win, tty: handle empty buffer in uv_tty_write_bufs

In uv_tty_write_bufs, if the console supports Virtual Terminal sequences,
we try to convert the passed in utf8 buffer to utf16. However, we need
to check if the buffer is of non-zero length- otherwise,
MultiByteToWideChar returns an error.

Fixes: https://github.com/libuv/libuv/issues/1135
Fixes: https://github.com/nodejs/node/issues/9542
PR-URL: https://github.com/libuv/libuv/pull/1139
Refs: https://github.com/libuv/libuv/pull/889
Reviewed-By: Bartosz Sosnowski <bartosz@janeasystems.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Imran Iqbal <imran@imraniqbal.org>

src/win/tty.c

@@ -1650,7 +1650,7 @@ static int uv_tty_write_bufs(uv_tty_t* handle,
     uv_buf_t buf = bufs[i];
     unsigned int j;
 
-  if (uv__vterm_state == UV_SUPPORTED) {
+  if (uv__vterm_state == UV_SUPPORTED && buf.len > 0) {
     utf16_buf_used = MultiByteToWideChar(CP_UTF8,
                                          0,
                                          buf.base,

test/test-list.h

@@ -47,6 +47,7 @@ TEST_DECLARE   (semaphore_3)
 TEST_DECLARE   (tty)
 #ifdef _WIN32
 TEST_DECLARE   (tty_raw)
+TEST_DECLARE   (tty_empty_write)
 #endif
 TEST_DECLARE   (tty_file)
 TEST_DECLARE   (tty_pty)
@@ -404,6 +405,7 @@ TASK_LIST_START
   TEST_ENTRY  (tty)
 #ifdef _WIN32
   TEST_ENTRY  (tty_raw)
+  TEST_ENTRY  (tty_empty_write)
 #endif
   TEST_ENTRY  (tty_file)
   TEST_ENTRY  (tty_pty)

test/test-tty.c

@@ -212,6 +212,48 @@ TEST_IMPL(tty_raw) {
   MAKE_VALGRIND_HAPPY();
   return 0;
 }
+
+TEST_IMPL(tty_empty_write) {
+  int r;
+  int ttyout_fd;
+  uv_tty_t tty_out;
+  uv_loop_t* loop = uv_default_loop();
+
+  /* Make sure we have an FD that refers to a tty */
+  HANDLE handle;
+
+  handle = CreateFileA("conout$",
+                       GENERIC_READ | GENERIC_WRITE,
+                       FILE_SHARE_READ | FILE_SHARE_WRITE,
+                       NULL,
+                       OPEN_EXISTING,
+                       FILE_ATTRIBUTE_NORMAL,
+                       NULL);
+  ASSERT(handle != INVALID_HANDLE_VALUE);
+  ttyout_fd = _open_osfhandle((intptr_t) handle, 0);
+
+  ASSERT(ttyout_fd >= 0);
+
+  ASSERT(UV_TTY == uv_guess_handle(ttyout_fd));
+
+  r = uv_tty_init(uv_default_loop(), &tty_out, ttyout_fd, 0);  /* Writable. */
+  ASSERT(r == 0);
+
+  char dummy[1];
+  uv_buf_t bufs[1];
+  bufs[0].len = 0;
+  bufs[0].base = &dummy;
+
+  r = uv_try_write((uv_stream_t*) &tty_out, bufs, 1);
+  ASSERT(r == 0);
+
+  uv_close((uv_handle_t*) &tty_out, NULL);
+
+  uv_run(loop, UV_RUN_DEFAULT);
+
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}
 #endif