Understanding READ_EXTERNAL_STORAGE/WRITE_EXTERNAL_STORAGE Permissions for RNFetchBlob CacheDir

If you are an entry-level user of React Native and RNFetchBlob, you might have come across the terms READ\_EXTERNAL\_STORAGE and WRITE\_EXTERNAL\_STORAGE permissions. These permissions are crucial for the RNFetchBlob library to cache files in the device's storage. In this article, we will explain what these permissions are, why they are essential, and how to use them with RNFetchBlob's CacheDir.

What are READ\_EXTERNAL\_STORAGE and WRITE\_EXTERNAL\_STORAGE Permissions?

READ\_EXTERNAL\_STORAGE and WRITE\_EXTERNAL\_STORAGE are Android permissions that allow an application to read and write files to the device's external storage, respectively. External storage refers to the device's SD card or internal storage that is accessible to other apps. These permissions are necessary for apps that need to access files outside their private sandboxed storage.

Why are READ\_EXTERNAL\_STORAGE and WRITE\_EXTERNAL\_STORAGE Permissions Important for RNFetchBlob CacheDir?

RNFetchBlob is a popular library for fetching, downloading, and uploading files in React Native. The library provides a CacheDir option that allows you to cache files in the device's storage. CacheDir is a convenient feature that can help you improve the performance of your app by reducing the amount of data that needs to be fetched over the network. However, to use CacheDir, you need to request the READ\_EXTERNAL\_STORAGE and WRITE\_EXTERNAL\_STORAGE permissions.

When you use RNFetchBlob's CacheDir, the library creates a directory in the device's external storage where it caches the files. The directory is private to your app, and other apps cannot access it. However, the directory is still located in the external storage, which means that your app needs permission to read and write files to it. Without these permissions, RNFetchBlob will not be able to cache files in the device's storage, and your app's performance may suffer.

How to Request READ\_EXTERNAL\_STORAGE and WRITE\_EXTERNAL\_STORAGE Permissions for RNFetchBlob CacheDir?

To request the READ\_EXTERNAL\_STORAGE and WRITE\_EXTERNAL\_STORAGE permissions, you need to add the following lines to your AndroidManifest.xml file:

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Adding these lines to your AndroidManifest.xml file will grant your app the necessary permissions to read and write files to the device's external storage. However, you should also check if the permissions are granted at runtime, as Android 6.0 (API level 23) and higher require runtime permissions.

To check if the permissions are granted at runtime, you can use the following code snippet:

const granted = await PermissionsAndroid.check(
PermissionsAndroid.PERMISSIONS.READ_EXTERNAL_STORAGE,
{
title: 'READ_EXTERNAL_STORAGE permission',
message:
'Please grant us permission to read files from your device.',
buttonNegative: 'Cancel',
buttonPositive: 'OK',
}
);
if (!granted) {
try {
const granted = await PermissionsAndroid.request(
PermissionsAndroid.PERMISSIONS.READ_EXTERNAL_STORAGE,
{
title: 'READ_EXTERNAL_STORAGE permission',
message:
'Please grant us permission to read files from your device.',
buttonNegative: 'Cancel',
buttonPositive: 'OK',
}
);
if (granted === PermissionsAndroid.RESULTS.GRANTED) {
console.log('You can use the READ_EXTERNAL_STORAGE permission');
} else {
console.log('READ_EXTERNAL_STORAGE permission denied');
}
} catch (err) {
console.warn(err);
}
}

This code snippet checks if the READ\_EXTERNAL\_STORAGE permission is granted. If the permission is not granted, the code requests the permission from the user. You can use a similar code snippet to check and request the WRITE\_EXTERNAL\_STORAGE permission.

Understanding READ\_EXTERNAL\_STORAGE and WRITE\_EXTERNAL\_STORAGE permissions is essential for using RNFetchBlob's CacheDir feature. These permissions allow your app to read and write files to the device's external storage, which can help you improve the performance of your app. By adding the necessary lines to your AndroidManifest.xml file and checking for the permissions at runtime, you can ensure that your app has the necessary permissions to use RNFetchBlob's CacheDir feature.

References