Zend_XmlRpc_Server catches Exceptions generated by a dispatched method, and generates an XML-RPC fault response when such an exception is caught. By default, however, the exception messages and codes are not used in a fault response. This is an intentional decision to protect your code; many exceptions expose more information about the code or environment than a developer would necessarily intend (a prime example includes database abstraction or access layer exceptions).

Exception classes can be whitelisted to be used as fault responses, however. To do so, simply utilize Zend_XmlRpc_Server_Fault::attachFaultException() to pass an exception class to whitelist:

If you utilize an exception class that your other project exceptions inherit, you can then whitelist a whole family of exceptions at a time. Zend_XmlRpc_Server_Exceptions are always whitelisted, to allow reporting specific internal errors (undefined methods, etc.).

Any exception not specifically whitelisted will generate a fault response with a code of '404' and a message of 'Unknown error'.