Android: “Permission denied” – no matter what I do

Explanation of the problem

The user is attempting to save base64 data to file, but is encountering Permission denied errors when accessing external storage (/storage/emulated/0) using either the createFile() or writeFile() functions. The user has requested permissions for read and write external storage and has also added the appropriate settings to AndroidManifest.xml. However, the only location that does not raise a Permission denied exception is RNFetchBlob.fs.dirs.DocumentDir, which maps to /data/user/0/{bundleId}/files. The user suspects this path translates to {Internal storage}/Android/data/{bundleId}/files, but even after running createFile() or writeFile() “successfully”, there is no file at that location. The user is unsure if there is anything they are missing and is seeking assistance to resolve the issue.

The code snippet shows the user requesting multiple permissions, including the permissions for read and write external storage, before attempting to write to a file. If both permissions are granted, the user attempts to create a file using the createFile() function from the RNFetchBlob library. The user has tried both base64 and utf8 encoding but is still unable to create a file. If the file is created successfully, the function returns the path of the created file. If not, it returns false with an appropriate warning message. The user is not sure if there is a problem with their code or with the library, and requires further assistance.

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Problem solution for Android: “Permission denied” – no matter what I do

Problem: Permission Denied error while writing to storage

One of the most common problems with RNFetchBlob is the Permission Denied error while writing to storage. This error occurs due to the new storage paradigm called scoped storage, introduced in Android 10.

Solution:

To resolve this issue, you can add the following code to your AndroidManifest.xml file:

<application android:requestLegacyExternalStorage="true" ... >
...
</application>

Problem: Large file uploads fail on iOS devices

Another common problem with RNFetchBlob is that large file uploads fail on iOS devices. This issue occurs due to a default timeout limit on the server.

Solution:

To resolve this issue, you can increase the timeout limit on the server or split the file into smaller chunks for upload.

Problem: Slow download speeds on Android devices

RNFetchBlob may also face slow download speeds on Android devices, particularly when downloading large files.

Solution:

1. File handling: RNFetchBlob can be used to perform various file handling operations such as reading and writing to files, creating directories, and moving files. Here is an example of how to write a string to a file using RNFetchBlob:

RNFetchBlob
  .config({ fileCache: true })
  .fetch('GET', 'https://example.com/image.jpg')
  .then((response) => response.blob())
  .then((blob) => {
    ImageResizer.createResizedImage(RNFetchBlob.wrap(blob), 800, 600, 'JPEG', 80)
      .then((resizedImage) => {
        // use resizedImage.path to access the resized image file
        console.log('Resized image saved to:', resizedImage.path);
      })
      .catch((error) => console.log('Error resizing image:', error));
  })
  .catch((error) => console.log('Error fetching image:', error));

2. Network requests: RNFetchBlob can be used to make HTTP/HTTPS requests and handle the response in various formats including text, JSON, and binary data. Here is an example of how to make a GET request and handle the response:

RNFetchBlob.config({
  fileCache: true,
})
.fetch('GET', 'https://example.com/api/data.json')
.then((response) => response.json())
.then((data) => console.log('Data received:', data))
.catch((error) => console.log('Error fetching data:', error));

RNFetchBlob
  .config({ fileCache: true })
  .fetch('GET', 'https://example.com/image.jpg')
  .then((response) => response.blob())
  .then((blob) => {
    ImageResizer.createResizedImage(RNFetchBlob.wrap(blob), 800, 600, 'JPEG', 80)
      .then((resizedImage) => {
        // use resizedImage.path to access the resized image file
        console.log('Resized image saved to:', resizedImage.path);
      })
      .catch((error) => console.log('Error resizing image:', error));
  })
  .catch((error) => console.log('Error fetching image:', error));