DownloadAsync for HTTP

WebUtils.cs

public static class WebUtils
    {
        private static Lazy<IWebProxy> proxy 
            = new Lazy<IWebProxy>(() => string.IsNullOrEmpty(Settings.Default.WebProxyAddress) ? null : 
                new WebProxy { Address = new Uri(Settings.Default.WebProxyAddress), UseDefaultCredentials = true });
 
        public static IWebProxy Proxy
        {
            get { return WebUtils.proxy.Value; }
        }
 
        public static Task DownloadAsync(string requestUri, string filename)
        {
            if (requestUri == null)
                throw new ArgumentNullException("requestUri");
 
            return DownloadAsync(new Uri(requestUri), filename);
        }
 
        public static async Task DownloadAsync(Uri requestUri, string filename)
        {
            if (filename == null)
                throw new ArgumentNullException("filename");
 
            if (Proxy != null)
            {
                WebRequest.DefaultWebProxy = Proxy;
            }
 
            using (var httpClient = new HttpClient())
            {
                using (var request = new HttpRequestMessage(HttpMethod.Get, requestUri))
                {
                    using (
                        Stream contentStream = await (await httpClient.SendAsync(request)).Content.ReadAsStreamAsync(),
                        stream = new FileStream(filename, FileMode.Create, FileAccess.Write, FileShare.None, Constants.LargeBufferSize, true))
                    {
                        await contentStream.CopyToAsync(stream);
                    }
                }
            }
        }
    }