Child pipe proof-of-concept

readme.md

Pros:

1. (against stdin/stdout usage) Leaves stdin for request data, stdout for response and stderr for logging.
2. Uses standard Node child_process.spawn options.stdio[3]='ipc' technique.

Cons:

1. Right now uses '\n' as separator - it's original flaw of Node 'ipc' implementation.
2. Unportable: Node 'ipc' uses different implementation for different OSes. I.e. on Windows it uses named pipes and I've failed to fix child.py to work on windows. I can't ever imagine what it will be on Mac.
3. Incompatible: Node 'ipc' can send handle via this socket. I had not yet found how it's implemented.

child.js

#!node
if(!process.send) {
  console.log("Not started with accessible parent IPC.");
  process.exit(1);
}
process.on('message', function(json) {
  console.log('parent->child message passed', json);
  process.send({type:'got', payload:json});
  if(json.type === 'exit') process.exit(0);
});

child.py

#!/usr/bin/env python
import os
import sys
import socket
import pprint
import json

#pprint.pprint(dict(os.environ))
#print 'NODE_CHANNEL_FD =', os.environ.get('NODE_CHANNEL_FD')
fd = int(os.environ['NODE_CHANNEL_FD'])
if sys.platform == 'win32':
  apiin = os.fdopen(fd, 'r')
  apiout = os.fdopen(fd+1, 'w')
else:
  api = socket.fromfd(fd, socket.AF_UNIX, socket.SOCK_STREAM)
  apiin = api.makefile('r')
  apiout = api.makefile('w')
while True:
  data = apiin.readline()
  data = json.loads(data)
  print 'parent->child message passed', data
  apiout.write(json.dumps({"type":"got", "payload":data})+'\n')
  apiout.flush()
  if data.get("type") == "exit":
    break

parent.js

#!node
var util = require('util');
var spawn = require('child_process').spawn;

//console.log(process.argv);
var action = process.argv[2]||'py';
//console.log('action =', action);
var child;
if(action === 'py') {
  var proc = 'python';
  var args = ['child.py'];
  if(process.platform == 'win32') {
    proc = 'py';
    args = ['-2', 'child.py'];
    //args = ['-3', 'child.py'];
  }
  //console.log(proc, args);
  child = spawn(proc, args, {stdio:[0, 1, 2, 'ipc']});
} else if(action === 'js') {
  child = spawn(process.execPath, ['child.js'], {stdio:[0, 1, 2, 'ipc']});
} else if(action === 'pfiles') {
  child = spawn(action, [process.pid], {stdio:[0, 1, 2, 'ipc']});
} else if(action === 'pfiles1') {
  child = spawn('sh', ['-c', 'exec pfiles $$'], {stdio:[0, 1, 2, 'ipc']});
} else {
  child = spawn(action, [], {stdio:[0, 1, 2, 'ipc']});
}
//child.stdout.on('data', function (data) {
//  console.log('stdout: ' + data);
//});
//child.stderr.on('data', function (data) {
//  console.log('stderr: ' + data);
//});
child.on('close', function (code) {
  console.log('child process exited with code ' + code);
});
child.on('error', function (err) {
  console.log('child process not started with error ' + err);
});
child.on('message', function(json) {
  console.log('child->parent message passed', json);
});
//console.log('child', child);
//console.log('child.stdio', child.stdio);
child.send({type:'intro'});
setTimeout(function() {
  child.send({type:'exit'});
}, 1500);