🐛 fix(main.py): add a custom 404 handler to return the index.html file when a 404 error occurs

The create_app function now accepts a static_path parameter that defaults to "static". The setup_static_files function is created to mount the static files directory to the app. A custom 404 handler is added to the app to return the index.html file when a 404 error occurs. This allows the app to serve static files such as HTML, CSS, and JavaScript files.
🚀 feat(__main__.py, main.py): add support for serving static files
✨ feat(__main__.py): create a setup_static_files function to mount the static files directory to the app

src/backend/langflow/__main__.py

@@ -1,5 +1,6 @@
 import sys
 import time
+from fastapi import FastAPI
 import httpx
 from multiprocess import Process, cpu_count  # type: ignore
 import platform
@@ -145,18 +146,16 @@ def serve(
     update_settings(
         config, dev=dev, database_url=database_url, remove_api_keys=remove_api_keys
     )
-    app = create_app()
     # get the directory of the current file
     if not path:
         frontend_path = Path(__file__).parent
         static_files_dir = frontend_path / "frontend"
     else:
         static_files_dir = Path(path)
-    app.mount(
-        "/",
-        StaticFiles(directory=static_files_dir, html=True),
-        name="static",
-    )
+
+    app = create_app(static_files_dir)
+    setup_static_files(app, static_files_dir)
+
     options = {
         "bind": f"{host}:{port}",
         "workers": get_number_of_workers(workers),
@@ -180,6 +179,21 @@ def serve(
         webbrowser.open(f"http://{host}:{port}")
 
 
+def setup_static_files(app: FastAPI, static_files_dir: str):
+    """
+    Setup the static files directory.
+
+    Args:
+        app (FastAPI): FastAPI app.
+        path (str): Path to the static files directory.
+    """
+    app.mount(
+        "/",
+        StaticFiles(directory=static_files_dir, html=True),
+        name="static",
+    )
+
+
 def print_banner(host, port):
     # console = Console()
 

src/backend/langflow/main.py

@@ -1,11 +1,12 @@
 from fastapi import FastAPI
+from fastapi.responses import FileResponse
 from fastapi.middleware.cors import CORSMiddleware
 
 from langflow.api import router
 from langflow.database.base import create_db_and_tables
 
 
-def create_app():
+def create_app(static_path: str = "static"):
     """Create the FastAPI app and include the router."""
     app = FastAPI()
 
@@ -17,6 +18,10 @@ def create_app():
     def get_health():
         return {"status": "OK"}
 
+    @app.exception_handler(404)
+    async def custom_404_handler(request, __):
+        return FileResponse(f"{static_path}/index.html")
+
     app.add_middleware(
         CORSMiddleware,
         allow_origins=origins,