Web Services with the Standard Library

Sun, 04 Oct 2026 00:00:00 +0000

Since Go 1.22, net/http.ServeMux handles methods and path parameters, so a typical JSON API needs no router library. Frameworks like gin or chi still work, but are no longer required.

Routing with `ServeMux`

mux := http.NewServeMux()

mux.HandleFunc("GET /healthz", health)
mux.HandleFunc("POST /api/join", join)
mux.HandleFunc("GET /api/quizzes/{id}", getQuiz)
mux.HandleFunc("PUT /api/quizzes/{id}", updateQuiz)
mux.HandleFunc("GET /files/{path...}", serveFile) // wildcard rest-of-path
mux.Handle("/", spaHandler)                       // catch-all

func getQuiz(w http.ResponseWriter, r *http.Request) {
    id := r.PathValue("id")
    ...
}

Method in the pattern: wrong method → automatic 405 with an Allow header.
Most specific pattern wins, regardless of registration order.
Ambiguous patterns panic at registration, so conflicts surface at startup, not in production:

panic: pattern "GET /" conflicts with pattern "/api/":
  GET / matches fewer methods than /api/, but has a more general path pattern

Middleware is a function

No framework concept needed: a middleware takes a handler and returns a handler.

Slog on Notes

Web Services with the Standard Library

Routing with ServeMux

Middleware is a function

Routing with `ServeMux`