In our , we previewed the Framework. For this article, let’s create a small demo project. To start with, let’s set up a scenario for the demo. previous NativeScript article SimpleFileTransfer is a virtual file locker. Users can sign up for the service and get 100 MB of free virtual storage space. Users can then download and upload files on a server. Users will be able to increase their storage space by filling a form. Let’s jot down the App functionalities before moving ahead: Signup: User can signup for the app. Login: Authenticates user. Details Page: Provides user details like current quota and total space. Also, we can display a list of files. Download file: Download file from the server to a device. Upload file: Upload files from a device to the server. Increase Quota: Increases storage quota of a user by a specified amount. You can find the whole code on . GitHub Structuring the Backend The backend must provide the functionalities of managing routes, providing basic authentication and storage, and facilitating file transfers. Based on the requirements above, we will be using the following stack: Node: Server : Middleware Express : ORM Middleware Sequelize SQLite: Database We will also be using libraries like and for specific functionalities that will be explained later on. multer bcrypt Initializing the Backend Project We will be using express-generator to set up the project. Install globally using: express-generator npm install express-generator -g Start a new project using the command: express file-server Navigate to the directory and install the dependencies using . Also, install the following dependencies: file-server npm install npm install multer async sequelize sqlite3 body-parser bcrypt --save Additionally, we will be creating some extra folders for: Database: Storing SQLite DB & DB script. Model: Storing Models. Upload: Temporarily storing uploaded files. Storage: storing file for specific users. Starting with Sequelize is an ORM middleware for SQLite, MySQL, PostgreSQL and MSSQL. For small projects, it’s convenient to use the Sequelize + SQLite combo. Sequelize In our current scenario, we require only one Model. We will define our model user as follows: const User = sequelize.define('user', {uid: { type: Sequelize.INTEGER, primaryKey: true, autoIncrement: true },username:  { type: Sequelize.STRING, unique: true },password: Sequelize.STRING,quota: {type: Sequelize.INTEGER, defaultValue: 104857600},createdAt: Sequelize.DATE,updatedAt: Sequelize.DATE,}) We can use Sequelize’s to initialize Models Table in a database. To initialize users table, we will be using the code below. Model.sync User.sync({force: true}).then(() => {// Table created}); We will store the user model in the file in the model folder. user.js This part is pretty straightforward. For signup, the server accepts a username and password and stores it in the database. We will be using the bcrypt library to salt the passwords. As shown below, we are salting the password 10 times before storing it in the database. We are using Sequelize’s to store the value. Once a user is created, we will create a directory on our server for his uploads. Model.create The code is as below: router.post('/', function(req, res, next) {console.log(req);bcrypt.hash(req.body.password, 10, function(err, hash) {User.create({ username: req.body.username, password: hash }).then(user => {if (!fs.existsSync('storage/'+user.get('uid'))){fs.mkdirSync('storage/'+user.get('uid'));}res.send({status: true, msg: 'User created', uid: user.get('uid')});}).catch(err => {res.send({status: false, msg: err });})});}); For login, the server accepts a username and password and validates it against the database. We are using to get the database record. We use to compare passwords. Model.findAll bcrypt.compare router.post('/', function(req, res, next) {console.log(req);User.findAll({attributes: ["username", "password"],where: {username: req.body.username}}).then(dbQ => {if(dbQ.length > 0) {bcrypt.compare(req.body.password, dbQ[0].dataValues.password, function(err, result) {if (result == true){res.send({status: true, msg: 'Login Success'});} else {res.send({status: false, msg: 'Incorrect Password'});}});} else {res.send({status: false, msg: 'User not found'});}});}); Defining the Users Route An authenticated user is allowed to perform the following functions: Upload file Download file Get Details Increase quota Let’s define the routes for those functions: Upload: POST /users/:id/upload Download: GET /users/:id/download/:filename Details: GET /users/:id/details Increase Quota: POST /users/:id/increasequota Uploading a File to the Server We will be using to handle uploads. multer The multer library is useful to handle multi-part form data. Initially, we will be uploading the file to the uploads folder. Then, the file will be moved to folder where uid is user id. /storage/uid var storage = multer.diskStorage({destination: function (req, file, cb) {cb(null, 'uploads/')},filename: function (req, file, cb) {cb(null, file.originalname )}}); router.post('/:id/upload', upload.single('fileparam'), function(req, res, next) {if (!req.file) {console.log("No file received");return res.send({success: false,msg: "Error Uploading files"});} else {console.log('file received');fs.rename('uploads/'+ req.file.originalname, 'storage/'+req.params.id+'/'+req.file.originalname, function (err) {if (err) {console.log(err);return;}return res.send({success: true,msg: "File Uploaded"})});}}); The method is used for handling uploads. This route is expecting a file with name in the URL call. This is quickly done by adding a name attribute an HTML form. We will need the name attribute app side. upload.single fileparam Download Route ExpressJS provides us with a function to set the download route, conveniently called download. This is the logic we are following: A user logs into the app. He selects a file and initiates the download. The server receives a request with userid and filename. The server sends the file back to the user. The code for the route is below router.get('/:id/download/:filename', function(req, res, next) {const file = 'storage/'+req.params.id + '/' + req.params.filename;res.download(file);}); Increase User Quota Route We will be invoking to adjust the quota. By default, we have 104857600 bytes — which is equivalent to 100 MB — assigned to each user. You can find the query below. Model.update router.post('/:id/increasequota', function(req, res, next) {User.update({quota: req.body.quota,}, {where: {uid: req.params.id}}).then(response => {res.send({status: true, msg: "Quota Increased"});}).catch(err => {res.send({status: false, msg: err});});}); User Details Route This is a route which we will be using for fetching multiple data, such as: Storage Limit of user: from the DB, Current File Space occupied: from the directory, /storage/userid Space Remaining: it’s just Point 1 — Point 2, File List: list of Files, We can fetch the storage limit of a user using . For fetching file names and storage space, we are using , and . Model.findAll fs .readdir fs.stat async function getStorageSpace(relpath) {let space = 0;let fileNames = [];let promise = new Promise(function (resolve, reject) {fs.readdir(relpath, function (err, items) {if (err){reject(err);}fileNames = items;let filesArr = items.map(function (val) {return relpath + '/' + val;});async.map(filesArr, fs.stat, function (err, results) { for (let i = 0; i < results.length; i++) {  
         if (err) {  
           reject(err);  
         }  
         space = space + results\[i\].size;  
       }  
       resolve({fileNames: fileNames, space: space });  
     });  
   });  
 });  
 return promise; } function getStorageLimit(uid){let promise = new Promise(function (resolve, reject) {User.findAll({attributes: ["quota"],where: {uid: uid}}).then(dbQ => { if(dbQ.length < 1) {  
       reject("Quota Not Found")  
     } else {  
       resolve(dbQ\[0\].dataValues.quota);  
     }       
   }).catch(err => {  
     reject(err);  
   });  
 });  
 return promise; } router.get('/:id/details', function(req, res, next) {let it;let relpath = 'storage/'+req.params.id;Promise.all([getStorageSpace(relpath), getStorageLimit(req.params.id)]).then(result => { res.send({storageLimit: result\[1\], occupiedSpace: result\[0\].space, fileNames: result\[0\].fileNames, remainingSpace: result\[1\]- result\[0\].space});  
 }) }); The code works on assumption that user is not allowed to create a subdirectory in his folder. N.B.: The code for enforcing storage limit will be discussed later in the article. NativeScript App For the app side, we will be taking an alternative approach. A demo project based on Angular-Blank template will be shared with users. A significant part of this article will cover details about plugins concerning the plugin functionalities. Consuming Web Services We are consuming data from simple web services for Login / Signup / User Details Page. As mentioned in the , we can access these webservices using the . The basic steps are as follows: previous article HttpClient Module Import in the PageModule. NativeScriptHttpClientModule Import and in Component or Provider. HttpClient HttpHeaders Consume the URL as you will in an Angular application. We will set header to . Content-Type application/json For the JavaScript/TypeScript templates, we can use the NativeScript Core module. The function provides the required framework to consume webservices. Alternatively, we can also use the module. http http. getJson fetch As a response from the server, we will be receiving the of a user. After authentication, we need to store the so we can allow a mobile user to access . uid uid /users/uid route Storing Data The NativeScript framework doesn’t have any method to store data persistently. We can add that functionality using plugins. We are going to look at two of these plugins. : This plugin provides an interface for the SQLite library. This works well if your app needs to store a large volume of records. Install it with: nativescript-sqlite tns plugin add nativescript-sqlite : This plugins provides a key value API for string data, similar to . This works well if your app doesn't have lot of records. Install it with: nativescipt-localstorage window.localstorage tns plugin add nativescript-localstorage The demo app will be using . nativescript-localstorage Uploading Files from a Device to a Server Let’s break this functionality into subtasks: Choose Files from the device. Get File Path. Upload File over uploads WebService. To choose a file and get a file path, we will be using the plugin. The plugin has multiple modes and we can customize it for specific use cases. You can check the plugin documentation . nativescript-mediapicker here To select a file, first, we need to define extensions. This is different for both OSes. For Android devices, we have to use file extensions based on mime types like For iOS devices, we have to define extensions from list for Unified Type identifiers: let extensions = ["xlsx", "xls", "doc", "docx", "ppt", "pptx", "pdf", "txt", "png"] let extensions = [kUTTypePDF, kUTTypeText]; You can read more about UTIs and . here here The code for invoking is as below: filepicker let options: FilePickerOptions = {android: {extensions: extensions,maxNumberFiles: 1},ios: {extensions: extensions,multipleSelection: false}}; let mediafilepicker = new Mediafilepicker();mediafilepicker.openFilePicker(options); `mediafilepicker.on("getFiles", function (res) {let results = res.object.get('results');console.dir(results);}); mediafilepicker.on("error", function (res) {let msg = res.object.get('msg');console.log(msg);}); mediafilepicker.on("cancel", function (res) {let msg = res.object.get('msg');console.log(msg);});` As above, we will receive the filepath of a file in the event. getFiles We will send the file to the server using the plugin. You can read about the plugin . nativescript-background-http here Earlier, we defined the route. As mentioned earlier, our server is expecting the file in the attribute named . /users/:id/upload fileparam The background provides us with two functions: and . Since we need to set the name attribute, we will be using the function. http uploadFile multipartUpload multiPartUpload let session = bgHttp.session("image-upload");let request: bgHttp.Request = {url: Config.apiUrl  + '/users/' + localStorage.getItem('uid') + '/upload'   ,method: "POST",headers: {"Content-Type": "multipart/form-data"},description: 'FileName'};let params = [{name: 'file',filename: path}];let task: bgHttp.Task = session.multipartUpload(params, request);task.on("error", (e) => {reject(e);});task.on("complete", (e) => {resolve(e);}); Downloading a File to the Device We will be using the core , and modules to achieve the result. Both Android and iOS handle downloads differently. We will be using and variables from platform module to segregate the code. file-system platform utils isAndroid isIOS The file-system module provides us with a sub-module. Three predefined folders for both Android and iOS are available: knownFolders knownFolders.currentApp() knownFolders.documents() knownFolders.temp() Additionally, an provides us with some other predefined folders. E.g: iOS sub-module knownFolders.ios.download knownFolders.ios.sharedPublic iOS Code On an iOS scenario, this is straightforward: Show a list of server files. Download the files to the documents folder. List downloaded files in a separate view Use the function to open the file. utils.openFile To download the files, we will be using the module of the NativeScript framework. The function can be used to fetch files from the server and save them to a specific file location. The snippet for iOS is below: http getFile let filePath: string = path.join(knownFolders.documents().path, fileName);getFile(download_url + fileName, filePath).then((resultFile) => {// The returned result will be File object}, (e) => {console.log(e); Once the file has been downloaded, we can use the function from the module to open a file on iOS. openFile utils Android Code The Android side of coding is a bit trickier. The locations of the module are as below. knownFolders currentFolder: /data/data/:appid/files/app documents: /data/user/:androiduser/:appid/files temp: /data/user/:androiduser/:appid/cache As you can see, all the folders are located in . is inaccessible to normal users. Furthermore, external apps won't be able to access the files in those folders. Also, there is no function for Android. /data /data openFile As of now, the best we can do is: Show a list of server files. Download a file to a user accessible location. List the files present in the location. To implement the functionality, we will be using a bit of native code.  Before moving ahead, we will have to install with: tns-platform-declarations npm i tns-platform-declarations --save Create a file in the root folder and add the following lines: reference.d.ts `/// <reference path="./node_modules/tns-platform-declarations/ios.d.ts" />``/// <reference path="./node_modules/tns-platform-declarations/android.d.ts" />` You can check the for more details. readme provides us with a function to access the external storage. Android OS We will be using the constant and the function to create a publicly accessible download location. DIRECTORY_DOWNLOADS getExternalStoragePublicDirectory We will append a path “SimpleFileTransfer” to create a custom and . folderPath filePath const androidDownloadsPath = android.os.Environment.getExternalStoragePublicDirectory(android.os.Environment.DIRECTORY_DOWNLOADS).toString();const androidFolderPath = fs.path.join(androidDownloadsPath, "SimpleFileTransfer");const filePath: string = fs.path.join(androidFolderPath, fileName);getFile(download_url + fileName, filePath).then((resultFile) => {// The returned result will be File object}, (e) => {console.log(e); If you check your file explorer, a new directory will be created in the Downloads folder called SimpleFileTransfer. You will find all the files downloaded there. Listing Downloaded Files We will be using the module. The Folder class of the module has a function which allows us to list files in a folder. As with in Node.js, we can only list the files. file-system file-system getEntities fs.readdir For iOS, the path is const folderPath: string = fs.knownFolders.documents().path; For Android, the path is const androidDownloadsPath  =  android.os.Environment.getExternalStoragePublicDirectory(android.os.Environment.DIRECTORY_DOWNLOADS).toString(); `const  folderPath=  fs.path.join(androidDownloadsPath, "SimpleFileTransfer");` To access the Folder functions, we define a folder using let internalFolder = fs.Folder.fromPath(folderPath); Then, we use to get a list of files: getEntities internalFolder.getEntities().then((entities) => {// entities is array with the document's files and folders. entities.forEach((entity) => {  
               let  fileSize  =  fs.File.fromPath(entity.path).size;  
                   this.listArray.push({  
                       name: entity.name,  
                       path: entity.path,  
                       lastModified: entity.lastModified.toString(),  
                       size : fileSize  
                   });  
               });                    
           }).catch((err) => {  
               // Failed to obtain folder's contents.  
               console.log(err.stack);  
           }); Additionally, we have used the size property of File class to get file size. Enforcing Storage Limit The storage limit can be enforced in two ways: Upload file to the server → Checking remaining space → Reject the upload on the server side. Check remaining space using webservice → Check file size → Cancel the upload on the app side. To enforce the former, we can modify the upload route as below: Promise.all([getStorageSpace(relpath), getStorageLimit(req.params.id)]).then(result => {if (result[1] - result[0].space > req.file.size){fs.rename('uploads/'+ req.file.originalname, 'storage/'+req.params.id+'/'+req.file.originalname, function (err) {if (err) {return res.send({success: false,msg: "Error Uploading files"});}return res.send({success: true,msg: "File Uploaded"})});} else {return res.send({success: false,msg: "Storage Limit Exceeded"});}}) To enforce the latter, we get the file size of the file selected by the plugin and check it against the space remaining using the details webservice. mediafilepicker `let  fileSize  =  fs.File.fromPath(results[0].file).size;` if(fileSize < remainingSpace){// Send To server}`else {// alert user about lack of space} Closing Thoughts This demo covers quite a few different concepts. We divided the solution in a series of functionalities. We used core NativeScript for UX, interacting with the backend, file system management, and Routing. We extended the framework by installing plugins for functionalities like picking files. Going further, we used a bit of native code for solving a specific problem. Using NativeScript allowed us to develop the app faster for both platforms as against individually. If you want to learn how you can secure your NativeScript source code against client-side attacks, sign up for our free upcoming webinar on “ ”. Also be sure to check our . Best Practices for Securing Your Mobile Apps tutorial Originally published at blog.jscrambler.com .

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