Chapter 28: gRPC Internals — The Wire Protocol
gRPC Message Framing
Each gRPC message on the wire is prefixed with a 5-byte header:
// Length-Prefixed Message format:
┌──────────────┬────────────────────────┐
│ Compressed │ Message Length │
│ (1 byte) │ (4 bytes, BE) │
├──────────────┴────────────────────────┤
│ Protobuf-encoded message │
│ (Message Length bytes) │
└────────────────────────────────────────┘
// Example: 10-byte protobuf message, uncompressed:
00 00 00 00 0A [10 bytes of protobuf data]HTTP/2 Mapping
// Request:
:method: POST
:path: /package.Service/Method
:authority: server:port
content-type: application/grpc
te: trailers
grpc-timeout: 5S
// Response trailers (AFTER body):
grpc-status: 0
grpc-message: (empty for success)Compression
// gRPC supports per-message compression:
// Compressed byte = 1 → message is gzip/deflate compressed
// Negotiated via grpc-accept-encoding header
// Useful for large messages, adds CPU overhead for small ones