grpc: Objective-C gRPC API v2 returning RST_STREAM error

What version of gRPC and what language are you using?

1.27.0, Objetive-C

What operating system (Linux, Windows,…) and version?

Mac OS Mojave, 10.14.6

What runtime / compiler are you using (e.g. python version or version of gcc)

Xcode 11.3

What did you do?

We have a few endpoints written in Go. When I try to send a request to them using the Objective-C gRPC the API v1 (which is deprecated), everything works great:

 /* This method belongs to a set of APIs that have been deprecated. Using the v2 API is recommended.
 */
- (void)someCallWithRequest:(XXXCallRequest *)request handler:(void(^)(XXXCallResponse *_Nullable response, NSError *_Nullable error))handler;

However, when I use the new API v2, some of the requests receive the following error:

Error Domain=io.grpc Code=13 "{"created":"@1589553479.630057000","description":"Error received from peer ipv4:x.x.x.x:443","file":"/Users/me/Documents/ourapp/App/Pods/gRPC-Core/src/core/lib/surface/call.cc","file_line":1056,"grpc_message":"Received RST_STREAM with error code 2","grpc_status":13}" UserInfo={io.grpc.HeadersKey={
    date = "Fri, 15 May 2020 14:37:58 GMT";
    server = "nginx/1.17.8";
    "strict-transport-security" = "max-age=15724800; includeSubDomains";
    trailer = "Grpc-Status";
}, io.grpc.TrailersKey={
}, NSDebugDescription={"created":"@1589553479.630057000","description":"Error received from peer ipv4:x.x.x.:443","file":"/Users/me/Documents/ourapp/App/Pods/gRPC-Core/src/core/lib/surface/call.cc","file_line":1056,"grpc_message":"Received RST_STREAM with error code 2","grpc_status":13}, NSLocalizedDescription=Received RST_STREAM with error code 2}.

The new v2 API has this signature:

- (GRPCUnaryProtoCall *)callWithMessage:(XXXCallRequest *)message responseHandler:(id<GRPCProtoResponseHandler>)handler callOptions:(GRPCCallOptions *_Nullable)callOptions;

After further debugging, I concluded a few things:

• The problem never happens with API v1
• The problem happens a lot with API v2, but not always
• The problem never happens if the backend is running locally in my computer

I fear that the bug here is related to the handler being deallocated. I tried a few things to ensure that the handler is not deallocated but without success. Maybe we removed some check from API v1 to v2 that was responsible for holding a handler reference?

What did you expect to see?

I expected to receive a success return to my requests, as the API v1 give.

What did you see instead?

I receive a RST_STREAM with internal_error description:

Error Domain=io.grpc Code=13 "{"created":"@1589553479.630057000","description":"Error received from peer ipv4:x.x.x.x:443","file":"/Users/me/Documents/ourapp/App/Pods/gRPC-Core/src/core/lib/surface/call.cc","file_line":1056,"grpc_message":"Received RST_STREAM with error code 2","grpc_status":13}" UserInfo={io.grpc.HeadersKey={
    date = "Fri, 15 May 2020 14:37:58 GMT";
    server = "nginx/1.17.8";
    "strict-transport-security" = "max-age=15724800; includeSubDomains";
    trailer = "Grpc-Status";
}, io.grpc.TrailersKey={
}, NSDebugDescription={"created":"@1589553479.630057000","description":"Error received from peer ipv4:x.x.x.:443","file":"/Users/me/Documents/ourapp/App/Pods/gRPC-Core/src/core/lib/surface/call.cc","file_line":1056,"grpc_message":"Received RST_STREAM with error code 2","grpc_status":13}, NSLocalizedDescription=Received RST_STREAM with error code 2}.

Anything else we should know about your project / environment?

The problem never occurs when the backend is running locally. I think the reason for this is: since the server is locally and the latency is minimum, it will always return before Objective-C deallocs the handler - which may not occur if the server is running in a different server.