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gRPC & High Performance APIs · Lesson

Streaming RPCs: Server, Client & Bidirectional

Go beyond unary calls and learn gRPC's three streaming modes for sending sequences of messages over a single call.

Streaming RPCs: Server, Client & Bidirectional is a free gRPC & High Performance APIs lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the gRPC & High Performance APIs learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Beyond Unary

A unary RPC is one request, one response. But many problems need a sequence of messages — feeds, uploads, chat.

gRPC offers three streaming modes built on HTTP/2 streams.

The Four Method Shapes

In a .proto service you can declare:

  • Unary: one in, one out.
  • Server streaming: one in, many out.
  • Client streaming: many in, one out.
  • Bidirectional: many in, many out.

Declaring Streams in Proto

The stream keyword marks a parameter as a stream.

service Feed {
  rpc Watch (WatchRequest) returns (stream Event);
  rpc Upload (stream Chunk) returns (UploadResult);
  rpc Chat (stream Message) returns (stream Message);
}

Server Streaming

The client sends one request; the server replies with many messages until it closes the stream.

Great for: live feeds, large result sets, progress updates.

// Server side (Go-style pseudocode)
func (s *server) Watch(req *WatchRequest, stream Feed_WatchServer) error {
  for _, e := range events {
    stream.Send(e)
  }
  return nil
}

Client Streaming

The client sends many messages, then the server returns a single response.

Great for: file uploads, batched ingestion, aggregations.

// Server reads the whole client stream, then replies once
func (s *server) Upload(stream Feed_UploadServer) error {
  for {
    chunk, err := stream.Recv()
    if err == io.EOF {
      return stream.SendAndClose(&UploadResult{})
    }
  }
}

Bidirectional Streaming

Both sides send streams independently over the same call. Messages can interleave freely.

Great for: chat, real-time collaboration, interactive protocols.

Why It's Efficient

All four shapes ride a single HTTP/2 stream — no new connection per message.

Multiplexing means many streaming calls share one connection without head-of-line blocking.

Flow Control

HTTP/2 provides built-in flow control, so a slow reader naturally backpressures a fast writer.

This prevents a streaming server from overwhelming a client that can't keep up.

Ending a Stream

Streams close explicitly:

  • Server streaming ends when the server returns.
  • Client streaming ends when the client signals end-of-stream and the server replies.
  • Bidirectional ends when both halves complete or an error/cancel occurs.

Errors & Cancellation

Either side can cancel or fail mid-stream. The peer receives a status code and should clean up.

Always handle EOF and error returns from Recv() / Send() to avoid leaks.

Choosing a Mode

Pick by data shape:

  • One-shot request/response: unary.
  • Push many results: server streaming.
  • Send many, get a summary: client streaming.
  • Continuous two-way: bidirectional.

Quick Check

Test your understanding of streaming RPCs.

Recap

You learned gRPC's streaming modes.

  • Unary, server streaming, client streaming, and bidirectional.
  • Mark streams with the stream keyword in proto.
  • All ride a single multiplexed HTTP/2 stream with built-in flow control.
  • Choose the mode that matches your data's shape.

Frequently asked questions

Is the “Streaming RPCs: Server, Client & Bidirectional” lesson free?

Yes — the full text of “Streaming RPCs: Server, Client & Bidirectional” is free to read here on the web, and the gRPC & High Performance APIs course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the gRPC & High Performance APIs course, upgrade to CoddyKit PRO.

What will I learn in “Streaming RPCs: Server, Client & Bidirectional”?

Go beyond unary calls and learn gRPC's three streaming modes for sending sequences of messages over a single call. You practise gRPC & High Performance APIs with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start gRPC & High Performance APIs?

No prior experience is required. gRPC & High Performance APIs on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Streaming RPCs: Server, Client & Bidirectional” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this gRPC & High Performance APIs lesson?

Yes. Every gRPC & High Performance APIs lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Protobuf Schema Definition
  2. Generating gRPC Code
  3. Simple Unary gRPC Service
  4. Streaming RPCs: Server, Client & Bidirectional
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