Perl socket programming problems after continuous write to socket

Question

I am using IO::Socket::INET to create socket like this:

$lsn1 = IO::Socket::INET->new(
                            PeerAddr => '192.168.0.2', 
                            PeerPort => 1850, 
                            Proto    => 'tcp', 
                            Type     => SOCK_STREAM
   ) || die "Can't connect to 192.168.0.2:1850 : $!\n"; 

$lsn2 = IO::Socket::INET->new(
                            PeerAddr => '192.168.0.2', 
                            PeerPort = >1852, 
                            Proto    => 'tcp', 
                            Type     => SOCK_STREAM
   ) || die "Can't connect to 192.168.0.2:1852 : $!\n";

then, I want to read and write data to both sockets, so the sequence is:

1. $lsn1->print(msg1);  send message 1 to server from $lsn1.
2. $line = <$lsn2>;     receive message 2 from server from $lsn2.
3. $lsn2->print(msg3);  send message 3 to server from $lsn2.
4. $lsn2->print(msg4);  send message 4 to server from $lsn2.
5. $line = <$lsn2>;     receive message 5 from server. But it is all zeros! However I can 
                        see the data on wireshark.

everything is fine until step 5. After the server side receive my message4 and send back msg5 which is supposed to be capture by $line = <$lsn2>, instead of capture meaningful value it capture all 0s'. I used wireshark to see what happened, a RST ACK from my side was send after the server send me msg5.

A function in server received msg4 and send back msg5 immediately. If I get rid of the sending of msg4 in that function, what follows the sending of msg5 is FIN ACK.

Can anyone tell me why RST ACK is happening? Can a perl script opens up two sockets and read and write like I did.

Answer 1

It is possible that you are not completely reading Message 2 leaving some data on the socket (line feed, null character, etc.). When you then attempt to read Message 5 you instead read this data and your program terminates before the server actually sends Message 5.