Yet another little micro-library designed to do one thing, and do it well:
I’ve recently been working on a personal project that lets me bookmark physical places.
To avoid having to build any of the authentication infrastructure, I decided to build on top of Twitter’s identity ecosystem. Any user on my system has a one-to-one mapping back to a Twitter account. Twitter get to deal with all the infrastructure around sign ups, forgotten passwords and so forth. I get to focus on features.
The other benefit I get is being able to easily grab an avatar image and display it on the ‘mark’ page like this:
(Sidenote: You might also notice why I recently built relativetime and crockford-base32.)
Well, it turns out that grabbing somebody’s Twitter avatar isn’t actually as easy as one might hope. The images are stored on Amazon S3 under a URL structure that requires you to know the user’s Twitter Id (the numeric one) and the original file name of the image they uploaded. To throw another spanner in the works, if the user uploads a new profile image, the URL changes and the old one stops working.
For most Twitter clients this isn’t an issue because the image URL is returned as part of the JSON blob for each status. In our case, it’s a bit annoying though.
Joe Stump set out to solve this problem by launching tweetimag.es. This service lets you use a nice URL like http://img.tweetimag.es/i/tathamoddie_n and let them worry about all the plumbing to make it work. Thanks Joe!
There’s a risk though … This is a free service, with no guarantees about its longevity. As such, I didn’t want to hardcode too many dependencies on it into my website.
This is where we introduce Twavatar. Here’s what my MVC view looks like:
@Html.TwitterAvatar(Model.OwnerHandle)
Ain’t that pretty?
We can also ask for a specific size:
@Html.TwitterAvatar(Model.OwnerHandle, Twavatar.Size.Bigger)
The big advantage here is that if / when tweetimag.es disappears, I can just push an updated version of Twavatar to NuGet and everybody’s site can keep working. We’ve cleanly isolated the current implementation into its own library.
It’s scenarios like this where NuGet really shines.
Update 1: Paul Jenkins pointed out a reasonably sane API endpoint offered by Twitter in the form of http://api.twitter.com/1/users/profile_image/tathamoddie?size=bigger. There are two problems with this API. First up, it issues a 302 redirect to the image resource rather than returning the data itself. This adds an extra DNS resolution and HTTP round trip to the page load. Second, the documentation for it states that it “must not be used as the image source URL presented to users of your application” (complete with the bold). To meet this requirement you’d need to call it from your application server-side, implement your own caching and so forth.
The tweetimag.es service most likely uses this API under the covers, but they do a good job of abstracting all the mess away from us. If the tweetimag.es service was ever to be discontinued, I imagine I’d update Twavatar to use this API directly.
Tatham Oddie 