Java gRPC: exception from client to server - grpc

Question

Is it's possible to throw an exception from the client to the server?
We have an open stream from the server to the client:
rpc addStream(Request) returns (stream StreamMessage) {}
When i try something like this:
throw Status.INTERNAL.withDescription(e.getMessage()).withCause(e.getCause()).asRuntimeException();
I got the exception in the StreamObserver.onError on the client, but there is no exception on the server-side.

Answer 1

Servers can respond with a "status" that the stub API exposes as a StatusRuntimeException. Clients, however, can only "cancel" the RPC. Servers will not know the source of the cancellation; it could be because the client cancelled or maybe the TCP connection broke.
In a client-streaming or bidi-streaming call, the client can cancel by calling observer.onError() (without ever calling onCompleted()). However, if the client called onCompleted() or the RPC has a unary request, then you need to use ClientCallStreamObserver or Context:
stub.someRpc(request, new ClientResponseObserver<Request, Response>() {
private ClientCallStreamObserver<Request> requestStream;
#Override public void beforeStart(ClientCallStreamObserver<Request> requestStream) {
this.requestStream = requestStream;
}
...
});
// And then where you want to cancel
// RequestStream is non-thread-safe. For unary requests, wait until
// stub.someRpc() returns, since it uses the stream internally.
// The string is not sent to the server. It is just "echoed"
// back to the client's `onError()` to make clear that the
// cancellation was locally caused.
requestStream.cancel("some message for yourself", null);
// For thread-safe cancellation (e.g., for client-streaming)
CancellableContext ctx = Context.current().withCancellation();
StreamObserver requestObserver = ctx.call(() ->
stub.someRpc(new StreamObserver<Response>() {
#Override public void onCompleted() {
// The ctx must be closed when done, to avoid leaks
ctx.cancel(null);
}
#Override public void onError() {
ctx.cancel(null);
}
}));
// The place you want to cancel
ctx.cancel(ex);