langflow-ai/langflow · error · HTTPException

str(exc)

Error message

str(exc)

What it means

This is the generic str(exc) detail on an HTTP 500 raised by the build-status exception handler in build.py. Any unexpected exception while checking/building the flow (that is not a LocalFileAccessError or a streaming misconfiguration) is re-raised as 500 with the raw exception message, after telemetry logging.

Source

Thrown at src/backend/base/langflow/api/build.py:576

            # We need to get the id of each vertex
            # and return the same structure but only with the ids
            components_count = len(graph.vertices)
            vertices_to_run = list(graph.vertices_to_run.union(get_top_level_vertices(graph, graph.vertices_to_run)))

            await chat_service.set_cache(flow_id_str, graph)
            await log_telemetry(start_time, components_count, run_id=build_run_id, success=True)

        except Exception as exc:
            await log_telemetry(
                start_time,
                components_count,
                run_id=build_run_id,
                success=False,
                error_message=str(exc),
            )

            if isinstance(exc, LocalFileAccessError) or "stream or streaming set to True" in str(exc):
                raise HTTPException(status_code=400, detail=str(exc)) from exc
            await logger.aexception("Error checking build status: " + str(exc))
            raise HTTPException(status_code=500, detail=str(exc)) from exc
        return first_layer, vertices_to_run, graph

    async def log_telemetry(
        start_time: float,
        components_count: int,
        *,
        run_id: str | None = None,
        success: bool,
        error_message: str | None = None,
    ):
        background_tasks.add_task(
            telemetry_service.log_package_playground,
            PlaygroundPayload(
                playground_seconds=int(time.perf_counter() - start_time),
                playground_component_count=components_count,
                playground_success=success,

View on GitHub (pinned to 976ec789d2)

Solutions

1. Read the full str(exc) message — it usually contains the underlying component/stack error
2. Check server logs: the handler calls logger.aexception('Error checking build status: ...') with the traceback
3. Reproduce with the component standalone (LFX_DEV=1 backend + single component) to isolate the failing node
4. If the message mentions streaming, set the chat/Streaming field to True or use the proper streaming input on Chat components

Example fix

// before: LLM node with streaming field left false but connected to a stream-only output
// after: set input_value 'stream or streaming set to True' per the 400 guidance, or fix the node raising the 500
// and inspect server log traceback:
await logger.aexception("Error checking build status: " + str(exc))

try { const res = await buildFlow(flowId) } catch (e) { console.error(e.response?.data?.detail); // contains root cause text
  if (e.response?.status === 400) fixLocalFileOrStreaming(e); else inspectServerLogs(); }

When it happens

Trigger: Any unhandled exception during flow build/status check: broken component code, invalid graph payload, missing API keys surfacing at build time, serialization errors in vertex data — anything not matching the two special-cased conditions (LocalFileAccessError, 'stream or streaming set to True').

Common situations: Custom component raising at build, invalid node connections, missing environment variables, incompatible component versions after upgrade.

Related errors

• str(e)
• Unexpected error: {exc!s}
• parse_exception(exc)
• HTTP error! status: ${response.status}
• Failed to load models. Please check your provider credential

AI-assisted analysis of langflow-ai/langflow@976ec789d2 (2026-08-14). Data as JSON: /api/errors/d52411c5793245e7. Report an issue: GitHub.