fix: respond with 500 when a handler throws a non-Error value

packages/micro/src/lib/index.ts

@@ -1,5 +1,6 @@
 // Native
 import { Stream, Readable } from 'stream';
+import { inspect } from 'util';
 // Packages
 import contentType from 'content-type';
 import getRawBody from 'raw-body';
@@ -148,9 +149,15 @@ export const run = (
       }
     })
     .catch((err: unknown) => {
-      if (isError(err)) {
-        sendError(req, res, err);
-      }
+      // A handler can throw or reject with any value. Always answer with an
+      // error response, otherwise the request never completes.
+      sendError(
+        req,
+        res,
+        isError(err)
+          ? err
+          : new Error(`Handler threw a non-Error value: ${inspect(err)}`),
+      );
     });
 
 // Maps requests to buffered raw bodies so that

test/suite/index.ts

@@ -696,3 +696,26 @@ void test('Content-Type header for JSON is set', async (t) => {
   t.equal(res.headers.get('content-type'), 'application/json; charset=utf-8');
   shutdown();
 });
+
+void test('throw (500) with a non-Error value', async (t) => {
+  const fn: RequestHandler = () => {
+    throw 'not an error object';
+  };
+
+  const [url, shutdown] = await startServer(fn);
+
+  const { status } = await fetch(url, { timeout: 2000 });
+  t.same(status, 500);
+  shutdown();
+});
+
+void test('rejected promise with a non-Error value sends 500', async (t) => {
+  // eslint-disable-next-line prefer-promise-reject-errors -- testing a non-Error rejection
+  const fn: RequestHandler = () => Promise.reject({ reason: 'plain object' });
+
+  const [url, shutdown] = await startServer(fn);
+
+  const { status } = await fetch(url, { timeout: 2000 });
+  t.same(status, 500);
+  shutdown();
+});