What are protoc plugins?

Once again, before diving into the actual code of the plugin, let us try to understand what protoc plugins are and what they do.

As we saw in the section on custom options, protoc plugins and custom options are generally used together. The custom options provide contextual information, and the plugin gets that information and acts on it. This action, more often than not, is a generation of some sort of code. We have already discussed protovalidate and gRPC-Gateway generating some code that can be used in your business logic.

Even though, in this section, we are going to generate code, it is important to understand that protoc plugins can do other things than generate code.

You can also, for example, generate documentation following the OpenAPI specification with the protoc-gen-openapiv2 provided by gRPC-Gateway. Let’s say you have the following schema:

syntax = "proto3";
import "google/api/annotations.proto";
import "...