protoc

Protoc, short for Protocol Buffers compiler, is a key component of Google's Protocol Buffers data interchange format. It reads .proto files that define messages, enums, services, and extensions, and generates source code in target languages to serialize, deserialize, and validate the defined data structures.

Protoc works with language-specific code generators, either built into the protoc distribution or provided as plugins. Supported languages include C++, Java, Python, Go, C#, JavaScript, Ruby, PHP, and Dart, among others. In addition to message definitions, protoc can generate gRPC service stubs using the corresponding grpc plugins (for example, protoc-gen-grpc-java). It can also emit descriptor sets that describe the entire schema for use in reflection-based tooling.

Typical usage involves invoking protoc with an input path and language-specific output options. For example, protoc -I=src --cpp_out=build/gen src/person.proto compiles to C++ code; protoc --java_out=build/gen src/person.proto compiles to Java code. You can generate code for multiple files in a single run, supply multiple --proto_path directories, and request additional artifacts such as --descriptor_set_out for a FileDescriptorSet. Plugins can be specified via --plugin to enable alternative code generators or gRPC stubs.

Protoc is distributed as part of the Protocol Buffers project, available as pre-built binaries or source. It is commonly integrated into build systems like Bazel, CMake, Gradle, or Maven. Proto syntax options (proto2 vs proto3) affect field semantics, with proto3 simplifying optional fields and removing required fields, which influences generated code behavior.