Subs calling themselves

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

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};
}
[download]

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;
}
[download]

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

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Re: Subs calling themselves by choroba (Cardinal) on May 07, 2021 at 12:51 UTC
> 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. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re^2: Subs calling themselves by Bod (Parson) on May 07, 2021 at 21:41 UTC
Thank you choroba - it was the two different methods having the same name that was throwing me! Now to work out why `$self->access_token` is undefined...	[reply] [d/l]
Re: Subs calling themselves by roboticus (Chancellor) on May 07, 2021 at 13:05 UTC
Bod: The second function, `access_token`, is fetching a value from the object referenced by `$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 [download] Hope this helps! ...roboticus When your only tool is a hammer, all problems look like your thumb.	[reply] [d/l] [select]
Re^2: Subs calling themselves by Bod (Parson) on May 07, 2021 at 21:43 UTC
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.	[reply] [d/l]