--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/libuv/test/test-udp-mmsg.c	Wed Jan 14 19:39:52 2026 -0800
@@ -0,0 +1,150 @@
+/* Copyright libuv 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_HANDLE(handle) \
+  ASSERT_NE((uv_udp_t*)(handle) == &recver || (uv_udp_t*)(handle) == &sender, 0)
+
+#define BUFFER_MULTIPLIER 20
+#define MAX_DGRAM_SIZE (64 * 1024)
+#define NUM_SENDS 40
+
+static uv_udp_t recver;
+static uv_udp_t sender;
+static int recv_cb_called;
+static int received_datagrams;
+static int read_bytes;
+static int close_cb_called;
+static int alloc_cb_called;
+
+
+static void alloc_cb(uv_handle_t* handle,
+                     size_t suggested_size,
+                     uv_buf_t* buf) {
+  size_t buffer_size;
+  CHECK_HANDLE(handle);
+
+  /* Only allocate enough room for multiple dgrams if we can actually recv them */
+  buffer_size = MAX_DGRAM_SIZE;
+  if (uv_udp_using_recvmmsg((uv_udp_t*)handle))
+    buffer_size *= BUFFER_MULTIPLIER;
+
+  /* Actually malloc to exercise free'ing the buffer later */
+  buf->base = malloc(buffer_size);
+  ASSERT_NOT_NULL(buf->base);
+  buf->len = buffer_size;
+  alloc_cb_called++;
+}
+
+
+static void close_cb(uv_handle_t* handle) {
+  CHECK_HANDLE(handle);
+  ASSERT(uv_is_closing(handle));
+  close_cb_called++;
+}
+
+
+static void recv_cb(uv_udp_t* handle,
+                    ssize_t nread,
+                    const uv_buf_t* rcvbuf,
+                    const struct sockaddr* addr,
+                    unsigned flags) {
+  ASSERT_GE(nread, 0);
+  read_bytes += nread;
+
+  /* free and return if this is a mmsg free-only callback invocation */
+  if (flags & UV_UDP_MMSG_FREE) {
+    ASSERT_OK(nread);
+    ASSERT_NULL(addr);
+    free(rcvbuf->base);
+    return;
+  }
+
+  if (nread == 0) {
+    /* There can be no more available data for the time being. */
+    ASSERT_NULL(addr);
+  } else {
+    ASSERT_EQ(4, nread);
+    ASSERT_NOT_NULL(addr);
+    ASSERT_MEM_EQ("PING", rcvbuf->base, nread);
+    received_datagrams++;
+  }
+
+  recv_cb_called++;
+  if (received_datagrams == NUM_SENDS) {
+    uv_close((uv_handle_t*) handle, close_cb);
+    uv_close((uv_handle_t*) &sender, close_cb);
+  }
+
+  /* Don't free if the buffer could be reused via mmsg */
+  if (rcvbuf && !(flags & UV_UDP_MMSG_CHUNK))
+    free(rcvbuf->base);
+}
+
+
+TEST_IMPL(udp_mmsg) {
+  struct sockaddr_in addr;
+  uv_buf_t buf;
+  int i;
+
+  ASSERT_OK(uv_ip4_addr("0.0.0.0", TEST_PORT, &addr));
+
+  ASSERT_OK(uv_udp_init_ex(uv_default_loop(), &recver,
+                           AF_UNSPEC | UV_UDP_RECVMMSG));
+
+  ASSERT_OK(uv_udp_bind(&recver, (const struct sockaddr*) &addr, 0));
+
+  ASSERT_OK(uv_udp_recv_start(&recver, alloc_cb, recv_cb));
+
+  ASSERT_OK(uv_ip4_addr("127.0.0.1", TEST_PORT, &addr));
+
+  ASSERT_OK(uv_udp_init(uv_default_loop(), &sender));
+
+  buf = uv_buf_init("PING", 4);
+  for (i = 0; i < NUM_SENDS; i++) {
+    ASSERT_EQ(4, uv_udp_try_send(&sender, &buf, 1, (const struct sockaddr*) &addr));
+  }
+
+  ASSERT_OK(uv_run(uv_default_loop(), UV_RUN_DEFAULT));
+
+  ASSERT_EQ(2, close_cb_called);
+  ASSERT_EQ(received_datagrams, NUM_SENDS);
+
+  ASSERT_OK(sender.send_queue_size);
+  ASSERT_OK(recver.send_queue_size);
+
+  printf("%d allocs for %d recvs\n", alloc_cb_called, recv_cb_called);
+
+  /* On platforms that don't support mmsg, each recv gets its own alloc */
+  if (uv_udp_using_recvmmsg(&recver))
+    ASSERT_EQ(read_bytes, NUM_SENDS * 4); /* we're sending 4 bytes per datagram */
+  else
+    ASSERT_EQ(alloc_cb_called, recv_cb_called);
+
+  MAKE_VALGRIND_HAPPY(uv_default_loop());
+  return 0;
+}