Working to solve the issue https://github.com/EddyVerbruggen/SocialSharing-PhoneGap-Plugin/issues/500#issuecomment-170147144

Convert the base64 string to stream in WinRT using Javascript

var file = fileOrFileArray[i];
if (file.indexOf("data:application") >= 0) {

    var fileData = Windows.Security.Cryptography.CryptographicBuffer.decodeFromBase64String(file.split(',')[1]);

    var memoryStream = new Windows.Storage.Streams.InMemoryRandomAccessStream();
    var dataWriter = new Windows.Storage.Streams.DataWriter(memoryStream);
    dataWriter.writeBuffer(fileData);

    dataWriter.storeAsync().done(function () {
        dataWriter.flushAsync().done(function () {
            var fileStream = dataWriter.detachStream();
            fileStream.seek(0);
            var streamReference = Windows.Storage.Streams.RandomAccessStreamReference.createFromStream(fileStream);

            //TODO...
            e.request.data.setBitmap(streamReference); //Attach the file without the file name, remove this!
            
            //We need to convert the stream to IStorageItem to use the following code
            //storageItems.push(storageItem);

            if (!--filesCount) {
                storageItems.length && e.request.data.setStorageItems(storageItems);
                deferral.complete();
            }
        });
    });

}

Solution

//Text Message
var message = args[0];
//Title 
var subject = args[1];
//File(s) Path
var fileOrFileArray = args[2];
//Web link
var url = args[3];

var folder = Windows.Storage.ApplicationData.current.temporaryFolder;

var getExtension = function (strBase64) {
    return strBase64.substring(strBase64.indexOf("/") + 1, strBase64.indexOf(";base64"));
};

var replaceAll = function (str, find, replace) {
    return str.replace(new RegExp(find, 'g'), replace);
};

var sanitizeFilename = function (name) {
    return replaceAll(name, "[:\\\\/*?|<> ]", "_");
};

var getFileName = function (position, fileExtension) {
    var fileName = (subject ? sanitizeFilename(subject) : "file") + (position == 0 ? "" : "_" + position) + "." + fileExtension;
    return fileName;
};

var createTemporalFile = function (fileName, buffer) {

    var filePath = "";
    return folder.createFileAsync(fileName, Windows.Storage.CreationCollisionOption.replaceExisting).then(function (file) {
        filePath = file.path;
        return Windows.Storage.FileIO.writeBufferAsync(file, buffer);
    }).then(function(){
        return Windows.Storage.StorageFile.getFileFromPathAsync(filePath);
    });
};

var doShare = function (e) {
    e.request.data.properties.title = subject?subject: "Sharing";
    if (message) e.request.data.setText(message);
    if (url) e.request.data.setWebLink(new Windows.Foundation.Uri(url));
    if (fileOrFileArray.length > 0) {
        var deferral = e.request.getDeferral();
        var storageItems = [];
        var filesCount = fileOrFileArray.length;

        var completeFile = function () {
            if (!--filesCount) {
                storageItems.length && e.request.data.setStorageItems(storageItems);
                deferral.complete();
            }
        };

        for (var i = 0; i < fileOrFileArray.length; i++) {

            var file = fileOrFileArray[i];
            if (file.indexOf("data:") >= 0) {                        
                var fileName = getFileName(i, getExtension(file));
                var buffer = Windows.Security.Cryptography.CryptographicBuffer.decodeFromBase64String(file.split(',')[1]);
                if (buffer) {
                    createTemporalFile(fileName, buffer).done(
                        function (file) {
                            storageItems.push(file);
                            completeFile();
                        },
                        function () {
                            completeFile();
                        }
                    );
                }
                else {
                    completeFile();
                }
            }
            else {
                Windows.Storage.StorageFile.getFileFromPathAsync(file).done(
                    function (file) {
                        storageItems.push(file);
                        completeFile();
                    },
                    function () {
                        completeFile();
                    }
                );
            }
        }
    }
};

You could always save the stream to a temporary file in ApplicationData.TemporaryFolder and open that as an IStorageItem afterwards to pass it forward. I don't have the time to create a sample at the moment, but it shouldn't be too difficult to make it work.

Hi @damirarh, thanks for your help! Exist any example to save the stream to a temporary file? ✌️ PD: I'm checking this :)

Done! Thanks for all! 👯