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