gRPC

gRPC is an RPC framework on top of protobuf + HTTP/2.

Service definition:

syntax = "proto3";

service UserService {
    rpc GetUser (GetUserRequest) returns (User);
    rpc CreateUser (CreateUserRequest) returns (User);
    rpc ListUsers (ListUsersRequest) returns (stream User);
    rpc UpdateUsers (stream UpdateUsersRequest) returns (UpdateUsersResponse);
    rpc Chat (stream ChatMessage) returns (stream ChatMessage);
}

4 RPC types:

1. Unary: 1 req → 1 resp.
2. Server streaming: 1 req → N resp.
3. Client streaming: N req → 1 resp.
4. Bidirectional streaming: N req ↔ N resp.

Generated code: stubs (client + server).

HTTP/2:

• Multiplexed: many RPCs over one connection.
• Bidi streams.
• Header compression (HPACK).
• Long-lived connections.

vs REST:

• Faster (binary, multiplex).
• Strict schema.
• Streaming native.
• Browser support poor (need gRPC-Web).
• Cross-org adoption: REST often easier.

Auth:

• TLS standard.
• Per-call metadata for auth tokens.
• mTLS for service-to-service.

Errors:

• Status codes: OK, INVALID_ARGUMENT, NOT_FOUND, INTERNAL, etc.
• Status details (proto): structured error info.

Deadlines:

• Per-RPC timeout.
• Propagated through call chain.
• Cancellation cascades.

Production gRPC:

• Used heavily in microservices (Google, Uber, Square).
• Service mesh integration (Envoy proxy).
• Observability: OpenTelemetry hooks.

Alternatives:

• REST + JSON: ubiquitous.
• Connect: gRPC + REST interop.
• GraphQL: query language; different abstraction.
• Twirp: simpler RPC over HTTP/1.1 + protobuf.