/**
* @param {string} haystack
* @param {string} needle
* @return {number}
*/
/**
* @param {string} haystack
* @param {string} needle
* @return {number}
*/
var strStr = function(haystack, needle) {
var match = 0;
// Edge case: if needle is an empty string, return 0
if (needle === "") {
return 0;
}
// Get the lengths of both strings
const haystackLen = haystack.length;
const needleleLen = needle.length;
// Iterate through the haystack string
for (let i = 0; i <= haystackLen - needleleLen; i++) {
var left = 0;
while(left < needleleLen && haystack[left + i] == needle[left]) {
left ++;
}
if(left == needleleLen) {
return i;
}
}
return -1;
};
Explanation:
Edge Case: If needle is an empty string, the function immediately returns 0.
Outer Loop: The outer loop iterates over each character in haystack where there is still enough remaining length to match the needle (i <= haystackLen - needleLen).
Inner Loop: The inner loop checks if the substring of haystack starting at i matches needle. It does this by comparing characters one-by-one.
Match Found: If a match is found (j === needleLen), the starting index i is returned.
No Match: If no match is found by the end of the loop, the function returns -1.
This implementation mimics a basic substring search without using any built-in functions. The time complexity is O(n * m), where n is the length of haystack and m is the length of needle.
function threeSumClosest(nums, target) {
// Sort the array first
nums.sort((a, b) => a - b);
let closestSum = Infinity;
// Iterate through the array
for (let i = 0; i < nums.length - 2; i++) {
let left = i + 1;
let right = nums.length - 1;
// Use two pointers to find the best sum
while (left < right) {
let currentSum = nums[i] + nums[left] + nums[right];
// Update the closest sum if needed
if (Math.abs(currentSum - target) < Math.abs(closestSum - target)) {
closestSum = currentSum;
}
// Move the pointers based on the current sum
if (currentSum < target) {
left++;
} else if (currentSum > target) {
right--;
} else {
// If the exact sum is found, return immediately
return currentSum;
}
}
}
return closestSum;
}
Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.
Notice that the solution set must not contain duplicate triplets.
Example 1:
Input:
nums = [-1,0,1,2,-1,-4]
Output:
[[-1,-1,2],[-1,0,1]]
Explanation:
nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0.
nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0.
nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0.
The distinct triplets are [-1,0,1] and [-1,-1,2].
Notice that the order of the output and the order of the triplets does not matter.
Sorting the Array: The array is first sorted to easily manage duplicates and use a two-pointer approach.
Iterating with a Loop: A loop iterates through the array, fixing one element (nums[i]) and then using a two-pointer approach to find the other two elements (nums[left] and nums[right]).
Avoiding Duplicates: Duplicate values are skipped using continue for the first element and while loops for the second and third elements to ensure the solution set contains only unique triplets.
Two-Pointer Approach: The sum is checked, and pointers are adjusted accordingly to find valid triplets.
Example Usage:
[-1, 0, 1, 2, -1, -4]
This would output:
[[-1, -1, 2], [-1, 0, 1]]
This solution efficiently finds all unique triplets that sum to zero in O(n^2) time complexity.
Skipping duplicates in the threeSum algorithm is crucial to ensure that the solution set contains only unique triplets. Here’s a detailed explanation of how duplicates are skipped at different stages:
1. Skipping Duplicates for the First Element (i):
When iterating through the array with the outer loop (for (let i = 0; i < nums.length - 2; i++)), the algorithm checks if the current element nums[i] is the same as the previous element nums[i - 1]. If they are the same, it means that any triplet starting with this element would already have been considered in a previous iteration, so the algorithm skips this iteration.
Code Example:
if (i > 0 && nums[i] === nums[i - 1]) continue;
Explanation:
i > 0: Ensures that we don’t check for a previous element when i is 0.
nums[i] === nums[i - 1]: If this condition is true, it means nums[i] is a duplicate of the previous element, so the loop skips to the next i using continue.
2. Skipping Duplicates for the Second and Third Elements (left and right):
After fixing the first element nums[i], the algorithm uses two pointers, left and right, to find the other two elements (nums[left] and nums[right]) that, together with nums[i], sum to zero.
Once a valid triplet is found, the algorithm moves both pointers inward but also checks for duplicates by comparing the current elements with the next ones in line. If the next element is the same as the current one, the algorithm skips the next element by advancing the pointer further.
Code Example:
// After finding a triplet while (left < right && nums[left] === nums[left + 1]) left++; while (left < right && nums[right] === nums[right - 1]) right--;
Explanation:
Left Pointer:
while (left < right && nums[left] === nums[left + 1]) left++;
This loop skips all duplicate values for nums[left] by incrementing left until it points to a new value.
Right Pointer:
while (left < right && nums[right] === nums[right - 1]) right--;
Similarly, this loop skips all duplicate values for nums[right] by decrementing right until it points to a new value.
Why This is Important:
Avoiding Redundant Triplets: Without skipping duplicates, the algorithm would include multiple instances of the same triplet in the result, which is inefficient and incorrect for this problem.
Efficiency: Skipping duplicates prevents unnecessary comparisons, speeding up the algorithm.
Example Walkthrough:
Consider the array [-1, 0, 1, 2, -1, -4]:
Sorting: The array becomes [-4, -1, -1, 0, 1, 2].
Iteration with i = 0 (nums[i] = -4):
No duplicates for nums[i], proceed with left = 1 and right = 5.
No valid triplet is found, move to the next i.
Iteration with i = 1 (nums[i] = -1):
Triplet [-1, -1, 2] is found.
Skip duplicates: left moves from index 2 to 3 because nums[2] === nums[3].
Triplet [-1, 0, 1] is found.
Iteration with i = 2 (nums[i] = -1):
Skip this iteration entirely because nums[2] === nums[1].
As a result, only unique triplets are returned: [[-1, -1, 2], [-1, 0, 1]].
/**
* @param {number[]} nums
* @return {number[][]}
*/
/**
* @param {number[]} nums
* @return {number[][]}
*/
var threeSum = function(nums) {
nums.sort((a, b) =>{ return a - b });
const result = [];
for(let i = 0; i < nums.length - 2; i ++) {
// Skip duplicate values for the first element of the triplet
if (i > 0 && nums[i] === nums[i - 1]) {
continue;
}
let left = i + 1;
let right = nums.length - 1;
while(left < right) {
const sum = nums[i] + nums[left] + nums[right];
if(sum === 0) {
result.push([nums[i], nums[left], nums[right]]);
// Skip duplicate values for the second and third elements of the triplet
while (left < right && nums[left] === nums[left + 1]) {
left++;
}
while (left < right && nums[right] === nums[right - 1]) {
right--;
}
left ++;
right --;
} else if(sum < 0) {
left ++;
} else {
right --;
}
}
}
return result;
};
This tutorial demonstrates how to ‘auto migrate’ the DB and how to store and retrieve data from JSONB field in postgreSQL database using GoLang.
Auto migrating the DB
In the context of Go programming language and GORM (Go Object Relational Mapping) library, automigration is a feature that automatically creates or updates database tables based on the Go struct definitions.
For the purpose of this example, we will create a table with id, username, email and meta data field. The meta data will be a JSONB field. We could use JSON as well but JSONB is stored in binary format, and although insert operations are slower searching is faster.
In general it is recommended to always use JSONB unless we have a real good reason to use JSON. For example JSON preserves formatting and allows for duplicate keys.
But before we could use JSONB with GORM we have to install the package
go get github.com/jackc/pgtype
Create a connection to PostgreSQL database.
Gorm supports different databases but here will do this exercise with PostgreSQL only.
Define the structure that will be used to create the the Users table
type User struct {
ID uint `gorm:"primaryKey"`
Username string `gorm:"unique"`
Email string
Age int
MetaData pgtype.JSONB `gorm:"type:jsonb" json:"fieldnameofjsonb"`
}
Now let’s create two helper functions that will create a new user:
func createuserWithMetaData(db *gorm.DB, username string, email string, metaData string) User {
jsonData := pgtype.JSONB{}
err := jsonData.Set([]byte(metaData))
if err != nil {
log.Fatal(err)
}
// Create a user
newUser := User{Username: username, Email: email, Age: 36, MetaData: jsonData}
err = createUser(db, &newUser)
if err != nil {
log.Fatal(err)
}
return newUser
}
func createUser(db *gorm.DB, user *User) error {
result := db.Create(user)
if result.Error != nil {
return result.Error
}
return nil
}
And let’s put it all together:
The entire code
package main
import (
"log"
"github.com/jackc/pgtype"
"gorm.io/driver/postgres"
"gorm.io/gorm"
)
type User struct {
ID uint `gorm:"primaryKey"`
Username string `gorm:"unique"`
Email string
Age int
MetaData pgtype.JSONB `gorm:"type:jsonb" json:"fieldnameofjsonb"`
}
func connectToPostgreSQL() (*gorm.DB, error) {
dsn := "user=toninichev dbname=tests host=localhost port=5432 sslmode=disable"
db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{})
if err != nil {
return nil, err
}
return db, nil
}
func createuserWithMetaData(db *gorm.DB, username string, email string, metaData string) User {
jsonData := pgtype.JSONB{}
err := jsonData.Set([]byte(metaData))
if err != nil {
log.Fatal(err)
}
// Create a user
newUser := User{Username: username, Email: email, Age: 36, MetaData: jsonData}
err = createUser(db, &newUser)
if err != nil {
log.Fatal(err)
}
return newUser
}
func createUser(db *gorm.DB, user *User) error {
result := db.Create(user)
if result.Error != nil {
return result.Error
}
return nil
}
func getUserByID(db *gorm.DB, userID uint) (*User, error) {
var user User
result := db.First(&user, userID)
if result.Error != nil {
return nil, result.Error
}
return &user, nil
}
func updateUser(db *gorm.DB, user *User) error {
result := db.Save(user)
if result.Error != nil {
return result.Error
}
return nil
}
func deleteUser(db *gorm.DB, user *User) error {
result := db.Delete(user)
if result.Error != nil {
return result.Error
}
return nil
}
func autoMigrateDB(db *gorm.DB) {
// Perform database migration
err := db.AutoMigrate(&User{})
if err != nil {
log.Fatal(err)
}
}
func main() {
db := func() *gorm.DB {
db, err := connectToPostgreSQL()
if err != nil {
log.Fatal(err)
}
return db
}()
autoMigrateDB(db)
//CRUD operations
func() {
newUser := createuserWithMetaData(db, "Toni", "toni@gmail.com", `{"key": "value", "days":[{"dayOne": "1"}], "user-id": "1"}`)
log.Println("Created user:", newUser)
}()
func() {
newUser := createuserWithMetaData(db, "John", "john@gmail.com", `{"key": "value two", "days":[{"dayOne": "2"}], "user-id": "2"}`)
log.Println("Created user:", newUser)
}()
func() {
newUser := createuserWithMetaData(db, "Sam", "sam@gmail.com", `{"key": "value three", "days":[{"dayOne": "3"}], "user-id": "3"}`)
log.Println("Created user:", newUser)
}()
// Query user by ID
user, err := getUserByID(db, 2)
if err != nil {
log.Fatal(err)
}
log.Println("User by ID:", user)
var result User
db.Where("meta_data->>'user-id' = ?", "2").First(&result)
log.Println(result)
}
Updates
We can use byte type instead of pgtype libray which simplifies the code a bit.
type Users struct {
ID uint `gorm:"primaryKey"`
Username string `gorm:"unique"`
MetaData []byte `gorm:"type:jsonb" json:"meta-data"`
}
we are going to use Gin Web framework to create simple HTTP server that we could query against, passing JWT in the header and then using secret or public key to validate the signature.
package main
import (
"github.com/gin-gonic/gin"
)
func AuthMiddleware() gin.HandlerFunc {
// In a real-world application, you would perform proper authentication here.
// For the sake of this example, we'll just check if an API key is present.
return func(c *gin.Context) {
apiKey := c.GetHeader("X-Auth-Token")
if apiKey == "" {
c.AbortWithStatusJSON(401, gin.H{"error": "Unauthorized"})
return
}
c.Next()
}
}
func main() {
// Create a new Gin router
router := gin.Default()
// Public routes (no authentication required)
public := router.Group("/public")
{
public.GET("/info", func(c *gin.Context) {
c.String(200, "Public information")
})
public.GET("/products", func(c *gin.Context) {
c.String(200, "Public product list")
})
}
// Private routes (require authentication)
private := router.Group("/private")
private.Use(AuthMiddleware())
{
private.GET("/data", func(c *gin.Context) {
c.String(200, "Private data accessible after authentication")
})
private.POST("/create", func(c *gin.Context) {
c.String(200, "Create a new resource")
})
}
router.POST("query", AuthMiddleware(), validateSession, returnData)
// Run the server on port 8080
router.Run(":8080")
}
We added validateSession middleware that will decode the token and verify the signature.
Creating JWT services to decode and validate signature
We are using jwt GoLang library to decode the token, and validate the signature.
There are two ways to encode JWT: using symmetric encryption (meaning that the same secret is used to sign and validate the signature. This is done in retreiveTokenWithSymmetrikKey and retreiveTokenWithAsymmetrikKey is used to validate signature using the public key from the private/public key pair used to sign the token.
Make sure that you comment and uncomment the right type of token that you want to use: asymmetric vs symmetric.
Run the project yarn start end copy the long string printed right after SIGNED JWT.
Create new postman POST request
Open Postman and create new POST request. In the url put http://localhost:8080/query this is where our Gin Web server running.
Add X-Auth-Token JWT
Open header section, and add X-Auth-Token key with the value the JWT copied from Sign, Verify and decode JWT
Add query parameters and variables.
We are going to pass dummy parameters just for testing except for product
We are going to use product parameter to distinguish between symmetric and asymmetric tokens.
Let’s assume that our app will except symmetric tokens for web and asymmetric for app so make sure that you will pass the right JWT.
Navigate to the GraphQL section of the request, and add the query and the variables.
Json Web Token become widely popular for creating data with optional signature and/or optional encryption and payload.
JWTs are a Base64 encoded string with a signature attached to it. JWT components are separated by . The components are:
Header: Contains metadata about the token, such as the signing algorithm used.
Payload: Contains the claims, which are statements about the subject of the token. For example, a JWT might contain claims about a user’s identity, such as their username and email address, or their authorization to access certain resources.
Signature: A digital signature that ensures the integrity of the header and payload. The signature is created using the header and payload and a secret key known only to the issuer.
echo 'eyJhdXRob3IiOiJUb25pIFkgTmljaGV2IiwiaWF0IjoxNzA2MTEzNDc0LCJkYXRhIjoiTmV3IEpXVCBnZW5lcmF0ZWQgYXQgV2VkIEphbiAyNCAyMDI0IDExOjI0OjM0IEdNVC0wNTAwIChFYXN0ZXJuIFN0YW5kYXJkIFRpbWUpIiwiZXhwIjoxNzA2MTU2Njc0LCJhdWQiOiJodHRwczovL215c29mdHdhcmUtY29ycC5jb20iLCJpc3MiOiJUb25pIE5pY2hldiIsInN1YiI6InRvbmkubmljaGV2QGdtYWlsLmNvbSJ9' |base64 -d
{"author":"Toni Y Nichev","iat":1706113474,"data":"New JWT generated at Wed Jan 24 2024 11:24:34 GMT-0500 (Eastern Standard Time)","exp":1706156674,"aud":"https://mysoftware-corp.com","iss":"Toni Nichev","sub":"toni.nichev@gmail.com"}
As we see JWT payload is not encrypted and could be decoded with any base64 decoder so never store sensitive data there. The purpose of signing with our private key is to make sure that ‘audience’ (who ever is going to use the token) will be able to verify the authenticity of this token with shared public key.
Claims to Verify
When code is presented with a JWT, it should verify certain claims. At a minimum, these claims should be checked out:
iss identifies the issuer of the JWT. (UUID, domain name, URL or something else)
aud identifies the audience of the token, that is, who should be consuming it. aud may be a scalar or an array value.
nbf and exp. These claims determine the timeframe for which the token is valid.
It doesn’t matter exactly what this strings are as long as the issuer and consumer of the JWT agree on the values.
JWT signing algorithms.
The default algorithm used is (HS256) which is symmetric: meaning that the same ‘secret’ is used for signing and verifying. In the example below `itsasecret123`
Once you create application, you have to create some products to sell.
In general there are these types of products supported by Apple’s App Store:
Consumables.
Consumables are products that can be used (‘consumed’) once and then repurchased multiple times.
Non-consumables
Non-consumables are products that are purchased once, have no expiry date, and remain permanently available within your app.
Auto-renewal subscriptions
Auto-renewal subscriptions are products or services that you pay for on a recurring basis. Developers love these, as they guarantee a steady income stream.
Non auto-renewal subscriptions.
Non auto-renewal subscriptions are those that run for a fixed period of time, after which you can choose to manually renew. Often, these last longer and cost more than auto-renewal subscriptions.
To create products navigate to the newly created app, and locate “MONETIZATION” on the left side. From there you could select to create “in-app-purchases” or “Subscriptions”
Refer to Apple documentation of how to create products: In-App purchase
When testing in the sandbox, subscription durations are shortened to help simulate different billing periods quickly:
1 week subscription = 3 minutes in sandbox
1 month subscription = 5 minutes in sandbox
3 months subscription = 15 minutes in sandbox
6 months subscription = 30 minutes in sandbox
1 year subscription = 1 hour in sandbox
Creating Sandbox testing users
Ahh, yeah … you need test users so you won’t be charged with each test.
Create new Xcode project and change the bundle id to the one that you set up above in the app store connect. (Refer to Creating application bundle in App Store connect in this article.)
In-app purchase is not enabled by default. Let’s add it in Signing & Capabilities
Add mainStore.storekit file by going to files->new and look for StoreKit2.
– Name it mainStore.storekit
– Make sure that you select ‘synced‘ so it will pull data from the actual App Store and select your apple bundle id (this is how the StoreKit2 will know which items to pull)4. Let’s add another Swift class which will be our shared Store.
store.swift
import StoreKit
@MainActor final class Store: ObservableObject {
// use the same ids that you defined in the App Store connect
private var productIDs = ["InAppPurchaseTutorialToniconsumableFuel", "InAppPurchaseTutorialToniConsumableOil", "BrakePads", "InAppPurchaseRenewalPro"]
private var updates: Task<Void, Never>?
@Published var products = [Product]()
@Published var activeTransactions: Set<StoreKit.Transaction> = []
init() {
Task {
await requestProducts()
}
Task {
await transactionUpdates()
}
}
deinit {
updates?.cancel()
}
func transactionUpdates () async {
for await update in StoreKit.Transaction.updates {
if let transaction = try? update.payloadValue {
activeTransactions.insert(transaction)
await transaction.finish()
}
}
}
func requestProducts() async {
do {
products = try await Product.products(for: productIDs)
} catch {
print(error)
}
}
func purchaseProduct(_ product: Product) async throws {
print("Purchase tapped ...")
let result = try await product.purchase()
switch result {
case .success(let verifyResult):
print("Purchase successfull!")
if let transaction = try? verifyResult.payloadValue {
activeTransactions.insert(transaction)
print("PURCHASE:")
try print(verifyResult.payloadValue)
print(transaction)
await transaction.finish()
}
case .userCancelled:
print("Purchase Canceled !")
break
case .pending:
print("Purchase pending ...")
break
@unknown default:
break
}
}
func fetchActiveTransactions() async {
var activeTransactions: Set<StoreKit.Transaction> = []
for await entitelment in StoreKit.Transaction.currentEntitlements {
if let transaction = try? entitelment.payloadValue {
activeTransactions.insert(transaction)
print("fetchActiveTransactions: ")
print(transaction)
}
}
}
}
In productIDs use the same ids that you defined in the App Store connect.
5. Edit the View to add purchase buttons.
Views/ContentView.swift
//
// ContentView.swift
// InAppPurchaseTutorial
//
// Created by Toni Nichev on 1/2/24.
//
import SwiftUI
import StoreKit
struct ContentView: View {
@EnvironmentObject var store: Store
var body: some View {
VStack {
Text("Welcome to my store").font(.title)
ProductView(id: "InAppPurchaseTutorialToniconsumableFuel") {
Image(systemName: "crown")
}
.productViewStyle(.compact)
.padding()
.onInAppPurchaseCompletion { product, result in
if case .success(.success(let transaction)) = result {
print("Purchased successfully: \(transaction.signedDate)")
} else {
print("Something else happened")
}
}
}
Section(header: Text("To buy:").font(.title)) {
ForEach(store.products, id: \.id) { product in
Button {
Task {
try await store.purchaseProduct(product)
}
} label: {
HStack {
Text(product.displayName + ":")
Text(verbatim: product.displayPrice)
}
}
.buttonStyle(.borderedProminent)
}
}
}
}
#Preview {
ContentView().environmentObject(Store())
}
6. Last part is to add method to retreive purchases when the application starts.
InAppPurchaseTutorialApp.swift
//
// InAppPurchaseTutorialApp.swift
// InAppPurchaseTutorial
//
// Created by Toni Nichev on 1/2/24.
//
import SwiftUI
@main
struct InAppPurchaseTutorialApp: App {
@Environment(\.scenePhase) private var sceneParse
@StateObject private var store = Store()
var body: some Scene {
WindowGroup {
ContentView()
.environmentObject(store)
.task(id: sceneParse) {
if sceneParse == .active {
await store.fetchActiveTransactions()
}
}
}
}
}
Setting up Backend server to listen to server-2-server notifications from Apple server
Apple server sends server-to-server notifications in real time when subscription event happens, like subscribed, cancel subscription, did renew etc.
Mode details of all notification types could be found in Apple documentation
Purpose: we can receive these notifications on transaction complete, on purchase made, on subscriptions: purchased, canceled, failed and we could grant access to subscribers to some paid services like (pro news, premium game levels etc.)
Copy the newly created PEM file to the root folder of the backend server handler, under ./assets folder.
Create your backend server handler, that Apple App Store server will notify.
I like to use PHP version cause it’s super easy to implement but any language works the same way:index.php
what we just did:
– decoded JWT
– Saved the decoded response in the data.txt file
so far so good, but we need to register our server-listener to the App-store connect so the Apple server will notify our server.
Now it’s a good time to testing with curl command and make sure that the script reads POST body data.
curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' https://yourserver.com/app-store-server-notification-tutorial/
After executing the command look at ./beep.txt file for the raw response. If you see it, you are ready to continue with a real test notification from Apple server.
Add your backend server url to Apps’ App Store Server notifications
If test notification is successful too, you could finally issue a real notification by doing test purchase from the app.
Now we could navigate to the physical phone, run the app and make a purchase.
Make sure that once prompted for the password you add the test account password.
Now we have server-2-server notification set up, but if we want to use more of Apple’s APIs (like transaction history, purchases, etc) we have to create an app to generate signed JWT.
Apple won’t accept JWT that lives longer than 20 min. so we have to make sure that this is the maximup ttl that we set up.
const expirationTime = now + 900; // Set to 15 minutes (900 seconds)
There are two types of Apple APIs like it was stated above:
If you don’t already have CocoaPods installed, follow the steps in the CocoaPods Getting Started guide.
Open a terminal window and navigate to the location of your app’s Xcode project.
If you have not already created a Podfile for your application, create one now:
pod init
Open the Podfile created for your application and add the following:
pod 'GoogleSignIn'
If you are using SwiftUI, also add the pod extension for the “Sign in with Google” button:
pod 'GoogleSignInSwiftSupport'
Save the file and run:
pod install
From now on Open the generated .xcworkspaceworkspace file for your application in Xcode. Use this file for all future development on your application. (Note that this is different from the included .xcodeprojproject file, which would result in build errors when opened.)
Now we are almost ready to start coding, but when we build the project we might (or might not depends of X-code version) face some issues..
Navigate to the Build Settings, find ‘User Script Sandboxing’ and
Flip it to No
Fixing “Your app is missing support for the following URL schemes:”
Copy missing scheme from the error message and add it in the info->url section
Let’s get started
Adding Google Client ID (GIDClientID)
Ether you face the problems before or not this is one thing that is mandatory.
1. Adding UserAuthModel to share between all views.
If you don’t know how to do this read about ObservableObject and @Published and sharing data between Views.
This class has to conform to the ObservableObject in order to have its properties reflecting the View.
We will create methods to check if user is signed in, and update shared parameters: givenName, userEmail, isLoggedIn …
import SwiftUI
import GoogleSignIn
import GoogleSignInSwift
final class UserAuthModel: ObservableObject {
@Published var givenName: String = ""
@Published var isLoggedIn: Bool = false
@Published var errorMessage: String = ""
@Published var userEmail: String = ""
@Published var profilePicUrl: String = ""
init() {
check()
}
func getUserStatus() {
if GIDSignIn.sharedInstance.currentUser != nil {
let user = GIDSignIn.sharedInstance.currentUser
guard let user = user else { return }
let givenName = user.profile?.givenName
self.givenName = givenName ?? ""
self.userEmail = user.profile!.email
self.profilePicUrl = user.profile!.imageURL(withDimension: 100)!.absoluteString
self.isLoggedIn = true
} else {
self.isLoggedIn = false
self.givenName = "Not Logged In"
}
}
func check() {
GIDSignIn.sharedInstance.restorePreviousSignIn { user, error in
if let error = error {
self.errorMessage = "error: \(error.localizedDescription)"
}
self.getUserStatus()
}
}
func gertRootViewController() -> UIViewController {
guard let screen = UIApplication.shared.connectedScenes.first as? UIWindowScene else {
return .init()
}
guard let root = screen.windows.first?.rootViewController else {
return .init()
}
return root
}
func signIn() {
GIDSignIn.sharedInstance.signIn(withPresenting: gertRootViewController()) { signInResult, error in
guard let result = signInResult else {
// Inspect error
print("Error occured in signIn()")
return
}
print("Signing in ...")
print(result.user.profile?.givenName ?? "")
self.getUserStatus()
}
}
func signOut() {
GIDSignIn.sharedInstance.signOut()
self.getUserStatus()
}
Now let’s edit the app starter and put userAuthModel in the environmentObject
//
// SignInWithGoogleTutorialApp.swift
// SignInWithGoogleTutorial
//
// Created by Toni Nichev on 1/3/24.
//
import SwiftUI
@main
struct SignInWithGoogleTutorialApp: App {
@StateObject var userAuthModel: UserAuthModel = UserAuthModel()
var body: some Scene {
WindowGroup {
NavigationView {
ContentView()
}
.environmentObject(userAuthModel)
}
}
}
The purpose of authentication on the backend server is to make sure that logged-in users could have access to some protected content, like subscriptions, pro-articles, etc.
Once the user signs-in in the native app, the app sends the id-token to the backend, and the backend validates the token and could return access-token back to the app.
In the previous chapter we added UserAuthModel.swift file.
This is the place to call the backend server.
func sendTokenToBackendServer() {
let user = GIDSignIn.sharedInstance.currentUser
guard let user = user else { return }
let stringToken = user.idToken!.tokenString
guard let authData = try? JSONEncoder().encode(["idToken" : stringToken]) else {
return
}
let url = URL(string: "https://regexor.net/examples/google-sign-in-server-notification/")!
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
let task = URLSession.shared.uploadTask(with: request, from: authData) { data, response, error in
print(response ?? ".")
// handle response from my backend.
if error != nil {
print("Error: \(String(describing: error))")
}
// Handle the response from the server
let dataString = String(data: data!, encoding: .utf8)
print ("got data: \(dataString!)")
}
task.resume()
}
and the final UserAuthenticationModel.swift will look like this:
import SwiftUI
import GoogleSignIn
import GoogleSignInSwift
final class UserAuthModel: ObservableObject {
@Published var givenName: String = ""
@Published var isLoggedIn: Bool = false
@Published var errorMessage: String = ""
@Published var userEmail: String = ""
@Published var profilePicUrl: String = ""
init() {
check()
}
func getUserStatus() {
if GIDSignIn.sharedInstance.currentUser != nil {
let user = GIDSignIn.sharedInstance.currentUser
guard let user = user else { return }
let givenName = user.profile?.givenName
self.givenName = givenName ?? ""
self.userEmail = user.profile!.email
self.profilePicUrl = user.profile!.imageURL(withDimension: 100)!.absoluteString
self.isLoggedIn = true
} else {
self.isLoggedIn = false
self.givenName = "Not Logged In"
}
}
func check() {
GIDSignIn.sharedInstance.restorePreviousSignIn { user, error in
if let error = error {
self.errorMessage = "error: \(error.localizedDescription)"
}
self.getUserStatus()
}
}
func gertRootViewController() -> UIViewController {
guard let screen = UIApplication.shared.connectedScenes.first as? UIWindowScene else {
return .init()
}
guard let root = screen.windows.first?.rootViewController else {
return .init()
}
return root
}
func signIn() {
GIDSignIn.sharedInstance.signIn(withPresenting: gertRootViewController()) { signInResult, error in
guard let result = signInResult else {
// Inspect error
print("Error occured in signIn()")
return
}
print("Signing in ...")
print(result.user.profile?.givenName ?? "")
self.getUserStatus()
self.sendTokenToBackendServer()
}
}
func signOut() {
GIDSignIn.sharedInstance.signOut()
self.getUserStatus()
}
func sendTokenToBackendServer() {
let user = GIDSignIn.sharedInstance.currentUser
guard let user = user else { return }
let stringToken = user.idToken!.tokenString
guard let authData = try? JSONEncoder().encode(["idToken" : stringToken]) else {
return
}
let url = URL(string: "https://regexor.net/examples/google-sign-in-server-notification/")!
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
let task = URLSession.shared.uploadTask(with: request, from: authData) { data, response, error in
print(response ?? ".")
// handle response from my backend.
if error != nil {
print("Error: \(String(describing: error))")
}
// Handle the response from the server
let dataString = String(data: data!, encoding: .utf8)
print ("got data: \(dataString!)")
}
task.resume()
}
}
Server script to get idToken form the native app:
In the example below we Just save the token to a file. In real life scenario, here we have to verify the identity of the id token before sending the access-token back to the app.
<?php
// SAVE RAW DATA
$appleData = file_get_contents('php://input');
// Just saves the token to a file.
// In real life scenario, here we have to verify the identity of the id token before sending the access-token back to the app
$file = fopen("./data.txt", "a");
fwrite($file, $appleData);
fclose($file);
echo "send something back to the native app like acccess-token";
//
// ContentView.swift
// Test
//
// Created by Toni Nichev on 1/3/24.
//
import SwiftUI
// Our observable object class
class GameSettings: ObservableObject {
@Published var scoree = 0
var test = 4
}
// A view that expects to find a GameSettings object
// in the environment, and shows its score.
struct ScoreView: View {
// 2: We are not instantiating gameSetting here since it's already done in ContentView.
@EnvironmentObject var gameSettings: GameSettings
var body: some View {
Text("Score: \(gameSettings.scoree)")
Text("Test: \(gameSettings.test)")
}
}
struct ContentView: View {
// 1: We instantiate GameSettings only here and pass it to the environmentObject at the end
@StateObject var gameSettings = GameSettings()
var body: some View {
NavigationStack {
VStack {
Image(systemName: "globe")
.imageScale(.large)
.foregroundStyle(.tint)
Button("Increase score") {
gameSettings.scoree += 1
gameSettings.test += 1
}
NavigationLink {
ScoreView()
} label: {
Text("Show score")
}
}
}
.environmentObject(gameSettings)
}
}
#Preview {
ContentView()
}
#Preview {
ScoreView().environmentObject(GameSettings())
}
4. Let’s add another Swift class which will be our shared Store.
