Golang を使用して RESTful API を構築し、エラーを処理するにはどうすればよいですか?

import (
    "encoding/json"
    "fmt"
    "log"
    "net/http"

    "github.com/gorilla/mux"
)

r := mux.NewRouter()

func indexHandler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprint(w, "Hello, World!")
}

func postHandler(w http.ResponseWriter, r *http.Request) {
    var data map[string]interface{}
    if err := json.NewDecoder(r.Body).Decode(&data); err != nil {
        http.Error(w, "Invalid JSON", http.StatusBadRequest)
        return
    }

    log.Printf("Received data: %v", data)
    json.NewEncoder(w).Encode(map[string]interface{}{"status": "success"})
}

r.HandleFunc("/", indexHandler).Methods("GET")
r.HandleFunc("/post", postHandler).Methods("POST")

http.ListenAndServe(":8080", r)

type User struct {
    Name  string `json:"name"`
    Email string `json:"email"`
}

func userHandler(w http.ResponseWriter, r *http.Request) {
    switch r.Method {
    case "GET":
        json.NewEncoder(w).Encode([]User{{Name: "John", Email: "john@example.com"}})
    case "POST":
        var user User
        if err := json.NewDecoder(r.Body).Decode(&user); err != nil {
            http.Error(w, "Invalid JSON", http.StatusBadRequest)
            return
        }
        fmt.Fprint(w, "User created:", user)
    default:
        http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
    }
}