@kesha-antonov/react-native-background-downloader

A library for React-Native to help you download large files on iOS and Android both in the foreground and most importantly in the background.

Why?

On iOS, if you want to download big files no matter the state of your app, wether it's in the background or terminated by the OS, you have to use a system API called NSURLSession.

This API handles your downloads separately from your app and only keeps it informed using delegates (Read: Downloading Files in the Background).

On Android we are using similar process with DownloadManager

The real challenge of using this method is making sure the app's UI is always up-to-date with the downloads that are happening in another process because your app might startup from scratch while the downloads are still running.

@kesha-antonov/react-native-background-downloader gives you an easy API to both downloading large files and re-attaching to those downloads once your app launches again.

ToC

• Usage
• API
• Constants

Getting started

yarn add @kesha-antonov/react-native-background-downloader

or

npm i @kesha-antonov/react-native-background-downloader

Then:

cd ios && pod install

Mostly automatic installation

Any React Native version >= 0.60 supports autolinking so nothing should be done.

For anything < 0.60 run the following link command

$ react-native link @kesha-antonov/react-native-background-downloader

Manual installation

iOS - Extra Mandatory Step

In your AppDelegate.m add the following code:

...
#import <RNBackgroundDownloader.h>

...

- (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)(void))completionHandler
{
  [RNBackgroundDownloader setCompletionHandlerWithIdentifier:identifier completionHandler:completionHandler];
}

...

Failing to add this code will result in canceled background downloads. If Xcode complains that RNBackgroundDownloader.h is missing, you might have forgotten to pod install first.

Usage

Downloading a file

import { Platform } from 'react-native'
import { download, completeHandler, directories } from '@kesha-antonov/react-native-background-downloader'

const jobId = 'file123'

let task = download({
  id: jobId,
  url: 'https://link-to-very.large/file.zip',
  destination: `${directories.documents}/file.zip`,
  metadata: {}
}).begin(({ expectedBytes, headers }) => {
  console.log(`Going to download ${expectedBytes} bytes!`)
}).progress(({ bytesDownloaded, bytesTotal }) => {
  console.log(`Downloaded: ${bytesDownloaded / bytesTotal * 100}%`)
}).done(({ bytesDownloaded, bytesTotal }) => {
  console.log('Download is done!', { bytesDownloaded, bytesTotal })

  // PROCESS YOUR STUFF

  // FINISH DOWNLOAD JOB
  completeHandler(jobId)
}).error(({ error, errorCode }) => {
  console.log('Download canceled due to error: ', { error, errorCode });
})

// Pause the task (iOS only)
task.pause()

// Resume after pause (iOS only)
task.resume()

// Cancel the task
task.stop()

Re-Attaching to background downloads

This is the main selling point of this library (but it's free!).

What happens to your downloads after the OS stopped your app? Well, they are still running, we just need to re-attach to them.

Add this code to app's init stage, and you'll never lose a download again!

import RNBackgroundDownloader from '@kesha-antonov/react-native-background-downloader'

let lostTasks = await RNBackgroundDownloader.checkForExistingDownloads()
for (let task of lostTasks) {
  console.log(`Task ${task.id} was found!`)
  task.progress(({ bytesDownloaded, bytesTotal }) => {
    console.log(`Downloaded: ${bytesDownloaded / bytesTotal * 100}%`)
  }).done(({ bytesDownloaded, bytesTotal }) => {
    console.log('Download is done!', { bytesDownloaded, bytesTotal })
  }).error(({ error, errorCode }) => {
    console.log('Download canceled due to error: ', { error, errorCode })
  })
}

task.id is very important for re-attaching the download task with any UI component representing that task. This is why you need to make sure to give sensible IDs that you know what to do with, try to avoid using random IDs.

Using custom headers

If you need to send custom headers with your download request, you can do in it 2 ways:

1) Globally using RNBackgroundDownloader.setConfig():

RNBackgroundDownloader.setConfig({
  headers: {
    Authorization: 'Bearer 2we$@$@Ddd223',
  }
})

This way, all downloads with have the given headers.

2) Per download by passing a headers object in the options of RNBackgroundDownloader.download():

let task = RNBackgroundDownloader.download({
  id: 'file123',
  url: 'https://link-to-very.large/file.zip'
  destination: `${RNBackgroundDownloader.directories.documents}/file.zip`,
  headers: {
    Authorization: 'Bearer 2we$@$@Ddd223'
  }
}).begin(({ expectedBytes, headers }) => {
  console.log(`Going to download ${expectedBytes} bytes!`)
}).progress(({ bytesDownloaded, bytesTotal }) => {
  console.log(`Downloaded: ${bytesDownloaded / bytesTotal * 100}%`)
}).done(({ bytesDownloaded, bytesTotal }) => {
  console.log('Download is done!', { bytesDownloaded, bytesTotal })
}).error(({ error, errorCode }) => {
  console.log('Download canceled due to error: ', { error, errorCode })
})

Headers given in the download function are merged with the ones given in setConfig({ headers: { ... } }).

API

RNBackgroundDownloader

download(options)

Download a file to destination

options

An object containing options properties

returns

DownloadTask - The download task to control and monitor this download

checkForExistingDownloads()

Checks for downloads that ran in background while you app was terminated. And also forces them to resume downloads.

Recommended to run at the init stage of the app.

returns

DownloadTask[] - Array of tasks that were running in the background so you can re-attach callbacks to them

setConfig({})

DownloadTask

A class representing a download task created by RNBackgroundDownloader.download

Members

completeHandler(jobId)

Finishes download job and informs OS that app can be closed in background if needed. After finishing download in background you have some time to process your JS logic and finish the job.

ensureDownloadsAreRunning (iOS only)

Pauses and resumes all downloads - this is fix for stuck downloads. Use it when your app loaded and is ready for handling downloads (all your logic loaded and ready to handle download callbacks).

Here's example of how you can use it:

1. When your app just loaded

Either stop all tasks:

const tasks = await checkForExistingDownloads()
for (const task of tasks)
  task.stop()

Or re-attach them:

const tasks = await checkForExistingDownloads()
for (const task of tasks) {
  task.pause()
  //
  // YOUR LOGIC OF RE-ATTACHING DOWLOADS TO YOUR STUFF
  // ...
  //
}

2. Prepare your app to handle downloads... (load your state etc.)

3. Add listener to handle when your app goes foreground (be sure to do it only after you stopped all tasks or re-attached them!)

function handleAppStateChange (appState) {
  if (appState !== 'active')
    return

  ensureDownloadsAreRunning()
}

const appStateChangeListener = AppState.addEventListener('change', handleAppStateChange)

4. Call ensureDownloadsAreRunning() after all was setup.

Callback Methods

Use these methods to stay updated on what's happening with the task.

All callback methods return the current instance of the DownloadTask for chaining.

pause() (iOS only)

Pauses the download

resume() (iOS only)

Resumes a paused download

stop()

Stops the download for good and removes the file that was written so far

Constants

directories

documents

An absolute path to the app's documents directory. It is recommended that you use this path as the target of downloaded files.

Rules for proguard-rules.pro

In case of error java.lang.IllegalStateException: TypeToken must be created with a type argument: new TypeToken<...>() in Android release add this to proguard-rules.pro:

# Application classes that will be serialized/deserialized over Gson
-keep class com.yourapplicationname.model.api.** { *; }

# Gson uses generic type information stored in a class file when working with
# fields. Proguard removes such information by default, keep it.
-keepattributes Signature

# This is also needed for R8 in compat mode since multiple
# optimizations will remove the generic signature such as class
# merging and argument removal. See:
# https://r8.googlesource.com/r8/+/refs/heads/main/compatibility-faq.md#troubleshooting-gson-gson
-keep class com.google.gson.reflect.TypeToken { *; }
-keep class * extends com.google.gson.reflect.TypeToken

# Optional. For using GSON @Expose annotation
-keepattributes AnnotationDefault,RuntimeVisibleAnnotations

TODO

• [ ] Write better examples - current kinda old and shallow
• [ ] Write better API for downloads - current kinda boilerplate
• [ ] Add more tests

Authors

Re-written & maintained by Kesha Antonov

Originally developed by Elad Gil of Eko

License

Apache 2