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Tutorial 3: Streaming Review

Subcommand: tutorial streaming-review Source: src/go/cmd/tutorial/streamingreview.go

What You Will Learn

  • How to enable streaming with Streaming: copilot.Bool(true)
  • How to consume streaming tokens via AssistantMessageDeltaData
  • How to print a response incrementally as it is generated
  • How to feed the model a unified diff read from a file or a built-in sample

Prerequisites

Step 1 — Enable streaming on the session

Streaming is a session-level setting. With Streaming: copilot.Bool(true), the runtime emits assistant.message_delta events as the response is generated instead of delivering it all at once:

session, err := client.CreateSession(ctx, &copilot.SessionConfig{
    OnPermissionRequest: copilot.PermissionHandler.ApproveAll,
    Streaming:           copilot.Bool(true), // ← streaming enabled
    SystemMessage: &copilot.SystemMessageConfig{
        Mode: "replace",
        Content: "You are a senior software engineer conducting a thorough code review. " +
            "For each change in the diff: identify bugs, security issues, and style problems. " +
            "Be concise but precise. Use Markdown formatting.",
    },
})

Step 2 — Print delta tokens as they arrive

Each AssistantMessageDeltaData event carries a DeltaContent fragment. Print it without a trailing newline so the output reads as continuous text:

session.On(func(event copilot.SessionEvent) {
    switch data := event.Data.(type) {
    case *copilot.AssistantMessageDeltaData:
        fmt.Print(data.DeltaContent)
    case *copilot.SessionErrorData:
        fmt.Fprintf(os.Stderr, "\n[Error] %s\n", data.Message)
    }
})

Note: With streaming enabled, the complete message still arrives as AssistantMessageData at the end of the turn. Use the deltas for live output and the full message when you need the final text in one piece.

Step 3 — Send the diff and wait for completion

Embed the diff in the prompt inside a fenced code block. SendPromptAndWait blocks until the session is idle; by then every delta has already been printed by the handler:

prompt := fmt.Sprintf("Please review the following diff and provide feedback:\n\n```diff\n%s\n```", diffText)
if _, err := session.SendPromptAndWait(ctx, prompt); err != nil {
    return err
}
fmt.Println("\n\n=== Review Complete ===")

The subcommand reviews a built-in sample diff by default. Pass --diff <path> to review your own unified diff; the file is read with os.ReadFile before the session starts.

Run the Subcommand

Build the CLI first, then run the streaming-review subcommand from the src/go directory:

cd src/go
make build

# Review the built-in sample diff
./dist/template-github-copilot-go tutorial streaming-review

# Review your own unified diff
git diff > /tmp/changes.diff
./dist/template-github-copilot-go tutorial streaming-review --diff /tmp/changes.diff

Flags

Flag Shorthand Default Description
--diff -d (empty) Path to a unified diff file (uses the built-in sample if not provided)
--cli-url -c (empty) Optional Copilot CLI server URL (e.g. localhost:3000)

The global --verbose/-v flag lowers the log level to DEBUG, surfacing the client connection mode and session lifecycle.

Next Steps