let backend processors specify the response error code

[mrcpvn]

the BackendGateway will always return FailBackendTransaction (554) if there is an error in one of the backend processors.
It would be useful if the error specified from the processor would be parsed and returned if valid...similar to this:

// wait for the save to complete
        // or timeout
        select {
        case status := <-workerMsg.notifyMe:
                defer workerMsgPool.Put(workerMsg) // can be recycled since we used the notifyMe channel
                if status.err != nil {
                        if _, err := strconv.Atoi(status.err.Error()[:3]); err != nil {
                                return NewResult(response.Canned.FailBackendTransaction + status.err.Error())
                        }
                        return NewResult(status.err.Error())
                }
                return NewResult(response.Canned.SuccessMessageQueued + status.queuedID)

        case <-time.After(gw.saveTimeout()):
                Log().Error("Backend has timed out while saving eamil")
                return NewResult(response.Canned.FailBackendTimeout)
        }

in this way the backend could respond 421 (for example) and allow the client to retry to send the email.

Another solution could be to add the backend result in the notifyMsg (or a pointer to it)

[flashmob]

Yeah, you're right - it's a limitation.

Would need to have a think about it. It seems like backend.Result and error could be married together. This is because there is only one result that is OK, all other result types are errors. So in other words, backend.Result could implement the error interface, and also have the ability to return the error as a response.

Edit: formatting