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protoc-gen-gotag (PGGT)

PGGT is a protoc plugin used to add/replace struct tags on generated protobuf messages.

The project maintenance and evolution has been embraced by @ucpr, @mesmerx and @Kavuti.

Get it using

go install github.com/srikrsna/protoc-gen-gotag@latest

It supports the following features,

Add/Replace Tags

New tags like xml, sql, bson etc... can be added to struct messages of protobuf. Example

syntax = "proto3";

package example;

import "tagger/tagger.proto";

message Example {
    string with_new_tags = 1 [(tagger.tags) = "graphql:\"withNewTags,optional\"" ];
    string with_new_multiple = 2 [(tagger.tags) = "graphql:\"withNewTags,optional\" xml:\"multi,omitempty\"" ];
    
    string replace_default = 3 [(tagger.tags) = "json:\"replacePrevious\""] ; 

    oneof one_of {
        option (tagger.oneof_tags) = "graphql:\"withNewTags,optional\"";
        string a = 5 [(tagger.tags) = "json:\"A\""];
        int32 b_jk = 6 [(tagger.tags) = "json:\"b_Jk\""];
    }
}

message SecondMessage {
    string with_new_tags = 1 [(tagger.tags) = "graphql:\"withNewTags,optional\"" ];
    string with_new_multiple = 2 [(tagger.tags) = "graphql:\"withNewTags,optional\" xml:\"multi,omitempty\"" ];
    
    string replace_default = 3 [(tagger.tags) = "json:\"replacePrevious\""] ; 
}

Then struct tags can be added by running this command after the regular protobuf generation command.

protoc -I /usr/local/include \
    -I . \
    --gotag_out=:. example/example.proto

In the above example tags like graphql and xml will be added whereas existing tags such as json are replaced with the supplied values.

Auto add tags on field

Automatically add custom tags to message field using provided transformer. It will compile the tag as tag:"snaked_key_name" by default if no transformer is being provide. To provide transformer, use: tagName-as-transformer instruction when running gotag

protoc -I /usr/local/include \
    -I . \
    --gotag_out=auto="form+db-as-camel":. example/example.proto

The above command will add two addtional tags (form and db) for each field. The form tag will be lower_snake_case and db tag will be lowerCamelCase

Supported transformers:

Keys Action Ex
"lower_snake", "lower_snake_case", "snake", "snake_case" Make lower snake case key someKey -> some_key
"upper_snake", "upper_snake_case" Make upper snake case key someKey -> Some_key
"lower_camel", "lower_camel_case", "camel", "camel_case" Make lower camel case key someKey -> someKey
"upper_camel", "upper_camel_case" Make upper camel case key someKey -> SomeKey
"dot_notation", "dot", "lower_dot_notation", "lower_dot" Make lower cased dot notation key someKey -> some.key
"upper_dot", "upper_dot_notation" Make upper cased dot notation key someKey -> Some.Key

Add tags to XXX* fields

It is very useful to ignore XXX* fields in protobuf generated messages. The go protocol buffer compiler adds json:"-" tag to all XXX* fields. Additional tags can be added to these fields using the 'xxx' option of PGGT. It can be done like this. All '+' characters will be replaced with ':'.

protoc -I /usr/local/include \
    -I . \
    --gotag_out=xxx="graphql+\"-\" bson+\"-\"":. example/example.proto

Output to a directory other than the current directory

When outputting to a directory other than the current directory, you will need to pass the output path twice using the "outdir" parameter. If you experience any no such file or directory, errors, try adding the "outdir" flag.

protoc -I /usr/local/include \
   -I ./pkg \
   --gotag_out=outdir="./pkg":./pkg example/example.proto

Note

This should always run after protocol buffer compiler has run. The command such as the one below will fail/produce unexpected results.

protoc -I /usr/local/include \
    -I . \
    --go_out=:. \
    --gotag_out=xxx="graphql+\"-\" bson+\"-\"":. example/example.proto