Add grpc.ForceCodec-like ServerOption based on encoding.Codec

[nadilas]

What version of gRPC are you using?

google.golang.org/grpc v1.29.1

What version of Go are you using (go version)?

go1.14.3 darwin/amd64

What did you do?

Following up on #2189, the server side was missed, it is still using the deprecated grpc.Codec interface.

What did you expect to see?

// CustomCodec returns a ServerOption that sets a codec for message marshaling and unmarshaling.
//
// This will override any lookups by content-subtype for Codecs registered with RegisterCodec.
func CustomCodec(codec encoding.Codec) ServerOption {
	return newFuncServerOption(func(o *serverOptions) {
		o.codec = codec
	})
}

What did you see instead?

// CustomCodec returns a ServerOption that sets a codec for message marshaling and unmarshaling.
//
// This will override any lookups by content-subtype for Codecs registered with RegisterCodec.
func CustomCodec(codec Codec) ServerOption {
	return newFuncServerOption(func(o *serverOptions) {
		o.codec = codec
	})
}



// Codec defines the interface gRPC uses to encode and decode messages.
// Note that implementations of this interface must be thread safe;
// a Codec's methods can be called from concurrent goroutines.
//
// Deprecated: use encoding.Codec instead.
type Codec interface {
	// Marshal returns the wire format of v.
	Marshal(v interface{}) ([]byte, error)
	// Unmarshal parses the wire format into v.
	Unmarshal(data []byte, v interface{}) error
	// String returns the name of the Codec implementation.  This is unused by
	// gRPC.
	String() string
}

[dfawley]

I believe CustomCodec should be marked deprecated, and there is no need to provide an alternative using encoding.Codec directly. Let me know if you have a use case for it.

[nadilas]

Same use case as mentioned in the linked issue: #2189

I am trying to use https://github.com/mwitkow/grpc-proxy

func ExampleRegisterService() {
	// A gRPC server with the proxying codec enabled.
	server := grpc.NewServer(grpc.CustomCodec(proxy.Codec()))
	// Register a TestService with 4 of its methods explicitly.
	proxy.RegisterService(server, director,
		"mwitkow.testproto.TestService",
		"PingEmpty", "Ping", "PingError", "PingList")
}

[dfawley]

I think we should keep this open to track adding a non-deprecated version of the API. The server-side use case seems just as appropriate as the client-side.

[ash2k]

Same issue here - I want to use a custom codec for a particular gRPC server. I have more than one server in the program and ideally I'd prefer not to register a global codec. Also, I wonder what is the reasoning for adding global registries for codec and compressor? Allowing a per-server configuration is much more flexible and there is no thread-safety issues (global registries are not thread safe at the moment).

[ash2k]

Sorry, more context: servers that I have should use different codecs for the same content type - global registry makes this hard to achieve. I can work this around, but it's not as clean as it could be with this issue resolved.

[ash2k]

I've opened a PR to add an option. Would be great to get some eyes on it. Thanks.

[FZambia]

I have a similar use case as @ash2k (several GRPC servers inside one program which must use different codecs for the same content type), really unfortunate to not have a non-deprecated way to set it on per-server basis.

[easwars]

Moving the ownership of the issue to @dfawley who is reviewing #4205.