How to stream from specific nodes? langgraph_node metadata missing

[octadion]

Hello!
I'm struggling to implement node-specific streaming based on the docs at https://langchain-ai.github.io/langgraph/how-tos/streaming-specific-nodes/
The docs say I should use stream_mode="messages" and filter by metadata["langgraph_node"], but I'm not seeing any langgraph_node field in my streamed events. I've tried examining the full event structure and there's no node metadata anywhere.

    event_type, event_data = event if isinstance(event, tuple) else (None, event)
    if event_type == "messages":
        # No langgraph_node metadata found here
        print(message_data.get('metadata', {}))

Has the API changed? What's the current way to stream from just one specific node?
Thanks!

[octadion]

@dosu ?

[octadion]

found it

[junzheng-wu-whitehorse]

would you mind sharing?

[octadion]

Hi @junzheng-wu-whitehorse,

to stream from a specific node:

1. get the node name for each message:
   For stream_mode="messages": current_node = stream_metadata.get("langgraph_node")
   For stream_mode=["values", "messages"] (when type is 'messages'): current_node = values[1].get("langgraph_node")

2. filter the stream:

TARGET_NODE = "your_specific_node_name"
# ... (inside your stream loop)
if current_node == TARGET_NODE:
    # Yield or process the message from this specific node
    yield stream_format("messages", msg_content) # Or similar

This way, you first identify the source node of a message and then decide if you want to stream it based on whether it's your target node.

[junzheng-wu-whitehorse]

Thanks a lot! Figured that out too