syswrite, closed socket and error handling

InfiniteLoop has asked for the wisdom of the Perl Monks concerning the following question:

Greetings monks,

This is a followup on my earlier query: syswrite and closed sockets. Although the excellent guide by fellow monks solved many of the problems, however I hit upon one more issue and request your insights.

I have the following piece of code, which uses IO::Socket::INET to open a blocking socket against a messaging server and attempts to write a text:

use IO::Socket::INET;
use Carp;

my $socket = IO::Socket::INET->new(
                                     PeerAddr=> $host,
                                     PeerPort=> $port,
                                     Proto=> "tcp",
                                     Blocking => 1 ) ;

for(1..100){
    print $_ . "..";
    sleep(2);

    eval{
      $output = $socket->syswrite($string);
    };

    croak "Could not syswrite: $@\n" if(!$output or $@);


    print "done\n";
}
[download]

While this code is running, I shutdown the message service. This causes the script to exit, after a couple of iteration. I was expecting to see the croak message, however the script just exits.

I tried to execute this script via Komodo IDE, and in the IDE output window I could see the croak message. Besides if I modified the error handling part to, lets say, write a message to a file and follow the process:

via a shell: no output and nor the file is being created
via Komodo: I see the croak message and the file is being created

My questions:

What is causing this behaviour ?
if syswrite does a exit, how can I handle it in a OO context ? (I know we can handle exits via WIFEXITED, but only if executed as a child process)

Comment on syswrite, closed socket and error handling Download Code

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Re: syswrite, closed socket and error handling by gcalexander (Novice) on Aug 15, 2006 at 00:56 UTC
You have to trap or 'IGNORE' SIGPIPE. SIGPIPE is thrown when you write to a broken pipe. Having never used Komodo before, I'm guessing it installs its own signal handlers or something?? If you do `$SIG{PIPE} = 'IGNORE';` [download] at the top of your script it won't die/exit silently. or you could do `my $connected = 0; $SIG{PIPE} = sub { warn "Lost connection to server: $!"; $connected = +0; }; use IO::Socket::INET; use Carp; sub new_connection { return IO::Socket::INET->new( PeerAddr=> $host, PeerPort=> $port, Proto=> "tcp", Blocking => 1 ) ; } my $socket = new_connection() or die "$!"; my $output; for(1..100){ print $_ . ".."; sleep(2); if ($connected) { $output = $socket->syswrite($string); } else { $socket = new_connection (); or die "$!" $connected = 1; } print "done\n"; }` [download] By no means optimal at all, but just to give you an idea.	[reply] [d/l] [select]

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Re: syswrite, closed socket and error handling
by gcalexander (Novice) on Aug 15, 2006 at 00:56 UTC

$SIG{PIPE} = 'IGNORE';
[download]

my $connected = 0;
$SIG{PIPE} = sub { warn "Lost connection to server: $!"; $connected = 
+0; };
use IO::Socket::INET;
use Carp;

sub new_connection
{
    return IO::Socket::INET->new(
                                     PeerAddr=> $host,
                                     PeerPort=> $port,
                                     Proto=> "tcp",
                                     Blocking => 1 ) ;
}

my $socket = new_connection()
   or die "$!";
my $output;

for(1..100){
    print $_ . "..";
    sleep(2);

    if ($connected)
    {
       $output = $socket->syswrite($string);
    }
    else
    {
       $socket = new_connection ();
                     or die "$!"
       $connected = 1;
    } 
 
    print "done\n";
}
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