Feb 07

Intercepting microformats in rails input

In Input formats and content types in Rails 1.2 I mentioned a project I’ve been working on that will provide a RESTful service interface which accepts its input in a number of formats, including microformatted HTML.

For certain types of data microformats provide a great way to receive input as they don’t require your clients to learn a new schema to send you data. They can take the same semantically rich HTML they’re displaying on their website and POST it to your endpoint. Or they can use a tool like Ryan King’s hcalendar creator to generate some sample input.

But intercepting and interpreting that data isn’t quite so simple as JSON or XML. Those formats have well defined content types that we can use to identify them, and use the parameter parsers I described in my earlier blog entry. Microformats are HTML and so will come with an HTML content type, just like other forms of input.

It would be nice if there were a simple way (short of running them through a full parser) to identify POSTs whose bodies contain microformats, but so far I haven’t come across one. What we can do is to override rails’ default handlers to parse the raw post data and see if it looks like regular form input. If it doesn’t, we can presume it’s meant to be considered to be microformat data and we can do some parsing using the excellent mofo (on which more, later). My code at present is:

microformat_interceptor = Proc.new do |data|
  parsed = CGI.parse(data)

  if parsed.collect { |key, value| key + '=' + value[0] }.first == data
    { :event => HCalendar.find(:text => data) }

Mime::FORM = Mime::Type.lookup("application/x-www-form-urlencoded")
ActionController::Base.param_parsers[Mime::FORM] = microformat_interceptor
ActionController::Base.param_parsers[Mime::HTML] = microformat_interceptor

With that code in environment.rb, a request with hCalendar data in its post body will look to our actions as if it had an HCalendar object in params[:event]. If we extend a few of our event model’s methods, our controller can treat this input just as it would XML or a standard query string.

Obviously this is a work in progress, its output is very simple, and it’s not all that versatile, but so far my tests stand up well, and it makes the code considerably more elegant.

For a little more on microformats and APIs, check out Drew’s “Can Your Website be Your API?” and the REST page on the microformats wiki.