spawn's stdio can result in stderr being closed in child

[sam-github]

var cp = require('child_process');
var fs = require('fs');

if (process.env.CHILD) {
  console.error('ERROR');
  return;
}
// open child stdout and stderr on our stderr
var options = {
  stdio: [0, 2, 2],
  env: { CHILD: true },
};
var c = cp.spawn(process.execPath, [__filename], options);

Result: 'ERROR' is not printed.

Excerpt from strace:

[pid 11780] write(2, "ERROR\n", 6)      = -1 EBADF (Bad file descriptor)
[pid 11780] write(2, "ERROR\n", 6)      = -1 EBADF (Bad file descriptor)
[pid 11780] epoll_ctl(4, EPOLL_CTL_DEL, 2, {EPOLLWRNORM|EPOLLHUP|EPOLLRDHUP|EPOLLET|0x242e0000, {u32=32767, u64=47321597480042495}}) = -1 ENOENT (No such file or directory)
[pid 11780] write(2, "events.js:141\n      throw er; //"..., 244) = -1 EBADF (Bad file descriptor)
[pid 11780] exit_group(1)               = ?
[pid 11785] +++ exited with 1 +++

This likely a bug in libuv, but reporting it here because that's where I saw it.

Affects node v0.10 and io.js.

/cc @saghul @bnoordhuis I think we tried to fix a variant of this a year or so ago.

[saghul]

I believe that's still not fixed. This is the closest open issue I could find: joyent/libuv#923

[bnoordhuis]

I think this asks for a two-pronged approach: libuv probably has a bug or two that need to be addressed but io.js could reopen fds 0-2 as /dev/null if they aren't valid file descriptors.

[vkurchatkin]

@bnoordhuis can you also comment on #831 ?

[sam-github]

Opening fd 2 on /dev/null would avoid the EBADF, and probably is a good idea, so fd 2 doesn't become some random open file, but wouldn't avoid the underlying problem, that console.error() never prints, because stderr is gone.

I dug up the last time I saw this:

• libuv/libuv@e403a2c
• uv_spawn won't duplicate the same original fd to two fds in the child joyent/libuv#1074

[sam-github]

@saghul I think I've fixed this, as well as some related bugs. I'm putting together some node tests, then I'll PR the fix to libuv.

[saghul]

Great! Thanks Sam.
On Feb 24, 2015 6:57 PM, "Sam Roberts" notifications@github.com wrote:

@saghul https://github.com/saghul I think I've fixed this, as well as
some related bugs. I'm putting together some node tests, then I'll PR the
fix to libuv.

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