WCF: Why is Contract on Endpoint and not on Service?

Question

Trying to really 'get' endpoint contracts:

I understand offering different endpoints to support different bindings, but when would one define n endpoints for a service, and use different contracts? Seems that in most cases (bar IMetadataExchange) the endpoint contract would be the same no matter the protocol, no?

If most of the time the contract would be the same across all endpoints, would it have been too simplistic (and why?) to define the service contract on the parent service instead of on each endpoint (seems cumbersome/repetitive), while alllowing an override on the endpoint for when needed (eg: IMetadataExchange).

Thanks for help with the small questions that keep me up at night ;-)

Answer 1

OK, well - the service that you define in the <service> tag is the actual implementation code - the actual C# or VB.NET lines that make up the service. Therefore, it's a concrete class (which might even implement multiple service contracts). This is server-side only.

The endpoint however is the communications channel between the server and the client, and between those two, you want to share only the contract - never any concrete implementation of that contract. The endpoint will only ever be used for a single service contract - if your concrete service implements multiple contracts, you need to expose multiple endpoints to the clients to provide all that functionality.

Does that make things a bit clearer?