fcopy - Copy data from one channel to another
fcopy inchan outchan ?
-size size?
?
-command callback?
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 or characters have been transferred;
size is in bytes
if the two channels are using the same encoding, and is in characters
otherwise. 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 or characters (using the same rules
as for the
-size option) 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 input operations with
inchan, or output
operations with
outchan, during a background
fcopy. The converse
is entirely legitimate, as exhibited by the bidirectional fcopy example below.
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 wrong-sided I/O attempted (by a
fileevent handler or otherwise) 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.
The first example transfers the contents of one channel exactly to another. Note
that when copying one file to another, it is better to use
file copy
which also copies file metadata (e.g. the file access permissions) where
possible.
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 $chunk]
vwait done
The fourth example starts an asynchronous, bidirectional fcopy between two
sockets. Those could also be pipes from two [open "|hal 9000" r+]
(though their conversation would remain secret to the script, since all four
fileevent slots are busy).
set flows 2
proc Done {dir args} {
global flows done
puts "$dir is over."
incr flows -1
if {$flows<=0} {set done 1}
}
fcopy $sok1 $sok2 -command [list Done UP]
fcopy $sok2 $sok1 -command [list Done DOWN]
vwait done
eof(3tcl),
fblocked(3tcl),
fconfigure(3tcl),
file(3tcl)
blocking, channel, end of line, end of file, nonblocking, read,
translation