Errors handling in web services

Current Moodle web services error handling

• 16 functions: all exceptions are caught by the server that generate its own error format. For example in REST:

<?xml version="1.0" encoding="UTF-8"?> <EXCEPTION class="invalid_parameter_exception">

   <MESSAGE>Invalid parameter value detected</MESSAGE>
   <DEBUGINFO></DEBUGINFO>

</EXCEPTION>

• 2 functions: the web service function catches some exceptions and return a string error message for each faulty element (create notes / send messages)

• download/upload script return string error message (JSON) + error code. The token script returns just an error message.

Main issue

it is difficult for client to programmatically know which exception is raised. It is difficult to display an accurate.

Suggestion

I think the web service developer still should choose if he wants to return an error message or an exception. The developer should still follow the rule about DB WRITE functions that must rollback when an exception is raised. We usually throw back the exception to the server.

The goal being to let the developer write his own error message, we should add some code error to all exceptions or messages.