middleware and stack functions invoker for expressjs and the response object capture

I see that expressjs app has a stack of Layer object Arrays. Which is the function that is used to pass the

I want to know:

• When a request is sent from the http client which function is invoked first and how is the stack array functions with middlewares invoked and results passed stepwise?
• Here is an example app.get(path, [middleware(req, res, next), m2(req, res, next), m3(req, res, next), m4(req, res, next)], handler(req, res)) => which function invokes functions stepwise => [middleware(req, res, next), m2(req, res, next), m3(req, res, next), m4(req, res, next), handler(req, res)]
• Where is the request and response objects created that is passed as arguments?
• Where is the response object callback function for send => onfinish/ onend functions which I can use to get the send/ sendfile's response object into a variable for an interceptor?

I am looking for the entry of the request and exit if the response (with the response result).

If you look at the code for app.listen() here, you see this:

app.listen = function listen() {
  var server = http.createServer(this);
  return server.listen.apply(server, arguments);
};

So, it is registering the app function object as a callback to http.createServer(). That will call the app function which is here for any incoming http request and that function looks like this:

var app = function(req, res, next) {
  app.handle(req, res, next);
};

Yes, this is a bit of weird design where the app object is actually a function (since functions are objects too), but that's the way Express did it.

So, the start of any routing is app.handle() here, which then ends up calling router.handle() here which then starts working with the layer objects to match defined routes.

You really shouldn't have to dive into any of this for anything other than curiosity. I have been able to do all sorts of custom things with Express by either listening to events that are already being fired on the req or res objects (such as when the request is done) or by overriding methods to intercept or modify or enhance functionality. All of this can be done from outside the source code and the private data structures of Express.

This is why I was asking you to describe your actual problem because there's a high likelihood that you don't have to go underneath the covers of Express into its private data structures to solve most actual problems. The public events and methods are quite capable.