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

I want to receive an XML packet using IO::Sockets. I have a script to do so but it cuts out sometimes causing the program to terminate. This is bad since it will be incorporated ino a much larger program. The script I have now is: 
#! perl -slw
use strict;
use IO::Socket;
use XML::Simple;

$SIG{PIPE} = "IGNORE";
$\="\n";

my $img = '"http://updraft.unl.edu/~uas/uas/uas.png"';
my $post_time;
my $test;
my $xs = XML::Simple->new( RootName=>'Telemetry', XMLDecl => 1);
my $check = 0; 

for (;;){
    
    my $tele_client = IO::Socket::INET->new( 'localhost:12345' ) or pr
+int $!;

    if ($tele_client){
        while( <$tele_client>) {
        #################################
            print "@@@ started @@@";
            if ($tele_client){
                print "*** Recv UA ***";
                $tele_client->recv($test, 100000000);
                print $test;
        
                #UAS Functions:
        print "Reading in XML";
                my $uasdata = $xs->XMLin($test);
                print "--- XML ---";
                print Dumper($uasdata);
        
                if ("$uasdata->{VehicleID}" eq 'Velocity'){
                    #Open Placefile
                    open UASPF,'>',"/home/uas/public_html/uas/uaspf.tx
+t.bak" or die "Cannot Open File uavpf.txt.bak!";
                    #open UASPF,'>',"uaspf.txt.bak" or die "Cannot Ope
+n File uavpf.txt.bak!";
                    &time;
                    #print placefile elements
                    print UASPF "Title: UAS GPS Position";
                    print UASPF "Threshold: 999";
                    print UASPF "RefreshSeconds: 2";
                    print UASPF "Iconfile: 1, 22, 21, 10, 14, $img\n";
                    print UASPF "Icon: $uasdata->{GPS}->{Latitude}, $u
+asdata->{GPS}->{Longitude}, $uasdata->{GPS}->{Heading}, 1, 1, $post_t
+ime Latitude: $uasdata->{GPS}->{Latitude} Longitude: $uasdata->{GPS}-
+>{Longitude} Heading: $uasdata->{GPS}->{Heading} Speed: $uasdata->{Ai
+rData}->{TrueAirSpeed} cm/s";
                    close UASPF;
        
                    rename("/home/uas/public_html/uas/uaspf.txt.bak", 
+"/home/uas/public_html/uas/uaspf.txt") or die"Unable to replace: $!";
                    #rename("uaspf.txt.bak", "uaspf.txt") or die"Unabl
+e to replace: $!";
                    print "*** UA Done ***";
                }
            }
        }
    }
    print "SLEEP";
    sleep 5;
}

[download]
The program stops here: $tele_client->recv($test, 100000000); The only way I have thought to fix it is by increasing the size of the received data. Is there a better way to do this?

Replies are listed 'Best First'.
Re: Receiving an XML packet using IO::Socket
by jettero (Monsignor) on Jun 03, 2008 at 17:28 UTC

    Why use raw IO::Sockets? Why not Net::Server, Net::Daemon, or even HTTP::Server::Simple? I think they'd save you a lot of trouble and do all the nasty parts for you.

    I'm particularly fond of Net::Server. You basically read from STDIN and write to STDOUT. It's identical to console programing in most respects.

    -Paul

[reply]
Re: Receiving an XML packet using IO::Socket
by moritz (Cardinal) on Jun 03, 2008 at 17:31 UTC
    So your program is blocking while it tries to read about 100MB (or until an EOF returns) from a socket. Apparently the server on the other side doesn't deliver that data.

    You could just set a timeout, so a recv will fail if it doesn't provide any data. Or you could investigate non-blocking IO. What do you want?

[reply]
[d/l]
Re: Receiving an XML packet using IO::Socket
by pc88mxer (Vicar) on Jun 03, 2008 at 18:04 UTC
    What is your protocol? Is a network connection limited to one request (one XML packet)?

    I see a potential problem with mixing buffered I/O with recv: 

            while( <$tele_client>) {
            if ($tele_client){
                $tele_client->recv($test, 100000000);

    [download]
    For stream sockets I believe send is equivalent to syswrite and recv is equivalent to sysread. In any case, mixing the two forms of I/O is not a good idea. You are aware that <$tele_client> will read a line from the socket connection, right?

    If your protocol is limited to one request per connection, why not just slurp in the entire XML packet: 

      $test = do { local $/; <$tele_client> };
  my $uasdata = $xs->XMLin($test);
  ...

    [download]
[reply]
[d/l]
[select]
Re: Receiving an XML packet using IO::Socket
by zentara (Cardinal) on Jun 03, 2008 at 18:33 UTC
[reply]

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