Node.js - what exactly happens upon a new client request

Question

I want to understand more exactly what happens when a server receives a client request on a Node.js server. With a more traditional server, a new thread is created to handle the new client session. But in Node.js and other event-loop style servers, what exactly happens? What part of the codebase first gets executed? With node, I am almost certain something in the http module handles the new request first.

I want to know a little more about the details of how this works in a sort of compare and contrast style between the two types of handling of client connections.

Answer 1

In a nutshell:

• Node uses libuv to manage incoming connections and data events
• Events are placed in a queue to be handled on the next tick of the event loop
• When bytes start arriving, they are fed in to the native-code http parser
• The parser calls a callback in JS-land with the header contents
• The rest of the JS HTTP code dispatches the request to user code, which may be Express