protoc-go-inject-tag

protoc-go-inject-tag

Why?

Golang protobuf doesn't support custom tags to generated structs. This tool injects custom tags to generated protobuf files, which is commonly used for validating fields, omitting fields from JSON data, etc.

Install

• protobuf version 3

  For OS X:

  $ brew install protobuf
  

• go support for protobuf: go get -u github.com/golang/protobuf/{proto,protoc-gen-go}

• go get github.com/favadi/protoc-go-inject-tag or download the binaries from the releases page.

Usage

$ protoc-go-inject-tag -h
Usage of protoc-go-inject-tag:
  -XXX_skip string
        tags that should be skipped (applies 'tag:"-"') for unknown fields (deprecated since protoc-gen-go v1.4.0)
  -input string
        pattern to match input file(s)
  -verbose
        verbose logging

Add a comment with the following syntax before fields, and these will be injected into the resulting .pb.go file. This can be specified above the field, or trailing the field.

// @gotags: custom_tag:"custom_value"

Example

// file: test.proto
syntax = "proto3";

package pb;
option go_package = "/pb";

message IP {
  // @gotags: valid:"ip"
  string Address = 1;

  // Or:
  string MAC = 2; // @gotags: validate:"omitempty"
}

Generate your .pb.go files with the protoc command as normal:

$ protoc --proto_path=. --go_out=paths=source_relative:. test.proto

Then run protoc-go-inject-tag against the generated files (e.g test.pb.go):

$ protoc-go-inject-tag -input=./test.pb.go
# or
$ protoc-go-inject-tag -input="*.pb.go"

The custom tags will be injected to test.pb.go:

type IP struct {
	// @gotags: valid:"ip"
	Address string `protobuf:"bytes,1,opt,name=Address,json=address" json:"Address,omitempty" valid:"ip"`
}

Deprecated functionality

Skip XXX_* fields

To skip the tag for the generated XXX_* fields (unknown fields), use the -XXX_skip=yaml,xml flag. This is deprecated, as this functionality hasn't existed in protoc-gen-go since v1.4.x.

inject_tag keyword

Since v1.3.0, we recommend using @gotags: rather than @inject_tags:, as @gotags is more indicative of the language the comment is for. We don't plan on removing @inject_tags: support anytime soon, however we strongly recommend switching to @gotags.