client does not receive gRPC error

We tried to use grpc-web with grpcwebproxy and ran into an issue that the client could not receive gPRC error.

1. When server returns an error, our callback gets {err: null, response: <empty>}.

GatewayClientBase.prototype.rpcCall calls the callback on stream “data” and error “status” events. However the stream error “status” event never fires because it tries to look up grpc-status while the trailers body contains Grpc-Status.

We found a related issue https://github.com/improbable-eng/grpc-web/issues/228.

Which component was supposed to handle this case mismatch?

1. Suppose the error “status” issue is fixed. When a gRPC error happens, the client first receives {err: null, response: <empty>}, then {err: <error>, response: null}. The client has to deal with the <empty> response everywhere, unable to tell easily it was a failure other than calling its getters returning undefined. What’s recommended pattern for a client to differentiate success vs. error?

[johanbrandhorst]

The improbable proxy should fix the issue of the upper-casing as it’s in violation of the spec. The grpc/grpc-web client could obviously implement a workaround but it should not be the one primarily responsible for fixing the incompatibility. I remain optimistic that it shouldn’t be very hard to fix, so if you want this done quickly you could take a look at submitting a PR to the improbable repo 😃.

[stanley-cheung]

We can certainly fix the upper-lower case issue.