Node ignoring redirections when redirected to a tty

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

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

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

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?

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

@saghul

/cc @saghul

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

libuv/libuv#528
libuv/libuv#526

@ELLIOTTCABLE

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.

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)

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

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

Fixed in libuv 1.9.0 upgrade #5994 c3cec1e

@ELLIOTTCABLE

@ELLIOTTCABLE can you confirm this is fixed in master now with libuv 1.9.0?

Closing as this issue should be fixed.

Can confirm, functioning as expected in v6.2.1. 💯

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Node ignoring redirections when redirected to a tty #4222

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	/* 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);

Node ignoring redirections when redirected to a tty #4222

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ljharb commented on Dec 10, 2015

kzc commented on Dec 10, 2015

ELLIOTTCABLE commented on Dec 10, 2015

kzc commented on Dec 10, 2015

kzc commented on Dec 10, 2015

ELLIOTTCABLE commented on Dec 10, 2015

saghul commented on Dec 10, 2015

kzc commented on Dec 10, 2015

kzc commented on Mar 23, 2016

Gottox commented on Mar 23, 2016

kzc commented on Apr 7, 2016

mscdex commented on Apr 7, 2016

jasnell commented on Jun 6, 2016

ELLIOTTCABLE commented on Jun 6, 2016

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