websocket infinit loop

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

I have a perl script that worked as a “middle men” between a local program and an external interactive website.

The problem is that the external website migrated from plain tcp connection to a websocket connection.

When the server was using tcp, after initial connection, the client (the script) and the server (external website) will go thru a handshake, then the script will send the username and password and server will finally respond with some encryption keys, afterwards the script will go into an infinite loop and waited for data from both connections and then process that data and "print" back to the connections as needed.

I had been able to establish the websocket connection with the server using the Mojo::UserAgent as well as with protocol::websocket, go thru the handshake and the other information exchange (username, password, etc), but I have not been able (or better said: I do not know how) to "throw" the websocket connection into the infinite loop via IO::Select ( The reason I want to use IO::Select is because doing so will require minimal changes to the script, but other suggestions are definitely welcome).

The relevant parts of the script are as follows:

# Creating connection for local program
$lsn=new IO::Socket::INET(
    Proto => 'tcp',
    LocalPort => 6000,
    Listen => 1,
);
unless(defined $lsn){
    print"$0: $!\n";
    exit 1;
}
print"Waiting for local program connection on port 6000\n";
$server=$lsn->accept;
$lsn->close;
unless(defined $server){
    print "$0: Unable to accept incoming connection: $!\n";
    exit 1;
    }
# At this point, the script is waiting for a connection from
# the local program on port 6000
printf"Connection accepted from %s\n",$server->peerhost;
select $server;
binmode $server;
$stdin=$server;
(select)->autoflush(1);
# Creating connection for external website
$net=new IO::Socket::INET(
    Proto => 'tcp',
    PeerAddr => $yog,
    PeerPort => $yserverport,
);

unless(defined($net)){
    print "Can't connect!\n";
    exit 1;
}
$net->autoflush(1);
####################################
# Here the script and server will  #
# exchange information few times   #
####################################
my $sel=new IO::Select($stdin,$net);
$net->autoflush(0);
while (1){
    foreach my $i($sel->can_read(0.05)){
        if($i==$net){
            &dosomething;
            $net->flush;
        }
        else{
            &dosomething2;
            $net->flush;
        }
    }   
}
[download]

The infinite loop examples that I have found, are not suitable in this case because I need to use an infinite loop that can check for incoming data on both connections.

Comment on websocket infinit loop Download Code

Replies are listed 'Best First'.
Re: websocket infinit loop by huck (Prior) on Dec 13, 2016 at 02:12 UTC
While you have told us what you have "done", you have neglected to tell us what has then happened. have you seen that the script progresses past # Here the script and server will exchange information few times ? What happens inside dosomething() and dosomething2(); There are people that will tell you not to use &sub to call a subroutine because of what happens to the parms list but i am sortof concerned that neither has any parms that you supply. i would expect then that they would start with something like `my $buf; my $rv = sysread($net, $buf, 641024, length($buf));` and `my $buf; my $rv = sysread($server, $buf, 641024, length($buf));` Since i dont see any `use warnings; use strict;` i expect you are assuming that $net and $server are globals and are available to those subs also after the $rv=sysread you should have some sort of test like `if (!$rv) { if (defined($rv)) { # eof state, remove from io::select; } else { # error state, remove from io::select; } } else { # process $buf; }` [download] I should also point out that 0.05 is rather short for the timeout, since can_read will block until it has something you can read. with the very short timeout while(1) will loop with nothing to do a LOT	[reply] [d/l] [select]
Re: websocket infinit loop by Anonymous Monk on Dec 13, 2016 at 02:09 UTC
The infinite loop examples that I have found, are not suitable in this case because I need to use an infinite loop that can check for incoming data on both connections. Look at the Mojo examples, the entire premise, is there is one loop, when an event happens, a subroutine is called ( a call back), the callback does the checking for things its concerned about ( one connection, another connection, something else ) All you do is "register" subroutines to respond to events, an event is anything, from connecting to a socket, to getting a message, to a timer expiring ... Example Re^4: real-time output from Mojolicious WebSockets? All these things can be part of the same program, as long as you're not blocking for long, it all just keep running https://metacpan.org/pod/Mojolicious::Guides::Cookbook#Non-blocking https://metacpan.org/pod/Mojolicious::Guides::Cookbook#WebSockets https://metacpan.org/pod/Mojolicious::Guides::Cookbook#Synchronizing-non-blocking-operations	[reply]


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