GetUsers     GET     /users
GetUser      GET     /users/{id}
CreateUser   POST    /users
UpdateUser   UPDATE  /users/{id}
DeleteUser   DELETE  /users/{id}

package main

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

  "github.com/gorilla/mux"
)

type User struct {
  ID        int    `json:"id,omitempty"`
  Firstname string `json:"firstname,omitempty"`
  Lastname  string `json:"lastname,omitempty"`
  Info      `json:"info,omitempty"`
}
type Info struct {
  City  string `json:"city,omitempty"`
  Phone int    `json:"phone,omitempty"`
}

var users []User

func GetUsers(w http.ResponseWriter, r *http.Request) {
  json.NewEncoder(w).Encode(users)
}

func GetUser(w http.ResponseWriter, r *http.Request) {
  id := convertParams(r)
  for _, u := range users {
      if u.ID == id {
          json.NewEncoder(w).Encode(u)
          return
      }
  }
  json.NewEncoder(w).Encode("User not found")
}

func CreateUser(w http.ResponseWriter, r *http.Request) {
  var user User
  _ = json.NewDecoder(r.Body).Decode(&user)
  users = append(users, user)
  json.NewEncoder(w).Encode(user)
}

func UpdateUser(w http.ResponseWriter, r *http.Request) {
  var user User
  id := convertParams(r)
  _ = json.NewDecoder(r.Body).Decode(&user)
  for i, u := range users {
      if u.ID == id {
          users[i] = user
          json.NewEncoder(w).Encode(user)
          break
      }
  }
}

func DeleteUser(w http.ResponseWriter, r *http.Request) {
  id := convertParams(r)
  for i, u := range users {
      if u.ID == id {
          copy(users[i:], users[i+1:])
          users = users[:len(users)-1]
          break
      }
  }
  json.NewEncoder(w).Encode(users)
}

func convertParams(r *http.Request) int {
  params := mux.Vars(r)
  id, err := strconv.Atoi(params["id"])
  if err != nil {
      log.Fatalf("err: %v", err)
  }
  return id
}

func main() {
  router := mux.NewRouter()
  user1 := User{ID: 1, Firstname: "hello", Lastname: "World", Info: Info{City: "Taipei", Phone: 123}}
  user2 := User{ID: 2, Firstname: "hello", Lastname: "World", Info: Info{City: "Taipei", Phone: 456}}
  users = append(users, user1, user2)
  router.HandleFunc("/users", GetUsers).Methods("GET")
  router.HandleFunc("/users/{id}", GetUser).Methods("GET")
  router.HandleFunc("/users", CreateUser).Methods("POST")
  router.HandleFunc("/users/{id}", UpdateUser).Methods("PUT")
  router.HandleFunc("/users/{id}", DeleteUser).Methods("DELETE")
  fmt.Println("Starting server on port 3000...")
  log.Fatal(http.ListenAndServe(":3000", router))
}

{
  "id": 3,
  "firstname": "hello",
  "lastname": "World",
  "info": {
    "city": "Taipei",
    "phone": 123
  }
}

go run main.go
// http://localhost:3000/users