--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/libuv/test/test-udp-recv-in-a-row.c	Wed Jan 14 19:39:52 2026 -0800
@@ -0,0 +1,128 @@
+/* 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>
+
+static uv_udp_t server;
+static uv_udp_t client;
+static uv_check_t check_handle;
+static uv_buf_t buf;
+static struct sockaddr_in addr;
+static char send_data[10];
+static int check_cb_called;
+
+#define N 5
+static int recv_cnt;
+
+static void alloc_cb(uv_handle_t* handle,
+                     size_t suggested_size,
+                     uv_buf_t* buf) {
+  static char slab[sizeof(send_data)];
+  buf->base = slab;
+  buf->len = sizeof(slab);
+}
+
+static void sv_recv_cb(uv_udp_t* handle,
+                       ssize_t nread,
+                       const uv_buf_t* rcvbuf,
+                       const struct sockaddr* addr,
+                       unsigned flags) {
+  /* |nread| can be zero when the kernel drops an incoming datagram after
+   * marking the file descriptor as readable but before libuv has a chance
+   * to receive it. Libuv still invokes the uv_udp_recv_cb callback to give
+   * back the memory from the uv_alloc_cb callback.
+   *
+   * See https://github.com/libuv/libuv/issues/4219.
+   */
+  recv_cnt++;
+  if (nread > 0)
+    ASSERT_EQ(nread, sizeof(send_data));
+}
+
+static void check_cb(uv_check_t* handle) {
+  ASSERT_PTR_EQ(&check_handle, handle);
+
+  /**
+   * sv_recv_cb() is called with nread set to zero to indicate
+   * there is no more udp packet in the kernel, so the actual
+   * recv_cnt is up to one larger than N. UDP being what it is,
+   * packets can get dropped so don't assume an exact count.
+   */
+  ASSERT_GE(recv_cnt, 1);
+  ASSERT_LE(recv_cnt, N+1);
+  check_cb_called = 1;
+
+  /* we are done */
+  ASSERT_OK(uv_check_stop(handle));
+  uv_close((uv_handle_t*) &client, NULL);
+  uv_close((uv_handle_t*) &check_handle, NULL);
+  uv_close((uv_handle_t*) &server, NULL);
+}
+
+
+TEST_IMPL(udp_recv_in_a_row) {
+  int i, r;
+  
+  ASSERT_OK(uv_check_init(uv_default_loop(), &check_handle));
+  ASSERT_OK(uv_check_start(&check_handle, check_cb));
+
+  ASSERT_OK(uv_ip4_addr("127.0.0.1", TEST_PORT, &addr));
+
+  ASSERT_OK(uv_udp_init(uv_default_loop(), &server));
+  ASSERT_OK(uv_udp_bind(&server, (const struct sockaddr*) &addr, 0));
+  ASSERT_OK(uv_udp_recv_start(&server, alloc_cb, sv_recv_cb));
+
+  ASSERT_OK(uv_udp_init(uv_default_loop(), &client));
+
+  /* send N-1 udp packets */
+  buf = uv_buf_init(send_data, sizeof(send_data));
+  for (i = 0; i < N - 1; i ++) {
+    r = uv_udp_try_send(&client,
+                        &buf,
+                        1,
+                        (const struct sockaddr*) &addr);
+    ASSERT_EQ(sizeof(send_data), r);
+  }
+
+  /* send an empty udp packet */
+  buf = uv_buf_init(NULL, 0);
+  r = uv_udp_try_send(&client,
+                      &buf,
+                      1,
+                      (const struct sockaddr*) &addr);
+  ASSERT_OK(r);
+
+  /* check_cb() asserts that the N packets can be received
+   * before it gets called. 
+   */
+
+  ASSERT_OK(uv_run(uv_default_loop(), UV_RUN_DEFAULT));
+
+  ASSERT(check_cb_called);
+
+  MAKE_VALGRIND_HAPPY(uv_default_loop());
+  return 0;
+}