Snow Crash - Neal Stephenson

I started reading Neal Stephenson at a friend's recommendation. That reminded me of the cyberpunk novels that I used to read in my teenage years and enjoy so much. However, I remember them slightly more fun :) That's why I would call Snow Crash more of a Cy-Fi novel, a piece of cyberpunk with a slightly overexagerated plot. Even Wikipedia calls it a post-cyberpunk novel. You see, when Gibson wrote about hackers and the artificial intelligences and the future, he was actually trying to convey a believable, predictable future. I believe Neal Stephenson actually crossed the line and pushed the vision a little in order to put some ideas on the table.

However, it was still a good novel, with interesting characters, fantastic vision of the future and quite a bit of research, which he modestly attributed to a lot of his friends.

The story revolves around Hiro Protagonist, a sword wielding computer hacker, and Y.T. (Yours Truly - a 15 years old skateboard courier), both caught in a complex plot that I cannot reveal without spoiling the read. It has some of the standard cyberpunk motiffs like the collapse of governments and law, the world being ruled by corporations like the Mafia, the church and Mr. Lee's greater Hong Kong (to name a few) and a focus on the services individual people can provide rather than the material benefits of technological items.

I recommend reading it, although some parts of the "future" are already old and silly by now. I've also read some short novels like The Great Simoleon Caper and Spew, that were both good reads, especially the latter. I am moving on to Diamond Age now.

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Internet Explorer Cannot Open the Internet Site ... Operation Aborted.

You usually get this using an Internet Explorer version 6 (but also later versions might exibit this) on pages that seem to be loading ok in the background. You press ok and the page disappears and the regular error page is displayed.

What is happening is that javascript is trying to change a html element that has not finished loading. The usual cause of this problem is an embedded script block that executes as it loads, rather than on the onload event of the page.

The fix is easy. Take all the scripts that execute as they load and either mark them as defer or encapsulate those commands in a function that is executed on the onload event of document.body. Be careful with defer. This post describes the various implementations of the keyword in various browsers.

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SilverLight 2.0 Beta 1 Relative Uri problem

Yay! My first real SilverLight post :)

Anyway, the problem is with controls in SilverLight that expect an URI as a parameter. It doesn't work. After trying all kind of stuff and googling a litle I found out that

1. the path is relative to the web application ClientBin directory
2. the path cannot contain .. or other directory/URI navigation markers like ~
3. the SilverLight control does not have access to a Request object like a web page does

This link already discusses it: Silverlight 2.0 Beta 1 Uri inconsistency, but I also have an additional solution to the ones listed there.

Here are the solutions for this:

• Provide an absolute Uri either statically or by generating it with this piece of code:

  New Uri(Application.Current.Host.Source.AbsolutePath + "../../../video.wmv", UriKind.Absolute)

• Copy the images, videos, files into the ClientBin directory then only provide their name
• Create virtual directories inside ClientBin that point to your resource directories. For example create a virtual directory Videos that points to the ~/Resources/Videos folder in the site, then simply use Videos/video.wmv as the URI

Of these three, the last I find the most elegant, even if the setup of the website itself might be rendered a lot more difficult by this.

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Javascript script blocks relative paths in ASP.Net

ASP.Net 2.0 added a very useful thing, the '~' sign, which indicates that a path is relative to the application directory. Since the application itself should be indifferent to its name, this little thing comes in useful when trying to set the location of user controls, style sheets and so on. The problem is that this feature only applies to user controls. That is not a problem for most tags, since even a link tag can be set as a user control with a runat=server attribute.

The problem comes when trying to set the location of javascript script blocks. A script block with runat=server must be a server code block by definition, i.e. C# or VB, whatever the site language is set to. One of the solutions often used to solve this is to use a code block inside the src attribute of the javascript block like this:

<script language="Javascript" type="text/javascript" 
   src='<% =ResolveUrl("~/scripts/myScript.js")%>'></script>

.

But this is still a nasty issue, because of the dreaded The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>). error. As in the post I linked to, the solution for this is to place all external script blocks within a server control like a PlaceHolder or a even a div with the runat=server attribute set. The drawback to this solution is that you can't do that in the <head> section of the HTML output.

The other solution is to use from within the server code the ScriptManager.RegisterClientScriptInclude method to add the script programatically to the page. While this is elegant, it also defeats the purpose of the aspx page, that is to separate content from code.

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How to add content at the end of an AutoCompleteExtender dropdown

Somebody asked me how to add things at the end of an AutoCompleteExtender div, something like a link. I thought it would be pretty easy, all I would have to do is catch the display function and add a little thing in the container. Well, it was that simple, but also complicated, because the onmousedown handler for the dropdown is on the entire div, not on the specific items. The link was easy to add, but there was no way to actually click on it!

Here is my solution:

function addLink(sender,args) {
    var div=sender.get_completionList();
    if (div) {
        var newDiv=document.createElement('div');
        newDiv.appendChild(getLink());
        div.appendChild(newDiv);
    }
}

function getLink() {
    var link=document.createElement('a');
    link.href='#';
    link.innerHTML='Click me for popup!'
    link.commandName='AutoCompleteLinkClick';
    return link;
}

function linkClicked() {
    alert('Popsicle!');
}

function ACitemSelected(sender,args) {
    var commandName=args.get_item().commandName;
    if (commandName=='AutoCompleteLinkClick') linkClicked();
}

The AutoCompleteExtender must have the two main functions as handlers for the item selected and popup shown set like this:

<ajaxControlToolkit:AutoCompleteExtender OnClientItemSelected="ACitemSelected" OnClientShown="addLink" ...>

Now, the explaining.

First we hook on OnClientShown and add our link. The link is added inside a div, because else it would have been shown as a list item (with highlight on mouse over). I also added a custom attribute to the link: commandName.

Second we hook on OnClientItemSelected and check if the selected item has a commandName attribute, and then we execute stuff depending on it.

That's it folks!

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Request.Url and the missing port

We have this web application that needs to call a third party site that then redirects back to us. The other app is using a configured URL to redirect back. In order to develop and debug the application, we used a router redirect with a different port like this: the external site calls http://myExternalIp:81 and it gets redirected to my own computer on port 80.

I was amazed to notice that when entering my local page, Request.Url would be in the format http://myExternalIp, without the 81 port. As the page was executed in order to debug it, I was baffled by this behaviour. I tried a few things, then I decided to replicate it on a simple empty site and there it was. The only thing I could find that had any information about the original port number was Request.Headers["Host"] which looked something like myExternalIp:81.

I guess this is a bug in the Request object, since it uses the port of the actual server instead of the one of the request, since my server was responding on port 80 on localhost and not 81.

Here is a small method that gets the real Request URL:

 public static Uri GetRealRequestUri()
 {
     if ((HttpContext.Current == null) || 
         (HttpContext.Current.Request == null))
         throw new ApplicationException("Cannot get current request.");
     return GetRealRequestUri(HttpContext.Current.Request);
 }

 public static Uri GetRealRequestUri(HttpRequest request)
 {
     if (String.IsNullOrEmpty(request.Headers["Host"]))
       return request.Url;
     UriBuilder ub = new UriBuilder(request.Url);
     string[] realHost = request.Headers["Host"].Split(':');
     string host = realHost[0];
     ub.Host = host;
     string portString = realHost.Length > 1 ? realHost[1] : "";
     int port;
     if (int.TryParse(portString, out port))
         ub.Port = port;
     return ub.Uri;
 }

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(Response.Redirect or Response.End) and 'Thread was being aborted' error

Just a short infomercial. Response.Redirect(url) is the same with Response.Redirect(url,true), which means that after the redirect, Response.End will be executed. In case you get a weird 'Thread was being aborted' exception, you probably have the Redirect/End methods inside a try/catch block. Remove them from the block and it will work. Probably the ending of the Response session doesn't look good to the debugger and that particularily obtuse exception is thrown.

If you absolutely must put the thing in a try/catch block, just put everything EXCEPT the Redirect/End. Another option (only for Response.Redirect) is to add a false parameter so to not execute Response.End.

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