPTION" +.IX Header "DESCRIPTION" +The xpans name server is an XPA-enabled program that is used to +manage the names and ports of \s-1XPA\s0 access points. It is started +automatically when an \s-1XPA\s0 access point is registered. You can access +the name server using xpaget to get a list of registered access points. +.PP +The \fIxpans\fR name server provides a crucial link between \s-1XPA\s0 +clients and servers. When an \s-1XPA\s0 server defines an access point using +\&\fIXPANew()\fR, \fIXPACmdNew()\fR, or \fIXPAInfoNew()\fR, 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 \s-1XPA\s0 +clients with these registered entries, so that the clients can +communicate with the appropriate servers. +.PP +The socket connection between an XPA-enabled program and +\&\fIxpans\fR is kept open until the former exits (or explicitly +closes the connection). Apparently, some Internet equipment (e.g. \s-1DSL\s0 +modems) can cause such a connection to time-out after a period of +inactivity. To prevent this from happening, you can use the \-k +[sec] switch to send a short keep-alive message to each open +connection after the specified time delay. (Note 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 \s-1DSL\s0 or similar equipment. \s-1XPA\s0 uses +the ordinary socket-level keep-alive, which works for all other cases.) +\&\s-1NB\s0 (12/2/2009): Out-of-band (\s-1URG\s0) \s-1TCP\s0 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 \s-1XPA\s0 server as well. Proceed with caution! +.PP +The \fIxpans\fR program will be started automatically (assuming it +can be found in the user's path) when the first \s-1XPA\s0 access point is +registered. It therefore need not be started explicitly. However, +when started automatically, the \fI\-e\fR switch is used, so that +the name server will exit when there are no more \s-1XPA\s0 access points +registered. If you wish to keep the name server running continually, +simply start it manually without the \fI\-e\fR switch. +.PP +The name server will keep a log of registered access points if the +\&\fI\-l [log]\fR switch is used on the command line (this is the +case for automatic start-up). The log contains enough name and connection +information to allow you to re-register all \s-1XPA\s0 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: +.PP +.Vb 1 +\& add 838e2f67:1863 ds9 ds9 gs eric +.Ve +.PP +If \fIxpans\fR is terminated but ds9 still is running, you +can re-register both access points for the ds9 process by running: +.PP +.Vb 1 +\& xpaset \-p 838e2f67:1863 \-nsconnect +.Ve +.PP +Notice that the ip:port specifier is used with \fIxpaset\fR to bypass +the need for contacting the name server (which does not have the name +registered yet!) +.PP +The name server will keep a log of security information if the \-s +[security log] switch is used on the command line. For each +accepted connection, (including connections via the \fIxpaget\fR +command), information will be logged about the host issuing the +command and the parameters passed into the program. This is most +useful when \fIxpans\fR is accepting connections from untrusted +machines. +.PP +When an \s-1XPA\s0 access point is removed by a server using \fI\fIXPAFree()\fI\fR, +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. +.PP +The name server itself has an \s-1XPA\s0 access point names \fIxpans\fR +registered through which you can find out information about currently +registered access points (assuming you have access to the name server; +see \s-1XPA\s0 Access Control for more information). +For each registered access point, the following information is returned: +.PP +.Vb 5 +\& class # class of the access point +\& name # name of the access point +\& access # allowed access (g=xpaget,s=xpaset,i=xpainfo) +\& id # socket access method (host:port for inet, file for local/unix) +\& user # user name of access point owner +.Ve +.PP +For example, to display all currently registered access points, simply execute: +.PP +.Vb 1 +\& xpaget xpans +.Ve +.PP +Continuing the example of ds9 above, this will return: +.PP +.Vb 1 +\& DS9 ds9 gs 838e2f67:1863 eric +.Ve +.PP +If the same program has been started with different \s-1XPA\s0 access names, +you can look up only names matching a specified template. For example, +assume that ds9 has been started up using: +.PP +.Vb 3 +\& ds9 & +\& ds9 \-title ds9\-1\-eric & +\& ds9 \-title ds9\-2\-eric & +.Ve +.PP +To lookup all ds9 access points which end in \*(L".eric\*(R" and which can +be accessed using \fIxpaset\fR, use: +.PP +.Vb 1 +\& xpaget xpans "DS9:*.eric" "s" "*" +.Ve +.PP +This will return: +.PP +.Vb 2 +\& DS9 ds9\-2\-eric gs 838e29d3:42102 eric +\& DS9 ds9\-1\-eric gs 838e29d3:42105 eric +.Ve +.PP +The third argument \*(L"*\*(R" 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. +.PP +The name server uses the \fI\s-1XPA_METHOD\s0\fR environment variable +to determine whether it should listen for requests on \s-1INET\s0 or \s-1LOCAL\s0 +sockets. Since \s-1XPA\s0 access points also use this environment variable, +the choice of socket method will be consistent. Note that, when \s-1INET\s0 +sockets are used, a local server can be accessed from remote machines +if the \fI\s-1XPA_NSINET\s0\fR environment variable is set to point to +the local machine. See +\&\s-1XPA\s0 Environment Variables +for more information. +.PP +An experimental feature of xpans is its ability to act as a proxy to +\&\s-1XPA\s0 servers behind firewalls that want to communicate with external +processes. The basic idea is the following: an \s-1XPA\s0 server (call it +\&\*(L"foo\*(R") on host1, possibly behind a firewall, makes a remote connection +to a proxy-enabled xpans program on host2 (specifying host2's \s-1XPA\s0 method). +For example: +.PP +.Vb 1 +\& xpaset \-p foo \-remote \*(Aqhost2:28571\*(Aq + \-proxy # on host1 +.Ve +.PP +When this is done, host2 can use xpaset, xpaget, and xpainfo calls to +communicate with the \s-1XPA\s0 server foo. All command communication is +performed via the xpans socket connection between foo on host1 and +xpans on host2 (which was initiated by foo from inside the firewall). +Data communication is similarly performed using a socket connection +initiated on host1 (usually with a port value two greater than the +port value of the main xpans socket connection). An xpaset or xpaget +call on host2 contacts xpans, which performs an \fIXPASet()\fR or \fIXPAGet()\fR +call to foo, passing commands and data back and forth between the two +programs. +.PP +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 (assuming pthreads are supported on your system). +Because xpa callback processing of any type can take a long time and +therefore can interfere with normal xpans processing, threaded proxy +connections (\-P 2) are recommended. When using proxy connections, it +might also be useful to set the \s-1XPA_IOCALLSXPA\s0 environment variable, so +that multiple proxy requests can be handled at the same time, instead of +serially. +.PP +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. (See http://chandra\-ed.cfa.harvard.edu and +http://hea\-www.harvard.edu/saord/ds9 for more details). As always, please +contact us if you have problems or questions. +.SH "SEE ALSO" +.IX Header "SEE ALSO" +See xpa(n) for a list of \s-1XPA\s0 help pages |