Override the root element of the response

Last week I showed how to override the root element of a request, but did not show a way to do the same thing for the root element of a response. So, read on if you would like to know how to modify the response's namespace, namespace prefix, encoding style, etc. It is not very intuitive, or pretty for that matter, but at least it is relatively simple.

The key in overriding properties of the root element of the response is to write a customer serializer. What is a serializer? A serializer converts abstract data into a format that can more easily be transmitted between endpoints. In this case, a serializer converts scalar and complex data into XML. By writing our own serializer we can tell SOAP::Lite how to construct the XML representing the response.

To create a custom serializer, you need to know a little bit about Perl OOP (Object Oriented Programing) and inheritence. The following code block shows a custom serializer which inherits all properties and behavior from the default SOAP::Lite Serializer, but overrides one of its methods/subroutines with its own:

package MySerializer;
@MySerializer::ISA = 'SOAP::Serializer';
sub envelope {
    $_[2] = SOAP::Data->name($_[2])->prefix('temp')->uri('urn:TemperatureService')
        if $_[1] =~ /^(?:method|response)$/;
    shift->SUPER::envelope(@_);
}

This is just a simple serializer, one that changes the root element only, but a serializer could be used to serialize any part of a message (in this case a response).

You can save your serializer to its own file (in the form of a perl module), and then 'use' it. Or alternatively, you can encapsulate the package in a BEGIN { } block anywhere in your code. Either way, to tell SOAP::Lite to use your serializer as opposed to its own, you will need to do the following within your Web service instance:

SOAP::Transport::HTTP::CGI
  ->serializer(MySerializer->new)
  ->dispatch_to('MyService')
  ->handle;

You can find an example of a trivial temperature conversion service which utilizes this custom serializer: here.