The Google API for Google Reader has not been released. At least officially. I found a real good head-up at Niall Kennedy’s weblog. The information there is more then enough to get you started. The information in the main article is not complete though. You can find out some more tidbits in the comments and I also found some more stuff while working on FeedME. It hadn’t occured to me how easy it actually is to get some information about the API. I figured, it’s a web application, so all the interesting communication happens at the server itself, no way I can get to that. I had even downloaded the javascript file Google Reader uses for it’s work when it occured to me that, yes, this is a web application. It’s a web 2.0 (I really hate that term, but now everybody should know what I mean) application. It uses Ajax, which means that all communication with the server backend originates from my own machine! Add Fiddler and you’ve got a neat protocol-sniffing-setup 
I’m thinking about doing a page on the Google Reader API to put all the info I have at one location.
Anyways this is not about the Google Reader API, at least not in depth. What I am going to write about is the HttpWebRequest, WebResponse and the Uri classes of the .NET framework 2.0.
These were the classes that I wanted to use for communicating with Google. The are built for that purpose! In fact, they worked perfectly for the first API I incorperated, the call to download your subscription list. After I had that working and had a really basic GUI I was ready to move on to the next thing: Downloading the articles for the feeds I’m subscribed to.
The Google Reader API is a REST API (or at least based on some REST principles). This means is uses simple HTTP GET and HTTP POST commands to communicate with XML. Okay, so this also covers SOAP, but the thing with REST is that it doesn’t have predefined XML to use. It’s all up to the implementation. Whereas SOAP has everything standardized except the data itself.
Getting your subscription list is just sending a GET at a specific URL, let’s say: “http://www.google.com/reader/api/subscriptions/” (This isn’t the real URL, just an example). You’ll then get some XML back that describes your subscriptions. Simple to do with HttpWebRequest.
To get the articles of a specific feed, you need to add the URL of the feed to the URL. An example (also not real): “http://www.google.com/reader/api/feed/http://www.digiwar.com/feeds/”
This would give you the articles from this website that Google have in their Reader database. Now here I ran into a problem.
The HttpWebRequest class takes, or converts your string into, a Uri object. The Uri object is a real useful class that does all kinds of useful stuff to the URL you supply. Like checking if it’s a valid URL, removing contradicting directory paths or removing those pesky doubles slashes some people put in their URLs by accident. Do you see the problem already? If not, I’ll give you 5 minutes to think about it.
Take your time.
You got it? Good. So you aggree with me that I was really frustrated that my HttpWebRequests ended up going to “http://www.google.com/reader/api/feed/http:/www.digiwar.com/feeds/” instead of the correct URL. Nothing I could do would help. I tried double-double slashes, tried escaping them, tried encoding them as “%2F”. Nothing worked. I did a lot of Googling on the subject, inquired in newsgroups. Nowhere did I find an answer. So what did I do? I wrote my own HttpRequest, HttpResponse and Url classes.
The Url class was really simple. It just houses a few strings and does some parsing in the constructor. It does no validation whatsoever.
The HttpRequest and the HttpResponse class where a bit harder. For them I P/Invoked a lot of WinInet functions. One important thing learned here: If you ever need the P/Invoke signature of a Win32 function, or at least a good pointer in the right direction, just google for “dllimport
And ofcourse, after I had everything up and running (beautifully I might add) some one found an answer for me. Apparently if you encode the second double slash as ‘\u2215′. So you’ll end up with “http://www.google.com/reader/api/feed/http:/\u2215www.digiwar.com/feeds/” and this seems to work. I still have to test it in a realy world scenario (such as my program), but I’ve just invested a lot of time in my custom classes and it’s working perfectly, so why switch?
I might switch back to the .NET classes sometime in the future, but for now I’m content with how it is.
[Now playing: The Kovenant - Jihad]