Programming Web Services with Perl

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

SOAP Transport

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RPC faults in SOAP 1.1 are simply implemented using the existing guidelines for

SOAP itself. It is expected that the

faultcode attribute would be specific to RPC

application, and that the remaining attributes would be correctly utilized. SOAP 1.2

takes a more thorough look at the fault model for RPC and provides a subsection

within the specification devoted to the subject.

The fault model in SOAP 1.2 uses an additional namespace identifier, which is given

the label

rpc in the specification. The URI for this namespace is http://www.w3.org/

2002/6/soap-rpc, as used for other RPC-specific elements described earlier. The spec-

ification provides four predefined QNames for RPC-specific faults, as shown in

Table 5-9. The table lists the faults in a decreasing order of precedence.

Aside from these predeclared fault codes, the mechanism itself is the same as for gen-

eral SOAP faults. Note that some transport bindings such as HTTP or SMTP may

define additional elements or additional fault codes. If any such definitions apply,

the application has a responsibility to use them as well.

In all RPC fault cases, the

detail and faultstring attributes are defined on a per-

implementation basis.

SOAP Transport

This section is going to briefly cover some of the different methods of transporting

SOAP messages. Later chapters will go into greater depth on some of these (such as

HTTP and SMTP).

Arguably the most significant difference between SOAP and XML-RPC is the fact

that the designers of SOAP refrained from binding it to a specific transport protocol.

While both versions of the protocol refer heavily to the application of HTTP as a

method of transport, this isn’t the only available option. SOAP has been demon-

strated using the Simple Mail Transfer Protocol (SMTP), the Jabber wire protocol,

Microsoft’s .NET framework, and others. Guidelines for protocols such as the Blocks

Table 5-9. RPC fault codes for SOAP 1.2

Fault code Meaning

env:Server

This code is recommended for situations in which the problem is server-related, such as

resource problems or a scheduled black-out period.

env:DataEncodingUnknown

All the elements are qualified to use the encodingStyle attribute provided by SOAP

itself. This code is recommended for cases in which a part of the message uses an

unknown encoding.

rpc:ProcedureNotPresent

If the requested method or procedure is unknown to the server, this fault code must be

used (unless a higher-priority condition was met first).

rpc:BadArguments

If there is a mismatch in the arguments against a specified signature, or when the server

is unable to process the arguments, this code must be used, unless a code of higher-pri-

ority has already been chosen.