fcopy $b $a -command [list geof $b]
		puts stderr 2COPY
	    }
	    puts stderr ...
	}
	puts stderr SRV
	set l {}
	set srv [socket -server new -myaddr 127.0.0.1 0]
        set port [lindex [fconfigure $srv -sockname] 2]
	puts stderr WAITING
	fileevent stdin readable bye
	puts "OK $port"
	vwait forever
    }
    # wait for OK from server.
    lassign [gets $pipe] ok port
    # Now the two clients.
    proc ::done {sock} {
	if {[eof $sock]} { close $sock ; return }
	lappend ::forever [gets $sock]
	return
    }
    set a [socket 127.0.0.1 $port]
    set b [socket 127.0.0.1 $port]
    fconfigure $a -translation binary -buffering none
    fconfigure $b -translation binary -buffering none
    fileevent  $a readable [list ::done $a]
    fileevent  $b readable [list ::done $b]
} -constraints {stdio fcopy} -body {
    # Now pass data through the server in both directions.
    set ::forever {}