WKWebViewConfiguration *config = [[WKWebViewConfiguration alloc] init];
    WKUserContentController *contentController = [[WKUserContentController alloc] init];
config.websiteDataStore  = [WKWebsiteDataStore nonPersistentDataStore];

- (void)webView:(WKWebView*)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler{
 NSURL *url = navigationAction.request.URL;
    NSURLRequest *request = navigationAction.request;
    NSString *urldown = url.absoluteString;
if([urldown containsString:@"messaging-attachmentFile"]) {
         // preforming download
[downLoader downloadFileFromURL:url.absoluteString]
        }

}