fcopy(n) Tcl (8.0) fcopy(n)
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NAME
fcopy - Copy data from one channel to another.
SYNOPSIS
fcopy inchan outchan ?-size size? ?-command callback?
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DESCRIPTION
The fcopy command copies data from one I/O channel, inchan
to another I/O channel, outchan. The fcopy command
leverages the buffering in the Tcl I/O system to avoid extra
copies and to avoid buffering too much data in main memory
when copying large files to slow destinations like network
sockets.
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.
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fcopy(n) Tcl (8.0) fcopy(n)
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.
EXAMPLE
This first 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 second 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 -command [list CopyMore $in $out $chunk] \
-size $chunk
}
}
set in [open $file1]
set out [socket $server $port]
set chunk 1024
set total 0
fcopy $in $out -command [list CopyMore $in $out $chunk] -size $chunk
vwait done
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fcopy(n) Tcl (8.0) fcopy(n)
SEE ALSO
eof(n), fblocked(n), fconfigure(n)
KEYWORDS
blocking, channel, end of line, end of file, nonblocking,
read, translation
Page 3 (printed 2/19/99)
