hot swapping for node.js

run_dev_server.js

/*
 * This file is part of the Spludo Framework.
 * Copyright (c) 2009-2010 DracoBlue, http://dracoblue.net/
 *
 * Licensed under the terms of MIT License. For the full copyright and license
 * information, please see the LICENSE file in the root folder.
 */

/*
 * based on https://github.com/DracoBlue/spludo/blob/master/build/run_dev_server.js
 * Rewritten by marcello@cellosoft.com
 */
var child_process = require('child_process'),
    fs = require("fs"),
    util = require("util"),
    path = require("path")

if (process.ARGV.length < 3) {
    util.debug("usage: %s %s <server.js>", process.ARGV[0], process.ARGV[1])
    process.exit(1)
}

var child = null,
    watchedFiles = [],
    restarting = false,
    shutdown = false,
    selfPath = path.resolve(__filename),
    pidPath = selfPath + '.pid',
    mainScript = process.ARGV[2] || "dev_server.js"

function restart() {
    if (!restarting) {
        restarting = true
        if (child) {
            stop()
        } else {
            start()
        }
    }
}

function start() {
    try {
        var pidData = fs.readFileSync(pidPath);
        var oldPid = parseInt(pidData)
        if (oldPid) {
            util.debug('Killing old server ('+oldPid+')')
            process.kill(oldPid)
        }
    } catch (e) {}

    watchFiles()

    child = child_process.spawn(process.ARGV[0], [mainScript])

    util.debug("<"+ mainScript + "> Started... (pid = "+child.pid+")")

    fs.writeFileSync(pidPath, String(child.pid))

    child.stdout.on('data', function (data) {
        process.stdout.write(data)
    });

    child.stderr.on('data', function (data) {
        util.print(data)
    });

    child.on('exit', function (code, signal) {
        child = null
        try {
            fs.unlinkSync(pidPath)
        } catch (e) {}
        if (restarting && !shutdown) {
            unwatchFiles()
            start()
        } else if ((code || signal) && !shutdown) {
            util.debug("<" + mainScript + "> Exited with code " + (code || signal) + ", waiting for file change...\n")
        } else {
            process.exit(code)
        }
        restarting = false
    });

}

function stop() {
    child && child.kill()
}

function watchFiles() {
    child_process.exec('find .', function(error, stdout, stderr) {
        var files = stdout.trim().split("\n")

        files.forEach(function(file) {
            var resolvedFile = path.resolve(file)
            if (path.resolve(pidPath) != resolvedFile) {
                var isRunScript = resolvedFile == selfPath
                watchedFiles.push(file);
                fs.watchFile(file, {interval:500}, function(current, previous) {
                    if (!shutdown && (current.mtime.valueOf() != previous.mtime.valueOf() ||
                                      current.ctime.valueOf() != previous.ctime.valueOf())) {
                        if (isRunScript) {
                            util.debug("<" + file + "> changed! (i.e. this hot swap code) Shutting down...")
                            shutdown = true
                            stop()
                        } else {
                            util.debug('<' + file + '> changed')
                            restart()
                        }
                    }
                })
            }
        })
    })
}

function unwatchFiles() {
    watchedFiles.forEach(function(file) { fs.unwatchFile(file) })
    watchedFiles = []
}

process.on('exit', stop)

start()