How to fork a child process that listens on a different debug port than the parent

Question

I am trying to use child_process.fork to spawn a process that breaks and listens on the V8 debug protocol.

However, I can\'t get the forked process to

Answer 1

Simple enough answer, found on this comment and with some help from #Node.js on Freenode:

Just move the --debug-brk into the execArgv key of the options param to fork:

// Excerpt:

args = [
   '127.0.0.1'
  , 3030
  , 'api-testing'
]

env = { 'DB_URI': 'mongodb://localhost/test' }

child = fork(nodeModule, args, {
    env: env
  , execArgv: ['--debug-brk=6001']
})
  .on('message', this.callback)

execArgv is the array of parameters passed to the node process. argv is the set passed to the main module. There's a dedicated parameter to child_process.fork for argv, but execArgvs have to be placed within the opts param. This works, and in the child process we have:

> process.execArgv 
["--debug-brk=6001"]
> process.argv
["/usr/local/Cellar/node/0.10.13/bin/node" "/Users/dmitry/dev/linksmotif/app.js", "127.0.0.1", "3030", "api-testing"] 

In summary

Node.js consistently treats execArgv and argv as separate sets of values.

Answer 2

Before to fork remove old debug-brk parameter :

process.execArgv = process.execArgv.filter(function(o){ 
    var x = "--debug-brk"; 
    return o.substring(0, x.length) !== x
});

and add a new one:

process.execArgv.push("--debug-brk=9999");