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From: weg@convx1.ccit.arizona.edu (Eythan Weg)
Newsgroups: comp.lang.perl
Subject: A perl novice problem
Message-ID: <WEG.91Jun12194458@convx1.convx1.ccit.arizona.edu>
Date: 13 Jun 91 02:44:58 GMT
Sender: news@amethyst.math.arizona.edu
Distribution: comp
Organization: University of Arizona, Economics Dept.
Lines: 113

Hi There:

To test my understanding of the mechanics of sockets I have been trying
to see how communications through these work, but ran into the problem
that neither client nor server can receive each other's messages.  The
client and server are form The Book with some (minor?) alterations.
Can someone explain what's wrong?  The programs follow.

Thanks,  Eythan


---------client
#!/usr/bin/perl

($them,$port) = @ARGV;
$port = 8492 unless $port;
chop($them = `hostname`)  unless $them;

$AF_INET = 2;
$SOCK_STREAM = 1;

$sockaddr = 'S n a4 x8';

chop($hostname = `hostname`);

($name,$aliases,$proto) = getprotobyname('tcp');
($name,$aliases,$port) = getservbyname($port,'tcp')
    unless $port =~ /^\d+$/;;
($name,$aliases,$type,$len,$thisaddr) =
	gethostbyname($hostname);
($name,$aliases,$type,$len,$thataddr) = gethostbyname($them);

$this = pack($sockaddr, $AF_INET, 0, $thisaddr);
$that = pack($sockaddr, $AF_INET, $port, $thataddr);

# Make the socket filehandle.

if (socket(S, $AF_INET, $SOCK_STREAM, $proto)) { 
    print "socket ok\n";
}
else {
    die $!;
}

# Give the socket an address.

if (bind(S, $this)) {
    print "bind ok\n";
}
else {
    die $!;
}

# Call up the server.

if (connect(S,$that)) {
    print "connect ok\n";
}
else {
    die $!;
}

# Set socket to be command buffered.

#select(S); $| = 1; select(STDOUT);

send(S,"ready",0)|| die "cannot send\n";
print "sent\n";
recv(S,$data,10,0) || die "cannot receive\  $!\n";
print "$data\n";

-----------------server
#!/usr/bin/perl

($port) = @ARGV;
$port = 8492 unless $port;

$AF_INET = 2;
$SOCK_STREAM = 1;

$sockaddr = 'S n a4 x8';

($name, $aliases, $proto) = getprotobyname('tcp');
if ($port !~ /^\d+$/) {
    ($name, $aliases, $port) = getservbyport($port, 'tcp');
}

print "Port = $port\n";

$this = pack($sockaddr, $AF_INET, $port, "\0\0\0\0");

select(NS); $| = 1; select(stdout);

socket(S, $AF_INET, $SOCK_STREAM, $proto) || die "socket: $!";
bind(S,$this) || die "bind: $!";
listen(S,5) || die "connect: $!";

print "Listening for connection....\n";

    ($addr = accept(NS,S)) || die $!;
$in='';
vec($in,fileno(NS),1)=1;
if (select($out=$in,undef,undef,undef)>0){
    if (vec($out,fileno(NS),1)){
	print "NS is ready\n";

	recv(NS,$msg,10,0)|| die "cannot receive\n";
	print "$msg\n";
    }
}
send(NS,"hello",0) || die "cannot send\n";

print "message sent\n";