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WCF Interop: Workaround for Incorrect Action values from WCF client

In my last blog entry, I described how WS-Addressing Action header value is calculated. A WSIT-enabled client/endpoint generates/expects the correct values per W3C Candidate Recommendation.  However Microsoft's WCF (Windows Communication Foundation) client does not generate the correct value of Action header in all cases. This blog describes the issue and workaround. 

As described in the previous blog, in the first case, where wsaw:Action is explicitly associated with wsdl:input message, WCF client generates the correct Action header value. In the second case where a non-empty soapAction is specified on wsdl:binding/wsdl:operation, WCF client generates the correct Action header value. In the third case where either soapAction is not specified or defined with an empty string as it's value, WCF client generates empty string as Action header instead of the default action. This causes an interoperability issue between WSIT and WCF starting Jun CTP. Lets understand this issue and see how it can be worked around.

If the WSDL has either of the following binding sections:  

<binding name="..." type="tns:wsaTestPortType">
  ...
  <operation name="echo">
    <soap:operation soapAction="">
    ...
  </operation>
</binding>

where soapAction's value is an empty string, or

<binding name="..." type="tns:wsaTestPortType">
    ...
  <operation name="echo">
    <soap:operation>
    ...
  </operation>
</binding>

where soapAction is not specified, then WCF client sends empty string as Action header value.

This is incorrect as W3C WS-Addressing WSDL Binding requires a default action to be generated/expected in this case. But because WSIT-based endpoint expects the correct value according to W3C Candidate Recommendation, there is a conflict and thus WSIT and WCF do not interoperate. Without getting into why there are different interpretations of the spec (probably another blog later), lets see how we can work around this.

WSIT Java-first endpoint, WCF client

If you build your Web service endpoint starting from Java (as opposed to starting from WSDL), then wsimport tool will generate a WSDL with soapAction="" in the SOAP binding. The reason it does that is because JSR 181 (Web Services Metadata for the Java^TM Platform) says all methods in a SEI (service endpoint interface) are mapped to WSDL operations. A @WebMethod annotation may be used to customize the mapping, but in it's absence a default @WebMethod is assumed on each method. The @WebMethod annotation has a member with name "action" that determines the value of soapAction for SOAP bindings. This member has a default value of "" (empty string). And thus, in this case, any WSDL generated by WSIT, either at runtime or using wsimport tool, where SEI does not have @WebMethod.action set to any non-empty-string value, has soapAction="" in the SOAP binding section.

So if your SEI looks like:

@WebService
public class AddNumbersImpl {

  public int addNumbers(int number1, int number2) {
    ...
  }
}

The generated SOAP binding will look like:

<operation name="addNumbers">
  <soap:operation soapAction="" />
  ...
</operation>

As explained above, WSIT and WCF do not interoperate for such a WSDL. The default value (empty string) of soapAction can easily be overridden by adding a @WebMethod annotation on your method as shown below. So if your SEI looks like:

@WebService
public class AddNumbersImpl {

  @WebMethod(action="addNumbers"
  public int addNumbers(int number1, int number2) {
    ...
  }
}

The generated SOAP binding in this case looks like:

<operation name="addNumbers">
  <soap:operation soapAction="addNumbers" />
  ...
</operation>

WCF client will generate "addNumbers" as the Action header and WSIT endpoint will accept it as a valid value.

WSIT WSDL-first endpoint, WCF client

If you are starting from WSDL, then you can either explicitly specify wsaw:Action attribute on the input message, as shown below:

<portType name="AddNumbersImpl">
  <operation name="addNumbers">
    <input message="tns:addNumbers" wsaw:Action="http://example.org/action/echoIn"/>
    <output message="tns:addNumbersResponse"/>
  </operation>
</portType>

Note, this is only required to be changed for input messages as WSIT endpoint generates the correct action on fault and output messages going back to WCF client.

Alternatively you can change, or add if missing, soapAction in the binding section, as shown below:

<operation name="addNumbers">
  <soap:operation soapAction="addNumbers" />
  ...
</operation>

As a convenience, you can use the operation name as the value of either wsaw:Action or soapAction since that is guaranteed to be unique.

WCF Endpoint, WSIT client

A WCF endpoint always generates explicit wsaw:Action for each message in the portType and exactly same value of soapAction. WSIT client is interoperable with WCF endpoints out of the box in this case.

Hopefully WCF will be fixed in the upcoming CTP and behave as per W3C standards. Then this workaround will not be required and life will be simpler again

Posted by Arun Gupta in webservices  |