Ez (or someone) asked on #merb tonight whether respond_to was the
right API for
what it does. After some discussion and pasties, I offer the
following proposed
API for content negotiation and response format selection:
First, what does respond_to do right now? I see at as performing 3
distinct
operations:
1. parse params[:format] and the accepts header to find out what
format the
client wants
2. look at all the calls to the responder to see what formats the
action
provides
3. reconcile 1 and 2 and pick a format
I propose that we split #2 and #3 into explicit steps.
Here's a sample controller using the new API:
class ManyFormats < Application
# controllers provide :html by default, so this is implied:
provides :html
# every action in this controller also provides :xml and :txt
provides :xml, :txt
def index
# index also provides :js
provides :js
# this is smart, and based on all the things
# currently provided and all the things the client
# accepts, returns a Symbol for the response format
case request.format
when :html, :txt
render
when :xml
SomeClass.to_xml
when :js
"Object.new()"
end
end
def textonlyaction
only_provides :txt
# this wipes out :html and :xml from the controller-level
# declarations
render
end
end
Win #1: respond_to is no longer a magic black box, we have explicit
definition of
our formats and explicit flow control of our rendering
Win #2: in the case where most/all formats use templates, we get
simpler code:
class CurrentWay < Application
def index
respond_to do |fmt|
fmt.html { render }
fmt.xml { render }
fmt.txt { render }
fmt.js { render }
end
end
end
class ProposedWay < Application
def index
provides :html, :xml, :txt, :js
render
end
end
Win #2.5: Say you wrote an app without respond_to, using only HTML,
and then
decide you want to support FBML or PBJML. With the current API you
have to
modify every single action in every single controller to add a
respond_to block.
With the proposed API you add "provides :pbjml" to Application and
add your
templates and it's done.
Added bonus: we can keep a respond_to on top of the provides()
variables for
people who like it.
Thoughts? Suggestions? I'm not too emotionally attached to this
yet, so feel
free to pick at it or shoot it down.
If it's still deemed viable by the weekend, I'll code it.
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