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Enabling Metadata Exchange 

Recall that WCF client applications communicate with the WCF service via an intervening proxy

type. While you could most certainly author the proxy code completely by hand, doing so would

be tedious and error-prone. Ideally, a tool could be used to generate the necessary grunge code

(including the client-side *.config file). Thankfully, the .NET Framework 3.5 SDK provides a com-

mand-line tool (svcutil.exe) for this very purpose. As well, Visual Studio 2008 provides similar

functionality via the Project ➤ Add Service Reference menu option. 

However, in order for these tools to generate the necessary proxy code/*.config file, they must

be able to discover the format of the WCF service interfaces and any defined data contracts (the

method names, type of parameters, etc.).

Metadata exchange (MEX) is a WCF 

service behavior that can be specified to fine-tune how the

WCF runtime handles your service. Simply put, each  element can define a set of activi-

ties a given service can subscribe to. WCF provides numerous behaviors out of the box, and it is

possible to build your own. 

The MEX behavior (which is disabled by default) will intercept any metadata requests sent via

HTTP GET. If you want to allow svcutil.exe or Visual Studio 2008 to automate the creation of the

required client-side proxy *.config file, you must enable MEX.

Enabling MEX is a matter of tweaking the host’s *.config file with the proper settings (or

authoring the corresponding C# code). First, you must add a new  just for MEX. Second,

you need to define a WCF behavior to allow HTTP GET access. Third, you need to associate this

behavior by name to your service via the behaviorConfiguration attribute on the opening 

element. Finally, you need to add a  element to define the base address of this service (MEX

will look here to figure out the locations of the types to describe).