Code Generation

protoc reads .proto files and generates language-specific code.

protoc --python_out=. --go_out=. --java_out=. user.proto

Generated Python:

Generated Go:

The generated code is large but fast: hand-written serialization for known schemas.

Plugins:

• protoc-gen-go: standard Go.
• protoc-gen-go-grpc: Go gRPC stubs.
• protoc-gen-doc: documentation.
• protoc-gen-validate: runtime validation.
• protoc-gen-openapi: REST/OpenAPI from proto.

Modern tools:

• buf: protobuf compiler + linter + formatter, faster than protoc.
• buf.gen.yaml: declarative generation config.
• Connect-RPC: REST-friendly gRPC alternative.

Build integration:

• Bazel: protoc rules.
• gradle/Maven: protoc plugin.
• Make/CMake: custom rules.
• Pre-commit: regenerate on proto change.

Reflection:

• protobuf can describe itself (FileDescriptor).
• Used by gRPC reflection (reflection.proto).
• grpcurl queries gRPC server's schema dynamically.

JSON mapping:

• Each proto type has canonical JSON form.
• For interop with non-proto consumers.
• google.protobuf.json_format.MessageToJson / Parse.