Node ignoring redirections when redirected to a tty

[ELLIOTTCABLE]

So, although redirects to other active file-descriptors work as expected, as do redirections to files and the /dev/null device, I cannot redirect successfully to a different tty:

$ node -e 'process.stdout.write("wtf!\n")' 1>/dev/ttys014
wtf!

Example:

# First term:                                                           │# Second term:
                                                                        │
$ tty                                                                   │$ tty
/dev/ttys013                                                            │/dev/ttys014
$ echo 'abc' 1>/dev/ttys014                                             │$ cat
$ ruby -e '$stdout.puts "okay"' 1>/dev/ttys014                          │abc
$ node -e 'process.stdout.write("wtf!\n")' 1>/dev/ttys014               │okay
wtf!                                                                    │
$ node -e 'process.stdout.write("this works\n")' 1>/dev/null            │
$ node -e 'process.stdout.write("this too\n")' 1>output                 │
$ cat output                                                            │
this too                                                                │

Environment:

System: Mac OS X El Capitan 10.11.1
Shell: Zsh 5.1.1 (x86_64-apple-darwin15.0.0)
Node: v4.2.3

[ljharb]

I've reproduced the same thing on Yosemite in stock bash, in node v5.1.1.

[kzc]

This behavior is due to uv_tty_init

node/deps/uv/src/unix/tty.c

Lines 54 to 65 in 65b86c0

	/* 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.
	*
	* Example: `node | cat` - if we put our fd 0 in non-blocking mode, it also
	* affects fd 1 of `cat` because both file descriptors refer to the same
	* 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 (type == UV_TTY) {
	r = uv__open_cloexec("/dev/tty", O_RDWR);

  /* 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.
   *
   * Example: `node | cat` - if we put our fd 0 in non-blocking mode, it also
   * affects fd 1 of `cat` because both file descriptors refer to the same
   * 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 (type == UV_TTY) {
    r = uv__open_cloexec("/dev/tty", O_RDWR);

It appears that libuv assumes if the fd is a tty it must be the originating console.

One workaround is to use an intermediate pipe:

node -e 'process.stdout.write("wtf!\n")' | cat >/dev/ttys014

[ELLIOTTCABLE]

Hm. Okay, thanks for hunting that down for me; I might try to patch upstream.

Either way, I'll leave this open until it's fixed there?

[kzc]

Yeah, I think it should be left open as it's a node regression.

It does not happen on jxcore which is a pre 0.12 node fork. Haven't tried running on older versions of node 0.10 or node 0.12

It was introduced here:

libuv/libuv@b197515

[kzc]

/cc @saghul

[ELLIOTTCABLE]

This looks like it may have been discussed before, by the way:

libuv/libuv#528
libuv/libuv#526

[saghul]

Ahoi! @ELLIOTTCABLE can you try the patch in libuv/libuv#528? It should apply pretty much cleanly to deps/uv and the rebuild Node and test. Let me know if you run into issues with it.

[kzc]

The patch in libuv/libuv#528 appears to work on Mac against node v5.1.1 sources with stdout and stderr tty redirects. (Edit: patch as of Dec 10, 2015)

[kzc]

libuv patch status update: libuv/libuv#528 (comment)

[Gottox]

Please have a look at libuv/libuv#779. I'm considering libuv/libuv#528 obsolete.

[kzc]

Fixed in libuv 1.9.0 upgrade #5994 c3cec1e