What causes "Unsupported response body type for streaming" in cube-js/cube?

Use a fetch implementation returning a ReadableStream body (native fetch in Node 18+ or browsers)

Unsupported response body type for streaming

Error message

Unsupported response body type for streaming

What it means

responseChunks() in streaming.ts can stream ReadableStream, AsyncIterable, and ArrayBuffer/TypedArray bodies. If the transport's underlying response body is any other type (e.g. a string or undefined), it throws 'Unsupported response body type for streaming'.

Source

Thrown at packages/cubejs-client-core/src/streaming.ts:32

      reader.releaseLock?.();
    }
    return;
  }

  // Node.js Readable (node-fetch v2 via cross-fetch)
  if (body && Symbol.asyncIterator in body) {
    for await (const chunk of body as AsyncIterable<Buffer | Uint8Array | string>) {
      if (typeof chunk === 'string') {
        // Convert string chunks to bytes (rare, but safe)
        yield new TextEncoder().encode(chunk);
      } else {
        yield new Uint8Array(chunk);
      }
    }
    return;
  }

  throw new Error('Unsupported response body type for streaming');
}

View on GitHub (pinned to 7d981676b3)

Solutions

Use a fetch implementation returning a ReadableStream body (native fetch in Node 18+ or browsers)
Fix custom transports to resolve with the raw Response object, not parsed text
Remove or upgrade fetch polyfills that don't support streaming bodies
If streaming is unsupported in your environment, fall back to non-streaming cubeSql()

Example fix

// before
requestStream: async (m, p) => ({ body: await res.text() })
// after
requestStream: async (m, p) => ({ body: res.body /* ReadableStream */ })

Defensive patterns

Strategy: validation

Validate before calling

const res = await doFetch();
if (!res.body || typeof res.body.getReader !== 'function') {
  throw new Error('fetch does not expose a ReadableStream body; use Node 18+ native fetch or a modern browser');
}

Type guard

function isStreamableBody(body) {
  return body instanceof ReadableStream ||
    (body && typeof body.getReader === 'function') ||
    body instanceof ArrayBuffer || ArrayBuffer.isView(body);
}

Try / catch

try { for await (const c of client.cubeSqlStream(sql)) {} } catch (e) {
  if (e.message === 'Unsupported response body type for streaming') {
    const res = await client.cubeSql(sql); // non-streaming fallback
  } else throw e;
}

Prevention

Use runtimes with native fetch streaming (Node 18+, modern browsers)
Do not parse response to text inside custom requestStream transports
Avoid fetch polyfills without ReadableStream body support

When it happens

Trigger: requestStream() receiving a response whose body is a plain string, Blob-like object, or undefined — typically from a custom transport or a mocked/polyfilled fetch without a ReadableStream body.

Common situations: Test environments (jsdom/node-fetch versions) where response.body isn't a ReadableStream; custom transports resolving with text instead of a stream; fetch polyfills lacking streaming body support.

Related errors

AI-assisted analysis of cube-js/cube@7d981676b3 (2026-09-02). Data as JSON: /api/errors/c78eb772e0dcfda7. Report an issue: GitHub.