fcopy(n)

NAME
fcopy - Copy data from one channel to another

SYNOPSIS
fcopy inputChan outputChan ?-size size? ?-command callback?

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 destinations like network sockets.

  DATA QUANTITY
All data until EOF is copied. In addition, the quantity of copied data may be specified by the option -size. The given size is in bytes, if the input channel is in binary mode. Otherwise, it is in characters.

Depreciated feature: the transfer is treated as a binary transfer, if the encoding profile is set to and the input encoding matches the output encoding. In this case, eventual encoding errors are not handled. An eventually given size is in bytes in this case.

  BLOCKING OPERATION MODE
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.

  BACKGROUND OPERATION MODE
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 error.

  CHANNEL TRANSLATION OPTIONS
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.

  CHANNEL ENCODING OPTIONS
Fcopy obeys the encodings, profiles and character translations configured for the channels. This means that the incoming characters are converted from the encoding configured for the input channel and then encoded as per the encoding of the output channel. See the manual entry for fconfigure for details on the -encoding and -profile options. No conversion is done if both channels are set to encoding and have matching translations.

Fcopy may throw encoding errors (error code EILSEQ), if input or output channel is configured to the encoding profile.

If an encoding error arises on the input channel, any data before the error byte is written to the output channel. The input file pointer is located just before the values causing the encoding error. Error inspection or recovery is possible by changing the encoding parameters and invoking a file command (read, fcopy).

If an encoding error arises on the output channel, the erroneous data is lost. To make the difference between the input error case and the output error case, only the error message may be inspected (read or write), as both throw the error code EILSEQ.

EXAMPLES

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

SEE ALSO
eof(n), fblocked(n), fconfigure(n), file(n)

KEYWORDS
blocking, channel, end of line, end of file, nonblocking, read, translation