NAME
       fcopy - Copy data from one channel to another.

SYNOPSIS
       fcopy inchan outchan ?-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 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 com-
       mand 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  transla-
       tions  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 syn-
       chronous 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(n), fblocked(n), fconfigure(n)


KEYWORDS
       blocking,  channel, end of line, end of file, nonblocking, read, trans-
