Allows easy composition of a chain of connect.js-style middlewares

compose_connect_middlware.js

// Allows easy composition of a chain of connect.js-style middlewares in node.js
// given:
// function A(req,res,next){}
// function B(req,res,next){}
// composeMiddleware(A,B) will return a function(req,res,next) that passes the request
// through both handlers,  just like Connect. If a next() is called with an error
// the call chain is stopped and the error is passed to the topmost next()
// If next() is called with the second parameter set to 'break' "next(null, 'break')"
// The chain is halted and route control is passed back to the original next()
function composeMiddleware(){
	var layers = Array.prototype.slice.call(arguments);
		
	var handler = function(req,res,next){
		var i = 0;
		
		// This is passed as the next() parameter
		function nextLayer(err, escapeStack){
			if(err)	return next(err);
			// if the second param is 'break', break out of this stack by calling
			// the original next()
			if(escapeStack == 'break') return next();
			
			// if there are still layers left
			if(i < layers.length){
				var layer = layers[i++];
				layer(req, res, nextLayer);
			} else next(); // we're done with the stack.
		}
		
		nextLayer();
	}
	
	return handler;
}