Fix spawn of cmd and bat files on Windows

[atrauzzi]

This ticket is specifically in reference to this: https://nodejs.org/api/child_process.html#child_process_spawning_bat_and_cmd_files_on_windows

I've put together a comparison as an example, basically it uses edgejs to spawn a command that's based off of a cmd file (electron): https://gist.github.com/atrauzzi/bbcc171b57a7ea276a2e6bf6419c7e51

The point of the comparison is to show that it is possible to run cmd and bat files without requiring a console window open the whole time. It would just be a matter of figuring out how .net is doing it and plugging into that same mechanism when running on Windows vs however nodejs is currently doing things.

But I really think this issue is long overdue to be addressed.

cc. #556

[mscdex]

For some reason, the process module in nodejs imposes that it be run in a console window.

I think this snippet from the C# code you referenced pretty much says it all:

WindowStyle = System.Diagnostics.ProcessWindowStyle.Hidden

A console window is still being created. So C# is really doing the same thing, except it is removing the window from the taskbar.

[atrauzzi]

Nice, that probably bodes well for a fix then because it means that nodejs isn't doing anything wrong in how it spawns, it's just not fully abstracted over this Windows-specific nuance?

[bnoordhuis]

Libuv supports it (the UV_PROCESS_WINDOWS_HIDE flag to uv_spawn()) but node.js hasn't exposed it so far.

[atrauzzi]

Cool, is this something that can be exposed as another option to spawn and exec? Without claiming to be a whiz with C++ or nodejs internals, conceptually this sounds pretty low risk. And I mean, this is an issue that's been spoken about since at least 2015 -- pretty low hanging fruit for such a high impact.

[cjihrig]

@atrauzzi if you follow the logic of windowsVerbatimArguments, you should be able to implement something similar for this flag.

[atrauzzi]

I suspect it would make more sense for someone familiar with C++ dev to implement this.

[cjihrig]

@atrauzzi I've opened #15380, which exposes UV_PROCESS_WINDOWS_HIDE as windowsHide in the child_process methods. I don't have a Windows box on hand to test with at the moment, so could you or another Windows user see if that fixes the problem.

[bzoz]

I've tested #15380 but it looks like it does not solve the issue. But I'm also not confident that I've tested the right thing.

@atrauzzi could you provide a small example of how to reproduce the console popping? It would be great if it would be in pure Node.js, but since this looks related to the PM2 internals, an example that uses PM2 will work for now.

[bnoordhuis]

Ping @atrauzzi.

[atrauzzi]

I put together a quick example as part of this ticket's initial description if that's enough?

[bzoz]

You mean this: https://gist.github.com/atrauzzi/bbcc171b57a7ea276a2e6bf6419c7e51 ?

[atrauzzi]

Yeah.

[refack]

How serendipitous 😄 this is what's been stopping me from using this in #14042

[bzoz]

@atrauzzi the example looks like workaround the issue using edge-js. Could you provide some code that demonstrates the console window popping in and out?

[atrauzzi]

You can play with this module and flip the flags around in the node-native spawn:

https://github.com/atrauzzi/gerty/blob/master/src/Spawn.ts#L15-L35

I can't remember off the top of my head at the moment what the correct combination is. But I believe there's a combination that results in a window popping open when it really shouldn't be.

[bzoz]

Well, an exact combination would be very helpful 😉. I'm not even sure what am I looking for, the more detailed instructions you provide the easier it will be for me to find the issue and fix it.

[bzoz]

After libuv PR it still looks like it does not work as intended.

I've included libuv/libuv#1558 and #15380 in my Node build. I've included windowsHide: true in the spawn call (ForkMode.js:94). Since MSDN says using detached: true disables flag from libuv/libuv#1558, I've tied this two times with and without detached: true (with pm2 update in the middle).

I've created an empty file test.js. And I called: node bin/pm2 start test.js. Once in a while a console window would pop in for a split-second.

[atrauzzi]

Sorry, been very busy lately, but I just wanted to catch up -- Will the fix(es?) planned allow me to spawn a process with a shell, but without a window accompanying it? My main case here is that I need to have access to the default shell environment of the current user when spawning.

[toddwong]

Will cluster.fork honor this windowsHide eventually? It calls child_process.fork without this option for now I think.