How to shut down express js gracefully while supporting keep-alive

expressjs-shutdown.js

// this is an excerpt of essential but non-working part extracted from local expressjs application ...

var app = require( "express" )();

var httpServer = require( "http" ).createServer( app );

httpServer.on( "connection", function( socket ) {
	socket.unref();
} );

httpServer.listen( CONFIG.port, CONFIG.ip );

app.use( function _gracefulShutdownSupporter( req, res, next ) {
	// mark connection to be actively serving request now
	req.connection.ref();

	// wrap genuine end() on response to clear mark afterwards
	res._genuineEnd = res.end;
	res.end = function() {
		var args = [], i, l, a, injected = false,
			socket = req.connection;

		for ( i = 0, l = arguments.length, args = []; i < l; i++ ) {
			a = arguments[i];

			if ( typeof a === "function" && !injected ) {
				injected = true;
				args[i] = (function( genuine ) {
					return function() {
						socket.unref();
						return genuine.apply( this, arguments );
					};
				})( a );
			} else {
				args[i] = a;
			}
		}

		if ( !injected ) {
			args.push( function() {
				socket.unref();
			} );
		}

		return res._genuineEnd.apply( this, args );
	};

	next();
} );

As a final note, gracefully shutting down expressjs application (involving database connection) was working finally using the latest approach given above.