in reply to Re: LWP handlers examples?
in thread LWP handlers examples?

It's strange that the message is printed twice since it is being called once!!! Why?

I added some code lines to trace the handlers at any moment, but as $ua->handlers() require an HTTP::Response object, I had to split the $ua->get() calls, and an extra call must be added at the beginning, giving:

#!perl

use strict;
use warnings;

use LWP::UserAgent qw( );

my $ua = LWP::UserAgent->new();
my $url = 'http://www.google.com/';
my $resp;

$resp = $ua->get($url); print($resp->status_line(), "\n");
show(1);
print("Added:\n");
$ua->add_handler(response_header => sub { print "HANDLER\n"; });
show(2);
$resp = $ua->get($url); print($resp->status_line(), "\n");
show(3);
print("Removed:\n");
$ua->remove_handler('response_header');
show(4);
$resp = $ua->get($url); print($resp->status_line(), "\n");
show(5);

sub show {
  print(join(" ", @_, $ua->handlers('response_header', $resp)), "\n");
}

[download]

Output:

200 OK
1 HASH(0x183657c)
Added:
2 HASH(0x183657c) HASH(0x1b79944)
HANDLER
HANDLER
200 OK
3 HASH(0x183657c) HASH(0x1b79944)
Removed:
4
200 OK
5

[download]

It seems that there is a default handler installed, and I would expect that trace lines 4 and 5 to show the same hash as line 1, not an empty list of handlers.

BTW, I changed your original test program to use a WWW::Mechanize object, and got the same output as you.

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Re^3: LWP handlers examples?
by almut (Canon) on Aug 12, 2009 at 21:51 UTC

    After a bit of RTFM-ing, reading the source and experimenting, I think the %matchspec is supposed to be used something like this: 

    use LWP::UserAgent qw( );

my $ua = LWP::UserAgent->new();
my $url = 'http://www.google.com/';
my $resp;

$resp = $ua->get($url); print($resp->status_line(), "\n");
show(1);
print("Added:\n");
$ua->add_handler( response_header => sub { print "HANDLER\n"; }, owner
+ => "myfunc");
show(2);
$resp = $ua->get($url); print($resp->status_line(), "\n");
show(3);
print("Removed:\n");
$ua->remove_handler('response_header', owner => "myfunc");
show(4);
$resp = $ua->get($url); print($resp->status_line(), "\n");
show(5);

sub show {
  print(join(" ", @_, $ua->handlers('response_header', $resp)), "\n");
}

__END__
200 OK
1 HASH(0x8c2440)
Added:
2 HASH(0x8c2440) HASH(0x93b0e0)
HANDLER
HANDLER
200 OK
3 HASH(0x8c2440) HASH(0x93b0e0)
Removed:
4 HASH(0x8c2440)
200 OK
5 HASH(0x8c2440)

    [download]

    where "myfunc" is some self-chosen name that you use to identify the callback for removal.

    (When you dump the hashes, you can see that the one associated with the internal handler (HASH(0x8c2440)) has owner => 'LWP::UserAgent::parse_head')

    As you can see, the internal callback remains intact this way.

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[select]

      This code works OK, even if I change it to use Mechanize instead of UserAgent, but does not work inside my original program... remove_handler() removes all available handlers, including the internal, ignoring %matchspec.

        print "Hdl1: ".join(" ",$mech->handlers('response_header', $mech->re
+sponse()))."\n";
  $mech->add_handler(response_header => \&response, owner => "vitoco")
+;
  print "Hdl2: ".join(" ",$mech->handlers('response_header', $mech->re
+sponse()))."\n";
  $mech->add_header('If-Modified-Since', time2str($current)) if $curre
+nt;
  my $resp = $mech->get($url, ':content_file' => "$file.tmp");
  $mech->delete_header('If-Modified-Since') if $current;
  $mech->remove_handler('response_header', owner => "vitoco");
  print "Hdl3: ".join(" ",$mech->handlers('response_header', $mech->re
+sponse()))."\n";
  print "Hdl4: ".join(" ",$mech->handlers('response_header', $resp))."
+\n";

      [download]
      Hdl1: HASH(0x1f87dbc)
Hdl2: HASH(0x1f87dbc) HASH(0x1f9d174)
Hdl3:
Hdl4:

      [download]

      I changed de example to use :content_file, and stil works, so it is not that. Note that Hdl3 and Hdl4 uses different response objects (or the same, obtained from different ways).

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Re^3: LWP handlers examples?
by ikegami (Patriarch) on Aug 12, 2009 at 20:06 UTC

    It's strange that the message is printed twice since it is being called once!!! Why?

    I suspect two responses were received, the first being a redirect.

[reply]

      You are right on this... change the unnamed sub to show that:

      $ua->add_handler(response_header => sub { print("HANDLER:", $_[0]->status_line(), "\n"); });

      That will be another thing I'll have to manage...

[reply]
[d/l]

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