RESTful Workflow Service Endpoints in WF4 / WCF

Question

Folks, I'm building a pretty standard workflow that I want exposed via a WCF endpoint - I'm using the "WCF Service Application" project template and I've got a .xamlx service. This is a very simple document interchange workflow service - I want consumers to POST me a blob of XML as the body of an HTTP post (with HTTP headers containing authentication tokens). In response, these consumers will get a blob of XML containing the reply. 2 goals for me using REST/POX here are the document/message-based nature of the interaction AND I want to make client development easy for non-.NET environments (especially limited environments like Silverlight and iPhone).

I don't really see how to make this possible using out of the box features (unless I'm missing something). Does anybody know how to create a RESTful (or even REST-ish, I'm not picky) endpoint for a WF4 service-hosted workflow? Any info leading in the right direction here would be great.

Answer 1

There is an unreleased item on CodePlex to cover this, which includes source code. Also see this SO answer which contains another idea for achieving this.

If you'd like to see the CodePlex activity released, please up-vote the UserVoice request.

Using a REST Pass-Through Service

As @Maurice mentions, you can also treat the WF service as a back-end service and expose a REST service that simply calls through to the WF service.

This method is a bit clumsy, but has the advantage that it doesn't use anything unreleased or really complicated.

If the back-end service runs on the same machine as the REST service (which is probably what you'd do), you should expose the WF service using the named pipes binding. This binding is fast, but only works when the caller and callee are on the same box.

A further thought: your REST pass-through service is blocked while the back-end service is being called. If your WF service is not very fast, you'd benefit from making your REST service asynchronous so it doesn't block a thread pool thread while the WF service is being called.

Answer 2

There are no out of the box activities that will allow you to use REST with WF, the Receice is pure SOAP.

You can either build a custom REST Receive activity and use that with your workflow. Depending on your needs this is going to be quite a handful to a lot of work. The easy option is use use a standard REST WCF endpoint and convert the REST data to SOAP, pass rhe request on to the workflow, and do the reverse on the result message.