CODEWITHSUNDEEP
jsongoreflectionprotocol-buffersdescriptor
Alexander Klauer
Alexander Klauer

Reputation: 1027

How to convert protobuf wireformat to JSON with just a message descriptor?

Normally, to convert a protobuf message from wire format to JSON, you simply unmarshal the wire format into a proto.Message whose dynamic type is a concrete Go type (generated by protoc-gen-go), and then unmarshal that to JSON with the protojson package.

I would like to know how to do the same if you don't have a concrete Go type, but a protoreflect.MessageDescriptor instead. The descriptor should have all the information necessary to parse the wire format and construct a JSON (or other formats) from it, but I can't seem to find an API for that. It seems like I need something like the following:

func UnmarshalFromWire(b []byte, desc protoreflect.MessageDescriptor) (protoreflect.Message, error)

func MarshalToJSON(m protoreflect.Message) ([]byte, error)

Is there an API like that or similar?

Upvotes: 0

Views: 3192

Answers (1)

Rafael Lerm
Rafael Lerm

Reputation: 1400

The dynamicpb module does the first part (from MessageDescriptor to proto.Message, not protoreflect.Message).

func UnmarshalFromWire(b []byte, desc protoreflect.MessageDescriptor) (proto.Message, error) {
  m := dynamicpb.NewMessage(desc)
  if err := proto.Unmarshal(b, m); err != nil {
    return nil, err
  }
  return m, nil
}

The second part is just your standard protojson.Marshal - since you now have a perfectly valid proto.Message.

Upvotes: 2

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