System.Net.WebClient unreasonably slow

Question

When using the System.Net.WebClient.DownloadData() method I\'m getting an unreasonably slow response time.

When fetching an url using the WebClient class in .NET it

Answer 1

Setting WebRequest.DefaultWebProxy = null; or client.Proxy = null didn't do anything for me, using Xamarin on iOS.

I did two things to fix this:

I wrote a downloadString function which does not use WebRequest and System.Net:

        public static async Task<string> FnDownloadStringWithoutWebRequest(string url)
        {
            using (var client = new HttpClient())
            {
                //Define Headers
                client.DefaultRequestHeaders.Accept.Clear();
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

                var response = await client.GetAsync(url);

                if (response.IsSuccessStatusCode)
                {
                    string responseContent = await response.Content.ReadAsStringAsync();
                    //dynamic json = Newtonsoft.Json.JsonConvert.DeserializeObject(responseContent);
                    return responseContent;
                }
                Logger.DefaultLogger.LogError(LogLevel.NORMAL, "GoogleLoginManager.FnDownloadString", "error fetching string, code: " + response.StatusCode);
                return "";
            }
        }

This is however still slow with Managed HttpClient.

So secondly, in Visual Studio Community for Mac, right click on your Project in the Solution -> Options -> set HttpClient implementation to NSUrlSession, instead of Managed.

Screenshot: Set HttpClient implementation to NSUrlSession instead of Managed

Managed is not fully integrated into iOS, doesn't support TLS 1.2, and thus does not support the ATS standards set as default in iOS9+, see here:

https://docs.microsoft.com/en-us/xamarin/ios/app-fundamentals/ats

With both these changes, string downloads are always very fast (<<1s). Without both of these changes, on every second or third try, downloadString took over a minute.

---

Just FYI, there's one more thing you could try, though it shouldn't be necessary anymore:

            //var authgoogle = new OAuth2Authenticator(...);
            //authgoogle.Completed...

            if (authgoogle.IsUsingNativeUI)
            {
                // Step 2.1 Creating Login UI 
                // In order to access SFSafariViewController API the cast is neccessary
                SafariServices.SFSafariViewController c = null;
                c = (SafariServices.SFSafariViewController)ui_object;
                PresentViewController(c, true, null);
            }
            else
            {
                PresentViewController(ui_object, true, null);
            }

Though in my experience, you probably don't need the SafariController.

Answer 2

What browser are you using to test?

Try using the default IE install. System.Net.WebClient uses the local IE settings, proxy etc. Maybe that has been mangled?