We need a decoder that allows users to define a mapping from arbitrary XML to a message structure, however, just like the (poorly named) LoglineDecoder converts regex-parse-able text to a message structure.
The decoder should assume that it will be handed message objects with valid XML in the payload, such as a message that might be generated by an HttpInput fetching XML documents from a remote HTTP URL.
Config should support use of xpath expressions to specify how the arbitrary XML should be mapped to message fields.
Closing this while I rewrite a minimal subset of XPath instead.
whoops. meant to close the pull request.
This might be useful: http://blog.labix.org/2013/06/07/efficient-xpath-for-go
added tests around PayloadXmlDecoder for issue #310