🔧 chore(chat.py): add SSE support to post_build endpoint

✨ feat(chat.py): add SSE support to post_build endpoint to stream build progress to the client
The post_build endpoint now returns a StreamingResponse object that streams Server-Sent Events (SSE) to the client. This allows the client to receive build progress updates in real-time. The event_stream function is responsible for generating the SSE events and is called by the StreamingResponse object. The SSE events contain information about the build progress, including whether the build was successful or not, the parameters used to build each node, and the node ID. The chat_manager.set_cache method is called to cache the built graph object.

src/backend/langflow/api/v1/chat.py

@@ -1,3 +1,4 @@
+import json
 from fastapi import (
     APIRouter,
     HTTPException,
@@ -6,8 +7,10 @@ from fastapi import (
     WebSocketException,
     status,
 )
+from fastapi.responses import StreamingResponse
 
 from langflow.chat.manager import ChatManager
+from langflow.graph.graph.base import Graph
 from langflow.utils.logger import logger
 
 router = APIRouter()
@@ -27,12 +30,34 @@ async def websocket_endpoint(client_id: str, websocket: WebSocket):
         await websocket.close(code=status.WS_1000_NORMAL_CLOSURE, reason=str(exc))
 
 
-@router.post("/build/{client_id}")
+@router.post("/build/{client_id}", response_class=StreamingResponse)
 async def post_build(client_id: str, graph_data: dict):
     """Build langchain object from data_graph."""
-    try:
-        if chat_manager.build(client_id, graph_data.get("data")):
-            return {"message": "Build successful"}
-    except Exception as exc:
-        logger.exception(exc)
-        raise HTTPException(status_code=500, detail=str(exc)) from exc
+
+    async def event_stream(graph_data):
+        try:
+            graph_data = graph_data.get("data")
+            if not graph_data:
+                raise HTTPException(status_code=400, detail="No data provided")
+
+            logger.debug("Building langchain object")
+            graph = Graph.from_payload(graph_data)
+            for node in graph.generator_build():
+                logger.debug(f"Building node {node.name}")
+                response = json.dumps(
+                    {
+                        "valid": True,
+                        "params": str(node._built_object_repr()),
+                        "id": node.id,
+                    }
+                )
+                yield f"data: {response}\n\n"  # SSE format
+
+            chat_manager.set_cache(client_id, graph.build())
+
+        except Exception as exc:
+            logger.exception(exc)
+            error_response = json.dumps({"error": str(exc)})
+            yield f"data: {error_response}\n\n"  # SSE format
+
+    return StreamingResponse(event_stream(graph_data), media_type="text/event-stream")