Why do goo.gl short URLs not return the expected status code of 301?

Question

When I make a HttpWebRequest to a URL with AllowAutoRedirect set to false, I expect a response with StatusCode "Moved" or "Moved Permanently". I am using .NetFramework , and if I use .NetCore, it would throw a web exception with the "Moved Permenently" status code.

But for some reason, goo.gl short URLs which re-direct to a full URL, just return a "Found" status code. Why does this happen? I am building a short URL resolver but goo.gl short URLs aren't behaving as expected.

I am using the code below and it works as expected for other short URLs.

  public static string GetFullUrl(string url)
        {
            if (string.IsNullOrWhiteSpace(url))
                return "";

            var req = (HttpWebRequest)WebRequest.Create(url);
            req.AllowAutoRedirect = false;
            try
            {
                var resp = req.GetResponse();
                return resp.ResponseUri.AbsoluteUri;
            }
            catch (WebException ex)
            {
                if (ex.Response != null)
                {
                    var longUrl = ex.Response.Headers["Location"];
                    if (longUrl.Contains('?') || longUrl.Length <= 35 || longUrl.StartsWith("https://news.google.com/"))
                    {
                        return GetFullUrl(longUrl);
                    }
                    return longUrl;
                }
                return url;
            }
            catch (Exception)
            {
                return url;
            }
        }

Answer 1

What makes you think it is unexpected? This is essentially a temporary redirect response; the intent here may be twofold:

1. to allow google to edit the URLs and have that work, without browsers and other things (proxies etc) ignoring all further checks (ignoring some is fine - the point is not to cache too aggressively)
2. to allow better hit-counting, by not having browsers and other things (proxies etc) not letting most of the requests hit google

Note that 307 ("Temporary Redirect") and 302 ("Found") have the same semantics, other than what to do about the HTTP method; 307 explicitly retains the original HTTP method ("POST", "GET", etc); 302 does not. In effect, this means that goo.gl is saying "temporary redirect, and you should feel free to do a "GET", regardless of what you did originally". Note that 301 ("Moved Permanently") and 308 ("Permanent Redirect") have the same duality, but for non-temporary redirects.