Protocolbuffers

Protocol Buffers, commonly referred to as protobuf, is a language-neutral, platform-neutral data serialization format developed by Google. It provides a compact binary representation of structured data and is designed for high performance and forward/backward compatibility. It is defined by a .proto schema file that describes the data structures and service interfaces.

A schema defines message types with fields assigned unique numeric tags. Each field has a type (such as int32, string, bool, bytes, or a nested message), a label (optional, repeated, or required in proto2), and a field number. The compiler generates source code in various languages to parse and construct messages.

Protobuf supports maps, enumerations, and nested message types. Proto3 simplifies the syntax by removing required fields, making fields optional by default, and not supporting extensions. It introduces oneof for mutually exclusive fields and map fields for associative arrays.

The binary wire format uses varint encoding and field tags to achieve compact size and fast parsing. The format is designed to be backward and forward compatible: unknown fields are ignored on parsing but can be preserved in some implementations, and new fields can be added with new numbers.

Protobuf is typically used with the protoc compiler to generate code in languages such as C++, Java, Python, Go, C#, Ruby, and JavaScript. It is widely used with gRPC, a high-performance RPC framework that uses protobuf to define service interfaces and payloads.

Advantages include compactness, speed, and strong typing; limitations include lack of self-describing data and potential schema drift if field numbers are reused. Alternatives include JSON-based formats or other IDL-based systems like FlatBuffers or Cap'n Proto.