Subs calling themselves

[Bod]

Continuing from my previous discussion about connecting to LinkedIn - see Injecting a value into HTTP::Header

I have managed to authenticate with LinkedIn using LWP::Authen::OAuth2::ServiceProvider::LinkedIn which I am writing. This is used by LWP::Authen::OAuth2. LinkedIn doesn't obey the OAuth2 standard which is why there was a need to add extra information.

But now I am having difficulty posting anything to LinkedIn and I am getting an error from LWP::Authen::OAuth2
Can't call method "request" on an undefined value at /home/shoples1/perl5/lib/perl5/LWP/Authen/OAuth2.pm line 107.

I've looked at the source code of LWP::Authen::OAuth2 to try and see what I need to do differently to make this work. However, I cannot fathom how that module is supposed to work. Clearly, it does work and it is my understanding that is missing because it is a working module. But these two subroutines just seem to be calling each other:

sub request {
    my ($self, $request, @rest) = @_;
    return $self->access_token->request($self, $request, @rest); # <- 
+line 107
}

sub access_token {
    my $self = shift;
 
    return $self->{access_token};
}

Having gone through the authentication and obtained a token, I am trying to make a post using the following code. I am not expecting it to actually make a post yet but I was expecting to get an error from LinkedIn and not an error from Perl.

my $params = {
    'content'    => {
        'title'       => 'Test Title',
        'descrition'  => 'Test message',
    },
};
my $res = $linkedin->post('https://api.linkedin.com/v2/shares', $param
+s);
if ($res) {
    print "Content-type: text/plain\n\n";
    print $res;
    exit 0;
}

Can you help me understand what the two subroutines in LWP::Authen::OAuth2 are actually doing?

[choroba]

> these two subroutines just seem to be calling each other

The access_token subroutine isn't calling any subroutine. It just accesses the hash referenced by $self and returns the value associated with the access_token key, i.e. it's a standard getter method.

What does request do with the value? It calls the method request on it. It seems confusing, but the access token is probably of a different class than $self, so it's calling a different request method.

Update: Indeed, see LWP::Authen::OAuth2::AccessToken.

[Bod]

Thank you choroba - it was the two different methods having the same name that was throwing me!

Now to work out why $self->access_token is undefined...

[roboticus]

Bod:

The second function, access_token, is fetching a value from the object referenced by $self, so it's pretty straightforward.

The request function is a *little* more subtle: As you notice, it calls the access_token function, but the result from that call is treated as a reference to an object that has a request function. Note that the object referenced by access_token is *not* necessarily the same class or object found in the request function you posted. So in order to understand what's happening, you'll need to figure out where the access_token member in the object is being set, so you can figure out what sort of object is being accessed.

Sometimes when tracking through the code is a bit annoying, I'll do something like a quick edit of the module:

$ # make a copy of the module so I don't mess it up
$ cp /home/shoples1/perl5/lib/perl5/LWP/Authen/OAuth2.pm foo.pm
$ vi /home/shoples1/perl5/lib/perl5/LWP/Authen/OAuth2.pm
 . . . edit the request subroutine to look like:
sub request {
    my ($self, $request, @rest) = @_;
    use Data::Dumper;
    my $temp = $self->access_token;
    print "access token is: ", Dumper($temp), "\n";
    return $temp->request($self, $request, @rest);
}
$ # run the project so I can see what I'm looking for
$ perl t.pl
blah, blah, blah
access token is:$VAR1 = bless( {
                 'baz' => 'boom',
                 'foo' => 'bar'
               }, 'Barsoom!' );

blah, blah, blah
$ # put things back so I don't cause more problems for myself
$ cp foo.pm /home/shoples1/perl5/lib/perl5/LWP/Authen/OAuth2.pm

Hope this helps!

...roboticus

When your only tool is a hammer, all problems look like your thumb.

[Bod]

Hope this helps!

Yes...it helps a lot. Thank you

I need to work out why $self->access_token ends up being undefined and having a way to peek inside the module has to be helpful in working that out.