Building Login and Register Application with Go

Building Login and Register Application with Go

I wrote this code in 2016 but re-shared it for newbies.

Basic knowledges we need to know to develop web app with Go; Login and Register!

For this reason, in this article, we will prepare examples for login and register.

Section 1:

To do list;

• Form data process
• Login example
• Register example

helpers/StringHelpers.go

package helpers

func IsEmpty(data string) bool {
	if len(data) == 0 {
		return true
	} else {
		return false
	}
}

main.go

package main

import (
	"fmt"
	"net/http"

	h "helpers"
)

func main() {

	uName, email, pwd, pwdConfirm := "", "", "", ""

	mux := http.NewServeMux()

	// Signup
	mux.HandleFunc("/signup", func(w http.ResponseWriter, r *http.Request) {
		r.ParseForm()

		/*
			// Available for testing.
			for key, value := range r.Form {
				fmt.Printf("%s = %s\n", key, value)
			}
		*/

		// Data from the form
                uName = r.FormValue("username")
                // Data from the form 
		email = r.FormValue("email")        
		// Data from the form
                pwd = r.FormValue("password")       
                // Data from the form
		pwdConfirm = r.FormValue("confirm") 

		// Empty data checking
		uNameCheck := h.IsEmpty(uName)
		emailCheck := h.IsEmpty(email)
		pwdCheck := h.IsEmpty(pwd)
		pwdConfirmCheck := h.IsEmpty(pwdConfirm)

		if uNameCheck || emailCheck || pwdCheck || pwdConfirmCheck {
			fmt.Fprintf(w, "ErrorCode is -10 : There is empty data.")
			return
		}

		if pwd == pwdConfirm {
	        	// Save to database (username, email and password)
			fmt.Fprintln(w, "Registration successful.")
		} else {
			fmt.Fprintln(w, "Password information must be the same.")
		}
	})

	// Login
	mux.HandleFunc("/login", func(w http.ResponseWriter, r *http.Request) {
		r.ParseForm()

		email = r.FormValue("email")  // Data from the form
		pwd = r.FormValue("password") // Data from the form

		// Empty data checking
		emailCheck := h.IsEmpty(email)
		pwdCheck := h.IsEmpty(pwd)

		if emailCheck || pwdCheck {
			fmt.Fprintf(w, "ErrorCode is -10 : There is empty data.")
			return
		}

		dbPwd := "1234!*."                   // DB simulation
		dbEmail := "cihan.ozhan@hotmail.com" // DB simulation

		if email == dbEmail && pwd == dbPwd {
			fmt.Fprintln(w, "Login succesful!")
		} else {
			fmt.Fprintln(w, "Login failed!")
		}
	})

	http.ListenAndServe(":8080", mux)
}

Section 2 : User login, register and cookie

To do list;

• Form data process
• Login example
• Register example

helpers/FileHelper.go

package helpers

import "io/ioutil"

func LoadFile(fileName string) (string, error) {
	bytes, err := ioutil.ReadFile(fileName)
	if err != nil {
		return "", err
	}
	return string(bytes), nil
}

helpers/StringHelper.go

package helpers

func IsEmpty(data string) bool {
	if len(data) <= 0 {
		return true
	} else {
		return false
	}
}

data/UserData.go

package data

func UserIsValid(uName, pwd string) bool {
	// DB simulation
	_uName, _pwd, _isValid := "cihanozhan", "1234!*.", false

	if uName == _uName && pwd == _pwd {
		_isValid = true
	} else {
		_isValid = false
	}

	return _isValid
}

common/Handlers.go

package handlers

import (
	"fmt"
	"net/http"

	"helpers"
	"data"
	"github.com/gorilla/securecookie"
)

var cookieHandler = securecookie.New(
	securecookie.GenerateRandomKey(64),
	securecookie.GenerateRandomKey(32))

// Handlers

// for GET
func LoginPageHandler(response http.ResponseWriter, request *http.Request) {
	var body, _ = helpers.LoadFile("templates/login.html")
	fmt.Fprintf(response, body)
}

// for POST
func LoginHandler(response http.ResponseWriter, request *http.Request) {
	name := request.FormValue("name")
	pass := request.FormValue("password")
	redirectTarget := "/"
	if !helpers.IsEmpty(name) && !helpers.IsEmpty(pass) {
		// Database check for user data!
		_userIsValid := data.UserIsValid(name, pass)

		if _userIsValid {
			SetCookie(name, response)
			redirectTarget = "/index"
		} else {
			redirectTarget = "/register"
		}
	}
	http.Redirect(response, request, redirectTarget, 302)
}

// for GET
func RegisterPageHandler(response http.ResponseWriter, request *http.Request) {
	var body, _ = helpers.LoadFile("templates/register.html")
	fmt.Fprintf(response, body)
}

// for POST
func RegisterHandler(w http.ResponseWriter, r *http.Request) {
	r.ParseForm()

	uName := r.FormValue("username")
	email := r.FormValue("email")
	pwd := r.FormValue("password")
	confirmPwd := r.FormValue("confirmPassword")

	_uName, _email, _pwd, _confirmPwd := false, false, false, false
	_uName = !helpers.IsEmpty(uName)
	_email = !helpers.IsEmpty(email)
	_pwd = !helpers.IsEmpty(pwd)
	_confirmPwd = !helpers.IsEmpty(confirmPwd)

	if _uName && _email && _pwd && _confirmPwd {
		fmt.Fprintln(w, "Username for Register : ", uName)
		fmt.Fprintln(w, "Email for Register : ", email)
		fmt.Fprintln(w, "Password for Register : ", pwd)
		fmt.Fprintln(w, "ConfirmPassword for Register : ", confirmPwd)
	} else {
		fmt.Fprintln(w, "This fields can not be blank!")
	}
}

// for GET
func IndexPageHandler(response http.ResponseWriter, request *http.Request) {
	userName := GetUserName(request)
	if !helpers.IsEmpty(userName) {
		var indexBody, _ = helpers.LoadFile("templates/index.html")
		fmt.Fprintf(response, indexBody, userName)
	} else {
		http.Redirect(response, request, "/", 302)
	}
}

// for POST
func LogoutHandler(response http.ResponseWriter, request *http.Request) {
	ClearCookie(response)
	http.Redirect(response, request, "/", 302)
}

// Cookie

func SetCookie(userName string, response http.ResponseWriter) {
	value := map[string]string{
		"name": userName,
	}
	if encoded, err := cookieHandler.Encode("cookie", value); err == nil {
		cookie := &http.Cookie{
			Name:  "cookie",
			Value: encoded,
			Path:  "/",
		}
		http.SetCookie(response, cookie)
	}
}

func ClearCookie(response http.ResponseWriter) {
	cookie := &http.Cookie{
		Name:   "cookie",
		Value:  "",
		Path:   "/",
		MaxAge: -1,
	}
	http.SetCookie(response, cookie)
}

func GetUserName(request *http.Request) (userName string) {
	if cookie, err := request.Cookie("cookie"); err == nil {
		cookieValue := make(map[string]string)
		if err = cookieHandler.Decode("cookie", cookie.Value, &cookieValue); err == nil {
			userName = cookieValue["name"]
		}
	}
	return userName
}

main.go

package main

import (
	"net/http"

	"github.com/gorilla/mux"

	"common"
)

var router = mux.NewRouter()

func main() {
	router.HandleFunc("/", common.LoginPageHandler) // GET

	router.HandleFunc("/index", common.IndexPageHandler) // GET
	router.HandleFunc("/login", common.LoginHandler).Methods("POST")

	router.HandleFunc("/register", common.RegisterPageHandler).Methods("GET")
	router.HandleFunc("/register", common.RegisterHandler).Methods("POST")

	router.HandleFunc("/logout", common.LogoutHandler).Methods("POST")

	http.Handle("/", router)
	http.ListenAndServe(":8080", nil)
}

Run it!

go run main.go