jesal gadhia » html

Cross-Domain Communication with IFrames

Tue, 21 Dec 2010 21:18:29 +0000

Recently I encountered a situation where I had to communicate between an iframe located on a different domain and its parent. Due to the “same origin policy”, a security concept for browsers, which only permits scripts running on pages originating from the same site, this was not possible to do right out of the box. After some Googling, I learned there were a couple of workarounds for it. You could use dynamic script tags included from external domains aka JSONP or use postMessage or the IFrame URL technique. All of these solutions are quite hackish or complicated and not 100% secure. Luckily I found this nice little library called easyXDM.

At the core easyXDM provides a transport stack capable of passing string based messages between two windows, a consumer (the main document) and a provider (a document included using an iframe). It does this by using one of several available techniques, always selecting the most efficient one for the current browser. For all implementations the transport stack offers bi-directionality, reliability, queueing and sender-verification.

Here’s a small test I created. It calls a function to scroll the page up from the remote site. Local and remote directories represent the servers where the files will be residing on.

local/methods.html



    
        easyXDM

remote/remotemethods.html



    
        easyXDM

remote/name.html

You can find lot more examples and documentation on easyXDM’s website.

How to easily parse HTML without RegEx

Tue, 06 May 2008 16:50:04 +0000

I recently discovered an absolutely amazing HTML parsing library for .NET called HtmlAgilityPack. It completely takes away the pain of parsing complicated HTML with regular expressions.

Here’s a very simple example of what you could do with it – I’m just extracting inner HTML from any element inside a HTML file which has a css class called “scrape” assigned to it:

using HtmlAgilityPack;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        HtmlDocument doc = new HtmlDocument();
        doc.Load(Server.MapPath(filePath));
        Parse(doc.DocumentNode);
    }
    private void Parse(HtmlNode n)
    {
        foreach (HtmlAttribute atr in n.Attributes)
        {
            if (atr.Name == "class" && atr.Value == "scrape")
            {
                Response.Write(n.InnerHtml);
            }
        }

        if (n.HasChildNodes)
        {
            foreach (HtmlNode cn in n.ChildNodes)
            {
                Parse(cn);
            }
        }
    }
}

That’s just a very small part of what it could do. I’ll expand upon this and post a few more examples in the future showing some interesting things you could do with this.

How to extract URLs (href property) from HTML

Sat, 05 Jan 2008 07:13:09 +0000

protected ArrayList getURL(string txtIn)
{
    ArrayList outURL = new ArrayList();
    Regex r = new Regex("href\\s*=\\s*(?:(?:\\\"(?[^\\\"]*)\\\")|(?[^\\s]* ))");
    MatchCollection mc1 = r.Matches(txtIn);

    foreach (Match m1 in mc1)
    {
        foreach (Group g in m1.Groups)
        {
            outURL.Add(g.Value);
        }
    }

    return outURL;
}

Strip out HTML tags using RegEx

Wed, 14 Nov 2007 04:16:51 +0000

This code will strip out all the HTML tags and truncate the text to 4 lines.

public static string TruncateText(string txtIn, int newLength)
{
    string txtOut = txtIn;
    string pattern = @"<(.|\n)*?>";

    //Strip out HTML tags
    if (Regex.IsMatch(txtIn, pattern, RegexOptions.None))
        txtOut = Regex.Replace(txtIn, pattern, string.Empty, RegexOptions.Multiline).Trim();

    if (txtOut.Length > newLength)
    {
        int endPos = txtOut.LastIndexOf(" ", newLength);
        txtOut = txtOut.Substring(0, endPos) + "...";
    }

    return txtOut;
}