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protoc-gen-go-json

This plugin is originally forked from protoc-gen-go-json . I have made some changes to make it with more options and more flexible.

This is a plugin for the Google Protocol Buffers compiler protoc that generates code to implement json.Marshaler and json.Unmarshaler using protojson.

This enables Go-generated protobuf messages to be embedded directly within other structs and encoded with the standard JSON library, since the standard encoding/json library can't encode certain protobuf messages such as those that contain oneof fields.

Install

go get github.com/RyoJerryYu/protoc-gen-go-json

Also required:

Usage

Define your messages like normal:

syntax = "proto3";

message Request {
  oneof kind {
    string name = 1;
    int32  code = 2;
  }
}

The example message purposely uses a oneof since this won't work by default with encoding/json. Next, generate the code:

protoc --go_out=. --go-json_out=. request.proto

Your output should contain a file request.pb.json.go which contains the implementation of json.Marshal/Unmarshal for all your message types. You can then encode your messages using standard encoding/json:

import "encoding/json"

// Marshal
bs, err := json.Marshal(&Request{
  Kind: &Kind_Name{
    Name: "alice",
  },
}

// Unmarshal
var result Request
json.Unmarshal(bs, &result)

Options

The generator supports options has same meaning as protojson supports.

Marshal Options

  • marshal_allow_partial - allow messages that have missing required fields to marshal without returning an error. If AllowPartial is false (the default), Marshal will return error if there are any missing required fields.
  • marshal_use_proto_names - use proto field name instead of lowerCamelCase name in JSON field names.
  • marshal_use_enum_numbers - emits enum values as numbers
  • marshal_emit_unpopulated - specifies whether to emit unpopulated fields. It does not emit unpopulated oneof fields or unpopulated extension fields.
  • marshal_emit_default_values - specifies whether to emit default-valued primitive fields, empty lists, and empty maps.

Unmarshal Options

  • unmarshal_allow_partial - if AllowPartial is set, input for messages that will result in missing required fields will not return an error.
  • unmarshal_discard_unknown - if DiscardUnknown is set, unknown fields are ignored.

Standard Options

It also includes the "standard" options available to all protogen-based plugins:

  • import_path={path} - Override the import path
  • paths=source_relative - Derive the output path from the input path
  • etc.

Using With protoc

These can be set as part of the --go-json_out value:

protoc --go-json_opt=emit_defaults=true:.

You can specify multiple using a ,:

protoc --go-json_out=enums_as_ints=true,emit_defaults=true:.

Alternatively, you may also specify options using the --go-json_opt value:

protoc --go-json_out:. --go-json_opt=emit_defaults=true,enums_as_ints=true