--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/libuv/test/test-udp-send-hang-loop.c	Wed Jan 14 19:39:52 2026 -0800
@@ -0,0 +1,99 @@
+/* Copyright The libuv project and contributors. All rights reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include "uv.h"
+#include "task.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define CHECK_OBJECT(handle, type, parent) \
+  ASSERT_PTR_EQ((type*)(handle), &(parent))
+
+static uv_udp_t client;
+static uv_idle_t idle_handle;
+static uv_udp_send_t send_req;
+static uv_buf_t buf;
+static struct sockaddr_in addr;
+static char send_data[1024];
+
+static int loop_hang_called;
+
+static void send_cb(uv_udp_send_t* req, int status);
+
+
+static void idle_cb(uv_idle_t* handle) {
+  int r;
+
+  ASSERT_NULL(send_req.handle);
+  CHECK_OBJECT(handle, uv_idle_t, idle_handle);
+  ASSERT_OK(uv_idle_stop(handle));
+
+  /* It probably would have stalled by now if it's going to stall at all. */
+  if (++loop_hang_called > 1000) {
+    uv_close((uv_handle_t*) &client, NULL);
+    uv_close((uv_handle_t*) &idle_handle, NULL);
+    return;
+  }
+
+  r = uv_udp_send(&send_req,
+                  &client,
+                  &buf,
+                  1,
+                  (const struct sockaddr*) &addr,
+                  send_cb);
+  ASSERT_OK(r);
+}
+
+
+static void send_cb(uv_udp_send_t* req, int status) {
+  ASSERT_NOT_NULL(req);
+  ASSERT(status == 0 || status == UV_ENETUNREACH);
+  CHECK_OBJECT(req->handle, uv_udp_t, client);
+  CHECK_OBJECT(req, uv_udp_send_t, send_req);
+  req->handle = NULL;
+
+  ASSERT_OK(uv_idle_start(&idle_handle, idle_cb));
+}
+
+
+TEST_IMPL(udp_send_hang_loop) {
+  ASSERT_OK(uv_idle_init(uv_default_loop(), &idle_handle));
+
+  /* 192.0.2.0/24 is "TEST-NET" and reserved for documentation.
+   * Good for us, though. Since we want to have something unreachable.
+   */
+  ASSERT_OK(uv_ip4_addr("192.0.2.3", TEST_PORT, &addr));
+
+  ASSERT_OK(uv_udp_init(uv_default_loop(), &client));
+
+  buf = uv_buf_init(send_data, sizeof(send_data));
+
+  ASSERT_OK(uv_idle_start(&idle_handle, idle_cb));
+
+  uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+
+  ASSERT_GT(loop_hang_called, 1000);
+
+  MAKE_VALGRIND_HAPPY(uv_default_loop());
+  return 0;
+}