.NET: Check URL's response status code?

问题:

What's the easiest way in .NET to check what status code a web server replies with to a GET request?

Note that I do not need the body of the response. In fact, if possible, only the header should be requested. Having said that, however, if requesting that the body of the response be omitted significantly increases the complexity of the code, receiving the body would be fine.

Also, I'm particularly interested in catching ALL the possible appropriate exceptions (System.Net.WebException, System.IO.IOException, System.Net.Sockets.SocketException, etc.), as this routine will run thousands of times a day.

回答1:

public HttpStatusCode GetHeaders(string url)
    {
        HttpStatusCode result = default(HttpStatusCode);

        var request = HttpWebRequest.Create(url);
        request.Method = "HEAD";
        using (var response = request.GetResponse() as HttpWebResponse)
        {
            if (response != null)
            {
                result = response.StatusCode;
                response.Close();
            }
        }

        return result;
    }

回答2:

Use the HTTP method HEAD, which is the same as GET except doesn't return the body:

var request = (HttpWebRequest)WebRequest.Create("http://www.example.com");
request.Method = "HEAD";
var response = (HttpWebResponse)request.GetResponse();

// status code...
response.StatusCode;

From Section 9.4 of RFC2616:

The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response. The metainformation contained in the HTTP headers in response to a HEAD request SHOULD be identical to the information sent in response to a GET request. This method can be used for obtaining metainformation about the entity implied by the request without transferring the entity-body itself. This method is often used for testing hypertext links for validity, accessibility, and recent modification.

回答3:

I've ended up with this method which combines Ivan Ferić's answer and with proper exceptional cases support:

public async Task<bool> IsAccessibleAsync (string url)
{
    if (url == null)
        throw new ArgumentNullException ("url");

    if (url.IndexOf (':') < 0)
        url = "http://" + url.TrimStart ('/');

    if (!Uri.IsWellFormedUriString (url, UriKind.Absolute))
        return false;

    var request = (HttpWebRequest) WebRequest.Create (url);
    request.Method = "HEAD";

    try
    {
        using (var response = await request.GetResponseAsync () as HttpWebResponse)
        {
            if (response != null && response.StatusCode == HttpStatusCode.OK)
                return true;

            return false;
        }
    }
    catch (WebException)
    {
        return false;
    }
}

回答4:

If you use HttpWebRequest, it's pretty easy:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://url");
request.Method = "GET";
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
HttpStatusCode status = response.StatusCode;

You can surround that with a blanket catch clause, or look at the docs for WebRequest.Create and .GetResponse to see what exceptions will get thrown.

回答5:

Here is what I came up with that handles 404 exceptions. There is also a test below.

public static HttpStatusCode GetUrlStatus(string url, string userAgent)
{
    HttpStatusCode result = default(HttpStatusCode);

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
    request.UserAgent = userAgent;
    request.Method = "HEAD";

    try
    {
        using (var response = request.GetResponse() as HttpWebResponse)
        {
            if (response != null)
            {
                result = response.StatusCode;
                response.Close();
            }
        }
    }
    catch (WebException we)
    {
        result = ((HttpWebResponse)we.Response).StatusCode;
    }

    return result;
}


[Test]
public void PageNotFoundShouldReturn404()
{
    //Arrange
    HttpStatusCode expected = HttpStatusCode.NotFound;
    string userAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36";

    //Act
    HttpStatusCode result = WebHelper.GetUrlStatus("http://www.kellermansoftware.com/SomePageThatDoesNotExist", userAgent);

    //Assert
    Assert.AreEqual(expected, result);
}