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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 DEBIAN

roar_socket_listen

roar_socket_listen(3)					System Manager's Manual: RoarAudio				     roar_socket_listen(3)

NAME

       roar_socket_listen - Opens a new listen socket

SYNOPSIS

       #include <roaraudio.h>

       int roar_socket_listen(int type, char * host, int port);

DESCRIPTION

       Opens a new listening socket for network clients to connect to.	You may accept new connections via accept(2).

PARAMETERS

       type   The type of the Socket. See the list below.

       host   The  host  or  path  name  to  listen  on.  This depends on the type argument.  For TCP/IP to listen on any interface use a value of
	      "0.0.0.0".

       port   The port number to listen on.  This may be ignored by types not supporting port numbers.

SOCKET TYPES

       ROAR_SOCKET_TYPE_UNKNOWN
	      The type will be auto detected. Don't use this if you know the type. Only use this to support user given addresses and  enable  auto
	      detection.

       ROAR_SOCKET_TYPE_TCP
	      Use  a TCP/IP connection. This is standard mode for networking.  host is the hostname or IP to listen on and port is the port number
	      to use.

       ROAR_SOCKET_TYPE_INET
	      Same as above but deprecated. Use ROAR_SOCKET_TYPE_TCP.

       ROAR_SOCKET_TYPE_UNIX
	      UNIX Domain Socket. This should be default for local connections.  host is the filename of the socket.

       ROAR_SOCKET_TYPE_DECNET
	      DECnet socket.

       ROAR_SOCKET_TYPE_FORK
	      This is to fork a roard to communicate with. Can't be use to listen on, just to connect to.  host and port is ignored at the moment.

       ROAR_SOCKET_TYPE_FILE
	      This is used to open a plain file. Can't be use to listen on, just to connect to.  host is the filename to connect to.

RETURN VALUE

       On success these calls return filehandle.  On error, -1 is returned.

BUGS

       Listening on UDP sockets is not supported at the moment.

EXAMPLES

       FIXME

SEE ALSO

       accept(2), libroar(7), RoarAudio(7).

RoarAudio							     May 2011						     roar_socket_listen(3)
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