How to Timeout a request using Html Agility Pack

.net asp.net-mvc-3 c# html-agility-pack timeout

Question

I'm making a request to a remote web server that is currently offline (on purpose).

I'd like to figure out the best way to time out the request. Basically if the request runs longer than "X" milliseconds, then exit the request and return a null response.

Currently the web request just sits there waiting for a response.....

How would I best approach this problem?

Here's a current code snippet

    public JsonpResult About(string HomePageUrl)
    {
        Models.Pocos.About about = null;
        if (HomePageUrl.RemoteFileExists())
        {
            // Using the Html Agility Pack, we want to extract only the
            // appropriate data from the remote page.
            HtmlWeb hw = new HtmlWeb();
            HtmlDocument doc = hw.Load(HomePageUrl);
            HtmlNode node = doc.DocumentNode.SelectSingleNode("//div[@class='wrapper1-border']");

            if (node != null)
            { 
                about = new Models.Pocos.About { html = node.InnerHtml };
            }
                //todo: look into whether this else statement is necessary
            else 
            {
                about = null;
            }
        }

        return this.Jsonp(about);
    }

Accepted Answer

I had to make a small adjustment to my originally posted code

    public JsonpResult About(string HomePageUrl)
    {
        Models.Pocos.About about = null;
        // ************* CHANGE HERE - added "timeout in milliseconds" to RemoteFileExists extension method.
        if (HomePageUrl.RemoteFileExists(1000))
        {
            // Using the Html Agility Pack, we want to extract only the
            // appropriate data from the remote page.
            HtmlWeb hw = new HtmlWeb();
            HtmlDocument doc = hw.Load(HomePageUrl);
            HtmlNode node = doc.DocumentNode.SelectSingleNode("//div[@class='wrapper1-border']");

            if (node != null)
            { 
                about = new Models.Pocos.About { html = node.InnerHtml };
            }
                //todo: look into whether this else statement is necessary
            else 
            {
                about = null;
            }
        }

        return this.Jsonp(about);
    }

Then I modified my RemoteFileExists extension method to have a timeout

    public static bool RemoteFileExists(this string url, int timeout)
    {
        try
        {
            //Creating the HttpWebRequest
            HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;

            // ************ ADDED HERE
            // timeout the request after x milliseconds
            request.Timeout = timeout;
            // ************

            //Setting the Request method HEAD, you can also use GET too.
            request.Method = "HEAD";
            //Getting the Web Response.
            HttpWebResponse response = request.GetResponse() as HttpWebResponse;
            //Returns TRUE if the Status code == 200
            return (response.StatusCode == HttpStatusCode.OK);
        }
        catch
        {
            //Any exception will returns false.
            return false;
        }
    }

In this approach, if my timeout fires before RemoteFileExists can determine the header response, then my bool will return false.


Popular Answer

Html Agility Pack is open souce. Thats why you may modify source yurself. For first add this code to class HtmlWeb:

private int _timeout = 20000;

public int Timeout 
    { 
        get { return _timeout; } 
        set
        {
            if (_timeout < 1) 
                throw new ArgumentException("Timeout must be greater then zero.");
            _timeout = value;
        }
    }

Then find this method

private HttpStatusCode Get(Uri uri, string method, string path, HtmlDocument doc, IWebProxy proxy, ICredentials creds)

and modify it:

req = WebRequest.Create(uri) as HttpWebRequest;
req.Method = method;
req.UserAgent = UserAgent;
req.Timeout = Timeout; //add this

Or something like that:

htmlWeb.PreRequest = request =>
            {
                request.Timeout = 15000;
                return true;
            };



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Is this KB legal? Yes, learn why