cat <(node -v) never exits after >= 12.5.0

[JounQin]

• Version: v12.5.0 and greater
• Platform: Darwin MacBook-Pro.local 18.6.0 Darwin Kernel Version 18.6.0: Thu Apr 25 23:16:27 PDT 2019; root:xnu-4903.261.4~2/RELEASE_X86_64 x86_64
• Subsystem:

Simply run cat <(node -v)
related: ohmyzsh/ohmyzsh#7972

[bnoordhuis]

I can reproduce. It's caused by #24260 except not really - the tcsetattr() call (which libc turns into an ioctl()) simply hangs when node tries to restore the state for fd 0, stdin.

I can't reproduce on Linux so this is with 99% certainty a bug in macOS's implementation of tcsetattr(). TBD if and how to work around that.

edit: libc turns tcsetattr(TCSANOW) into ioctl(TIOCSETA) so this is most likely a kernel bug, not a libc bug.

[bnoordhuis]

This minimal C test case shows the exact same behavior:

#include <err.h>
#include <termios.h>

int
main(void)
{
        struct termios t;
        if (tcgetattr(0, &t))
                err(1, "tcgetattr");
        if (tcsetattr(0, TCSANOW, &t))
                err(1, "tcsetattr");
        return 0;
}

$ cc t.c

$ ./a.out
# ok

$ cat <(./a.out)
# hangs

IOW, not a Node.js bug. I'll see if I can devise a workaround.

[bnoordhuis]

Okay, I figured it out. The tcsetattr() call makes the kernel suspend node with a SIGTTOU signal.

Apparently cat <(node -v) spawns node as a background job that doesn't own the TTY. On Linux that results in the tcsetattr() call failing with EIO (expected), on macOS it sends a SIGTTOU instead.

A fix is on the way.

[sam-github]

FWIW, I can repro on Linux, maybe because I'm using zsh not bash.