http.createServer方法中添加了选项参数的用例是什么

Question

Upon going through the node.js documentation I realized the createServer method on the http module has been updated to receive an options argument. It was not included before in previous versions of node.js if I remember correctly

http.createServer([options][, requestlistener])

Link: https://nodejs.org/dist/latest-v10.x/docs/api/http.html#http_http_createserver_options_requestlistener

It is not clear what the options can be used for but it is an object that has the properties IncomingMessage and ServerResponse .

I just want clarification on what it can be used for and a code example.

Answer 1

The server does create an IncomingRequest and ServerResponse instance for each request it receives, and passes them to the request event listener - they are the objects that you receive in the typical (req, res) => { … } functions.

In particular they are instantiated here and there , in the internals of the http library (and also, similarly, in the https and http2 libraries). The createServer options allow you to customise which classes exactly are used for these objects. A simple example:

import { IncomingMessage, ServerResponse, createServer } from 'http';

class MyIncomingMessage extends IncomingMessage {
  …
}
class MyServerResponse extends ServerResponse {
  …
}

const server = createServer({
  IncomingMessage: MyIncomingMessage,
  ServerResponse: MyServerResponse,
});
server.on('request', (req, res) => {
  console.assert(req instanceof MyIncomingMessage);
  console.assert(res instanceof MyServerResponse);

  res.statusCode = 200;
  res.end('Hello!');
});

A simple customisation would be adding your own methods, and otherwise inheriting from the builtin default classes. You could also overwrite some methods, or you could roll your own implementation.