Unable to write to child.stdin on Windows

[dmytrokyrychuk]

I wrote the two scripts to illustrate a problem. Script in JS uses child_process to execute a script written in Python. JS one then writes something to child's stdin. Child then should print everything to stdout.

const child_process = require('child_process');

function log(data) {
  process.stdout.write(data);
}

log('Initializing child process\n');

const program = child_process.exec('python echo.py', {stdio: 'pipe'});
program.stdin.setEncoding('utf8');
program.stdout.pipe(process.stdout);
program.stderr.on('data', function(data) {
  log('error: ' + data);
});

const result = program.stdin.write('check\n', function(){
  log('write completed\n');
});
log('write succeded: ' + result + '\n');

setTimeout(function(){program.kill();}, 3000);

log('Initializing completed\n');

import sys
import msvcrt

while True:
    print 'Input: ', msvcrt.getch()

Below is the output I get when I run the script.

>node.exe echo.js
Initializing child process
write succeded: true
Initializing completed
write completed

Nothing happens after. However, when I run python script directly and type anything into a terminal, it prints input back as expected, which means that the python script works correctly and the problem is probably caused on the js side.

I don't experience such bug on Linux.

Can somebody explain, why can't I write into a child's stdin on Windows?

Thanks in advance.

[ivankravets]

+1

[cjihrig]

I would suggest using spawn() or even execFile(), as they do not run your program in a shell like exec() does. I think python might have an interactive flag, similar to Node's -i flag. Either way, both of these work for me on OS X and Windows 7 with the latest from master.

Using spawn():

'use strict';
const cp = require('child_process');
const child = cp.spawn('node', ['-i']);

child.stdout.pipe(process.stdout);
child.stderr.pipe(process.stderr);

child.stdin.write('process.versions;\n');
child.stdin.end();

Using execFile():

'use strict';
const cp = require('child_process');
const child = cp.execFile('node', ['-i'], (err, stdout, stderr) => {
  console.log(stdout);
});

child.stdin.write('process.versions;\n');
child.stdin.end();

[jasnell]

Closing as there does not appear to be anything further to do here. Can reopen if that assumption is incorrect.