A very simple protobuf plugin, using @bufbuild/protoplugin

buf.gen.yaml

version: v1
plugins:
  - name: foo
    path: ./protoc-gen-foo.ts
    out: gen
    opt: target=ts

# run `buf generate` to generate code for example.proto

example.proto

syntax="proto3";

message Foo {
  string foo = 1;
  bool bar = 2;
}

package.json

{
  "name": "pluginfoo",
  "version": "1.0.0",
  "dependencies": {
    "@bufbuild/protoplugin": "0.1.1",
    "tsx": "^3.10.1"
  }
}

protoc-gen-foo.ts

#!/usr/bin/env npx tsx

// make sure to make this file executable with `chmod +x protoc-gen-foo.ts`

import {createEcmaScriptPlugin, runNodeJs} from "@bufbuild/protoplugin";

const plugin = createEcmaScriptPlugin({name: "foo", version: "0.0.1"},
  schema => {
    for (const file of schema.files) {
        const openApi = {
            messages: [],
        };
        for (const message of file.messages) {
            openApi.messages.push(message.proto.toJson());
        }
        const f = schema.generateFile(file.name + "_openapi.json");
        f.print(JSON.stringify(openApi));
    }
});

runNodeJs(plugin);