Download a file via HTML5 Blob API: Failed to get remote object proxy

[loretoparisi]

I'm using the recent (actually not so recent) HTML5 Blob API to download a file from a JavaScript client like

/**
     * Save a text as file using HTML <a> temporary element and Blob
    */
    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('my_report.json',jsonString);

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}

I'm not sure if this is connected to the secure transport due to the NSAppTransportSecurity, but in my case I'm creating a downloadable content on the fly, which url is on localhost.

I have also tried to intercept the link click through the PolicyDelegate, but for some reason I do not get any log here:

- (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];
}

[loretoparisi]

[UPDATE] Okay, I have found out the issue with the new frame / frame delegates, I was in fact missing the latter WebPolicyDecisionListener listener:

- (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...
}

So I guess now I need to handle the download policy here in some way...

[loretoparisi]

[UPDATE] - PART II So, in the Objective-C / Cocoa Realm I have approached the following

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;
        }

Basically I intercept the blob: urls that is a typical HTML5 Blob url, 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 coruse

<!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 this...