IO::Socket echo server not echoing

Discussion in 'Perl Misc' started by paulmlieberman, Apr 22, 2005.

  1. The following code, modified from Lincoln Stein's "Network Programming
    with Perl", doesn't work properly on Unix (5.6.1) or Windows systems
    (5.8.6). The server receives the first message, but doesn't echo it
    properly. Why?

    #!/usr/bin/perl
    # IOserver.pl

    use strict;
    use IO::Socket::INET;

    use constant SIMPLE_TCP_PORT => 4001;
    use constant MAX_RECV_LEN => 65536;

    print "Hello, World...\n";

    my $local_port = shift || SIMPLE_TCP_PORT;
    my $server = IO::Socket::INET->new(Proto => 'tcp',
    Type => SOCK_STREAM,
    Reuse => 1,
    Timeout => 60 * 60,
    LocalPort => $local_port,
    Listen => SOMAXCONN)
    or die "Can't create server\n";

    my $fromWho;
    my $peeraddr;

    while($fromWho = $server->accept())
    {
    my $hostinfo;
    my $data;
    $fromWho->recv($data, MAX_RECV_LEN);
    if($fromWho)
    {
    $peeraddr = $fromWho->peeraddr();
    $hostinfo = gethostbyaddr($peeraddr, AF_INET);
    warn "Received from server: ", length($data), ' -> ', $data, "\n";
    }
    else
    {
    warn "IOserver: problem with recv: $!\n";
    next;
    }
    sleep(3);
    warn "Sending back to client...\n";
    if (! $server->send($data, 0, $fromWho)) {
    my $so_error = $server->sockopt(SO_ERROR);
    die "IOserver: error $so_error sending message to $hostinfo: $!\n";
    }
    }
    $server->close()
    or warn "IOserver: close failed: $!\n";

    ===========================================================================

    #!/usr/bin/perl
    # IOclient.pl

    use strict;
    use IO::Socket::INET;

    use constant SIMPLE_TCP_PORT => 4001;
    use constant REMOTE_HOST => 'localhost';

    use constant MAX_RECV_LEN => 65536;

    my $remote_host = shift || REMOTE_HOST;
    my $remote_port = shift || SIMPLE_TCP_PORT;
    my $msg_count = 1;
    my $big_chunk = 'x' x 65000;

    my $client = IO::Socket::INET->new(Proto => 'tcp',
    Type => SOCK_STREAM,
    PeerAddr => $remote_host,
    PeerPort => $remote_port)
    or die "connection to remote system failed: $!\n";

    while($msg_count)
    {
    next unless $client;

    print "Enter string to echo: ";
    $big_chunk = <STDIN>;
    my $data = $client->sockhost() .' '. $msg_count . ' -> ' .
    $big_chunk;

    warn "Sending echo string to server...\n";

    $client->send($data, 0)
    or warn "problem with send...\n";

    sleep(1);

    my $fromWho = $client->recv($data, MAX_RECV_LEN, 0)
    or die "Problem with recv(): $!\n";

    if($fromWho)
    {
    my $remote_name = $client->peerhost();
    warn "Received from $remote_name: ", length($data), ' => ',$data,
    "\n";
    }
    else
    {
    warn "problem with recv: $!\n";
    $client->close()
    or warn "close failed: $!\n";
    }
    }
    continue{
    $msg_count++;
    }
    $client->close()
    or warn "tcp_cli: close failed: $!\n";
     
    paulmlieberman, Apr 22, 2005
    #1
    1. Advertisements

  2. You are trying to send on the listening socket, not the connected one.
    try
    $fromWho->send( $data, 0 )

    You need to look at the return value of recv:

    recv SOCKET,SCALAR,LENGTH,FLAGS
    Receives a message on a socket. Attempts to receive
    LENGTH characters of data into variable SCALAR from
    the specified SOCKET filehandle. SCALAR will be
    grown or shrunk to the length actually read. Takes
    the same flags as the system call of the same name.
    Returns the address of the sender if SOCKET's
    protocol supports this; returns an empty string
    otherwise. If there's an error, returns the
    undefined value. This call is actually implemented
    in terms of recvfrom(2) system call. See "UDP

    ie the error condition is undef, so your check should be


    if(defined $fromWho){

    With these modifications:

    bob 606 $ perl testechoclient.pl
    Enter string to echo: sdfg
    Sending echo string to server...
    Received at server: 20 -> 127.0.0.1 1 -> sdfg

    Sending back to client...
    Received from 127.0.0.1: 20 => 127.0.0.1 1 -> sdfg


    regards,

    Mark
     
    Mark Clements, Apr 22, 2005
    #2
    1. Advertisements

  3. OK! With those changes, it now works for the first iteration: the
    client sends, the server echos. But when the client tries to send a
    second string, it fails.

    Here's my modified code.

    - Paul

    #!/usr/bin/perl
    # IOserver.pl

    use strict;
    use IO::Socket::INET;

    use constant SIMPLE_TCP_PORT => 4001;
    use constant MAX_RECV_LEN => 65536;

    print "Hello, World...\n";

    my $local_port = shift || SIMPLE_TCP_PORT;
    my $server = IO::Socket::INET->new(Proto => 'tcp',
    Type => SOCK_STREAM,
    Reuse => 1,
    Timeout => 60 * 60,
    LocalPort => $local_port,
    Listen => SOMAXCONN)
    or die "Can't create server\n";

    my $fromWho;
    my $peeraddr;

    while($fromWho = $server->accept())
    {
    my $hostinfo;
    my $data;
    $fromWho->recv($data, MAX_RECV_LEN);
    if(defined $fromWho)
    {
    $peeraddr = $fromWho->peeraddr();
    $hostinfo = gethostbyaddr($peeraddr, AF_INET);
    warn "Received from server: ", length($data), ' -> ', $data, "\n";
    }
    else
    {
    warn "IOserver: problem with recv: $!\n";
    next;
    }
    sleep(3);
    warn "Sending back to client...\n";
    if (! $fromWho->send($data, 0)) {
    my $so_error = $fromWho->sockopt(SO_ERROR);
    die "IOserver: error $so_error sending message to $hostinfo: $!\n";
    }
    close($fromWho)
    or warn "IOserver: close failed: $!\n";
    warn "Waiting for another connection!\n";
    }
    =================================================================
    #!/usr/bin/perl
    # IOclient.pl

    use strict;
    use IO::Socket::INET;

    use constant SIMPLE_TCP_PORT => 4001;
    use constant REMOTE_HOST => 'localhost';

    use constant MAX_RECV_LEN => 65536;

    my $remote_host = shift || REMOTE_HOST;
    my $remote_port = shift || SIMPLE_TCP_PORT;
    my $msg_count = 1;
    my $big_chunk = 'x' x 65000;

    my $client = IO::Socket::INET->new(Proto => 'tcp',
    Type => SOCK_STREAM,
    PeerAddr => $remote_host,
    PeerPort => $remote_port)
    or die "connection to remote system failed: $!\n";

    while($msg_count)
    {
    next unless $client;

    print "Enter string to echo: ";
    $big_chunk = <STDIN>;
    my $data = $client->sockhost() .' '. $msg_count . ' -> ' .
    $big_chunk;

    warn "Sending echo string to server...\n";

    $client->send($data, 0)
    or warn "problem with send...\n";

    sleep(1);

    my $fromWho = $client->recv($data, MAX_RECV_LEN, 0)
    or die "Problem with recv(): $!\n";

    if(defined $fromWho)
    {
    my $remote_name = $client->peerhost();
    warn "Received from $remote_name: ", length($data), ' => ',$data,
    "\n";
    }
    else
    {
    warn "problem with recv: $!\n";
    $client->close()
    or warn "close failed: $!\n";
    }
    }
    continue{
    $msg_count++;
    }
    $client->close()
    or warn "IOclient: close failed: $!\n";
     
    paulmlieberman, Apr 23, 2005
    #3
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.