i8 datatype support (8-byte integers, i.e. 64-bit integers) because the application I was interfacing with always used that datatype when responding with integers, regardless of whether or not it was necessary. I added
buffer datatype support (Base64 encoded data) just a volunteer contribution, though I had no need for it.
The original stream XML-RPC parser was unable to handle chunked responses correctly for element inner-text. This meant that if a chunk ended inside an element, that inner-text would become truncated. I fixed it by continuing to collect the inner-text until an end-of-element event was fired by the XML parser.
Finally, I added support for basic HTTP authentication.