splitting and joining a network message

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

Folks, I am trying to write a simulator based on SIP (session initiation protocol). When it receives a request, it needs to send a response as follows.
Received request:

      INVITE sip:bob@biloxi.com SIP/2.0
      Via: SIP/2.0/UDP pc33.atlanta.com;branch=z9hG4bK776asdhds
      Max-Forwards: 70
      To: Bob <sip:bob@biloxi.com>
      From: Alice <sip:alice@atlanta.com>;tag=1928301774
      Call-ID: a84b4c76e66710@pc33.atlanta.com
      CSeq: 314159 INVITE
      Contact: <sip:alice@pc33.atlanta.com>
      Content-Length: 0
[download]

And the response must be something like

      200 SIP/2.0 OK
      Via: SIP/2.0/UDP pc33.atlanta.com;branch=z9hG4bK776asdhds
      Max-Forwards: 70
      To: Bob <sip:bob@biloxi.com>
      From: Alice <sip:alice@atlanta.com>;tag=1928301774
      Call-ID: a84b4c76e66710@pc33.atlanta.com
      CSeq: 314159 INVITE
      Contact: <sip:alice@pc33.atlanta.com>
      Content-Length: 0
[download]

Only the first line in the response changes. Everything else is same from received request. This is what I tried but didnt help....
------------------------------------------

    my $length = $sock->recv($sip_request,1000);
    print "\nReceived message '", $request,"'\n";

    my @headers = split/\n/, $request;

    my $tmp = 0;
    foreach my $line (@headers)
    {
        if ($tmp gt 0)
        {
            $sip_response = join($sip_response, $line, "\n");
        }
        $tmp++;
    }

    print "Our response is : \n";
    print $sip_response;
[download]

---------------------------------------------
But I am not able to form the proper response. Could any of you help me out?

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Re: splitting and joining a network message by davido (Cardinal) on Apr 12, 2006 at 16:23 UTC
You are using join wrong. Join's args are (first) the new delimiter, and (second) the list of strings being joined. I think that you probably don't even want join at all, you probably (based on your existing code) simply want concatenation as follows: `if( $tmp > 0 ) { $sip_response .= "$line\n"; }` [download] Also notice the use of '>' instead of 'gt'. 'gt' is for strings, and '>' is for numbers. Your use of 'gt' works for you, but only by virtue of the fact that Perl considers any non-empty, non-zero string to be "true". Additional thought: An easier way to do the whole thing is probably something like this: `my $sip_response = $response; # Make a copy of the response. if( $sip_response =~ s{^[^\n]+}[200 SIP/2.0 OK] ) { print $sip_response; } else { die "Didn't understand the response: $response\n"; }` [download] ...just a thought... Dave	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re: splitting and joining a network message
by davido (Cardinal) on Apr 12, 2006 at 16:23 UTC

You are using join wrong. Join's args are (first) the new delimiter, and (second) the list of strings being joined. I think that you probably don't even want join at all, you probably (based on your existing code) simply want concatenation as follows:

if( $tmp > 0 ) {
    $sip_response .= "$line\n";
}
[download]

Also notice the use of '>' instead of 'gt'. 'gt' is for strings, and '>' is for numbers. Your use of 'gt' works for you, but only by virtue of the fact that Perl considers any non-empty, non-zero string to be "true".

Additional thought:
An easier way to do the whole thing is probably something like this:

my $sip_response = $response; # Make a copy of the response.
if( $sip_response =~ s{^[^\n]+}[200 SIP/2.0 OK] ) {
    print $sip_response;
} else {
    die "Didn't understand the response: $response\n";
}
[download]

...just a thought...

Dave

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