Using the .NET SoapFormatter

SOAP RPC messages can carry message headers, just like regular messages do. We learned how to add headers to document-style message in section 13.3.4 and we saw how complicated it is to extract them out of the message later on. With RPC-style messages adding headers is just as easy as it was with document-style messages, but retrieving them is a lot easier.

Adding Headers to an RPC Message

To add headers to an RPC message we have to assign an array of Header objects to the Headers property of the ISoapMessage object we are serializing. These are the same Header objects from the System.Runtime.Remoting.Messaging namespace we used to add header entries in section 13.3.4.1. However, when we serialize an ISoapMessage object the SoapFormatter ignores any Header object passed to the Serialize() method. Only the headers in the array assigned to the Headers property of the ISoapMessage are written to the generated message. The formatter will not even add Headers passed to Serialize() when the Headers property on the interface is empty or set to null.

In our sender class we take the same approach we took previously to add a transaction ID header entry. We add it inside the Send() method like in the listing below.

Listing A Send() method to send RPC messages with headers

public void Send( ISoapMessage msg, long transactionId )

{

  msg.Headers = new Header[] { new Header("TransactionId",

      transactionId) };

  _Sender.SendObject( msg );

}