I'm using the HTML5 Blob API to download a file from a JavaScript client in a WebView based macOS application:
/** * Save a text as file using HTML <a> temporary element and Blob * @author Loreto Parisi */ var saveAsFile = function(fileName,fileContents) { if(typeof(Blob)!='undefined') { // using Blob var textFileAsBlob = new Blob([fileContents], { type: 'text/plain' }); var downloadLink = document.createElement("a"); downloadLink.download = fileName; if (window.webkitURL != null) { downloadLink.href = window.webkitURL.createObjectURL(textFileAsBlob); } else { downloadLink.href = window.URL.createObjectURL(textFileAsBlob); downloadLink.onclick = document.body.removeChild(event.target); downloadLink.style.display = "none"; document.body.appendChild(downloadLink); } downloadLink.click(); } else { var pp = document.createElement('a'); pp.setAttribute('href', 'data:text/plain;charset=utf-8,' + encodeURIComponent(fileContents)); pp.setAttribute('download', fileName); pp.onclick = document.body.removeChild(event.target); pp.click(); } }//saveAsFile When the Blob is not supported it uses the standard DOM way. When I run my application within MacGap2 running this code called let's say like saveAsFile('out.json',jsonString);
it will lead to this error:
2018-04-23 19:35:08.270857+0200 sendMessageWithDictionary: Failed to get remote object proxy: Error Domain=NSCocoaErrorDomain Code=4097 "connection to service named com.apple.rtcreportingd" UserInfo={NSDebugDescription=connection to service named com.apple.rtcreportingd} So I have configured the App Sandbox for Outgoing Connections (Client), I have also tried to intercept the link click through the PolicyDelegate:
- (void)webView:(WebView *)webView decidePolicyForNewWindowAction:(NSDictionary *)actionInformation request:(NSURLRequest *)request newFrameName:(NSString *)frameName decisionListener:(id < WebPolicyDecisionListener >)listener { if (WebNavigationTypeLinkClicked == [[actionInformation objectForKey:WebActionNavigationTypeKey] intValue]) { NSLog(@"CLICKED %@", [request URL]); } [[NSWorkspace sharedWorkspace] openURL:[request URL]]; [listener ignore]; } - (void)webView:(WebView *)webView decidePolicyForNavigationAction:(NSDictionary *)actionInformation request:(NSURLRequest *)request frame:(WebFrame *)frame decisionListener:(id<WebPolicyDecisionListener>)listener { if (WebNavigationTypeLinkClicked == [[actionInformation objectForKey:WebActionNavigationTypeKey] intValue]) { NSLog(@"CLICKED %@", [request URL]); } [listener use]; // Say for webview to do it work... } At this point I can get the Blob url clicked in the latter delegate, so, in the Objective-C / Cocoa Realm, I have approached the following (that currently works on macOS High Sierra / Xcode 9.3 / macOS 10.13
NSLog(@"CLICKED %@", [request URL]); NSString *needle = @"blob:"; if( [[[request URL] absoluteString] hasPrefix:needle] ) { // create a download link from blob url NSRange blobRange = [[[request URL] absoluteString] rangeOfString:needle]; NSString * blobURL = [[[request URL] absoluteString] substringFromIndex:blobRange.location + needle.length]; NSURLRequest *downloadURLRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:blobURL]]; NSLog(@"BLOB URL:%@", [[downloadURLRequest URL] absoluteString]); NSURLSessionDownloadTask *downloadTask = [[NSURLSession sharedSession] downloadTaskWithRequest:downloadURLRequest completionHandler:^(NSURL *location, __unused NSURLResponse *response, NSError *error) { if (location) { // get download folders NSArray *docDirs = NSSearchPathForDirectoriesInDomains(NSDownloadsDirectory, NSUserDomainMask, YES); NSString *destinationFilename = [docDirs objectAtIndex:0]; if (destinationFilename) { destinationFilename = [destinationFilename stringByAppendingPathComponent:@"out.json"]; NSLog(@"LOCATION %@ DOWNLOAD %@", [location absoluteString], destinationFilename); NSFileManager *fileManager = [NSFileManager defaultManager]; NSError *anError = nil; NSString *fromPath = [location path]; if ([fileManager fileExistsAtPath:destinationFilename]) [fileManager removeItemAtPath:destinationFilename error:&anError]; BOOL fileCopied = [fileManager moveItemAtPath:fromPath toPath:destinationFilename error:&anError]; if (fileCopied == NO) { } else { NSLog(@"Downloaded!"); } } } else { NSLog(@"Error:%@", [error description]); } }]; [downloadTask resume]; return; } To enable file download I had to additionally enable the Download folders read/write policy in the App Sandbox. Basically now I can intercept the blob: urls that is a typical HTML5 Blob url (blob:https://myserver/BLOB_ID), and I try to download, but - of course ? it does not work because that url it seems not be a valid url, so I get an error back from the file server - of course
<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <title>Error</title> </head> <body> <pre>Cannot GET /57de17ae-92bc-4553-a9d8-ac1b0f1f6c4f</pre> </body> </html> So despite the fact that the code above is generally working fine for real files (i.e. having a valid URI), I was wrong about the Blob files, since these files are not actual files, so there must be a different way to handle client side Blob urls in a macOS WebView.
[UPDATE] It seems that there are different tricks to make this working via
- XMLHttpRequest plus FileReader API
- requestFileSystem + FileWriter API
So I'm posting here https://gist.github.com/loretoparisi/84df6a7c19f411dbf9d0a0d10505e222