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

The customer I am working with uses sockets in a way I am not used to.
I need to behave as a client program, I read data from their socket (host/port on their machine) and respond with an ack.
When I want to send the data I do the usual and write to their host/port and wait for an ack.
Using the following simple read I continually see the most recent write by them on their port till the replace it with new data. Is that expected or am I doing something wrong? 
#!/usr/local/bin/perl
use strict;
use Socket;
use IO::Handle;
my $prot = getprotobyname('tcp');
my $host = inet_aton("localhost");
socket(SOCK, AF_INET, SOCK_STREAM, $prot) or die("socket failed to sta
+rt");
my $dest_addr = sockaddr_in(5003, $host);
connect(SOCK, $dest_addr) or die("Connect failed");
my $data;
while (1) {
   print STDERR "do a read\n";
   sysread(SOCK, $data, 1024);           # reads the data on the serve
+rs socket
                                         # but when loop around again 
+the data is still there as server 
                                         # has not written anything ne
+w
   print STDERR "data was $data\n";
   sleep 10;
}
close SOCK;

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Replies are listed 'Best First'.
Re: Read Socket on Server
by Illuminatus (Curate) on Sep 29, 2008 at 22:07 UTC
    You are not checking the result of the sysread. To do so could be enlightening...
[reply]
      It contains the length of the message. In this case 62 on each read.
      The full program does the if defined, if rc>0 and $!==EWOULDBLOCK for a non-blocking socket.
      Speaking of non-blocking I am testing on WinXP. Is it another aberration of windows and I should switch to testing on unix (which is where the client will be).
[reply]
        Do you actually get the output you describe from the posted version or only the non-blocking version? Something is seriously messed up to get the behaviour you described from the code you posted. It makes more sense for the non-blocking version since you never clear $data.

        Update: To clarify, by "you never clear $data", I mean you rely on sysread to clear $data, and it's entirely reasonable to fit to not do so when it detects there's nothing to read.

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Re: Read Socket on Server
by kubrat (Scribe) on Sep 30, 2008 at 22:22 UTC

    What happens if you connect to the server using telnet?

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