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 lever
ages 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. With
out 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 cur
rent 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
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 sim
plified example could be done without the command call
back.
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
eof(n), fblocked(n), fconfigure(n)
KEYWORDS
blocking, channel, end of line, end of file, nonblocking,
read, translation
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