Custom Struct Tags

Introduction

By default, the golang code generated from an IDL will have thrift, frugal, and json tags.

When an annotation go.tag = "xxx" is added after a field definition in the IDL, the corresponding content will be used as the tags for the corresponding field in the Go struct.

Usage Instructions

When the following struct is defined in the IDL (note the use of \ for escaping):

struct foo {
  1: required string Bar (go.tag = "some_tag:\"some_tag_value\"")
}

The generated Go struct will be:

type Foo struct {
  Bar string `thrift:"bar,1,required" frugal:"1,required,string" some_tag:"some_tag_value"`
}

As you can see, the original thrift tag and frugal tag still exist, but other tags (especially the JSON tag) have been replaced with the content specified in the go.tag.

Notes

Custom Tags Override the Default JSON Tag

The JSON tag is a default tag, and once a custom tag is specified using go.tag, the original JSON tag will no longer be generated.

Solution:

• Upgrade thriftgo to version >=0.2.10 and use the -thrift always_gen_json_tag flag when running kitex.

  # Upgrade thriftgo
  go install github.com/cloudwego/thriftgo@latest
  
  # Regenerate with the argument
  kitex -thrift always_gen_json_tag -module $mod -service $svc xxx.thrift
  

• Include the desired JSON tag in the go.tag. For example:

  // You can copy the previously generated JSON tag (note the escaping)
  struct foo {
    1: required string Bar (go.tag = "json=\"Bar,omitempty\" some_tag:\"xxx\"")
  }