From the producers who brought you 'Tengo and Cache', we present 'Cache me if you can'.
The concept is all about HTML delivery into iOS devices alongside a mechanism for updating the application without going through the Apple app store. Loading HTML from a local file is not a new idea, as a few companies and projects have sprung up around this type of mobile app development have emerged, most notably Phonegap and more recently Apparatio.
During a hack day for the Guardian, I extended this work to add a further downstream cache. Although every effort is made to cache resources before loading, some files may be requested which are not included in the manifest. Overriding the NSURLCache class, the application can intercept any calls which attempt to go out to the web. This cache then retrieves the file, stores it, and then serves this instead of continuing down the pipeline. The next time this file is requested, the cache serves the file on disk instead of hitting the web at all.
Now that I had an iOS application that should pre-cache and intercept, I needed some content to install onto a device. I had wanted to use a Wordpress blog, or RSS feed, but felt that this content could prove difficult. Without knowing what content would be delivered, I couldn't build a manifest file that would capture the entire content. Also, I thought it might prove to be bad user experience if something that would work on a web page when online might not work offline. Even something as ubiquitous as search might look to have failed miserably.
I decided to use something I knew I had control over, the Guardian Content API. Using a small NodeJS application, I could retrieve a query and present that as HTML, alongside an appropriate manifest file. Then all that was required was a small property change in the iOS app and a native application was ready to be launched.