HttpEndpoint Activity Performance - allow direct response and process other steps asynchronously

[jdevillard]

TLDR : We should offer a simple way to let the workflow write to the http response directly and perhaps resume asynchronously

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After doing some test on HttpEndpoint Activity and WriteHttpResponse, here are my observations :

• Elsa.Http.Middleware.WorkflowMiddleware is responsible to :
  • react to the Http Input (Path etc..)
  • found the Workflow to instanciate,
  • execute the Workflow Instance
  • Respond to the caller (return in the middleware)
• WriteHttpResponse modify the HttpContext to allow the wokflow to customise the Response of the workflow

BUT even if we use the WriteHttpResponse at the begining of the workflow , the call to ExecuteWorkflowAsync is blocked and will be unblock only if workflow is suspended / finished.

So for example, a simple workflow HttpEndpoint -> HttpWriteResponse -> Delay 5Sec (blocking, without suspend state) , the response is received by the client at the end of the workflow so 5sec after the HttpWriteResponse.

Technically , this behavior can also lead to performance issue, due to any backend work that can be done by the framework (persistence etc...)

Another functional example is, HttpEndpoint -> doing some verification -> HttpWriteResponse (ok) -> doing some other work -> put the workflow in error state du to second step work issue. In this case, the Http Client receive a 500 error which is not necessary what we want.