Part 2
3 chapters
Protocol Buffers: the Contract Language
Model the shipping domain in protobuf and make it the Buf-enforced single source of truth both stacks generate from.
Chapter 3
Protocol Buffers in depth
The proto3 language in full: scalars, messages, enums, oneof, map, packages, options, field presence, and the tag-number math that turns a message into bytes.
Chapter 4
Well-known types and JSON mapping
Timestamp, Duration, FieldMask, Any, Struct, and the wrapper types, plus the canonical proto3-to-JSON mapping that renders them at the REST and grpcurl edges.
Chapter 5
Contract-first with Buf
Gate the shipping proto with buf lint, buf build, and buf breaking, generate stubs on both stacks, and serve RoutingService.GetQuote end to end, traced.