Accessing process.stdin hangs on Windows

[segrey]

Let's consider this example project consisting of 3 files:

// main.js
var spawn = require('child_process').spawn;
var middle = spawn(process.execPath, ['middle.js'], {
 'stdio': 'pipe'
});

middle.stdout.on('data', function(data) {
 process.stdout.write('stdout from middle: ' + data);
});

middle.stderr.on('data', function(data) {
 process.stdout.write('stderr from middle: ' + data);
});

middle.on('close', function(code) {
 process.stdout.write('middle process finished with exit code ' + code);
});

// middle.js
var spawn = require('child_process').spawn;
var stdin = process.stdin;
console.log('middle: isatty(stdin)=' +require('tty').isatty(stdin));
spawn(process.execPath, ['child.js'], {
 'stdio': [process.stdin, process.stdout, process.stderr]
});

// child.js
console.log('child: accessing process.stdin');
console.log('child: done successfully ' + process.stdin);

Running node main.js in cmd.exe should normally output these lines and exit

stdout from middle: middle: isatty(stdin)=false
stdout from middle: child: accessing process.stdin
stdout from middle: child: done successfully [object Object]
middle process finished with exit code 0

However, from time to time it outputs only two first lines and hangs:

stdout from middle: middle: isatty(stdin)=false
stdout from middle: child: accessing process.stdin

The hanging is caused by accessing process.stdin in child.js. Please note it works fine if process.stdin is replaced with 'pipe' here:

// middle.js
...
spawn(process.execPath, ['child.js'], {
 'stdio': ['pipe', process.stdout, process.stderr]
});

Node.js v7.4.0
OS Windows 10

[addaleax]

/cc @nodejs/platform-windows

[seishun]

See also #5620

[Fishrock123]

Does changing the spawn option to 'inherit' for stdin make any difference?

[segrey]

@Fishrock123 If you meant changing middle.js, like

// middle.js
...
spawn(process.execPath, ['child.js'], {
 'stdio': 'inherit'
});

Then, no, it doesn't make any difference for me.
As for changing main.js, it's will change the behavior, yes. However, middle.js is executed with piped standard streams (not tty) in my environment, so it's impossible to make this change for me.

[Fishrock123]

If you meant changing middle.js, like

Correct. Just making sure there wasn't any hidden Windows logic in inherit.