danielmiessler/Fabric · error · ChatError

NULL_RESPONSE

NULL_RESPONSE

Error message

Response body is null

What it means

ChatError('Response body is null', 'NULL_RESPONSE') fires when POST /api/chat returned 2xx but response.body is null so no reader can be obtained. In practice on the web platform this almost always indicates an opaque/filtered response or a consumed body rather than a genuinely empty successful reply.

Source

Thrown at web/src/lib/services/ChatService.ts:79

			);

			const response = await fetch("/api/chat", {
				method: "POST",
				headers: { "Content-Type": "application/json" },
				body: JSON.stringify(request),
			});

			if (!response.ok) {
				throw new ChatError(
					`HTTP error! status: ${response.status}`,
					"HTTP_ERROR",
					{ status: response.status },
				);
			}

			const reader = response.body?.getReader();
			if (!reader) {
				throw new ChatError("Response body is null", "NULL_RESPONSE");
			}

			return this.createMessageStream(reader);
		} catch (error) {
			if (error instanceof ChatError) throw error;
			throw new ChatError("Failed to fetch chat stream", "FETCH_ERROR", error);
		}
	}

	/**
	 * Clean up pattern output for display. Should only be called on complete/accumulated content,
	 * never on individual streaming tokens (which have leading spaces as word separators).
	 */
	public cleanPatternOutput(content: string): string {
		// Remove markdown fence if present
		let cleaned = content.replace(/^```markdown\n/, "");
		cleaned = cleaned.replace(/\n```$/, "");

View on GitHub (pinned to 338b89cfe9)

Solutions

1. Disable any service worker / PWA caching for /api/chat POSTs and retest
2. Check navigator/browsed environment supports response.body (evergreen browsers, not legacy webviews)
3. If mocking fetch in tests, make the mock return a real ReadableStream

if (typeof ReadableStream === 'undefined') {
  throw new Error('This browser does not support streaming responses');
}

function isNullResponseError(e: unknown): boolean {
  return e instanceof ChatError && e.code === 'NULL_RESPONSE';
}

try { stream = await chatService.sendMessage(request); }
catch (e) {
  if (isNullResponseError(e)) { /* bypass service worker / retry without SW */ }
  else throw e;
}

When it happens

Trigger: A service worker or proxy returning an opaque response for /api/chat; the Response object being reused after body consumption; a runtime without fetch streaming support.

Common situations: PWA/service worker caching interfering with POST /api/chat; older browser or webview lacking ReadableStream on responses; test environment mocking fetch without a body.

Related errors

• Response body is null
• HTTP_ERROR
• FETCH_ERROR
• STREAM_CONTENT_ERROR
• HTTP error! status: ${response.status}

AI-assisted analysis of danielmiessler/Fabric@338b89cfe9 (2026-08-15). Data as JSON: /api/errors/1e2bb149da843b71. Report an issue: GitHub.