The middleware concept

Learn the middleware concept and layered structure.

The middleware concept

Middleware is an intermediate layer that runs before and after an HTTP request reaches the real handler. It gathers work that repeats on every route — logging, authentication, compression, timing — in one place.

request → [log] → [auth] → handler
response ← [log] ← [auth] ← handler

In Go, middleware is simply a function that takes an http.Handler and returns a new http.Handler.

Why middleware?

Copying the same log and permission code to the top of every handler means duplication and the risk of forgetting it. With middleware this code is written once and applied to the routes you choose. Handlers also focus only on their own job, which makes them easier to test.

Exercise First middleware

Write func etiket(next http.Handler) http.Handler: it adds the header X-Ders: go to the response and calls next.ServeHTTP(w, r). Test it with httptest and print the header.

Show example solution

package main

import (
    "fmt"
    "net/http"
    "net/http/httptest"
)

func etiket(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("X-Ders", "go")
        next.ServeHTTP(w, r)
    })
}

func main() {
    h := etiket(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
    rec := httptest.NewRecorder()
    h.ServeHTTP(rec, httptest.NewRequest("GET", "/", nil))
    fmt.Println(rec.Header().Get("X-Ders"))
}

Test yourself

What is the typical middleware signature in Go?
- func(http.ResponseWriter)
- func() error
- func(*http.Request) bool
- func(http.Handler) http.Handler
Show answer

func(http.Handler) http.Handler — Middleware wraps a handler: it takes one and returns a new handler that adds work around it.

The wrapped type

func logla(next http.____) http.Handler {

Show answer

func logla(next http.Handler) http.Handler {

Middleware uses

Log

Records the request
Auth

Checks permission
Recover

Catches panics
Gzip

Compresses the response

Next lesson: HTTP middleware

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies