Cordova file-transfer plugin not working in simulator

Question

I'm trying to get the example code for the file-transfer plugin working, it's taken straight from the Cordova docs:

function downloadFile2() {
    window.requestFileSystem(window.TEMPORARY, 5 * 1024 * 1024, function (fs) {

        console.log('file system open: ' + fs.name);

        // Make sure you add the domain name to the Content-Security-Policy <meta> element.
        var url = 'http://cordova.apache.org/static/img/cordova_bot.png';
        // Parameters passed to getFile create a new file or return the file if it already exists.
        fs.root.getFile('downloaded-image.png', { create: true, exclusive: false }, function (fileEntry) {
            download2(fileEntry, url, true);

        }, function () { logError('Error creating file'); });

    }, function () { logError('Error creating fs'); });
}

function download2(fileEntry, uri, readBinaryData) {

    var fileTransfer = new FileTransfer();
    var fileURL = fileEntry.toURL();

    console.log('Downloading ' + uri + ' to ' + fileURL);
    fileTransfer.download(
        uri,
        fileURL,
        function (entry) {
            console.log("Successful download...");
            console.log("download complete: " + entry.toURL());
            if (false && readBinaryData) {
                // Read the file...
                readBinaryFile(entry);
            }
            else {
                // Or just display it.
                displayImageByFileURL(entry);
            }
        },
        function (error) {
            console.log("download error source " + error.source);
            console.log("download error target " + error.target);
            console.log("upload error code" + error.code);
        },
        null, // or, pass false
        {
            //headers: {
            //    "Authorization": "Basic dGVzdHVzZXJuYW1lOnRlc3RwYXNzd29yZA=="
            //}
        }
    );
}

function displayImageByFileURL(fileEntry) {
    var elem = document.getElementById('imageElement');
    elem.src = fileEntry.toURL();
}

I'm using the latest versions of the file-transfer and file plugins (1.7.1/6.0.1). I have added the domain to the Content-Security-Policy element as mentioned in the example:

<meta http-equiv="Content-Security-Policy" content="default-src 'self' data: gap: http://cordova.apache.org https://ssl.gstatic.com 'unsafe-eval'; style-src 'self' 'unsafe-inline'; media-src *">

When I run it up in the simulator (Android/iOS) from VS2017 the download fails silently. Neither the success or error callbacks are called, and it doesn't appear to generate a network request. The console log is as follows:

file system open: http_localhost_4400:Temporary
Downloading http://cordova.apache.org/static/img/cordova_bot.png to filesystem:http://localhost:4400/temporary/downloaded-image.png

That filesystem URL looked a bit odd to me, so I have tried other variants such as the full file path, using persistent storage instead of temporary, using 'cdvfile://localhost/persistent/downloaded-image.png', all with the same result. I'm at a loss as to how I can debug this further and wondering if I've missed something really obvious, so any advice appreciated...

Edit I tried running it again today, and a dialog pooped up in Visual Studio with the message:

There is no handler for the following exec call:
FileTransfer.download("http://cordova.apache.org/static/img/cordova_bot.png", "cdvfile://localhost/persistent/downloaded-image.png", true, 1, null)

Answer 1

I did some more experimenting, including running it up in the VS simulator for Android. For some reason it had trouble connecting to cordova.apache.org (I was also unable to access this site in the browser on the emulator), but downloading a file from github worked correctly....