Brent has released a new version of his Cocoa XML-RPC implementation. It’s BSD’d open source. If you are using XML-RPC on the OSX platform, you should probably look at Brent’s code over Apple’s WebServicesCore:
At this writing (7 March 2003) the implementation of XML-RPC in Apple’s WebServicesCore has a crashing bug. Whenever a method response contains an empty element, there’s a crash.