http://www.perlmonks.org?node_id=914343


in reply to Re: IO::Select - reading multiple lines
in thread IO::Select - reading multiple lines

Monks,

I've many questions raising now., Let me tell what's in my mind.

So, is it a very worse idea to use <$fh> to read from a socket? Because, it is failing straight away without doing lot of magic(stuffs) in the code.

Server side 
while(@ready = $sel->can_read) {
        if($fh == $lsn) {
            # Accept the socket
            $new = $lsn->accept;
            $sel->add($new);
            print "New client accepted\n";

            print $new "abc\n";
            print $new "abcd\n";
            print $new "abcde\n";
            print $new "abcdef\n";
        }
         else {
            # Process socket
            $a = <$fh> ;
             if (not defined $a)  {
                $sel->remove($fh);
                $fh->close;
                print "Client closed\n";
             }
             else  {
                print $a;
             }
         }
}

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Client side 
while(@ready = $sel->can_read) {
    foreach $fh (@ready) {
        my $rr = <$fh>;
        
        exit if ( not defined $rr );
        print $rr;
    }
}

[download]

In the above sample, client is receiving only abc(first message) sent by server. When server quits, can_read is returning and client is receiving the remaining messages, not blocking. Getting messages one after another.

Then, I tried with sysread as suggested here. When using sysread, should I read byte by byte till '\n'? Because, I don't know the size of the message. Is it a good way to read byte by byte, do concatenation and then process the message?(I don't think so.)

Please, explain me some way to write a error free way(pleasant way too) to receive messages in socket.. or let me know what am I doing wrong.

Thanks.

Replies are listed 'Best First'.
Re^3: IO::Select - reading multiple lines
by zentara (Archbishop) on Jul 14, 2011 at 19:20 UTC
    is it a very worse idea to use <$fh> to read from a socket

    Yeah, you are best off using sysread, and there are a few ways to use sysread, depending on your situation, you can put it in various staement forms 

     while( sysread $fh, $str, 8192, length $str ) {
#or
 do { $rc = sysread(FH, $buff, 5000000, length($buff)) ; } while ($rc
#or
if ( sysread( $cli, $buffer, 1024 ) ) {}
# etc etc

    [download]
    I'm not really a human, but I play one on earth.
    Old Perl Programmer Haiku ................... flash japh
[reply]
[d/l]
      sysread returns 0, only when the other end exits. Getting into blocking mode, which is not desired. I expect the program to wait in select not in sysread.
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