Re^2: poorly documented behaviour of readline() and IO::Select

[vsespb]

Just wrote a POC solution which seems to fix issue with sysread/syswrite and specifying length of the message in the beginning of it (of course this solution is suitable if you can patch both client and server i.e. modify your protocol).

It works fine (linux ubuntu).

#!/usr/bin/perl -w 

use strict; 
use IO::Select; 
use IO::Pipe;

  my $fromchild = new IO::Pipe;
  my $tochild = new IO::Pipe;
  my $pid;
  my $parent_pid = $$;
  if($pid = fork()) { # Parent
   $fromchild->reader();
   $fromchild->autoflush(1);
   $fromchild->blocking(1);
   binmode $fromchild;
   $tochild->writer();
   $tochild->autoflush(1);
   $tochild->blocking(1);
   binmode $tochild;

   my $read_set = new IO::Select(); # create handle set for reading
   $read_set->add($fromchild);

   while(1) {
    print "before select\n";
    my ($rh_set, undef, $ex_set) = IO::Select->select($read_set, undef
+, $read_set, 30);
    print "after select\n";
    for my $rh (@$rh_set) {
        my $s =  receive_line($rh);
        print "command: $s";
    }
   }
  } elsif (defined ($pid)) { # Child
   $fromchild->writer();
   $fromchild->autoflush(1);
   $fromchild->blocking(1);
   binmode $fromchild;
   $tochild->reader();
   $tochild->autoflush(1);
   $tochild->blocking(1);
   binmode $tochild;
   send_line($fromchild, "abc\n");
   send_line($fromchild, "def\n");

   sleep(86400);
   die;
  }

sub send_line
{
  my ($socket, $line) = @_;
  my $msg = sprintf("%07d %s", length($line), $line);
  syswrite $socket, $msg;
}

sub receive_line
{
  my ($socket) = @_;
  sysread $socket, my $len, 8;
  sysread $socket, my $line, $len, 8;
  return $line;
}


__END__

Output:
before select
after select
command: abc
before select
after select
command: def
before select