Parent-child pipes not relayed

[antoinep92]

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Minimal reproduction URL

https://stackblitz.com/edit/node-qzmjn4?file=main.js

Problem & expected behavior (under 200 words)

I'm not aware of how tsx works internally, but apparently it breaks at least some forms of inter-process communication. I setup a child process to have a stream (fd 3) to talk with it's parent, but that becomes unusable when using tsx. Spent quite a bit of time to track the issue to tsx actually ^_^

I don't know if this is easily fixable, but at least it should be documented somewhere.

Bugs are expected to be fixed by those affected by it

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[privatenumber]

This happens because tsx also spawns a node process and isn't relaying the pipes it receives from the parent process:

tsx/src/run.ts

Lines 15 to 19 in 2688300

	const stdio: StdioOptions = [
	'inherit', // stdin
	'inherit', // stdout
	'inherit', // stderr
	];

Do you know if there's a good way to detect all the pipes attached to the current process by the parent? Not a lot of info in the docs: https://nodejs.org/api/child_process.html#optionsstdio

As far as I understand, the only way is to do something like:

import fs from 'fs';

const stdio = [];

for (let fd = 0; fd < 100; fd++) { // Arbitrary upper limit for file descriptors
  try {
    fs.fstatSync(fd); // If this doesn't throw, fd is valid
    stdio.push('inherit');
  } catch (err) {
    if (err.code !== 'EBADF') { // EBADF means fd is not valid
      throw err;
    }
  }
}

But I prefer we're not doing an arbitrary number of stat and try-catches on startup.

[antoinep92]

Hi, thanks for the quick feedback !

There are platform specific ways, e.g. Linux (or unix like MacOS) have /proc/fd which lists open files and I believe it would be quite efficient to scan that on startup. There must be a windows API for that also, but not necessarily available from node. But at this point it's probably more trouble than it's worth. I don't see a standard, cross-platform way of doing it, apart from what you propose, which does not seem very nice.

Also, just adding a bunch of "inherit" to stdio options just in case is not a good option either because it changes the error code when trying to open a file descriptor which could also break some edge cases.

I guess one option would be to have a way to configure this through command line parameters or otherwise, but I understand one of the point of this project is to "just work" with no configuration, so I don't know if that fits.

Also if you look at the broader picture, there are many IPC mechanisms ; detecting and forwarding them all seems unrealistic. So maybe the easier resolution is to accept that this use-case is not handled by tsx, but it should be documented.

In the meantime I'm gonna try my luck with ts-imp (ts-node also breaks on our code, but for different reasons 😭 )