Reattaching to spawned process via nodejs

Question

I am creating a small proprietary game server manager in Node.js; currently it runs the game by spawning via child_process:

var server = spawn(cmd, args, { cwd: 'something' });

So long as the manager continues to run I can pipe commands and deal with the child as I would like. However, consider the possibility that my manager crashes or is closed. How would I then reattach to the previously spawned child process (which was still running while the manager was down)? I can store pidfiles to try and reconnect based on pid; but I'm not sure how to get a child_process object with access to the child's stdio objects.

I really would like this to be recoverable; any help is appreciated, thanks!

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Please note: The game servers are proprietary, some examples are Minecraft, Source DS, etc. Assume i do not have access to the sever source.

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EDIT

After reading some source code from node's child_process it looks like if you specify a property in the options called stdinStream, stdoutStream, or stderrStream it should just open a socket to it. (See lines 428 - 496). So the issue then is, how do I stop spawn from actually doing a spawn and instead just settings its values based on a specified pid and streams I pass. (I would get my stdinStream by doing fs.createWriteStream('/proc/PID/fd/0'); which should work since that fd is created as a pipe.)

Answer 1

After speaking with some of the guys on the node project, it looks like the only way I can accomplish this is by dealing with the raw file descriptors in the proc fs. I will probably mock up something similar to a child_process object and create its streams like:

var child = {};
child.stdin = fs.createWriteStream('/proc/PID/fd/0');
child.stdout = fs.createReadStream('/proc/PID/fd/1');
child.stderr = fs.createReadStream('/proc/PID/fd/2');

Answer 2

To extend what someone said in a comment above, you may be able to use http://nodejs.org/api/net.html where each child process creates a server (net.createServer()) and you keep a list of what children are listening at what ports somewhere, and then when your master restarts, it goes and finds that list of children and connects to each their servers. The Sockets that you get from net.createConnection() replace the child_process objects in your master.

net servers and sockets implement the same Readable and Writable Stream interfaces as stdio, so after setting up and connecting, you should be able to write(...) and pipe() events like you've been doing.

This may not be the best solution but I believe it will work.