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protoc-go-inject-tag

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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 install github.com/favadi/protoc-go-inject-tag@latest 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
  -remove_tag_comment
        removes tag comments from the generated file(s)

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"`
}

Remove gotag comments from generated output

Utilizing the -remove_tag_comment flag, you can remove the gotag comment that is normally annotated to the generated code. This allows more seamless support with libraries like swag/openapi generators that use code comments to generate openapi files.

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.