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.  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  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 option. No conversion is done if both channels
       are set to encoding "binary". 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.

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

SEE ALSO

       eof(3tcl), fblocked(3tcl), fconfigure(3tcl)

KEYWORDS

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