receiving Blolbs and save them in a string

public void ProcessRequest(HttpContext context)
{
    try
    {
        long length = context.Request.ContentLength;
        byte[] buffer = new byte[context.Request.ContentLength];
        context.Request.InputStream.Read(buffer, 0, context.Request.ContentLength);
        string fileName = context.Request.Headers.Get("X_FILE_NAME");
        AppendAllBytes(context.Server.MapPath("~/upload/" + fileName), buffer);
    }
    catch (Exception)
    {

        throw;
    }
}
public static void AppendAllBytes(string path, byte[] bytes)
{
    try
    {

        using (var stream = new FileStream(path, FileMode.Append))
        {
            stream.Write(bytes, 0, bytes.Length);
        }
    }
    catch (Exception)
    {
        throw;
    }
}

$(document).ready(function () {
    $("#btnUpload").click(function (evt) {

        var fl = document.getElementById("files");
        var L = fl.files.length;
        var xhr;
        if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari
            xhr = new XMLHttpRequest();
        }
        else {// code for IE6, IE5
            xhr = new ActiveXObject("Microsoft.XMLHTTP");
        }
        for (var i = 0; i < L ; i++) {
            var file = fl.files[i];
            var blobs = [];
            var start = 0;
            var end = chunkSize;
            var size = file.size;
            var j = chunkSize;
            while (start < size) {
                //push the fragments to an array
                blobs.push(file.slice(start, end));
                start = j;
                j = start + chunkSize;;
                end = start + chunkSize;
                if (end > size) {
                    end = size;
                }
            }
            var fileName = file.name;
            var count = 0;

            while (blob = blobs.shift()) {
                xhr.open('POST', 'FileUploadHandler.ashx', false);
                xhr.setRequestHeader('X_Offset', chunkSize);
                xhr.setRequestHeader('X_Blob_Number', count);
                xhr.setRequestHeader('X_FILE_NAME', fileName);
                xhr.send(blob);
                count++;
            }
        }
    });
});