The fcopy command transfers data from inchan until end of file or size bytes have been transferred. If no -size argument is given, then the copy goes until end of file. All the data read from inchan is copied to outchan. Without the -command option, fcopy blocks until the copy is complete and returns the number of bytes written to outchan.
The -command argument makes fcopy work in the background. In this case it returns immediately and the callback is invoked later when the copy completes. The callback is called with one or two additional arguments that indicates how many bytes were written to outchan. If an error occurred during the background copy, the second argument is the error string associated with the error. With a background copy, it is not necessary to put inchan or outchan into non-blocking mode; the fcopy command takes care of that automatically. However, it is necessary to enter the event loop by using the vwait command or by using Tk.
You are not allowed to do other I/O operations with inchan or outchan during a background fcopy. If either inchan or outchan get closed while the copy is in progress, the current copy is stopped and the command callback is not made. If inchan is closed, then all data already queued for outchan is written out.
Note that inchan can become readable during a background copy. You should turn off any fileevent handlers during a background copy so those handlers do not interfere with the copy. Any I/O attempted by a fileevent handler will get a “channel busy” error.
Fcopy translates end-of-line sequences in inchan and outchan according to the -translation option for these channels. See the manual entry for fconfigure for details on the -translation option. The translations mean that the number of bytes read from inchan can be different than the number of bytes written to outchan. Only the number of bytes written to outchan is reported, either as the return value of a synchronous fcopy or as the argument to the callback for an asynchronous fcopy.
Fcopy obeys the encodings and character translations configured for the channels. This means that the incoming characters are converted internally first UTF-8 and then into the encoding of the channel fcopy writes to. See the manual entry for fconfigure for details on the -encoding and -translation options. No conversion is done if both channels are set to encoding “binary” and have matching translations. If only the output channel is set to encoding “binary” the system will write the internal UTF-8 representation of the incoming characters. If only the input channel is set to encoding “binary” the system will assume that the incoming bytes are valid UTF-8 characters and convert them according to the output encoding. The behaviour of the system for bytes which are not valid UTF-8 characters is undefined in this case.
fconfigure $in -translation binary fconfigure $out -translation binary fcopy $in $out
This second example shows how the callback gets passed the number of bytes transferred. It also uses vwait to put the application into the event loop. Of course, this simplified example could be done without the command callback.
proc Cleanup {in out bytes {error {}}} {
global total
set total $bytes
close $in
close $out
if {[string length $error] != 0} {
# error occurred during the copy
}
}
set in [open $file1]
set out [socket $server $port]
fcopy $in $out -command [list Cleanup $in $out]
vwait total
The third example copies in chunks and tests for end of file in the command callback
proc CopyMore {in out chunk bytes {error {}}} {
global total done
incr total $bytes
if {([string length $error] != 0) || [eof $in]} {
set done $total
close $in
close $out
} else {
fcopy $in $out -size $chunk \
-command [list CopyMore $in $out $chunk]
}
}
set in [open $file1]
set out [socket $server $port]
set chunk 1024
set total 0
fcopy $in $out -size $chunk \
-command [list CopyMore $in $out $chunk]
vwait done