gRPC Contract Design

In a REST API, a caller can read the documentation and try an operation with an ordinary HTTP client. In gRPC the contract starts somewhere else: one schema file, from which both the client and the server generate code.

The notation changes, but the design questions remain. Define the clients, operations, field meanings, errors, retries, deadlines, and compatibility rules.

The most permanent decision here is not the method name. It is the number beside each field.

1. The Schema Is the Contract

A gRPC contract is usually written in a .proto file.

syntax = "proto3";