Perl doesn't enforce access to modules' namespaces. This would usually be considered a bad thing, but sometimes it allows us to work around problems in modules without changing their code. Here's a perfect example:

I've been writing a script to talk to an XML-RPC endpoint, using Frontier::Client but for one of the requests, the script throws the following error:

wanted a data type, got `ex:i8'

Turning on debugging showed the response type was indeed ex:i8, which isn't one of the types that Frontier::Client supports.

<?xml version="1.0" encoding="UTF-8"?>
<methodResponse xmlns:ex="http://ws.apache.org/xmlrpc/namespaces/extensions">
  <params>
    <param>
      <value>
        <ex:i8>161</ex:i8>
      </value>
    </param>
  </params>
</methodResponse>

Searching through the code shows Frontier::Client is a wrapper around Frontier::RPC2 and the error message happens at the following section:

   } elsif ($scalars{$tag}) {
       $expat->{'rpc_text'} = "";
       push @{ $expat->{'rpc_state'} }, 'cdata';
   } else {
       Frontier::RPC2::die($expat, "wanted a data type, got \`$tag'\n");
   }

So we can see that it's looking up the tag into a hash called %scalars to see if the type is a scalar type, otherwise throws the error we saw. Looking at the top, we can see this hash:

%scalars = (
    'base64' => 1,
    'boolean' => 1,
    'dateTime.iso8601' => 1,
    'double' => 1,
    'int' => 1,
    'i4' => 1,
    'string' => 1,
);

So, if we could add ex:i8 to this scalar, we could fix the problem. We could fix the module, but that would require every user of the script to patch their copy of the module. The alternative is to inject something into that hash across module boundaries, which we can do by just refering to the hash by it's complete name including the package name. We can use:

$Frontier::RPC2::scalars{'ex:i8'} = 1;

Now when we run the script, everything works. It's not nice and it's dependent on Frontier::RPC2 not changing. but it allows us to get on with our script.

I just emailed my MP the following letter:

Dear David Lepper,

I would just like to thank you for signing Auston Mitchell's Early Day Motion 1155 Photography In Public Areas. I have been increasingly concerned with reports of police action against innocent photographers, including most recently a man assaulted by several security guards in Stoke (http://www.flickr.com/photos/happyaslarry/2420960125/). I'm sure you appreciate Brighton's reputation as an artistic city and your support for this motion shows your continued support for the photography community in Brighton.

Yours sincerely, David Pashley

If your MP hasn't signed this EDM, I recommend you contact them to urge them to sign it and if they have, contact them again to thank them.