68 lines
2.3 KiB
Plaintext
68 lines
2.3 KiB
Plaintext
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'\"
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'\" Copyright (c) 1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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.TH fblocked n 7.5 Tcl "Tcl Built-In Commands"
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.BS
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'\" Note: do not modify the .SH NAME line immediately below!
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.SH NAME
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fblocked \- Test whether the last input operation exhausted all available input
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.SH SYNOPSIS
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\fBfblocked \fIchannelId\fR
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.BE
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.SH DESCRIPTION
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.PP
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The \fBfblocked\fR command returns 1 if the most recent input operation
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on \fIchannelId\fR returned less information than requested because all
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available input was exhausted.
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For example, if \fBgets\fR is invoked when there are only three
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characters available for input and no end-of-line sequence, \fBgets\fR
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returns an empty string and a subsequent call to \fBfblocked\fR will
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return 1.
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.PP
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\fIChannelId\fR must be an identifier for an open channel such as a
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Tcl standard channel (\fBstdin\fR, \fBstdout\fR, or \fBstderr\fR),
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the return value from an invocation of \fBopen\fR or \fBsocket\fR, or
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the result of a channel creation command provided by a Tcl extension.
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.SH EXAMPLE
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The \fBfblocked\fR command is particularly useful when writing network
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servers, as it allows you to write your code in a line-by-line style
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without preventing the servicing of other connections. This can be
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seen in this simple echo-service:
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.PP
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.CS
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# This is called whenever a new client connects to the server
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proc connect {chan host port} {
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set clientName [format <%s:%d> $host $port]
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puts "connection from $clientName"
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fconfigure $chan -blocking 0 -buffering line
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fileevent $chan readable [list echoLine $chan $clientName]
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}
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# This is called whenever either at least one byte of input
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# data is available, or the channel was closed by the client.
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proc echoLine {chan clientName} {
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gets $chan line
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if {[eof $chan]} {
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puts "finishing connection from $clientName"
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close $chan
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} elseif {![\fBfblocked\fR $chan]} {
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# Didn't block waiting for end-of-line
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puts "$clientName - $line"
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puts $chan $line
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}
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}
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# Create the server socket and enter the event-loop to wait
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# for incoming connections...
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socket -server connect 12345
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vwait forever
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.CE
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.SH "SEE ALSO"
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gets(n), open(n), read(n), socket(n), Tcl_StandardChannels(3)
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.SH KEYWORDS
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blocking, nonblocking
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