Go HTTP middleware explained: what it is, how it works, and how to build your own

This is part 2 of 2 in the series Go HTTP middleware from scratch. If you're new to Go types, → read part 1 first.

The same code keeps showing up everywhere

You're building an HTTP server. Every request needs a unique ID for tracing. Every request needs to check authentication. Every request needs its duration logged. The naive approach: copy that code into every handler.

// Without middleware — same boilerplate in every single handler

func getUserHandler(w http.ResponseWriter, r *http.Request) {