--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/libuv/test/test-callback-stack.c	Wed Jan 14 19:39:52 2026 -0800
@@ -0,0 +1,209 @@
+/* Copyright Joyent, Inc. and other Node 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.
+ */
+
+/*
+ * TODO: Add explanation of why we want on_close to be called from fresh
+ * stack.
+ */
+
+#include "uv.h"
+#include "task.h"
+
+
+static const char MESSAGE[] = "Failure is for the weak. Everyone dies alone.";
+
+static uv_tcp_t client;
+static uv_timer_t timer;
+static uv_connect_t connect_req;
+static uv_write_t write_req;
+static uv_shutdown_t shutdown_req;
+
+static int nested = 0;
+static int close_cb_called = 0;
+static int connect_cb_called = 0;
+static int write_cb_called = 0;
+static int timer_cb_called = 0;
+static int bytes_received = 0;
+static int shutdown_cb_called = 0;
+
+
+static void alloc_cb(uv_handle_t* handle, size_t size, uv_buf_t* buf) {
+  buf->len = size;
+  buf->base = malloc(size);
+  ASSERT_NOT_NULL(buf->base);
+}
+
+
+static void close_cb(uv_handle_t* handle) {
+  ASSERT(nested == 0 && "close_cb must be called from a fresh stack");
+
+  close_cb_called++;
+}
+
+
+static void shutdown_cb(uv_shutdown_t* req, int status) {
+  ASSERT_OK(status);
+  ASSERT(nested == 0 && "shutdown_cb must be called from a fresh stack");
+
+  shutdown_cb_called++;
+}
+
+
+static void read_cb(uv_stream_t* tcp, ssize_t nread, const uv_buf_t* buf) {
+  ASSERT(nested == 0 && "read_cb must be called from a fresh stack");
+
+  printf("Read. nread == %d\n", (int)nread);
+  free(buf->base);
+
+  if (nread == 0) {
+    return;
+
+  } else if (nread < 0) {
+    ASSERT_EQ(nread, UV_EOF);
+
+    nested++;
+    uv_close((uv_handle_t*)tcp, close_cb);
+    nested--;
+
+    return;
+  }
+
+  bytes_received += nread;
+
+  /* We call shutdown here because when bytes_received == sizeof MESSAGE there
+   * will be no more data sent nor received, so here it would be possible for a
+   * backend to call shutdown_cb immediately and *not* from a fresh stack. */
+  if (bytes_received == sizeof MESSAGE) {
+    nested++;
+
+    puts("Shutdown");
+
+    if (uv_shutdown(&shutdown_req, (uv_stream_t*)tcp, shutdown_cb)) {
+      FATAL("uv_shutdown failed");
+    }
+    nested--;
+  }
+}
+
+
+static void timer_cb(uv_timer_t* handle) {
+  ASSERT_PTR_EQ(handle, &timer);
+  ASSERT(nested == 0 && "timer_cb must be called from a fresh stack");
+
+  puts("Timeout complete. Now read data...");
+
+  nested++;
+  if (uv_read_start((uv_stream_t*)&client, alloc_cb, read_cb)) {
+    FATAL("uv_read_start failed");
+  }
+  nested--;
+
+  timer_cb_called++;
+
+  uv_close((uv_handle_t*)handle, close_cb);
+}
+
+
+static void write_cb(uv_write_t* req, int status) {
+  int r;
+
+  ASSERT_OK(status);
+  ASSERT(nested == 0 && "write_cb must be called from a fresh stack");
+
+  puts("Data written. 500ms timeout...");
+
+  /* After the data has been sent, we're going to wait for a while, then start
+   * reading. This makes us certain that the message has been echoed back to
+   * our receive buffer when we start reading. This maximizes the temptation
+   * for the backend to use dirty stack for calling read_cb. */
+  nested++;
+  r = uv_timer_init(uv_default_loop(), &timer);
+  ASSERT_OK(r);
+  r = uv_timer_start(&timer, timer_cb, 500, 0);
+  ASSERT_OK(r);
+  nested--;
+
+  write_cb_called++;
+}
+
+
+static void connect_cb(uv_connect_t* req, int status) {
+  uv_buf_t buf;
+
+  puts("Connected. Write some data to echo server...");
+
+  ASSERT_OK(status);
+  ASSERT(nested == 0 && "connect_cb must be called from a fresh stack");
+
+  nested++;
+
+  buf.base = (char*) &MESSAGE;
+  buf.len = sizeof MESSAGE;
+
+  if (uv_write(&write_req, (uv_stream_t*)req->handle, &buf, 1, write_cb)) {
+    FATAL("uv_write failed");
+  }
+
+  nested--;
+
+  connect_cb_called++;
+}
+
+
+TEST_IMPL(callback_stack) {
+  struct sockaddr_in addr;
+
+  ASSERT_OK(uv_ip4_addr("127.0.0.1", TEST_PORT, &addr));
+
+  if (uv_tcp_init(uv_default_loop(), &client)) {
+    FATAL("uv_tcp_init failed");
+  }
+
+  puts("Connecting...");
+
+  nested++;
+
+  if (uv_tcp_connect(&connect_req,
+                     &client,
+                     (const struct sockaddr*) &addr,
+                     connect_cb)) {
+    FATAL("uv_tcp_connect failed");
+  }
+  nested--;
+
+  uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+
+  ASSERT_OK(nested);
+  ASSERT_NE(connect_cb_called == 1 && \
+            "connect_cb must be called exactly once", 0);
+  ASSERT_NE(write_cb_called == 1 && "write_cb must be called exactly once",
+            0);
+  ASSERT_NE(timer_cb_called == 1 && "timer_cb must be called exactly once",
+            0);
+  ASSERT_EQ(bytes_received, sizeof MESSAGE);
+  ASSERT_NE(shutdown_cb_called == 1 && \
+            "shutdown_cb must be called exactly once", 0);
+  ASSERT_NE(close_cb_called == 2 && "close_cb must be called exactly twice",
+            0);
+
+  MAKE_VALGRIND_HAPPY(uv_default_loop());
+  return 0;
+}