Rails core - Sep 2010 - Responding to a non-registered MIME type?

I''m trying to figure out how attachments are supposed to work with MIME
type-based responses. What makes attachments special is that in many 
cases they are allowed to be arbitrary files. It would be too 
restrictive to require that all possible types are registered 
(Mime::Type.register).

Let''s say for GET requests on an attachment resource I want to return 
metadata if the requested format is XML or JSON. Otherwise I want to 
return the attachment itself.

  class AttachmentsController < ApplicationController
    respond_to :xml, :json
    respond_to :all, :only => :show

    def show
      @attachment = ...
      respond_with(@attachment) do
        format.any { send_file @attachment.path }
      end
    end
  end

This doesn''t work, because #any really means any, including :xml and 
:json. This doesn''t work as intended, either

      respond_with(@attachment) do
        format.xml
        format.json
        format.any { send_file @attachment.path }
      end

It has to be

      respond_with(@attachment) do
        format.xml  {}
        format.json {}
        format.any  { send_file @attachment.path }
      end

But that is not the kind of code I''d like to write. I''d rather
write

      respond_with(@attachment) do
        format.default { send_file @attachment.path }
      end

With the intended meaning that the default block is only used if 
respond_to :all is active for the action and there is no more specific 
explicit or implicit response for the format.

Did I miss how to do this with the existing responder code? Are there 
serious reasons why it should not be done anyway?

Michael

-- 
Michael Schuerig
mailto:michael@schuerig.de
http://www.schuerig.de/michael/

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