HTTP/2 and Protocol Buffers

Binary messages over multiplexed streams

gRPC runs over HTTP/2, which multiplexes many concurrent calls over one TCP connection, compresses headers, and supports streaming in both directions. Messages are encoded with Protocol Buffers (protobuf), a compact binary format that is smaller and faster to parse than JSON and is generated from the schema. Each call maps to an HTTP/2 request: the path is /package.Service/Method, metadata travels as headers, and the status is sent in trailers.

One unary call on the wire

Simplified view of the HTTP/2 frames.

HEADERS  :method POST
         :path /shop.v1.OrderService/GetOrder
         content-type: application/grpc
         grpc-timeout: 2S
         authorization: Bearer <token>
DATA     <5-byte prefix: compressed flag + length><protobuf-encoded GetOrderRequest>

<- HEADERS :status 200, content-type: application/grpc
<- DATA    <prefix><protobuf-encoded Order>
<- TRAILERS grpc-status: 0  (OK)

Reuse channels

Creating a channel (connection) per call wastes the main benefit of HTTP/2; create channels once and share them.

Quick check: Where does gRPC send the final status of a call?

• In HTTP/2 trailers (grpc-status)
• In the URL
• In the first request header only
• In a separate TCP connection