HTTP Servers With net/http

ServeMux patterns and handlers

net/http provides production-grade HTTP servers and clients. Since Go 1.22 the built-in ServeMux supports method and wildcard patterns such as "GET /products/{id}", read with r.PathValue("id"), and automatically answers 405 Method Not Allowed for other methods. Handlers write status, headers and body through http.ResponseWriter. httptest runs real servers on random ports for tests. In production, set server timeouts (ReadHeaderTimeout and friends) and shut down gracefully.

HTTP, JSON and time out of the box

Go's standard library covers most needs of a web service without extra dependencies.

A product endpoint tested with httptest, run

I ran this with Go 1.27.1 (go run . in a module named demo, standard library only). The server returns JSON for product 1, a 404 for an unknown id, and 405 for a POST because the pattern only allows GET.

package main

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/http/httptest"
)

type Product struct {
	ID    int     `json:"id"`
	Name  string  `json:"name"`
	Price float64 `json:"price"`
}

func newMux() *http.ServeMux {
	mux := http.NewServeMux()
	products := map[string]Product{"1": {1, "Notebook", 120}}
	mux.HandleFunc("GET /products/{id}", func(w http.ResponseWriter, r *http.Request) { // Go 1.22+ patterns
		p, ok := products[r.PathValue("id")]
		if !ok {
			http.Error(w, "product not found", http.StatusNotFound)
			return
		}
		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(p)
	})
	return mux
}

func main() {
	srv := httptest.NewServer(newMux()) // a real HTTP server on a random local port
	defer srv.Close()
	for _, path := range []string{"/products/1", "/products/9"} {
		resp, err := http.Get(srv.URL + path)
		if err != nil {
			panic(err)
		}
		body, _ := io.ReadAll(resp.Body)
		resp.Body.Close()
		fmt.Printf("GET %s -> %d %s", path, resp.StatusCode, body)
	}
	resp, _ := http.Post(srv.URL+"/products/1", "application/json", nil)
	fmt.Println("POST /products/1 ->", resp.StatusCode)
}

Output:

GET /products/1 -> 200 {"id":1,"name":"Notebook","price":120}
GET /products/9 -> 404 product not found
POST /products/1 -> 405

Never use the default server without timeouts

Create an http.Server with ReadHeaderTimeout, ReadTimeout and WriteTimeout to protect against slow clients.

त्वरित जाँच: What does the pattern "GET /products/{id}" do with a POST request?

• The mux responds 405 Method Not Allowed
• Calls the handler anyway
• Returns 404 always
• Crashes the server