Untyped Messages In some scenarios, you may not know the structure of messages passed between a client and service at design time For instance, intelligence might be built in to the messages themselves, such as routing and service operations that are determined at runtime Or a layer of software (or hardware) might be between the client and service that manipulates SOAP messages

and requires special data formats For these cases, untyped operation contracts can be very useful Untyped operation contracts enable the client and service to pass virtually any content in the SOAP body, as long as the content can be encoded by the binding stack being used for communication The contents of the message are effectively opaque to the WSDL because there is no XSD to de ne class, which is the data The client and service work with the , to create, read, and write de ned in messages Listing 230 shows an operation contract that uses the type as method of the message is a input and output Notice that the generic method that deserializes the message body into a type This method element of the SOAP message uses an XMLReader to read the can be read only once; if you Because it uses an XML Reader, the want to read it more than once, you should use the method of the message The SOAP action on the reply is the request action with Response concatenated to the end This can be overridden by a in the attribute class has numerous methods for creating, reading, and The writing the message contents The client is responsible for creating a message before sending it to the service and the service is responsible for creating a message to send back Before sending the message, the contents , must be placed in the body This can be done with , or methods

The client code is similar to the service code, using to create the message with the proper version to match the binding and then to read the result that comes back from the service Note that using method used takes three parameters: the version, the the action, and the string message When creating the message, the version of the message must be compatible with the binding used to communicate with the service, as de ned by the MessageVersion property in the channel , is The action, in this case used by SOAP and the WCF infrastructure to route the message to the proper operation in the service Listing 231 shows client code that initiates communications with the service listed in Listing 230

Listing 232 shows the SOAP message transmitted back from the service to the client in response to the request in Listing 231 Notice that the action in the SOAP header has Response concatenated to the end, and that the body of the SOAP message is a string with no XML formatting

Using SOAP Headers with Untyped Messages Whether you re working with typed or untyped messages, you may want to pass information in the SOAP header in addition to the SOAP body A common need is to pass session or context information along with a message So, rather than creating additional wrapper messages, the SOAP header is a convenient and well-understood mechanism of passing that information If you re using typed messages, WCF explicitly supports this through attribute as demonstrated in Listing 228 If using an the untyped message, however, you need to explicitly add an untyped message header Listing 233 shows a service contract that implements an untyped message operation and reads data from the message header Note how the , is accessible with one line of code message header data,