Errors handling in web services

Exceptions

Format

Exceptions are caught by the server that generate its own error format. All exceptions contain a translated message + debuginfo.

REST-XML

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

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

</EXCEPTION>

How to handle exception on the client side

Code error: the code error is the exception class name. You can implement logic on it in your client. However they are often similar between them. You'll most likely have more information in the debuginfo. Message: translated error Debuginfo: not translated error containing detailled information

When to send an exception on the server side

• DB WRITE functions must rollback when an exception is raised. We usually throw back the exception to the server.
• Example: the user does not have appropriate access rights to call the function)

Warning messages

Format

The warning format is different following the protocol. It can be JSON or XML. REST/SOAP/XMLRPC all got different XML format. However they all implement the following structure: list of (

   object {
       'key' string   //the key can be matched by the client developer
                       to find out what kind of error happened and implement a specific behavior against this error. 
                       For example: "userdoesntexist"
       'debug' string   //a not translated debug message to help the client developer to 
                          know straight away what is the issue
       'elementsdesc' string  Optional //explaination of the elements. For example:
                                        "elements is an array containing the missing user id" 
                                        "elements is a list of failing course id" or 
                                        "elements is an array(context, component, area, itemid) - the failing grade" or
                                        "elements is a list of non existing course/category 
                                        like (courseid1, categoryid1, courseid2, categoryid2...)"
       'elements'   //list of element
           list of ( 
               string/id/boolean/... (primary type)
           }
   }

}

When to send a warning on the server side

Most of the time you send warning in get_xxx() functions.

• Example: the user is requesting information for a list of courses and one of those courses in no longer available