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POE method problem (building applications with POE)

by Orchid_NL (Novice)
on Dec 31, 2004 at 11:36 UTC ( #418516=perlquestion: print w/replies, xml ) Need Help??
Orchid_NL has asked for the wisdom of the Perl Monks concerning the following question:

I'm trying to get the hang of POE and followed this tutorial on Building Applications with POE.

Problem is when I try the code used in the tutorial (copy & past, the download doesn't work) it only works partially.

The TCP-server starts up, accepts connections but after entering a test string ('foo=bar&quux=perl') and hitting enter it stops with this failure message:
Can't call method "put" on an undefined value at ./ line 110.

Problem is the method put is called with a defined value, Data Dumper gives this:

$VAR1 = { 'quux' => 'perl', 'foo' => 'bar' }; $VAR1 = 2;
Code snippet (line 110 is the $_HEAP part)

sub client_input { my ($input, $wheel_id) = @_[ARG0, ARG1]; use Data::Dumper; print Dumper $input; print Dumper $wheel_id; $_[HEAP]->{clients}->{ $wheel_id }->put( $input ); }
Complete code can be found here: Orchid's scratchpad
Help much appreciated (if you need more information let me know!).

Replies are listed 'Best First'.
Re: POE method problem (building applications with POE)
by RMGir (Prior) on Dec 31, 2004 at 14:04 UTC
    Interesting... I'd suggest adding a debugging print to factory_success, probably like so:
    sub factory_success { my( $handle, $wheel_id ) = @_[ARG0, ARG1]; $_[HEAP]->{clients}->{ $wheel_id } = POE::Wheel::ReadWrite->new( Handle => $handle, Driver => POE::Driver::SysRW->new(), Filter => POE::Filter::SimpleQueryString->new(), InputEvent => 'client_input', ); print "factory_success called, creating wheel $wheel_id for handle + $handle\n"; }
    and then add a similar print to client_input.

    I don't see any obvious typos in your code or in the article; the perldoc for POE::Wheel::ReadWrite says ARG0 and ARG1 are what you say they are.

    (Although the perldoc for the version I have has a whacky example:

    sub input_state { my ($heap, $input, $wheel_id) = @_[HEAP, ARG0, ARG1]; print "Echoing input from wheel $wheel_id: $input\n"; $heap->{wheel}->put($input); # Echo it back. }
    Note the use of wheel rather than wheel_id :) )

    Wish I could be more help, but the link to the example code in that article is dead, so I can't run a local copy to see if I get the same problems you do.

      Let me start with a "Happy New Year!" to all perlmonks.
      Your debugging print tip did the trick: it showed that $wheel_id (ARG1) is empty.
      POE::Wheel::SocketFactory uses ARG3 not ARG1 for the wheels id.

      Because of this I had to change the way the wheel id is passed from subroutine 'start' to 'factory_succes' to 'client_input'.
      I used the HEAP variable (is this the correct way?)

      Problem is now that it works with one telnet session. As soon a second telnet session is started the script breaks connection with telnet session one.
      As far I can see this is because POE::Wheel::SocketFactory reuses the wheel id from telnet session one for telnet session two.
      I don't know why it does this because according to the documentation it should start a new 'wheel'.
      Can somebody help me with this problem?

      In the second part of the article concurrent telnet sessions work by using POE::Component::Server:TCP.
      But I'm a bit stubborn and want to get the basics right before moving on...

      Here is the code I modified:

      #!/usr/bin/perl -w use warnings; use strict; use Carp qw(carp croak); use POE qw( Wheel::SocketFactory Driver::SysRW Wheel::ReadWrite); { package POE::Filter::SimpleQueryString; use Carp qw(carp croak); sub new { my $class = shift; my $self = bless {}, $class; return $self; } sub get { my $self = shift; my $buffer = shift; my @chunks; foreach my $record (@$buffer) { $record =~ s/\x0d\x0a$//; my @pairs = split(/&/, $record); my %chunk; foreach my $pair (@pairs) { my ($key, $value) = split(/=/, $pair, 2); if(defined $chunk{$key}) { if(ref $chunk{$key} eq 'ARRAY') { push @{ $chunk{$key} }, $value; } else { $chunk{$key} = [ $chunk{$key}, $value ], } } else { $chunk{$key} = $value; } } push @chunks, \%chunk; } return \@chunks; } sub put { my $self = shift; my $records = shift; print "$self\n$records\n"; my @raw; foreach my $record (@$records) { my @chunks; foreach my $key (sort keys %$record) { if(ref $record->{$key}) { if(ref $record->{$key} eq 'ARRAY') { foreach my $value ( @{ $record->{$key} } ) { push @chunks, $key."=".$value; } } else { carp __PACKAGE__." cannot handle data of type ".ref $record->{$key}; } } else { push @chunks, $key."=".$record->{$key}; } } push @raw, join('&',@chunks)."\x0d\x0a"; } return \@raw; } } sub start { $_[HEAP]->{factory} = POE::Wheel::SocketFactory->new( BindAddress + => '', BindPort + => '31337', SuccessEvent + => 'factory_success', FailureEvent + => 'fatal_error', SocketProtocol + => 'tcp', Reuse + => 'on', ); } sub factory_success { my ($handle, $wheel_id) = @_[ARG0, ARG3]; my $temp_rw_id = POE::Wheel::ReadWrite->new( Handle => $handle, Driver => POE::Dri +ver::SysRW->new(), Filter => POE::Fil +ter::SimpleQueryString->new(), InputEvent => 'client_ +input', ); $_[HEAP]->{clients}->{$wheel_id} = $temp_rw_id; + $_[HEAP]->{current_client}->{$temp_rw_id->ID} = $wheel_id; print "factory_success called, creating wheel $wheel_id for handle $ +handle | ( ".$temp_rw_id->ID." )\n"; } sub client_input { my ($input, $wheel_id) = @_[ARG0, ARG1]; my $factory_id = $_[HEAP]->{current_client}->{$wheel_id}; use Data::Dumper; print Dumper $input; print "wheel_id is: $wheel_id\n"; print "factory_id is: $factory_id\n"; $_[HEAP]->{clients}->{$factory_id}->put($input); } POE::Session->create( inline_states => { _start => \&start, factory_success => \&factory_ +success, client_input => \&client_i +nput, client_error => \&client_e +rror, fatal_error => sub { die +"A fatal error occurred" }, _stop => sub {}, }, ); POE::Kernel->run();

      PS I mailed the editors of and asked them to fix the download link in the article.

        I don't have POE installed on this PC, but I'm pretty sure the reason you're losing your connection when you get a new one is your factory_success method.

        When you create a connection, you store it as:

        $_[HEAP]->{clients}->{$wheel_id} = $temp_rw_id;
        But $wheel_id is the same from one connection to another, so when the next connection comes along, you overwrite the last reference to the previous Wheel:RW, and it gets destroyed.

        Try keeping a hash of active wheels, something like

        instead. When you're done with a wheel, just "delete" it from that hash.

        This way, you're keeping a live reference to all active wheels.

        Hope this helps!

Re: POE method problem (building applications with POE)
by PodMaster (Abbot) on Dec 31, 2004 at 12:53 UTC
    `perldoc diagnostics', `perldoc perldiag'
    Can't call method ``%s'' on an undefined value
    (F) You used the syntax of a method call,
    but the slot filled by the object reference
    or package name contains an undefined value.
    Something like this will reproduce the error: 
        $BADREF = undef;
        process $BADREF 1,2,3;

    MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!"
    I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README).
    ** The third rule of perl club is a statement of fact: pod is sexy.

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