fix: make serialization errors in component update show up in the UI (#5332)

* feat: Add SerializationError exception for improved error handling during data serialization

- Introduced a new SerializationError class to handle errors when serializing data to JSON.
- The class provides detailed error messages based on the type of serialization issue encountered, including async function handling and unsupported object types.
- Enhances the robustness of the application by providing clearer feedback for serialization-related errors.

* fix: Improve error handling in custom component update to include SerializationError

src/backend/base/langflow/api/v1/endpoints.py

@@ -7,16 +7,8 @@ from typing import TYPE_CHECKING, Annotated
 from uuid import UUID
 
 import sqlalchemy as sa
-from fastapi import (
-    APIRouter,
-    BackgroundTasks,
-    Body,
-    Depends,
-    HTTPException,
-    Request,
-    UploadFile,
-    status,
-)
+from fastapi import APIRouter, BackgroundTasks, Body, Depends, HTTPException, Request, UploadFile, status
+from fastapi.encoders import jsonable_encoder
 from loguru import logger
 from sqlmodel import select
 
@@ -35,6 +27,7 @@ from langflow.api.v1.schemas import (
 from langflow.custom.custom_component.component import Component
 from langflow.custom.utils import build_custom_component_template, get_instance_name, update_component_build_config
 from langflow.exceptions.api import APIException, InvalidChatInputError
+from langflow.exceptions.serialization import SerializationError
 from langflow.graph.graph.base import Graph
 from langflow.graph.schema import RunOutputs
 from langflow.helpers.flow import get_flow_by_id_or_endpoint_name
@@ -46,9 +39,7 @@ from langflow.services.auth.utils import api_key_security, get_current_active_us
 from langflow.services.cache.utils import save_uploaded_file
 from langflow.services.database.models.flow import Flow
 from langflow.services.database.models.flow.model import FlowRead
-from langflow.services.database.models.flow.utils import (
-    get_all_webhook_components_in_flow,
-)
+from langflow.services.database.models.flow.utils import get_all_webhook_components_in_flow
 from langflow.services.database.models.user.model import User, UserRead
 from langflow.services.deps import get_session_service, get_settings_service, get_task_service, get_telemetry_service
 from langflow.services.settings.feature_flags import FEATURE_FLAGS
@@ -605,6 +596,9 @@ async def custom_component_update(
     Returns:
         dict: The updated custom component node.
 
+    Raises:
+        HTTPException: If there's an error building or updating the component
+        SerializationError: If there's an error serializing the component to JSON
     """
     try:
         component = Component(_code=code_request.code)
@@ -649,7 +643,11 @@ async def custom_component_update(
 
     except Exception as exc:
         raise HTTPException(status_code=400, detail=str(exc)) from exc
-    return component_node
+
+    try:
+        return jsonable_encoder(component_node)
+    except Exception as exc:
+        raise SerializationError.from_exception(exc, data=component_node) from exc
 
 
 @router.get("/config", response_model=ConfigResponse)

src/backend/base/langflow/exceptions/serialization.py

@@ -0,0 +1,56 @@
+from typing import Any
+
+from fastapi import HTTPException, status
+
+
+class SerializationError(HTTPException):
+    """Exception raised when there are errors serializing data to JSON."""
+
+    def __init__(
+        self,
+        detail: str,
+        original_error: Exception | None = None,
+        data: Any = None,
+        status_code: int = status.HTTP_500_INTERNAL_SERVER_ERROR,
+    ) -> None:
+        super().__init__(status_code=status_code, detail=detail)
+        self.original_error = original_error
+        self.data = data
+
+    @classmethod
+    def from_exception(cls, exc: Exception, data: Any = None) -> "SerializationError":
+        """Create a SerializationError from an existing exception."""
+        errors = exc.args[0] if exc.args else []
+
+        if isinstance(errors, list):
+            for error in errors:
+                if isinstance(error, TypeError):
+                    if "'coroutine'" in str(error):
+                        return cls(
+                            detail=(
+                                "The component contains async functions that need to be awaited. Please add 'await' "
+                                "before any async function calls in your component code."
+                            ),
+                            original_error=exc,
+                            data=data,
+                        )
+                    if "vars()" in str(error):
+                        return cls(
+                            detail=(
+                                "The component contains objects that cannot be converted to JSON. Please ensure all "
+                                "properties and return values in your component are basic Python types like strings, "
+                                "numbers, lists, or dictionaries."
+                            ),
+                            original_error=exc,
+                            data=data,
+                        )
+
+        # Generic error for other cases
+        return cls(
+            detail=(
+                "The component returned invalid data. Please check that all values in your component (properties, "
+                "return values, etc.) are basic Python types that can be converted to JSON."
+            ),
+            original_error=exc,
+            data=data,
+        )