feat: exception and error middleware (langflow-ai#2590)

exception and error middleware

src/backend/base/langflow/main.py

@@ -7,10 +7,11 @@
 from urllib.parse import urlencode
 
 import nest_asyncio  # type: ignore
-from fastapi import FastAPI, Request, Response
+from fastapi import FastAPI, Request, Response, HTTPException
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import FileResponse
+from fastapi.responses import FileResponse, JSONResponse
 from fastapi.staticfiles import StaticFiles
+from http import HTTPStatus
 from loguru import logger
 from pydantic import PydanticDeprecatedSince20
 from rich import print as rprint
@@ -158,6 +159,21 @@ async def flatten_query_string_lists(request: Request, call_next):
     app.include_router(router)
     app.include_router(health_check_router)
 
+    @app.exception_handler(Exception)
+    async def exception_handler(request: Request, exc: Exception):
+        if isinstance(exc, HTTPException):
+            logger.error(f"HTTPException: {exc.detail}")
+            return JSONResponse(
+                status_code=exc.status_code,
+                content={"message": str(exc.detail)},
+            )
+        else:
+            logger.error(f"unhandled error: {exc}")
+            return JSONResponse(
+                status_code=HTTPStatus.INTERNAL_SERVER_ERROR,
+                content={"message": str(exc)},
+            )
+
     FastAPIInstrumentor.instrument_app(app)
 
     return app