How has http.ServeMux evolved in Go 1.22 and what routing patterns does it support?

Go 1.22 significantly upgraded http.ServeMux with method-based routing, path parameters, and wildcard matching — reducing the need for third-party routers in many applications.

mux := http.NewServeMux()

// Go 1.22+ enhanced routing patterns:

// Method + exact path
mux.HandleFunc("GET /health", func(w http.ResponseWriter, r *http.Request) {
    w.WriteHeader(http.StatusOK)
    w.Write([]byte(`{"status":"ok"}`))
})

// Method + path with named parameter {id}
mux.HandleFunc("GET /users/{id}", func(w http.ResponseWriter, r *http.Request) {
    id := r.PathValue("id")  // extract path variable
    fmt.Fprintf(w, "user %s", id)
})

// Method + path with wildcard {path...} (matches remainder)
mux.HandleFunc("GET /files/{path...}", func(w http.ResponseWriter, r *http.Request) {
    path := r.PathValue("path")
    http.ServeFile(w, r, filepath.Join("/static", path))
})

// POST with body
mux.HandleFunc("POST /users", createUserHandler)

// DELETE
mux.HandleFunc("DELETE /users/{id}", deleteUserHandler)

// Host-based routing
mux.HandleFunc("api.example.com/GET /v1/", apiV1Handler)

// Trailing slash subtree pattern (matches /api/ and all sub-paths)
mux.HandleFunc("/api/", apiHandler)

// Pre-1.22 pattern: no method prefix, manual method check
// mux.HandleFunc("/users", func(w http.ResponseWriter, r *http.Request) {
//     switch r.Method {
//     case http.MethodGet:  listUsers(w, r)
//     case http.MethodPost: createUser(w, r)
//     default:              http.Error(w, "method not allowed", 405)
//     }
// })

Go 1.22 routing precedence: more specific patterns win over less specific ones. A pattern with a method is more specific than one without. An exact path is more specific than a wildcard. If two patterns conflict (same specificity, overlapping matches), the registration panics at startup — catching routing mistakes at boot time rather than silently returning wrong responses.

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