Problems reading back from socket

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

Hi guys, I have a socket set up with IO::Socket::INET. It works in that I am able to write to the socket, however I can't capture what the remote host sends back. I just get nothing. I know the connection works, because I can use telnet to drive the dialogue manually and when I send the 'status' request, I get a dump of data back. How can I get my socket to capture this so that I can do something useful with it? Here's a snip of the code I'm using:

my $sock = new IO::Socket::INET (
      PeerAddr => "$hostname",
      PeerPort => "$port",
      Blocking => 0,
      Proto => 'tcp',
 );

 print $sock "Action: Login\r\n";
 print $sock "UserName: $foo\r\n";
 print $sock "Secret: $bar\r\n\r\n";
 print $sock "Action: status\r\n\r\n";

 $/="\r\n";
 open(FH,">>/home/chris/statusdump.txt");
 while(my $data=<$sock>){
      $data =~ /[a-z]/ || next;
      print FH $data;
 }
 close FH;
[download]

I have opened up the permissions on that temporary file and I'm tail -f'ing it to see what comes in, but the file doesn't grow at all. What's the obvious mistake please? thanks christo

Comment on Problems reading back from socket Download Code

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Re: Problems reading back from socket by sgifford (Prior) on Nov 16, 2005 at 16:47 UTC
Why are you making your TCP socket nonblocking (with the `Blocking => 0` parameter)? A nonblocking socket will return if there's nothing to read; I suspect that when you try to read it with `my $data=<$sock>`, there's no data to read, so it returns false and the whole program exits. I suspect removing this parameter would solve your problem, but I haven't tested it. You could confirm this by adding debugging output to your program, or running it in the Perl debugger. I'd also recommend adding more error checking; right now you wouldn't notice if the socket creation failed, or the `print`s to the socket failed, since you're not checking their return values. Checking the return value from `close` also sometimes shows errors that were delayed, or caused the socket to close.	[reply] [d/l] [select]
Re: Problems reading back from socket by vek (Prior) on Nov 17, 2005 at 06:50 UTC
Is it possible that the remote server has not recognized that you've finished sending data? Have you tried issuing a more forceful method of indicating you're done via shutdown? `$sock->shutdown(1); # done writing but still open for reading` [download] Do you have access to the remote server? Can you verify that your data is received correctly and that the remote server is actually attempting to send you data back? -- vek --	[reply] [d/l]
Re: Problems reading back from socket by rupesh (Hermit) on Nov 16, 2005 at 13:00 UTC
A basic client and server, socket implementation(untested). Server: `use strict; use IO::Socket; my $sock = new IO::Socket::INET (LocalHost => 'localhost', LocalPort => 5004, Proto => 'tcp', Listen => 5, Reuse => 1 + ); die "Socket could not be created. Reason: $!" unless $sock; my ($new_sock, $buf); while ($new_sock = $sock->accept()) { print "Connection from ", $new_sock->peerhost, ": on port ", $new_s +ock->peerport,"\n"; print $new_sock "Hello from the server"; while (defined ($buf = <$new_sock>)) { print $buf; } } close ($sock);` [download] Client: `use strict; use IO::Socket; my $line; my $socket = new IO::Socket::INET ( PeerAddr => 'localhost', PeerPort => '5004', Proto => 'tcp', ); die "Could not create socket: $!\n" unless $socket; $socket->recv($line, 80); print "$line"; print $socket "Hello from the Client!\n"; close($socket);` [download] Cheers, Rupesh.	[reply] [d/l] [select]
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