AJ's blog

January 15, 2015

WCF Policy – Part 5: Addendum: Policy Support in WCF

Another addendum before we move on…

As MSDN states in regard to WS-Policy 1.2 and 1.5:

“WCF uses the WS-Policy specification together with domain-specific assertions to describe service requirements and capabilities.”

(In case you are wondering: you can choose the policy version for your service using configuration, namely the serviceMetadata element, policyVersion attribute; default is WS-Policy 1.2.)

Regarding WS-PolicyAttachment the claim is:

“WCF implements WS-PolicyAttachment to attach policy expressions at various scopes in Web Services Description Language (WSDL).”

Sounds great, doesn’t it? But if you read carefully, WCF “using” WS-Policy and “implementing” WS-PolicyAttachment to achieve something actually does not imply fully supporting it.

 

The one pitfall I have found is the way policy expressions are identified and referenced. WS-Policy supports two ways to identify policy expressions, either by a Name attribute, or by a wsu:Id attribute (as shown in part 2 of this series). wsu:Id is used to identify policies residing in the same XML document, Name becomes necessary for policies in separate XML documents, for example imported using wsdl:import. The pitfall I mentioned: WCF does not support policies in separate XML documents, i.e. policy references using the Name attribute.

Now, as long as you are working within WCF on both client and server, this will never be an issues. However if your policy is provided by a Java Metro service, there is a choice, as documented here. Example 19.1 works fine with WCF clients, examples 19.2 and following are not supported. Other technologies may provide similar options, or – even worse – be limited to the Name attribute.

It’s not as if Microsoft doesn’t know the standards, they explained it quite well in “Understanding Web Services Policy”, chapter 2.8, “Referencing Policy Expressions”. They also know about the issue. Unfortunately they are not going to do something about it:

“At this point of time WCF only supports policies included in the same WSDL file and identified via the wsu:ID attribute.
Unfortunately, we are not seeing large customer demand supporting policies residing in secondary WSDL documents, so I will be resolving this bug as "Wont Fix".”

Sic!

Having had to support both, .NET and Java, I ended up writing a little command line application, that downloads and patches the WSDL of services using the Name attribute…

 

That’s all for now folks,
AJ.NET

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