streaming_modes

Streaming Modes Example

Background

For long-running LLM chains or complex agent workflows, waiting for the final result is often unacceptable. Users expect real-time feedback. LangGraph Go supports a robust streaming architecture that allows you to subscribe to events as they happen. Different use cases require different "views" of the stream—sometimes you want every token, sometimes just the final output of each node. Streaming Modes allow you to configure this granularity.

Features

• StreamModeUpdates: Emits the output of each node as it completes. Useful for showing progress (e.g., "Step 1 done", "Tool executed").
• StreamModeValues: Emits the full graph state after each step. Useful for debugging or UIs that render the entire context.
• StreamModeMessages: (Planned) Emits LLM tokens for typewriter effects.
• StreamModeDebug: Emits all internal events for deep inspection.

Implementation Principle

The streaming logic is handled by StreamingRunnable in graph/streaming.go.

1. It injects a StreamingListener (which implements GraphCallbackHandler and NodeListener) into the execution context.
2. As the graph executes, nodes and the graph engine emit events (NodeEventComplete, OnGraphStep, etc.).
3. The StreamingListener.shouldEmit method filters these events based on the configured StreamMode.
4. Allowed events are sent to a Go channel returned to the caller.

Code Walkthrough

In main.go:

1. Configuration:

   g.SetStreamConfig(graph.StreamConfig{
       Mode: graph.StreamModeUpdates,
   })
   

   We configure the graph to stream in updates mode.

2. Execution:

   streamResult := runnable.Stream(context.Background(), nil)
   for event := range streamResult.Events { ... }
   

   We iterate over the Events channel.

3. Output: You will see events printed in real-time as step_1 and step_2 complete, rather than waiting for the entire graph to finish.

How to Run

go run main.go