node.js doesn't capture stdout or stderr from spawned process

[AndrewPardoe]

• A brief description
  node.js running under WSL doesn't appear to capture stdout or stderr from a spawned Windows process. My test uses a small app that just prints to stdout and stderr. Running it under three configurations gives three results:

1. spawning Linux app: stdout and stderr are captured in the node.js program (correct behavior)
2. spawning Windows app from WSL file path: WSL error message about CWD is captured in stderr, no stdout is captured.
3. spawning Windows app from Windows file path: no stderr, no stdout captured

• Expected results
  node.js should capture the stdout and stderr from the child process

• Actual results (with terminal output if applicable)
  no stdout and no stderr is captured

• Your Windows build number
  16167.rs_lkg, Ubuntu 16.04.2 LTS

• Steps / All commands required to reproduce the error from a brand new installation

1. Create apps that output to stdout and stderr on both Windows path (in my code, c:\tmp) and WSL path (in my code, ~/tmp). I've called the apps hellostd.exe and hellostd.

#include <stdio.h>
int main() {
    fprintf(stderr, "hello stderr\n");
    fflush(stderr);   
    fprintf(stdout, "hello stdout\n");
    fflush(stdout);
    return 0;
}

node.js exectest.js. You have to uncomment each test--I'm not good enough at JavaScript to make this test handle all the cases. The output gets interleaved if they all run in one invocation.

const spawn = require('child_process').spawn;

// Running Linux app properly captures stderr & stdout
//const test = spawn('./hellostd');

// Running Windows app fills stderr with "Unable to translate CWD" error
//const test = spawn('/mnt/c/tmp/hellostd.exe');

// Changing directory into "Windows" leaves empty stderr & stdout
const test = spawn('/mnt/c/tmp/hellostd.exe', {
    cwd: "/mnt/c/tmp"
});


test.stdout.on('data', (data) => {
    console.log(`process stdout is: ${data}`);
});


test.stderr.on('data', (data) => {
    console.log(`process stderr is: ${data}`);
});

test.on('close', (code) => {
    console.log(`child process exited with code ${code}`);
});

• Strace of the failing command
  https://gist.github.com/AndrewPardoe/d57c9dda3b77fccedbe2afbdf9e55ace

• Required packages and commands to install
  node.js

This may be related to closed issue #1774 dealing with race conditions in node.js code running under WSL.

I'm internal to Microsoft, working on the MSVC team. Feel free to contact me directly.

[benhillis]

Thanks for reporting this, I've dug into this and figured out the issue. It has to do with us reporting WSL socket file descriptors as "FILE_DEVICE_UNKNOWN" on NT which causes crt to not set up the stdout / stderr handles correctly. I'll get this fixed.

[benhillis]

Look for this to be fixed soon after we begin flighting Windows vNext builds.