path: root/tests/iogt.test

# -*- tcl -*-
# Commands covered:  transform, and stacking in general
#
# This file contains a collection of tests for Giot
#
# See the file "license.terms" for information on usage and redistribution of
# this file, and for a DISCLAIMER OF ALL WARRANTIES.
# 
# Copyright (c) 2000 Ajuba Solutions.
# Copyright (c) 2000 Andreas Kupries.
# All rights reserved.

if {[catch {package require tcltest 2.1}]} {
    puts stderr "Skipping tests in [info script].  tcltest 2.1 required."
    return
}

::tcltest::loadTestedCommands
catch [list package require -exact Tcltest [info patchlevel]]

namespace eval ::tcl::test::iogt {
    namespace import ::tcltest::*

testConstraint testchannel [llength [info commands testchannel]]

set path(dummy) [makeFile {abcdefghijklmnopqrstuvwxyz0123456789,./?><;'\|":[]\}\{`~!@#$%^&*()_+-=
} dummy]

# " capture coloring of quotes

set path(dummyout) [makeFile {} dummyout]

set path(__echo_srv__.tcl) [makeFile {
#!/usr/local/bin/tclsh
# -*- tcl -*-
# echo server
#
# arguments, options: port to listen on for connections.
#                     delay till echo of first block
#                     delay between blocks
#                     blocksize ...

set port [lindex $argv 0]
set fdelay [lindex $argv 1]
set idelay [lindex $argv 2]
set bsizes [lrange $argv 3 end]
set c 0

proc newconn {sock rhost rport} {
    variable fdelay
    variable c
    incr c
    namespace upvar [namespace current] c$c conn

    #puts stdout "C $sock $rhost $rport / $fdelay" ; flush stdout

    set conn(after) {}
    set conn(state) 0
    set conn(size) 0
    set conn(data) ""
    set conn(delay) $fdelay

    fileevent $sock readable [list echoGet $c $sock]
    fconfigure $sock -translation binary -buffering none -blocking 0
}

proc echoGet {c sock} {
    variable fdelay
    namespace upvar [namespace current] c$c conn

    if {[eof $sock]} {
	# one-shot echo
	exit
    }
    append conn(data) [read $sock]

    #puts stdout "G $c $sock $conn(data) <<$conn(data)>>" ; flush stdout

    if {$conn(after) == {}} {
	set conn(after) [after $conn(delay) [list echoPut $c $sock]]
    }
}

proc echoPut {c sock} {
    variable idelay
    variable fdelay
    variable bsizes
    namespace upvar [namespace current] c$c conn

    if {[string length $conn(data)] == 0} {
	#puts stdout "C $c $sock" ; flush stdout
	# auto terminate
	close $sock
	exit
	#set conn(delay) $fdelay
	return
    }

    set conn(delay) $idelay
    set n [lindex $bsizes $conn(size)]

    #puts stdout "P $c $sock $n >>" ; flush stdout

    #puts __________________________________________
    #parray conn
    #puts n=<$n>

    if {[string length $conn(data)] >= $n} {
	puts -nonewline $sock [string range $conn(data) 0 $n]
	set conn(data) [string range $conn(data) [incr n] end]
    }

    incr conn(size)
    if {$conn(size) >= [llength $bsizes]} {
	set conn(size) [expr {[llength $bsizes]-1}]
    }

    set conn(after) [after $conn(delay) [list echoPut $c $sock]]
}

#fileevent stdin readable {exit ;#cut}

# main
socket -server newconn -myaddr 127.0.0.1 $port
vwait forever
} __echo_srv__.tcl]

########################################################################

proc fevent {fdelay idelay blocks script data} {
    # Start and initialize an echo server, prepare data transmission, then
    # hand over to the test script.  This has to start real transmission via
    # 'flush'.  The server is stopped after completion of the test.

    upvar 1 sock sk

    # Fixed port, not so good. Lets hope for the best, for now.
    set port 4000

    exec tclsh __echo_srv__.tcl $port $fdelay $idelay {*}$blocks >@stdout &
    after 500

    #puts stdout "> $port"; flush stdout

    set sk [socket localhost $port]
    fconfigure $sk -blocking 0 -buffering full \
	-buffersize [expr {10+[llength $data]}]
    puts -nonewline $sk $data

    # The channel is prepared to go off.

    #puts stdout ">>>>>"; flush stdout

    set res [uplevel 1 $script]
    catch {close $sk}
    return $res
}

# --------------------------------------------------------------
# utility transformations ...

proc id {op data} {
    switch -- $op {
	create/write - create/read - delete/write - delete/read - clear_read {
	    #ignore
	}
	flush/write - flush/read - write - read {
	    return $data
	}
	query/maxRead {
	    return -1
	}
    }
}

proc id_optrail {var op data} {
    variable $var
    upvar 0 $var trail

    lappend trail $op
    switch -- $op {
	create/write - create/read - delete/write - delete/read -
	flush/read - clear/read {
	    #ignore
	}
	flush/write - write - read {
	    return $data
	}
	query/maxRead {
	    return -1
	}
	default {
	    lappend trail "error $op"
	    error $op
	}
    }
}

proc id_fulltrail {var op data} {
    namespace upvar [namespace current] $var trail

    #puts stdout ">> $var $op $data" ; flush stdout

    switch -- $op {
	create/write - create/read - delete/write - delete/read - clear_read {
	    set res *ignored*
	}
	flush/write - flush/read - write - read {
	    set res $data
	}
	query/maxRead {
	    set res -1
	}
    }

    #catch {puts stdout "\t>* $res" ; flush stdout}
    #catch {puts stdout "x$res"} msg

    lappend trail [list $op $data $res]
    return $res
}

proc id_torture {chan op data} {
    switch -- $op {
	create/write -
	create/read  -
	delete/write -
	delete/read  -
	clear_read   {;#ignore}
	flush/write -
	flush/read  {}
	write       {
	    global level
	    if {$level} {
		return
	    }
	    incr level
	    testchannel unstack $chan
	    testchannel transform $chan \
		-command [namespace code [list id_torture $chan]]
	    return $data
	}
	read        {
	    testchannel unstack $chan
	    testchannel transform $chan \
		-command [namespace code [list id_torture $chan]]
	    return $data
	}
	query/maxRead {return -1}
    }
}

proc counter {var op data} {
    namespace upvar [namespace current] $var n

    switch -- $op {
	create/write - create/read - delete/write - delete/read - clear_read {
	    #ignore
	}
	flush/write - flush/read {
	    return {}
	}
	write {
	    return $data
	}
	read {
	    if {$n > 0} {
		incr n -[string length $data]
		if {$n < 0} {
		    set n 0
		}
	    }
	    return $data
	}
	query/maxRead {
	    return $n
	}
    }
}

proc counter_audit {var vtrail op data} {
    namespace upvar [namespace current] $var n $vtrail trail

    switch -- $op {
	create/write - create/read - delete/write - delete/read - clear_read {
	    set res {}
	}
	flush/write - flush/read {
	    set res {}
	}
	write {
	    set res $data
	}
	read {
	    if {$n > 0} {
		incr n -[string length $data]
		if {$n < 0} {
		    set n 0
		}
	    }
	    set res $data
	}
	query/maxRead {
	    set res $n
	}
    }

    lappend trail [list counter:$op $data $res]
    return $res
}

proc rblocks {var vtrail n op data} {
    namespace upvar [namespace current] $var n $vtrail trail

    set res {}

    switch -- $op {
	create/write - create/read - delete/write - delete/read - clear_read {
	    set buf {}
	}
	flush/write {
	}
	flush/read {
	    set res $buf
	    set buf {}
	}
	write {
	    set data
	}
	read {
	    append buf $data
	    set b [expr {$n * ([string length $buf] / $n)}]
	    append op " $n [string length $buf] :- $b"
	    set res [string range $buf 0 [incr b -1]]
	    set buf [string range $buf [incr b] end]
	    #return $res
	}
	query/maxRead {
	    set res -1
	}
    }

    lappend trail [list rblock | $op $data $res | $buf]
    return $res
}

# --------------------------------------------------------------
# ... and convenience procedures to stack them

proc identity {-attach channel} {
    testchannel transform $channel -command [namespace code id]
}
proc audit_ops {var -attach channel} {
    testchannel transform $channel -command [namespace code [list id_optrail $var]]
}
proc audit_flow {var -attach channel} {
    testchannel transform $channel -command [namespace code [list id_fulltrail $var]]
}

proc torture {-attach channel} {
    testchannel transform $channel -command [namespace code [list id_torture $channel]]
}

proc stopafter {var n -attach channel} {
    namespace upvar [namespace current] $var vn
    set vn $n
    testchannel transform $channel -command [namespace code [list counter $var]]
}
proc stopafter_audit {var trail n -attach channel} {
    namespace upvar [namespace current] $var vn
    set vn $n
    testchannel transform $channel -command [namespace code [list counter_audit $var $trail]]
}
proc rblocks_t {var trail n -attach channel} {
    testchannel transform $channel -command [namespace code [list rblocks $var $trail $n]]
}

# --------------------------------------------------------------
# serialize an array, with keys in sorted order.

proc array_sget {v} {
    upvar $v a
    set res [list]
    foreach n [lsort [array names a]] {
	lappend res $n $a($n)
    }
    set res
}
proc asort {alist} {
    # sort a list of key/value pairs by key, removes duplicates too.
    array set a $alist
    array_sget a
}

########################################################################

test iogt-1.1 {stack/unstack} testchannel {
    set fh [open $path(dummy) r]
    identity -attach $fh
    testchannel unstack $fh
    close $fh
} {}
test iogt-1.2 {stack/close} testchannel {
    set fh [open $path(dummy) r]
    identity -attach $fh
    close $fh
} {}
test iogt-1.3 {stack/unstack, configuration, options} testchannel {
    set fh [open $path(dummy) r]
    set ca [asort [fconfigure $fh]]
    identity -attach $fh
    set cb [asort [fconfigure $fh]]
    testchannel unstack $fh
    set cc [asort [fconfigure $fh]]
    close $fh
    # With this system none of the buffering, translation and encoding option
    # may change their values with channels stacked upon each other or not.
    # cb == ca == cc
    list [string equal $ca $cb] [string equal $cb $cc] [string equal $ca $cc]
} {1 1 1}
test iogt-1.4 {stack/unstack, configuration} -setup {
    set fh [open $path(dummy) r]
} -constraints testchannel -body {
    set ca [asort [fconfigure $fh]]
    identity -attach $fh
    fconfigure $fh -buffering line -translation cr -encoding shiftjis
    testchannel unstack $fh
    set cc [asort [fconfigure $fh]]
    list [string equal $ca $cc] [fconfigure $fh -buffering] \
	[fconfigure $fh -translation] [fconfigure $fh -encoding]
} -cleanup {
    close $fh
} -result {0 line cr shiftjis}

test iogt-2.0 {basic I/O going through transform} -setup {
    set fin [open $path(dummy) r]
    set fout [open $path(dummyout) w]
} -constraints testchannel -body {
    identity -attach $fin
    identity -attach $fout
    fcopy $fin $fout
    close $fin
    close $fout
    set fin [open $path(dummy) r]
    set fout [open $path(dummyout) r]
    list [string equal [set in [read $fin]] [set out [read $fout]]] \
	[string length $in] [string length $out]
} -cleanup {
    close $fin
    close $fout
} -result {1 71 71}
test iogt-2.1 {basic I/O, operation trail} {testchannel unix} {
    set fin [open $path(dummy) r]
    set fout [open $path(dummyout) w]
    set ain [list]; set aout [list]
    audit_ops ain -attach $fin
    audit_ops aout -attach $fout
    fconfigure $fin -buffersize 10
    fconfigure $fout -buffersize 10
    fcopy $fin $fout
    close $fin
    close $fout
    set res "[join $ain \n]\n--------\n[join $aout \n]"
} {create/read
query/maxRead
read
query/maxRead
read
query/maxRead
read
query/maxRead
read
query/maxRead
read
query/maxRead
read
query/maxRead
read
query/maxRead
read
query/maxRead
flush/read
delete/read
--------
create/write
write
write
write
write
write
write
write
write
flush/write
delete/write}
test iogt-2.2 {basic I/O, data trail} {testchannel unix} {
    set fin [open $path(dummy) r]
    set fout [open $path(dummyout) w]
    set ain [list]; set aout [list]
    audit_flow ain -attach $fin
    audit_flow aout -attach $fout
    fconfigure $fin -buffersize 10
    fconfigure $fout -buffersize 10
    fcopy $fin $fout
    close $fin
    close $fout
    set res "[join $ain \n]\n--------\n[join $aout \n]"
} {create/read {} *ignored*
query/maxRead {} -1
read abcdefghij abcdefghij
query/maxRead {} -1
read klmnopqrst klmnopqrst
query/maxRead {} -1
read uvwxyz0123 uvwxyz0123
query/maxRead {} -1
read 456789,./? 456789,./?
query/maxRead {} -1
read {><;'\|":[]} {><;'\|":[]}
query/maxRead {} -1
read {\}\{`~!@#$} {\}\{`~!@#$}
query/maxRead {} -1
read %^&*()_+-= %^&*()_+-=
query/maxRead {} -1
read {
} {
}
query/maxRead {} -1
flush/read {} {}
delete/read {} *ignored*
--------
create/write {} *ignored*
write abcdefghij abcdefghij
write klmnopqrst klmnopqrst
write uvwxyz0123 uvwxyz0123
write 456789,./? 456789,./?
write {><;'\|":[]} {><;'\|":[]}
write {\}\{`~!@#$} {\}\{`~!@#$}
write %^&*()_+-= %^&*()_+-=
write {
} {
}
flush/write {} {}
delete/write {} *ignored*}
test iogt-2.3 {basic I/O, mixed trail} {testchannel unix} {
    set fin [open $path(dummy) r]
    set fout [open $path(dummyout) w]
    set trail [list]
    audit_flow trail -attach $fin
    audit_flow trail -attach $fout
    fconfigure $fin -buffersize 20
    fconfigure $fout -buffersize 10
    fcopy $fin $fout
    close $fin
    close $fout
    join $trail \n
} {create/read {} *ignored*
create/write {} *ignored*
query/maxRead {} -1
read abcdefghijklmnopqrst abcdefghijklmnopqrst
write abcdefghij abcdefghij
write klmnopqrst klmnopqrst
query/maxRead {} -1
read uvwxyz0123456789,./? uvwxyz0123456789,./?
write uvwxyz0123 uvwxyz0123
write 456789,./? 456789,./?
query/maxRead {} -1
read {><;'\|":[]\}\{`~!@#$} {><;'\|":[]\}\{`~!@#$}
write {><;'\|":[]} {><;'\|":[]}
write {\}\{`~!@#$} {\}\{`~!@#$}
query/maxRead {} -1
read {%^&*()_+-=
} {%^&*()_+-=
}
query/maxRead {} -1
flush/read {} {}
write %^&*()_+-= %^&*()_+-=
write {
} {
}
delete/read {} *ignored*
flush/write {} {}
delete/write {} *ignored*}

test iogt-2.4 {basic I/O, mixed trail} {testchannel} {
    set fh [open $path(dummy) r]
    torture -attach $fh
    chan configure $fh -buffersize 2
    set x [read $fh]
    testchannel unstack $fh
    close   $fh
    set x
} {}
test iogt-2.5 {basic I/O, mixed trail} {testchannel} {
    set ::level 0
    set fh [open $path(dummyout) w]
    torture -attach $fh
    puts -nonewline $fh abcdef
    flush $fh
    testchannel unstack $fh
    close   $fh
} {}

test iogt-3.0 {Tcl_Channel valid after stack/unstack, fevent handling} -setup {
    proc DoneCopy {n {err {}}} {
	variable copy 1
    }
} -constraints {testchannel hangs} -body {
    # This test to check the validity of aquired Tcl_Channel references is not
    # possible because even a backgrounded fcopy will immediately start to
    # copy data, without waiting for the event loop. This is done only in case
    # of an underflow on the read size!. So stacking transforms after the
    # fcopy will miss information, or are not used at all.
    #
    # I was able to circumvent this by using the echo.tcl server with a big
    # delay, causing the fcopy to underflow immediately.
    set fin [open $path(dummy) r]
    fevent 1000 500 {20 20 20 10 1 1} {
	close $fin
	set fout [open dummyout w]
	flush $sock;	# now, or fcopy will error us out
	# But the 1 second delay should be enough to initialize everything
	# else here.
	fcopy $sock $fout -command [namespace code DoneCopy]
	# Transform after fcopy got its handles!  They should be still valid
	# for fcopy.
	set trail [list]
	audit_ops trail -attach $fout
	vwait [namespace which -variable copy]
    } [read $fin];	# {}
    close $fout
    # Check result of copy.
    set fin [open $path(dummy) r]
    set fout [open $path(dummyout) r]
    set res [string equal [read $fin] [read $fout]]
    close $fin
    close $fout
    list $res $trail
} -cleanup {
    rename DoneCopy {}
} -result {1 {create/write create/read write flush/write flush/read delete/write delete/read}}

test iogt-4.0 {fileevent readable, after transform} -setup {
    set fin [open $path(dummy) r]
    set data [read $fin]
    close $fin
    set trail [list]
    set got [list]
    proc Done {args} {
	variable stop 1
    }
} -constraints {testchannel hangs} -body {
    fevent 1000 500 {20 20 20 10 1} {
	audit_flow trail -attach $sock
	rblocks_t rbuf trail 23 -attach $sock
	fileevent $sock readable [namespace code {
	    if {[eof $sock]} {
		Done
		lappend trail "xxxxxxxxxxxxx"
		close $sock
	    } else {
		lappend trail "vvvvvvvvvvvvv"
		lappend trail "\tgot: [lappend got "\[\[[read $sock]\]\]"]"
		lappend trail "============="
		#puts stdout $__; flush stdout
		#read $sock
	    }
	}]
	flush $sock;		# Now, or fcopy will error us out
	# But the 1 second delay should be enough to initialize everything
	# else here.
	vwait [namespace which -variable stop]
    } $data
    join [list [join $got \n] ~~~~~~~~ [join $trail \n]] \n
} -cleanup {
    rename Done {}
} -result {[[]]
[[abcdefghijklmnopqrstuvw]]
[[xyz0123456789,./?><;'\|]]
[[]]
[[]]
[[":[]\}\{`~!@#$%^&*()]]
[[]]
~~~~~~~~
create/write {} *ignored*
create/read {} *ignored*
rblock | create/write {} {} | {}
rblock | create/read {} {} | {}
vvvvvvvvvvvvv
rblock | query/maxRead {} -1 | {}
query/maxRead {} -1
read abcdefghijklmnopqrstu abcdefghijklmnopqrstu
query/maxRead {} -1
rblock | {read 23 21 :- 0} abcdefghijklmnopqrstu {} | abcdefghijklmnopqrstu
rblock | query/maxRead {} -1 | abcdefghijklmnopqrstu
query/maxRead {} -1
	got: {[[]]}
=============
vvvvvvvvvvvvv
rblock | query/maxRead {} -1 | abcdefghijklmnopqrstu
query/maxRead {} -1
read vwxyz0123456789,./?>< vwxyz0123456789,./?><
query/maxRead {} -1
rblock | {read 23 42 :- 23} vwxyz0123456789,./?>< abcdefghijklmnopqrstuvw | xyz0123456789,./?><
rblock | query/maxRead {} -1 | xyz0123456789,./?><
query/maxRead {} -1
	got: {[[]]} {[[abcdefghijklmnopqrstuvw]]}
=============
vvvvvvvvvvvvv
rblock | query/maxRead {} -1 | xyz0123456789,./?><
query/maxRead {} -1
read {;'\|":[]\}\{`~!@#$%^&} {;'\|":[]\}\{`~!@#$%^&}
query/maxRead {} -1
rblock | {read 23 40 :- 23} {;'\|":[]\}\{`~!@#$%^&} {xyz0123456789,./?><;'\|} | {":[]\}\{`~!@#$%^&}
rblock | query/maxRead {} -1 | {":[]\}\{`~!@#$%^&}
query/maxRead {} -1
	got: {[[]]} {[[abcdefghijklmnopqrstuvw]]} {[[xyz0123456789,./?><;'\|]]}
=============
vvvvvvvvvvvvv
rblock | query/maxRead {} -1 | {":[]\}\{`~!@#$%^&}
query/maxRead {} -1
read *( *(
query/maxRead {} -1
rblock | {read 23 19 :- 0} *( {} | {":[]\}\{`~!@#$%^&*(}
rblock | query/maxRead {} -1 | {":[]\}\{`~!@#$%^&*(}
query/maxRead {} -1
	got: {[[]]} {[[abcdefghijklmnopqrstuvw]]} {[[xyz0123456789,./?><;'\|]]} {[[]]}
=============
vvvvvvvvvvvvv
rblock | query/maxRead {} -1 | {":[]\}\{`~!@#$%^&*(}
query/maxRead {} -1
read ) )
query/maxRead {} -1
rblock | {read 23 20 :- 0} ) {} | {":[]\}\{`~!@#$%^&*()}
rblock | query/maxRead {} -1 | {":[]\}\{`~!@#$%^&*()}
query/maxRead {} -1
	got: {[[]]} {[[abcdefghijklmnopqrstuvw]]} {[[xyz0123456789,./?><;'\|]]} {[[]]} {[[]]}
=============
vvvvvvvvvvvvv
rblock | query/maxRead {} -1 | {":[]\}\{`~!@#$%^&*()}
query/maxRead {} -1
flush/read {} {}
rblock | flush/read {} {":[]\}\{`~!@#$%^&*()} | {}
rblock | query/maxRead {} -1 | {}
query/maxRead {} -1
	got: {[[]]} {[[abcdefghijklmnopqrstuvw]]} {[[xyz0123456789,./?><;'\|]]} {[[]]} {[[]]} {[[":[]\}\{`~!@#$%^&*()]]}
=============
vvvvvvvvvvvvv
rblock | query/maxRead {} -1 | {}
query/maxRead {} -1
	got: {[[]]} {[[abcdefghijklmnopqrstuvw]]} {[[xyz0123456789,./?><;'\|]]} {[[]]} {[[]]} {[[":[]\}\{`~!@#$%^&*()]]} {[[]]}
xxxxxxxxxxxxx
rblock | flush/write {} {} | {}
rblock | delete/write {} {} | {}
rblock | delete/read {} {} | {}
flush/write {} {}
delete/write {} *ignored*
delete/read {} *ignored*};	# catch unescaped quote "

test iogt-5.0 {EOF simulation} -setup {
    set fin [open $path(dummy) r]
    set fout [open $path(dummyout) w]
    set trail [list]
} -constraints {testchannel unknownFailure} -result {
    audit_flow trail -attach $fin
    stopafter_audit d trail 20 -attach $fin
    audit_flow trail -attach $fout
    fconfigure $fin -buffersize 20
    fconfigure $fout -buffersize 10
    fcopy $fin $fout
    testchannel unstack $fin
    # now copy the rest in the channel
    lappend trail {**after unstack**}
    fcopy $fin $fout
    close $fin
    close $fout
    join $trail \n
} -result {create/read {} *ignored*
counter:create/read {} {}
create/write {} *ignored*
counter:query/maxRead {} 20
query/maxRead {} -1
read {abcdefghijklmnopqrstuvwxyz0123456789,./?><;'\|":[]\}\{`~!@#$%^&*()_+-=
} {abcdefghijklmnopqrstuvwxyz0123456789,./?><;'\|":[]\}\{`~!@#$%^&*()_+-=
}
query/maxRead {} -1
flush/read {} {}
counter:read abcdefghijklmnopqrst abcdefghijklmnopqrst
write abcdefghij abcdefghij
write klmnopqrst klmnopqrst
counter:query/maxRead {} 0
counter:flush/read {} {}
counter:delete/read {} {}
**after unstack**
query/maxRead {} -1
write uvwxyz0123 uvwxyz0123
write 456789,./? 456789,./?
write {><;'\|":[]} {><;'\|":[]}
write {\}\{`~!@#$} {\}\{`~!@#$}
write %^&*()_+-= %^&*()_+-=
write {
} {
}
query/maxRead {} -1
delete/read {} *ignored*
flush/write {} {}
delete/write {} *ignored*}

proc constX {op data} {
    # replace anything coming in with a same-length string of x'es.
    switch -- $op {
	create/write - create/read - delete/write - delete/read - clear_read {
	    #ignore
	}
	flush/write - flush/read - write - read {
	    return [string repeat x [string length $data]]
	}
	query/maxRead {
	    return -1
	}
    }
}
proc constx {-attach channel} {
    testchannel transform $channel -command [namespace code constX]
}

test iogt-6.0 {Push back} -constraints testchannel -body {
    set f [open $path(dummy) r]
    # contents of dummy = "abcdefghi..."
    read $f 3;		# skip behind "abc"
    constx -attach $f
    # expect to get "xxx" from the transform because of unread "def" input to
    # transform which returns "xxx".
    #
    # Actually the IO layer pre-read the whole file and will read "def"
    # directly from the buffer without bothering to consult the newly stacked
    # transformation. This is wrong.
    read $f 3
} -cleanup {
    close $f
} -result {xxx}
test iogt-6.1 {Push back and up} -constraints {testchannel knownBug} -body {
    set f [open $path(dummy) r]
    # contents of dummy = "abcdefghi..."
    read $f 3;		# skip behind "abc"
    constx -attach $f
    set res [read $f 3]
    testchannel unstack $f
    append res [read $f 3]
} -cleanup {
    close $f
} -result {xxxghi}

# cleanup
foreach file [list dummy dummyout __echo_srv__.tcl] {
    removeFile $file
}
cleanupTests
}
namespace delete ::tcl::test::iogt
return