Cordova File Plugin: SECURITY_ERR

I have a hybrid app in production (iOS/Android) that uses Cordova plugins. I have one Android user who is getting a SECURITY_ERR when using the File plugin. This seems to be happening on a call to writeFile(). The file path I'm writing to for Android is externalRootDirectory.

Can anyone help me understand why 1 user (out of 300-400) would have this problem? The user is on Android 6.0.1 if that helps.

Some code is below. The error I'm getting is [Error creating file] – Error Msg: [SECURITY_ERR], so the .writeFile() catch is being hit in this case.

  //Handle Native download
  if (this.appConfig.isNative) {
    this.loggingService.debug("Starting to create native file");
    //Get base file path for android/ios
    let filePath = (this.appConfig.isNativeAndroid) ? this.file.externalRootDirectory : this.file.cacheDirectory;

    //Write the file
    this.file.writeFile(filePath, fileName, data, { replace: true })
          .then((fileEntry: FileEntry) => {
              this.loggingService.debug("Created file: " + fileEntry.toURL());          
              //Open with File Opener plugin
              this.fileOpener.open(fileEntry.toURL(), data.type)
                .then(() => this.loggingService.debug('File is opened'))
                .catch(e => this.loggingService.error('Error openening file', e));
            })
          .catch((err) => {
             this.loggingService.error("Error creating file", err);
             throw err;  //Rethrow - will be caught by caller
          });
      }

Solution

I was able to figure this one out. Looks like after Android 6.0 certain permissions must be requested during use of the app (not just at install time). This is also alluded to in the Cordova File plugin docs, under Android Quirks.

Marshmallow requires the apps to ask for permissions when reading/writing to external locations. By default, your app has permission to write to cordova.file.applicationStorageDirectory and cordova.file.externalApplicationStorageDirectory, and the plugin doesn't request permission for these two directories unless external storage is not mounted. However due to a limitation, when external storage is not mounted, it would ask for permission to write to cordova.file.externalApplicationStorageDirectory.

So on Android 6.0+, when writing a file to disk the Cordova File plugin will display a prompt similar to:

Allow APP_NAME to access photos, media and files on your device?

If the user selects Deny to this request, then the Cordova file write will get this SECURITY_ERR, even if the app requests this permission at install time.