gRPC & Streaming

Remote calls as HTTP/2 streams: unary, server streaming, and the head-of-line blocking gRPC inherits from TCP.

An interactive Networking lesson: 18 steps, about 32 minutes, on a live simulation in your browser.

The shop's page is assembled from small services: the cart, the price, the stock count, the user. Each one is a tiny question with a tiny answer, asked thousands of times a second between programs that trust each other.

REST can do this: one HTTP request per question, text JSON back. But every call pays for text headers, text bodies, and a request-response pattern that only ever carries one answer. For service-to-service chatter that is a lot of packaging for very little content.

What you will learn

1. Many small calls

   • Death by a thousand calls: gRPC is remote procedure calls on HTTP/2 streams: function calls in code, numbered frames on the wire.
   • The contract comes first: In gRPC the .proto file is the contract: both sides generate their code from it, so drift becomes a compile error.

2. Unary: one stream

   • One call, one stream: A unary call is one HTTP/2 stream: one request out, one response back, multiplexed with everything else on the connection.
   • The second call is cheap: New calls on an open HTTP/2 connection cost no handshake: each one is the next odd-numbered stream.
   • Binary on the wire: Every gRPC message wears a 5-byte header, 1 flag byte plus 4 length bytes, then that many bytes of protobuf.

3. Streaming patterns

   • Four patterns, one idea: Unary, server, client and bidirectional streaming differ only in who sends how many messages on one stream.
   • One request, many responses: Server streaming is one request opening a stream that many responses share, until the server closes it.
   • The mirror image, honestly: Client streaming is server streaming with the direction flipped; bidirectional lets both sides send whenever they like.

4. The honest limitation

   • Break it: lose one segment
   • TCP knows no streams: gRPC inherits TCP head-of-line blocking: one lost segment stalls every call sharing the connection.

5. Deadlines and operations

   • A call with a deadline: A deadline is a client-side budget: past it, the call is abandoned no matter how close the answer is.
   • Status codes and safe retries: The status code decides the retry: UNAVAILABLE may repeat, and only calls safe to run twice actually do.
   • Drill: list the services
   • Drill: force HTTP/2
   • Break it: the server stops
   • When gRPC fits: gRPC fits services talking to services. Browsers get REST, grpc-web, or a translating gateway.

6. Recap & playground

   • Cheat sheet
   • Playground