ISoapMessage Message Headers

Accessing header entries in RPC messages works just the opposite way of adding them. The SoapFormatter’s stores the headers it found in the processed message in the Headers property of the object assigned to the TopObject property. That is all there is to reading headers from an RPC message.

We can re-use the HeaderProcessor class we wrote in the previous chapter to process header entries from RPC messages when we extend our example to act on message headers. All we need to do is to extract them from the SoapMessage and pass them off to the processor object.

One possible place to add this functionality is in the SoapMessageReceiver’s ProcessSoapStream() method, just before we pass the SoapMessage to the stub. Processing headers there allows us to can skip invoking the server method when a message header indicates that the message is not intended for us. The modified method is shown in the listing below. In some applications it may make more sense to have the stub object process the SOAP headers, but let’s not argue this here.

Listing Processing message headers from RPC messages

public new void ProcessSoapStream( Stream stream )

{

  try

  {

    SoapMessage msg = new SoapMessage();

    _Formatter.TopObject = msg;          | #1

    _Formatter.Deserialize( stream );    |

    HeaderProcessor processor = new HeaderProcessor(); |#2

    processor.HandleHeaders( msg.Headers );            |

    _Stub.DispatchMessage( msg );                      |

  }

  catch(HeaderException ex)                           

  {                                                  

      Console.WriteLine( "Incompatible Headers:" );  

      Console.WriteLine( ex.Message );               

  }                                                  

} // ProcessSoapStream()

(annotation) <#1  Deserialize the RPC message .>

(annotation) <#2 The Headers property contains the header entries of a deserialized RPC message.>

Retrieving headers with a HeaderHandler method

Do you remember how we can register a HeaderHandler to process headers when call Deserialize() from the last chapter? We learned this technique to retrieve headers in section 13.3.4.3. Registering a handler can save us some unnecessary processing because the SoapFormatter calls the handler before it deserializes the complete message. When we detect from the headers that the message is not intended for us, we can stop processing the message right there.

If you remember, we ran into some problems deserializing objects and registering a HeaderHandler at the same time, because we could not determine the type of the serialized object. For with RPC messages we do not have to determine the type because the entry describes the method call. We still have to set up the object to return from Deserialize() manually, but we know that the caller always expects an object that implements the ISoapMessage interface. Ideally we would return a SoapMessage object, but SoapMessage does not implement ISerializable. However, we can derive a class from SoapMessage and implement ISerializable there. Then we can return such an object directly from the HeaderHandler method populate it in the deserialization constructor just as if the HeaderHandler was never in the picture.