withastro/astro · error · AstroError

MiddlewareNoDataOrNextCalled

MiddlewareNoDataOrNextCalled

Error message

Make sure your middleware returns a `Response` object, either directly or by returning the `Response` from calling the `next` function.

What it means

callMiddleware throws AstroErrorData.MiddlewareNoDataOrNextCalled when the middleware neither called next() nor returned anything. Astro requires exactly one of those two outcomes per request — the middleware must either delegate to the rest of the pipeline or produce a Response itself. This error means some code path fell through doing neither.

Solutions

Make every branch end in `return next()` or `return <Response>`
Add a final `return next();` at the bottom of the middleware as a safe default
Type the middleware with defineMiddleware so return paths are easier to audit; add a unit test hitting the deny path

Example fix

// before — deny path returns undefined
export const onRequest = async (context, next) => {
  if (context.cookies.get('session')) return next();
};

// after
export const onRequest = async (context, next) => {
  if (!context.cookies.get('session')) return context.redirect('/login', 302);
  return next();
};

Defensive patterns

Strategy: validation

Validate before calling

export const onRequest = async (context, next) => {
  if (!isAuthorized(context)) return context.redirect('/login', 302); // deny path returns a Response
  return next(); // fall-through path delegates
};

Prevention

End every branch with `return next()` or `return <Response>`
Add a final `return next();` as the last statement of each middleware
Write tests for the deny path — it is the branch that usually falls through

When it happens

Trigger: An auth middleware with `if (authorized) return next();` but no else branch; an async middleware whose early return was removed during refactoring; a middleware returning undefined from a conditional block (e.g. inside a switch) on the deny path.

Common situations: Adding conditional logic to existing middleware and forgetting the negative path; renaming or refactoring that drops a `return`; TypeScript not flagging it because the handler type permits undefined at runtime.

Related errors

AI-assisted analysis of withastro/astro@52e6c34790 (2026-08-18). Data as JSON: /api/errors/3bb59f3bf6da7839. Report an issue: GitHub.

Appendix: source

Thrown at packages/astro/src/core/middleware/callMiddleware.ts:96

				return value;
			} else {
				/**
				 * Here we handle the case where `next` was called and returned nothing.
				 */
				if (responseFunctionPromise) {
					return responseFunctionPromise;
				} else {
					throw new AstroError(AstroErrorData.MiddlewareNotAResponse);
				}
			}
		} else if (typeof value === 'undefined') {
			/**
			 * There might be cases where `next` isn't called and the middleware **must** return
			 * something.
			 *
			 * If not thing is returned, then we raise an Astro error.
			 */
			throw new AstroError(AstroErrorData.MiddlewareNoDataOrNextCalled);
		} else if (value instanceof Response === false) {
			throw new AstroError(AstroErrorData.MiddlewareNotAResponse);
		} else {
			// Middleware did not call resolve and returned a value
			return value;
		}
	});
}

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