From 49ba7ae6036b0722a7bcd88e2111695d2173079b Mon Sep 17 00:00:00 2001
From: RaphaelFakhri <153192858+RaphaelFakhri@users.noreply.github.com>
Date: Tue, 29 Sep 2026 17:42:06 +0300
Subject: [PATCH] fix: abort the connection when a handler throws after the
 response started

---
 packages/micro/src/lib/index.ts |  9 ++++++++-
 test/suite/index.ts             | 21 +++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/packages/micro/src/lib/index.ts b/packages/micro/src/lib/index.ts
index 8977b35..707c7ee 100644
--- a/packages/micro/src/lib/index.ts
+++ b/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');
 
diff --git a/test/suite/index.ts b/test/suite/index.ts
index 563f77c..01e9de5 100644
--- a/test/suite/index.ts
+++ b/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();
+});