Cancel Method not working reliably on iOS

[majirosstefan]

When trying to cancel a small file download, it happens pretty often that the cancel method call gets ignored.

const download = async () => {
  const hasPermission = await getPermissionToDownload();
  if (hasPermission) {            
      setDownloadModalVisible(true);
      let DownloadDir = ReactNativeBlobUtil.fs.dirs.DownloadDir;
      let name = props.message.data.attachments[0].name;        
    
       let task = ReactNativeBlobUtil.config({          
        fileCache: true,
        appendExt: props.message.data.attachments[0].extension,
        addAndroidDownloads: {
          useDownloadManager: true,
          notification: true,
          path: DownloadDir + "/" + name,
        },
      }).fetch("GET", url, { });
                              
      downloadTask = task;                         
      
      await sleep(5000);
      
      task.then( res => {
        setDownloadModalVisible(false);
        console.log("res: ", res, JSON.stringify(res));                                            
       }).catch(err => {
        setDownloadModalVisible(false);
        console.log("Could be cancelledd", err);                  
       });                 
  } else {
    console.log("Storage permission denied");
  }
};

As you can see, I am opening the modal where I intend to put the progress indicator and cancel button that calls the following function that closes modal, and should pause download:

const onCancelDownload =  async () => {
    try {      
      console.log("Cancelling", downloadTask)
      await downloadTask.cancel(() => "canceled");
      setDownloadModalVisible(false);                
      downloadTask = null;      
    } catch(err){
      console.log(err)
    }    
  }

Also,

let downloadTask = null; 

is placed outside functional component that has onCancelDownload, and download methods.

However, it happens pretty often, that after calling the 'downloadTask.cancel', nothing happens, and downloading continues.
But sometimes it does resolve properly, as I would expect (that the canceled error is thrown).

Dependencies: "react-native": "~0.63.4", "react": "16.13.1", "react-native-blob-util": "^0.13.18",

[RonRadtke]

This might be related to: #130