Error Handling

For a successful client-server communication, the underlying protocol has to provide extensive and extensible error handling. SOAP fulfills this task by defining a so-called ``fault message'' which includes four specific fault elements:

1. Faultcode:

This element is mandatory and describes four main types of faults¹⁷:

VersionMismatch:

The processing SOAP application found an invalid namespace for the SOAP Envelope.

MustUnderstand:

The receiving SOAP processor did not understand a header element that was intended for that application and had the ``MustUnderstand'' attribute set.

Server:

This error applies to situations where the server received a valid message but cannot process it due to a server specific error.

Client:

In this case, the SOAP message itself contains errors that make it impossible for the server to process it.

2. Faultstring:

This mandatory element contains a description of the error in human-readable text.

3. Faultactor:

As a SOAP message can travel along many nodes with several actors, this element contains the actor where the error emerged.

4. Detail:

If the error took place while the SOAP application processed the body, it has to denote this application-specific fault in this element. This element is mandatory for SOAP Body specific errors and is absent when the fault occurred during the SOAP Header processing.

Listing 6 could be a possible response to a request shown in 5 which produced an error due to a corrupted database.

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