macOS WebView Download a HTML5 Blob file

Question

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

标签： objective-c html5 webview blob

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