HttpWatch includes automation samples in C# and in a previous post we used C# to create simple empty cache and primed cache tests. However, a number of customers have recently asked how they can get started with HttpWatch and VB.Net. To use Visual Basic simply follow these steps:

1. Create a VB.Net Project

In Visual Studio create a new console application for Visual Basic:

2. Add a Reference for HttpWatch

To use the COM based HttpWatch automation API you need to create a  reference by right clicking on the project and going to ‘Add Reference…’ :

When the ‘Add Reference’ dialog opens click on the COM tab. If you have HttpWatch Basic or Professional Edition installed you should be able to find HttpWatch in the list of COM type libraries. A quick way to do this is to type ‘httpwatch’ into the References dialog. Once you have found the HttpWatch Automation library; select it and click on OK:

3. Start Writing Code!

The HttpWatch automation objects are now available in VB.Net. To make life easier you may want to add an Imports HttpWatch statement into your code so that you don’t have to add the HttpWatch namespace onto the name of every automation class and interface. There’s documentation for the API in the HttpWatch help file and you’ll see Intellisense prompts as you start writing code:

Here’s an example of a simple program to test how long a page takes to load:

Imports HttpWatch 
Imports System       
 
Module Module1       
 
    Sub Main() 
        Dim url As String = "http://www.httpwatch.com"       
 
        Dim controller As Controller = New Controller       
 
        ' Create a new instance of IE 
        Dim plugin As Plugin = controller.[New]       
 
        plugin.Record() 
        plugin.GotoURL(url)       
 
        ' Wait for page to load 
        controller.Wait(plugin, -1)       
 
        plugin.Stop()       
 
        Dim pageLoadTime As Double = _ 
            plugin.Log.Pages(0).Entries.Summary.Time       
 
        Console.WriteLine("The page loaded in " + _ 
            pageLoadTime.ToString() + " secs")       
 
        plugin.Container.Quit() ' Close IE 
    End Sub       
 
End Module

And here is the empty cache test converted to VB.Net:

 
Imports HttpWatch 
Imports System     
 
Module Module1     
 
    Sub Main() 
        Dim url As String = "http://www.httpwatch.com" 
        Dim controller As Controller = New Controller     
 
        ' Create a new instance of IE 
        Dim plugin As Plugin = controller.[New]     
 
        'Clear out all existing cache entries 
        plugin.ClearCache()     
 
        plugin.Record() 
        plugin.GotoURL(url)     
 
        ' Wait for page to load 
        controller.Wait(plugin, -1)     
 
        plugin.Stop()     
 
        Dim pageLoadTime As Double = _ 
            plugin.Log.Pages(0).Entries.Summary.Time     
 
        Console.WriteLine("The page loaded in " + _ 
            pageLoadTime.ToString() + " secs")     
 
        ' Uncomment the next line to save the results 
        ' plugin.Log.Save("c:\temp\emptycachetest.hwl")     
 
        plugin.Container.Quit() ' Close IE 
    End Sub     
 
End Module

The recently announced Google Ajax Libraries API caught our attention because it offers some significant performance improvements if you use a popular Javascript library (e.g. JQuery, prototype, script_aculo_us, MooTools or dojo)  on your site. You can now reference these libraries at Google rather than having to host your own copy. The benefits of this approach are:

• The libraries are hosted on Google’s high speed global network providing fast access from most locations world wide
• HTTP compression minimizes the size of the download
• Minimized versions of the each library are available to further reduce download size
• The library that your site uses may already be in the user’s browser cache if the user has visited another site that uses the Google hosted libraries
• You can specify which version of a library should be used with a hard coded URL or allow for automatic version upgrades using the google.load() function
• Downloading from a different hostname (i.e. ajax.googleapis.com) frees up an HTTP connection in the browser that can be used to download other resources from your site
• Google picks up the bandwidth bill for the hosted Javascript libraries

Based on these benefits, we decided to upgrade our Ajax gallery page to use the Google hosted version of jQuery. To do this we simply changed the script tag to use the URL of the minimized version of jQuery 1.2.6 at Google:

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.2.6/jquery.min.js">                                                                                                  
</script>

The Google hosted version of the jQuery library gave us a consistent decrease in page load time of about 0.5 seconds. This benefit was largely achieved through the use of a different hostname (ajax.googleapis.com) which avoided Blocked time on the library download. You can see this clearly by first looking at the HttpWatch time chart of the Ajax page load in IE 7 using our own hosted copy of jQuery:

and then the time chart of the page load using the Google hosted version:

We also saw a reduction in the Wait time displayed in HttpWatch. It reduced from about 150 ms with our hosted version to about 60 ms from Google. This was probably due to the use of Google’s Content Delivery Network (CDN). Our web server is hosted in Dallas, Texas and has a ping time of about 140 ms from our office in the UK. The Google host ajax.googleapis.com has a much lower ping time of 29 ms from here in the UK.

However, the overall response time for the library download, ignoring Blocked time, was slightly longer from Google because it incurred an extra DNS look-up and TCP connection. Here is the request level time chart for our hosted version of the library:

and the Google hosted version:

One slight disappointment was that Google has set the cache expiration time of the library to one year in the future:

On most other Google sites they use very long expiration times as described in our Two Simple Rules for HTTP Caching post. They could have done this here, but it probably helps them to gather some usage statistics on these libraries and the chances of a cached Javascript library surviving in a browser cache for more than a year are fairly low.

In the end though, we hit one problem that stopped us using the Google hosted library. There appears to be no support for using HTTPS to download the library. Our Ajax page can be used in HTTP and HTTPS mode. If we simply hard-coded the HTTP download URL for Google we would end up with the dreaded ‘Do you want to display nonsecure items ?’ that we described in a previous post:

So, if you are only using HTTP there are some excellent performance benefits from using the Google hosted Javascript libraries, but if your site needs HTTPS you’ll be forced to use your own hosted version on secure pages. Let’s hope that Google adds SSL support to ajax.googleapis.com.

We’ve added a page to our HTTP Gallery that provides an introduction to Ajax and some simple working examples. The new page is available here:

http://www.httpwatch.com/httpgallery/ajax/

BTW, you can view the AJAX requests made by this page using the free Basic Edition of HttpWatch.