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書名： Microsoft Windows Communication Foundation 4.0 Cookbook for Developing SOA Applications
作者名： Steven Cheng
本章字數： 463字
更新時間： 2021-04-13 17:04:05

Sharing a physical address between multiple endpoints

WCF supports exposing a single service through multiple heterogeneous endpoints. Another great feature is letting multiple endpoints listen over the same physical transport address. For example, you want to host a WCF service that has multiple endpoints exposed. However, you only have a single HTTP URL open for listening. Then you can use this feature to make all those endpoints (as long as they’re using the same transport protocol) listen on the same URL.

How to do it...

Our sample service will expose two endpoints (one is IFoo and the other is IBar) and both of them will listen on the same HTTP URL:

The first thing we need to do is configure the service endpoints. We will still specify different values for the address attribute of the two endpoints. However, we will use a special attribute named listenUri to supply the physical address (identical for both endpoints). The following screenshot shows the usage of both attributes:
It is also important to configure the client endpoint so that the client proxy or ChannelFactory can correctly locate the service endpoint. WCF provides a ClientViaBehavior type for specifying the physical address of a client endpoint. You can use the ChannelFactory.Endpoint.Behaviors collection to inject the behavior in code, shown as follows:
```
ChannelFactory<SharedAddressService.IFoo> fooFactory = new ChannelFactory<SharedAddressService.IFoo>(new WSHttpBinding(SecurityMode.None));

SharedAddressService.IFoo foo = fooFactory.CreateChannel(
 new EndpointAddress(“urn:Foo”), /* logical address */
 new Uri(“http://localhost:8731/FooBarService/Operations”)); /*physical address*/
           foo.Foo();
```
Alternatively, you can also use the <clientVia> element to supply the physical address in a configuration file, as shown in the following screenshot:

How it works...

Generally, we will use the address attribute to specify the URL on which the endpoint will listen. However, this address is actually a logical address and WCF runtime will use it as a physical address also, if we haven’t explicitly provided a physical address. The listenUri, on the contrary, represents the physical transport address the service endpoint listens on.

Also, for the endpoints that share the same physical address, they will share the same service dispatcher and channel stack. Then, how does the WCF runtime differentiate these operation requests when there are multiple endpoints listening on a single physical address? The answer is WCF runtime will try to resolve the request target by the combination of two parts:

The Service/Operation Contract
The logical address specified the via address attribute

Therefore, the dispatcher/channel stack can correctly redirect the requests to the corresponding endpoint even if we supply an identical value for both logical and physical address.

There’s more...

For more in-depth explanation on WCF Addressing, you can have a look at the WCF Addressing In Depth MSDN article written by Aaron Skonnard (http://msdn.microsoft.com/en-us/magazine/cc163412.aspx).

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Microsoft Windows Communication Foundation 4.0 Cookbook for Developing SOA Applications