Last night I was plumbing in access to an XML-RPC server from a Java application. I was using the excellent XML-RPC package from Apache for the client. It is a beautifully crafted piece of software, just for the sheer ease of use alone.

However, I came a little unstuck when hitting one particular server. I know the default value for XML-RPC is to assume the <string> type, but this server was looking for it and kept throwing invalid RPC request. This is an example of the output that was passed out to the server:

<?xml version="1.0" encoding="ISO-8859-1"?>
<methodCall>
  <methodName>blogger.getUsersBlogs</methodName>
  <params>
    <param><value>1070485999648</value></param>
    <param><value>xxxx@xxxx.com</value></param>
    <param><value>xxxx</value></param>
  </params>
</methodCall>

Which is perfectly legal, even though it doesn't explicitly type the value of the params. Trawling through Google, I noticed this tripping a few others as well. Usually Apache are quite anal about following standards, so it was a bit of a surprise to see this one slipping through the net.

So if you are doing any XML-RPC stuff, watch out for this one, just incase your server's implementation isn't too flexible.