In this post I am implementing the Delphi way to request the Google Toolbar’s PageRank (PR). As an example, if I want to look up the PR of my blog (http://www.yanniel.info/), I will have to query the following URL:
So, if you try
You will get the following output:
Oops, at this moment my PageRank is pathetic (PR = 0). Hopefully it will get better someday ;-)
You can find the implementation of the Curl function in my previous post: Fetching a web page with Delphi.
Now that you get the idea, it’s time to generalize our implementation in order to get the PR of any web page.
In the URL above there are two dynamic parameters that we need to understand:
Parameter q: This is the concatenation of “info:” plus the encoded URL for which we want to get the PR. It is mandatory to lead the encoded URL with “http://”. Don’t forget to put a “/” after the top domain, ei, “.info/”, not “.info”.
Parameter ch: Obtaining this parameter is the tricky part. We have to hash the concatenation of “info:” plus our target URL (ei. http://www.yanniel.info/) using the minimal perfect hashing algorithm invented by Bob Jenkins. The outcome will be a number, which corresponds to the value of our ch parameter. We are hashing something like “info:http://www.yanniel.info/”.
I didn’t have the time (or the desire) to understand and implement the minimal perfect hashing algorithm from scratch. So, I ported this C# implementation into Delphi code.
There’s one detail worth mentioning about the implementation. In the original C# code there’s a switch statement that falls all the way through the different cases. I needed to combine a case statement and some goto statements in order to accomplish the same in Delphi.
I wrote the strikeout text above initially; but Brian (first comment below) found a clean way to avoid the goto in this situation. I really thank Brian for his contribution, and next time, I won't quit that easily in removing the goto ;-)
I am putting everything together in the Delphi console application below. I bet you can reuse the BobJenkinsHash function in the Generics.Default.pas unit to make the PR implementation more compact. I didn’t know about the BobJenkinsHash function shipped with Delphi before reading Nick’s post; which is why I am keeping my original implementation.
Finally, this is how you request the Google PageRank in Delphi: