golang protobuf remove omitempty tag from generated json tags

问题

I am using google grpc with a json proxy. for some reason i need to remove the omitempty tags from the struct generated in the *.pb.go files.

if i have a proto message like this

message Status {
  int32 code = 1;
  string message = 2;
}

The generated struct looks like this

type Status struct {
  Code int32 `protobuf:"varint,1,opt,name=code" json:"code,omitempty"`
  Message string `protobuf:"bytes,2,opt,name=message" json:"message,omitempty"`
}

But My need is to remove the omitempty tag from the generated structs. How can i do this?

回答1:

If you are using grpc-gateway and you need the default values to be present during json marshaling, you may consider to add the following option when creating your servemux

    gwmux := runtime.NewServeMux(runtime.WithMarshalerOption(runtime.MIMEWildcard, &runtime.JSONPb{OrigName: true, EmitDefaults: true}))

Outside of grpc-gateway, if you want to marshal your protocul buffer message, use github.com/golang/protobuf/jsonpb package instead of encoding/json

func sendProtoMessage(resp proto.Message, w http.ResponseWriter) {
    w.Header().Set("Content-Type", "application/json; charset=utf-8")
    m := jsonpb.Marshaler{EmitDefaults: true}
    m.Marshal(w, resp) // You should check for errors here
}

回答2:

A [more] portable solution:

Use sed to strip the tags after generating via protoc.

Example of what I actually use in my go:generate script after having generated the *.pb.go files:

ls *.pb.go | xargs -n1 -IX bash -c 'sed s/,omitempty// X > X.tmp && mv X{.tmp,}'

Note: sed -i (inline-replacement) is not used here because that flag isn't portable between standard OS-X and Linux.

回答3:

You can try using gogo proto (https://github.com/gogo/protobuf) With the jsontag extension, your proto message would look like

message Status {
  int32 code = 1 [(gogoproto.jsontag) = "code"];
  string message = 2 [(gogoproto.jsontag) = "message"];
}

You can also add more tags, if you like.

回答4:

I found that the omitempty json tag is hard-coded into the protoc-gen-go source around line 1778:

tag := fmt.Sprintf("protobuf:%s json:%q",
    g.goTag(message, field, wiretype), jsonName+",omitempty")

it will be easy changing the source and make a new protoc-gen-go binary yourself.

It's worth noting that this is likely inadvisable and not recommended for several reasons, particularly because you will then be responsible for ensuring that the hacked up binary always gets used if the protobufs need to be regenerated.

回答5:

The Marshaler under the jsonpb package has a EmitDefaults field. Setting this to true, will just ignore the omitempty tag in struct.

https://godoc.org/github.com/golang/protobuf/jsonpb#JSONPBMarshaler

回答6:

You could use "sed" command to remove this text from files like following

sed -i "" -e "s/,omitempty//g" ./api/proto/*.go

where args:

-i "" is meaning that keep same name of files
-e "s/,omitempty//g" = format to replace like "s/SEARCH/INSERT/g"

回答7:

you can copy the encoding/json package to your own folder for example my_json, and modify omitEmpty field to false, and use my_json.Marshal() to encode the struct to json string.

来源：https://stackoverflow.com/questions/34716238/golang-protobuf-remove-omitempty-tag-from-generated-json-tags

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grpc

protocol-buffers

proto3