fix: abort the connection when a handler throws after the response started

packages/micro/src/lib/index.ts

@@ -114,7 +114,14 @@ export const sendError = (
   res: ServerResponse,
   errorObj: Error | HttpError,
 ) => {
-  if ('statusCode' in errorObj && errorObj.statusCode) {
+  if (res.headersSent) {
+    // The status line and headers are already on the wire, so an error
+    // response can't be sent. Abort the connection so the client doesn't
+    // mistake the truncated body for a complete one.
+    if (!res.writableEnded) {
+      res.destroy();
+    }
+  } else if ('statusCode' in errorObj && errorObj.statusCode) {
     send(res, errorObj.statusCode, errorObj.message);
   } else send(res, 500, 'Internal Server Error');
 

test/suite/index.ts

@@ -696,3 +696,24 @@ 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 after the response has started does not reject run()', async (t) => {
+  let outcome: Promise<unknown> = Promise.resolve();
+  const fn: RequestHandler = (req, res) => {
+    res.write('partial');
+    throw new Error('500 from test (expected)');
+  };
+
+  const server = http.createServer((req, res) => {
+    outcome = run(req, res, fn);
+  });
+  await new Promise<void>((resolve) => {
+    server.listen(resolve);
+  });
+  const { port } = server.address() as AddressInfo;
+
+  const res = await fetch(`http://localhost:${port}`, { timeout: 2000 });
+  await res.text().catch(() => undefined);
+  await t.resolves(outcome);
+  server.close();
+});