In the last in the series of posts on writing a .NET application to communicate over HTTP, I thought I'd talk about HtmlAgilityPack (download available here). This tool allows you to write XPATH-like expressions to parse HTML files easily.

In my application, I upload a file and some form variables to a web server, which then responds with an HTML page. On that HTML page, buried in the middle, is a confirmation ID. In order to easily grab that ID and store it for later use, I use code like the following:

        private string CheckResponse(string response)
        {
            HtmlAgilityPack.HtmlDocument doc = new HtmlAgilityPack.HtmlDocument();
            doc.LoadHtml(response);
            HtmlNodeCollection coll = doc.DocumentNode.SelectNodes("//td[@id]");
            if (coll == null) 
                return null;

            foreach (HtmlNode node in coll)
            {
                if (node.Attributes["id"].Value.Equals("confirmation"))
                {
                    return node.InnerText;
                }
            }

            return null;
        }