Messages in C#

Generation QR Code 2d barcode in C# Messages

The final element of WCF is the actual message . WCF messages are modeled on SOAP messages . They are composed of an envelope, a header, a body, and addressing information . Of course, messages also include the information being exchanged . WCF supports three message exchange patterns: one way, request response, and duplex . One-way messages are passed from the transmitter to the receiver only . Messages passed using the request response pattern are sent from the transmitter to the receiver, and the receiver is expected to send a reply back to the originator . Messages using the request response pattern block until the receiver sends a response to the originator . In duplex messaging, services can call back to the client while executing a service requested by the client . The default message exchange pattern is request response .

Although WCF applications can be hosted by manually written servers, ASP .NET makes a perfectly good host . You can either write your own Windows Service to act as a host, or you can take advantage of a readily available Windows Service, Internet Information Services (IIS), and consequently ASP .NET . WCF and ASP .NET can coexist on a single computer in two different modes: side-by-side mode and ASP .NET compatibility mode . Here s a rundown of these two modes .

When running in side-by-side mode, WCF services hosted by IIS are colocated with ASP .NET applications composed of ASPX files and ASMX files (and ASCX and ASHX files when necessary) . ASP .NET files and WCF services reside inside a single, common application domain (AppDomain) . When run this way, ASP .NET provides common infrastructure services such as AppDomain management and dynamic compilation for both WCF and the ASP .NET HTTP runtime . WCF runs in side-by-side mode with ASP .NET by default . When running in side-by-side mode, the ASP .NET runtime manages only ASP .NET requests . Requests intended for a WCF service go straight to the WCF-based service . Although the ASP .NET runtime does not participate in processing the requests, there are some specific ramifications of running in side-by-side mode . First, ASP .NET and WCF services can share AppDomain state . This includes such items as static variables and public events . Although it shares an AppDomain with ASP .NET, WCF runs independently some features you might count on when working with ASP .NET become unavailable . Probably the major restriction is that there s no such thing as a current HttpContext from within a WCF service (despite the architectural similarity of WCF to the ASP .NET runtime pipeline) . Architecturally speaking, WCF can communicate over many different protocols, including but not limited to HTTP, so an HTTP-specific context might not even make sense in many scenarios . Second, authentication and authorization can get a bit tricky . For example, a client might be authenticated on an ASP .NET site using Forms Authentication, and then suddenly require reauthentication to accommodate a service call if the service call requires a different authentication scheme . In this case, the site might need to support two authentication and authorization schemes . Even though WCF applications do not interfere with ASP .NET applications, WCF applications can access various parts of the ASP .NET infrastructure such as the application data cache . In fact, this chapter s example shows one approach to accessing the cache .

WCF is designed primarily to unify the programming model over a number of transports and hosting environments . However, there are times when a uniform programming model with this much flexibility is not necessary and the application might desire or even require some of the services provided by the ASP .NET runtime . For those cases, WCF introduces the ASP .NET compatibility mode . With ASP .NET compatibility mode, you can run your WCF application as a full-fledged ASP .NET citizen, complete with all the functionality and services available through ASP .NET . WCF services that run using ASP .NET compatibility mode have full access to the ASP .NET pipeline and execute through the entire ASP .NET HTTP request life cycle . In ASP .NET compatibility mode, WCF includes an implementation of IHttpHandler that wraps WCF services and moves them through the ASP .NET HTTP pipeline . In effect, a WCF service running in ASP .NET compatibility mode looks, tastes, and feels just like a standard ASP .NET Web service (that is, an ASMX file) . WCF applications running under ASP .NET compatibility mode get a current HttpContext with all its contents the session state, the Server object, the Response object, and the Request object . WCF applications running as ASP .NET-compatible applications can implement security by associating Windows access control lists (ACLs) to the service .svc file . In this manner, only specific Windows users could use the WCF service . ASP .NET URL authorization also works for WCF applications running as ASP .NET-compatible applications . The pipeline remains arbitrarily extensible for WCF applications running as ASP .NET applications because service requests are not intercepted as they are with the general-purpose side-by-side mode they re managed by ASP .NET for the entire request life cycle . You can turn on WCF ASP .NET compatibility mode at the application level through the application s web .config file . You can also apply ASP .NET compatibility to a specific WCF service implementation .