Simple calculator API server in Golang

calculator_api_server.go

package main

import (
	"encoding/json"
	"fmt"
	"math"
	"net/http"
  // go get "github.com/gorilla/mux"
	"github.com/gorilla/mux"
)

type MathObject struct {
	Operand string `json:"operand"`
	FirstNumber int `json:"first_number"`
	SecondNumber int `json:"second_number"`
}

type ResponseObject struct {
	Message string `json:"message"`
	Result float64 `json:"result"`
	Code int `json:"code"`
}

func (ro *ResponseObject) assignSuccessResponse(result float64) {
	ro.Result = result
	ro.Code = 200
	ro.Message = "Result calculated successfully!"
}

func (ro *ResponseObject) assignErrorResponse(code int, msg string) {
	ro.Code = code
	ro.Message = msg
}

func main() {
	myRouter := mux.NewRouter().StrictSlash(true)
	myRouter.HandleFunc("/", handleHomePage)
	myRouter.HandleFunc("/math", handleMath)
	http.ListenAndServe(":70", myRouter)
}

func handleHomePage(w http.ResponseWriter, req *http.Request) {
	fmt.Fprint(w, "Hello friend!\nIt's calculator app!")
}

func handleMath(w http.ResponseWriter, req *http.Request) {
	request := &MathObject{}
	defer req.Body.Close()
	err := json.NewDecoder(req.Body).Decode(request)
	if err != nil {
		fmt.Println("Error Decoding request body!", err)
	}
	response := &ResponseObject{}
	switch request.Operand {
	case "+":
		response.assignSuccessResponse(
			float64(request.FirstNumber + request.SecondNumber),
		)
	
	case "-":
		response.assignSuccessResponse(
			float64(request.FirstNumber - request.SecondNumber),
		)
		
	case "*":
		response.assignSuccessResponse(
			float64(request.FirstNumber * request.SecondNumber),
		)

	case "/":
		if request.SecondNumber == 0 {
			response.assignErrorResponse(400, "Bad Request: Division by zero is impossible!")
		} else {
			response.assignSuccessResponse(float64(request.FirstNumber) / float64(request.SecondNumber))
		}
	case "^": 
		response.assignSuccessResponse(math.Pow(float64(request.FirstNumber), float64(request.SecondNumber)))
	default:
		response.assignErrorResponse(400, "Bad Request: Operand is not defined!")
	}

	json.NewEncoder(w).Encode(response)
}