memoized-server.js

var cache = require('continuable-cache');
var extend = require('xtend/mutable');

function MemoizedServer(createServer) {
    var createCachedServer = cache(createServer);

    var started = false;
    var server = {
        start: function start(callback) {
            server.counter++;
            var _server = createCachedServer(function () {
                var args = arguments;
                var self = this;
                process.nextTick(function () {
                    callback.apply(self, args);
                });
            });

            if (!started) {
                started = true;
                extend(server, _server);
            }

            return server;
        },
        counter: 0,
        shutdown: function shutdown(callback) {
            server.counter--;

            if (server.counter === 0) {
                server.close(function () {
                    // we closed the server, reset the 
                    // state machine
                    createCachedServer = cache(createServer);
                    started = false;

                    callback.apply(this, arguments);
                });
            } else {
                callback(null);
            }
        }
    };

    return server;
}

module.exports = MemoizedServer;