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Full Discussion: Perl and Sockets - Error handling
Top Forums Shell Programming and Scripting Perl and Sockets - Error handling Post 302400337 by Hollinch on Wednesday 3rd of March 2010 02:21:46 AM
Old 03-03-2010
Perl and Sockets - Error handling
Hello all,

I have created a Perl script that tries to open connections to various systems on different ports in order to see if the machines are reachable, the ports are open, etc.

There appears to be a difference between Solaris (10) and Linux (RH/Oracle and Ubuntu) in the status or error it throws. On Solaris I get expected results when I check $! after opening and connecting a socket, and I have a simple routine to catch messages like 'Connection timed out', 'Connection refused', etc.

On Linux, however, both the creation of the socket and the connect statements deliver an 'Illegal seek' status via $! for servers/ports that respond.

The question first revolves around whether I have taken an incorrect approach in order to retrieve and use the status of the connection, but secondly also about error handling.

The many examples available on the internet almost always use the 'die' statement when creating or connecting a socket - not a very neat way to handle exceptions. I haven't seen many alternative means of catching exceptions and dealing with them effectively.

The code:

Code:
use strict;
use IO::Socket;
use vars qw($configfile @listen @filter @unknown @nlisten @pingable);

sub test_connect {
        my ($srvproto, $host, $port) = @_;
        # print "$srvproto\t$host\t$port\n";
        # get the port address
        my $iaddr = inet_aton($host);
        if (defined $iaddr) {
                my $paddr = sockaddr_in($port, $iaddr);
                my $proto = getprotobyname($srvproto);
                # create the socket, connect to the port
                socket(MYSOCK, PF_INET, SOCK_STREAM, $proto)|| die "Failed: $!\n";
                connect(MYSOCK, $paddr);
                my $sockstat=$!;
                if ($sockstat eq "") {
                        @listen=(@listen, [$srvproto, $host, $port]);
                        }
                elsif ($sockstat eq "Connection timed out") {
                        @filter=(@filter, [$srvproto, $host, $port]);
                        }
                elsif ($sockstat eq "Connection refused") {
                        @nlisten=(@nlisten, [$srvproto, $host, $port]);
                        }
                elsif ($sockstat eq "Illegal seek") {
                        @listen=(@listen, [$srvproto, $host, $port]);
                        }
                else {
                        print $sockstat . "\n";
                        }
                close MYSOCK or die "close: $!";
        } else {
                @unknown=(@unknown, [$srvproto, $host, $port]);
        }
}

You can see I have created an 'elsif' statement for the 'Illegal seek' message, which wasn't necessary on Solaris.

Any help or advice on how to 1. change the script to act accordingly, and 2. how to generally implement these types of exception handling, are very very much welcome.

Many thanks, kind regards.
 

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LEARN ABOUT LINUX

sockstat

SOCKSTAT(1)						    BSD General Commands Manual 					       SOCKSTAT(1)

NAME

     sockstat -- list open sockets

SYNOPSIS

     sockstat [-clh] [-p ports] [-P pid|process] [-U uid|user] [-G gid|group]

DESCRIPTION

     The sockstat command lists open Internet or UNIX domain sockets.

     The following options are available:

     -c 	 Show connected sockets.

     -l 	 Show listening sockets.

     -h 	 Show a usage summary.

     -p ports	 Only show Internet sockets if either the local or foreign port number is on the specified list.  The ports argument is a comma-
		 separated list of port numbers and ranges specified as first and last port separated by a dash.

     -P pid|process
		 Only show sockets of the specified pid|process.  The pid|process argument is a process name or pid.

     -U uid|user
		 Only show sockets of the specified uid|user.  The uid|user argument is a username or uid.

     -G gid|group
		 Only show sockets of the specified gid|group.	The gid|group argument is a groupname or gid.

     If neither -c or -l is specified, sockstat will list both listening and connected sockets.

     The information listed for each socket is:

     USER	      The user who owns the socket.

     COMMAND	      The command which holds the socket.

     PID	      The process ID of the command which holds the socket.

     FD 	      The file descriptor number of the socket.

     PROTO	      The transport protocol associated with the socket for Internet sockets, or the type of socket (stream or datagram) for UNIX
		      sockets.

     LOCAL ADDRESS    For Internet sockets, this is the address the local end of the socket is bound to (see getsockname(2)).  For bound UNIX
		      sockets, it is the socket's filename.  For other UNIX sockets, it is a right arrow followed by the endpoint's filename, or
		      ``??'' if the endpoint could not be determined.

     FOREIGN ADDRESS  (Internet sockets only) The address the foreign end of the socket is bound to (see getpeername(2)).

SEE ALSO

     netstat(1), protocols(5)

HISTORY

     The sockstat command appeared in FreeBSD 3.1.

AUTHORS

     The sockstat command and this manual page were written by Dag-Erling Smorgrav <des@FreeBSD.org>.

     The sockstat command was ported to Linux by William Pitcock <nenolod@nenolod.net>.

BSD
								   May 18, 2008 							       BSD
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