Node.js ruby subprocess hangs

Question

Based on the example here, I'm trying to spawn a ruby process (v1.8.7) from Node.js (v0.4.8). A process and an empty log file are created, but nothing happens until I kill it. If I leave out the STDIN.each_line bit, the code runs fine.

I suspect something stdin doesn't finish so ruby is still waiting for input. Perhaps ruby.stdin.write("ping\n"); doesn't do what I think it should do?

Have you run the ruby code by itself? Do you see the same behavior, or does it run as expected? — Pat
– Pat, Commented Aug 1, 2011 at 18:29
@pat If I run the ruby code from the command line, type some random text and press enter and it echoes the text and creates a log file in the same directory. — Sjors Provoost
– Sjors Provoost, Commented Aug 1, 2011 at 18:33
Correction: it does create an empty process log file, just not where I expected. I'll update my question. I also find that the ruby file works fine if I leave out the STDIN.each_line part. — Sjors Provoost
– Sjors Provoost, Commented Aug 1, 2011 at 19:02

Hank · Accepted Answer · 2011-08-01 19:20:47Z

1

Here's what I have that seems to do what you want:

var util  = require('util'),
    sys   = require('sys'),
    spawn = require('child_process').spawn,
    ruby  = spawn('ruby', [__dirname + '/process.rb']);

function trim(str) {
  return str.replace(/^\s+|\s+$/, '');
}

ruby.stdout.on('data', function(data) {
  console.log('stdout: ' + trim(data.toString()));
});

ruby.stdout.on('end', function(data) {
  ruby.stdout.flush();
});

ruby.stderr.on('data', function(data) {
  console.log('stderr: ' + data);
});

ruby.on('exit', function(code, signal) {
  if(code != null) console.log('exit: ' + code);
  else if(signal != null) console.log('killed: ' + signal);
});

ruby.stdin.write("ping\n");
ruby.stdin.end();

answered Aug 1, 2011 at 19:20

Hank

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