Question when developing a grpc proxy: how to specify the Codec method for only one end?

[ancientmodern]

We have a service that needs to use grpc proxy, so I implemented a custom one based on this repo. It works well as I use grpc.NewServer(grpc.CustomCodec(proxy.Codec()), ...) to receive the requests from client and then send them to the server with grpc.DialContext(ctx, target, grpc.WithCodec(proxy.Codec()), grpc.WithInsecure()), where proxy.Codec() is a custom Codec that "basically treats a gRPC message frame as raw bytes, however, if the server handler, or the client caller are not proxy-internal functions it will fall back to trying to decode the message using a fallback codec."

Then I found that grpc.Codec, grpc.WithCodec(), grpc.CustomCodec() had been deprecated and it's recommended to use encoding.RegisterCodec() to register codecs. I replaced them, however the client then reported an error failed to unmarshal, message is *proxy.frame, want proto.Message. After reading the encoding.md, I realized the problem was that my client used the default "proto" Codec, so the proxy will automatically chose using the "proto" codec instead of proxy.Codec() that I've registered. To deal with this, I have to add grpc.WithDefaultCallOptions(grpc.CallContentSubtype("MyCodec")) as the client 's dial option, which deviated from intention of using a user-unaware proxy.

Is there any method to force using a certain encoding.Codec for only one end like previously we used grpc.CustomCodec() and grpc.WithCodec()?

[dfawley]

Sorry for the late reply. For this kind of situation, it sounds like you should use the newly-merged (#4205) https://pkg.go.dev/google.golang.org/grpc@master#ForceServerCodec in the proxy's server and https://pkg.go.dev/google.golang.org/grpc@master#ForceCodec in the proxy's clients. This will allow you to use the new, non-deprecated encoding.Codecs in a way that avoids using the registered codecs. Let us know if you encounter any problems with that approach.