unix: reopen tty as /dev/tty

Reopen the file descriptor when it refers to a tty. This lets us put the tty in
non-blocking mode without affecting other processes that share it with us.

Fixes #601.

src/unix/tty.c

@@ -34,18 +34,53 @@ static struct termios orig_termios;
 
 
 int uv_tty_init(uv_loop_t* loop, uv_tty_t* tty, int fd, int readable) {
+  int flags;
+  int newfd;
+  int r;
+
   uv__stream_init(loop, (uv_stream_t*)tty, UV_TTY);
 
-  if (readable) {
+  /* Reopen the file descriptor when it refers to a tty. This lets us put the
-    uv__nonblock(fd, 1);
+   * tty in non-blocking mode without affecting other processes that share it
-    uv__stream_open((uv_stream_t*)tty, fd, UV_STREAM_READABLE);
+   * with us.
-  } else {
+   *
-    /* Note: writable tty we set to blocking mode. */
+   * Example: `node | cat` - if we put our fd 0 in non-blocking mode, it also
-    uv__stream_open((uv_stream_t*)tty, fd, UV_STREAM_WRITABLE);
+   * affects fd 1 of `cat` because both file descriptors refer to the same
-    tty->flags |= UV_STREAM_BLOCKING;
+   * struct file in the kernel. When we reopen our fd 0, it points to a
+   * different struct file, hence changing its properties doesn't affect
+   * other processes.
+   */
+  if (isatty(fd)) {
+    newfd = open("/dev/tty", O_RDWR);
+
+    if (newfd == -1)
+      return uv__set_sys_error(loop, errno);
+
+    do
+      r = dup2(newfd, fd);
+    while (r == -1 && (errno == EINTR || errno == EBUSY));
+
+    /* EINVAL means newfd == fd which could conceivably happen if another
+     * thread called close(fd) between our calls to isatty() and open().
+     * That's a rather unlikely event but let's handle it anyway.
+     */
+    if (r == -1 && errno != EINVAL) {
+      close(newfd);
+      return uv__set_sys_error(loop, errno);
+    }
+
+    fd = newfd;
   }
 
+  if (readable)
+    flags = UV_STREAM_READABLE;
+  else
+    flags = UV_STREAM_WRITABLE;
+
+  uv__nonblock(fd, 1);
+  uv__stream_open((uv_stream_t*)tty, fd, flags);
   tty->mode = 0;
+
   return 0;
 }