Handle file download from WKWebview using a WKDownload

Question

I am trying to download a file from a WKWebview and show an iOS Share Sheet so that the user can decide what to do with the file. Everything works as expected in the browser.

My iOS code was previously working, but doesn't seem to be working anymore (haven't tested in a while, but I am on iOS 16.4 right now). The share sheet pops up correctly and I am able to save the file. However, it appears that the file is not being saved to the system correctly because it prints "Optional(0 bytes)" in the downloadDidFinish function, and downloaded file is 0 as well.

My code as well as the errors are below.

var filePathDestination: URL?

func download(_ download: WKDownload, decideDestinationUsing response: URLResponse, suggestedFilename: String, completionHandler: @escaping (URL?) -> Void) {
    let temporaryDir = NSTemporaryDirectory()
    let now = NSDate()
    let nowTimeStamp = getTimeStamp(dateToConvert: now)
    let fileName = temporaryDir + nowTimeStamp + suggestedFilename
    let url = URL(fileURLWithPath: fileName)
    filePathDestination=url
    completionHandler(url)
}

func downloadDidFinish(_ download: WKDownload) {
    let data = try? Data(contentsOf: filePathDestination!) 
    print(data)
    let items = [filePathDestination!]
    let ac = UIActivityViewController(activityItems: items, applicationActivities: nil)
    ac.modalPresentationStyle = UIModalPresentationStyle.popover
    ac.preferredContentSize = CGSize(width: self.view.bounds.size.width/2.0, height: self.view.bounds.size.height/2.0)
    ac.popoverPresentationController?.permittedArrowDirections = UIPopoverArrowDirection(rawValue: 0)
    ac.popoverPresentationController?.sourceView = self.view;
    let midx=self.view.bounds.midX;
    let midy=self.view.bounds.midY;

    let rect=CGRect(x: 0.5*midx, y: 0.5*midy, width: midx, height: midy);
    ac.popoverPresentationController?.sourceRect = rect;
    ac.popoverPresentationController?.sourceRect = CGRect(x: self.view.bounds.size.width / 2.0, y: self.view.bounds.size.height / 3.0, width: 1.0, height: 1.0)

    present(ac, animated: true, completion: nil)

}

Errors:

[ShareSheet] Failed to request default share mode for fileURL:file:///Users/user/Library/Developer/CoreSimulator/Devices/5FD5D8D3-9C13-4DFB-A434-119B430C29B7/data/Containers/Data/Application/B4232467-20FC-4269-B6B5-19F07EC1A41B/tmp/20230421%20175423%20filename.png error:Error Domain=NSOSStatusErrorDomain Code=-10814 "(null)" UserInfo={_LSLine=1538, _LSFunction=runEvaluator}
[ShareSheet] Only support loading options for CKShare and SWY types.
[ShareSheet] error fetching item for URL:file:///Users/user/Library/Developer/CoreSimulator/Devices/5FD5D8D3-9C13-4DFB-A434-119B430C29B7/data/Containers/Data/Application/B4232467-20FC-4269-B6B5-19F07EC1A41B/tmp/20230421%20175423%20filename.png : (null)
[ShareSheet] error fetching file provider domain for URL:file:///Users/user/Library/Developer/CoreSimulator/Devices/5FD5D8D3-9C13-4DFB-A434-119B430C29B7/data/Containers/Data/Application/B4232467-20FC-4269-B6B5-19F07EC1A41B/tmp/20230421%20175423%20filename.png : (null)
[ShareSheet] error loading metadata for documentURL:file:///Users/user/Library/Developer/CoreSimulator/Devices/5FD5D8D3-9C13-4DFB-A434-119B430C29B7/data/Containers/Data/Application/B4232467-20FC-4269-B6B5-19F07EC1A41B/tmp/20230421%20175423%20filename.png error:Error Domain=NSFileProviderInternalErrorDomain Code=0 "No valid file provider found from URL file:///Users/user/Library/Developer/CoreSimulator/Devices/5FD5D8D3-9C13-4DFB-A434-119B430C29B7/data/Containers/Data/Application/B4232467-20FC-4269-B6B5-19F07EC1A41B/tmp/20230421%20175423%20filename.png." UserInfo={NSLocalizedDescription=No valid file provider found from URL file:///Users/user/Library/Developer/CoreSimulator/Devices/5FD5D8D3-9C13-4DFB-A434-119B430C29B7/data/Containers/Data/Application/B4232467-20FC-4269-B6B5-19F07EC1A41B/tmp/20230421%20175423%20filename.png.}

score 0 · Answer 1 · answered Apr 22 '23 at 14:52

Finally figured out the issue. It wasn't a problem in the above swift code, it was actually a problem in the javascript on iOS safari.

I was getting the following warning in the javascript console:

[Warning] Canvas area exceeds the maximum limit (width * height > 16777216). (studio.js, line 3593)

I was turning this canvas into a dataURL and then downloading it, but the dataURL was empty because of this warning, and that is why I was seeing the 0 Bytes file in my original question. I need to lower the quality of the canvas, and then everything works as expected.

More info can be found here:

https://pqina.nl/blog/canvas-area-exceeds-the-maximum-limit/

Handle file download from WKWebview using a WKDownload

1 Answers1