langflow-ai/langflow · error · Error

Error in streaming request.

Error message

Error in streaming request.

What it means

Thrown by performStreamingRequest in controllers/API when the fetch for a streaming endpoint returns a non-OK response and no onError callback was supplied. The helper delegates status handling to onError; without it, all it can do is raise this generic error, and the stream is never read.

Source

Thrown at src/frontend/src/controllers/API/api.tsx:347

  const params: RequestInit = {
    method: method,
    headers: headers,
    signal: buildController.signal,
    credentials: getFetchCredentials(),
  };
  if (body) {
    params.body = JSON.stringify(body);
  }
  let current: string[] = [];
  const textDecoder = new TextDecoder();

  try {
    const response = await fetch(url, params);
    if (!response.ok) {
      if (onError) {
        onError(response.status);
      } else {
        throw new Error("Error in streaming request.");
      }
    }
    if (response.body === null) {
      return;
    }
    const reader = response.body.getReader();
    while (true) {
      const { done, value } = await reader.read();
      if (done) {
        break;
      }
      const decodedChunk = textDecoder.decode(value);
      const all = decodedChunk.split("\n\n");

      // Parse all complete events from this chunk first
      const parsedEvents: object[] = [];
      for (const string of all) {
        if (string.endsWith("}")) {

View on GitHub (pinned to 976ec789d2)

Solutions

1. Pass an onError callback so callers receive the real status code instead of a generic throw
2. Check devtools for the actual status of the failing stream request and fix the underlying cause (auth, 404, 500)
3. If 401/403, refresh the session and retry once
4. Verify the URL and payload shape match the current backend version after upgrades

Example fix

// before
await performStreamingRequest({ method: "POST", url, body });

// after
await performStreamingRequest({
  method: "POST",
  url,
  body,
  onError: (status) => {
    if (status === 401) refreshSession();
    else setStreamError(`Stream failed with ${status}`);
  },
});

try {
  await performStreamingRequest({ method, url, body, onError: (status) => {
    streamErrors.push(status); // always pass onError; the generic throw is the no-onError fallback
  }});
} catch (e) {
  if (e instanceof Error && e.message === "Error in streaming request.") {
    // no onError was wired; add one to learn the real status
  } else throw e;
}

When it happens

Trigger: Calling performStreamingRequest({url, ...}) where url returns 4xx/5xx and the options object omits onError — e.g. an SSE/build/chat endpoint returning 401 after token expiry or 404 for a missing resource.

Common situations: New call sites forgetting the onError parameter; expired sessions hitting stream endpoints; endpoints returning 404 after a route rename in a newer backend.

Related errors

• Error processing build events
• Error starting build process
• Build job not found
• Invalid flow data
• Deployment name is required

AI-assisted analysis of langflow-ai/langflow@976ec789d2 (2026-08-14). Data as JSON: /api/errors/017d7fd548976d77. Report an issue: GitHub.