Module: Merb::ResponderMixin

The ResponderMixin adds methods that help you manage what formats your controllers have available, determine what format(s) the client requested and is capable of handling, and perform content negotiation to pick the proper content format to deliver.

If you hear someone say "Use provides" they‘re talking about the Responder. If you hear someone ask "What happened to respond_to?" it was replaced by provides and the other Responder methods.

A simple example

The best way to understand how all of these pieces fit together is with an example. Here‘s a simple web-service ready resource that provides a list of all the widgets we know about. The widget list is available in 3 formats: :html (the default), plus :xml and :text.

    class Widgets < Application
      provides :html   # This is the default, but you can
                       # be explicit if you like.
      provides :xml, :text

      def index
        @widgets = Widget.fetch
        render @widgets
      end
    end

Let‘s look at some example requests for this list of widgets. We‘ll assume they‘re all GET requests, but that‘s only to make the examples easier; this works for the full set of RESTful methods.

The simplest case, /widgets.html Since the request includes a specific format (.html) we know what format to return. Since :html is in our list of provided formats, that‘s what we‘ll return. render will look for an index.html.erb (or another template format like index.html.mab; see the documentation on Template engines)
Almost as simple, /widgets.xml This is very similar. They want :xml, we have :xml, so that‘s what they get. If render doesn‘t find an index.xml.builder or similar template, it will call to_xml on @widgets. This may or may not do something useful, but you can see how it works.
A browser request for /widgets This time the URL doesn‘t say what format is being requested, so we‘ll look to the HTTP Accept: header. If it‘s ’*/*’ (anything), we‘ll use the first format on our list, :html by default.
If it parses to a list of accepted formats, we‘ll look through them, in order, until we find one we have available. If we find one, we‘ll use that. Otherwise, we can‘t fulfill the request: they asked for a format we don‘t have. So we raise 406: Not Acceptable.

A more complex example

Sometimes you don‘t have the same code to handle each available format. Sometimes you need to load different data to serve /widgets.xml versus /widgets.txt. In that case, you can use content_type to determine what format will be delivered.

    class Widgets < Application
      def action1
        if content_type == :text
          Widget.load_text_formatted(params[:id])
        else
          render
        end
      end

      def action2
        case content_type
        when :html
          handle_html()
        when :xml
          handle_xml()
        when :text
          handle_text()
        else
          render
        end
      end
    end

You can do any standard Ruby flow control using content_type. If you don‘t call it yourself, it will be called (triggering content negotiation) by render.

Once content_type has been called, the output format is frozen, and none of the provides methods can be used.

Methods

_accept_types _perform_content_negotiation _provided_formats content_type content_type= does_not_provide included only_provides provides

Classes and Modules

Module Merb::ResponderMixin::ClassMethods
Class Merb::ResponderMixin::ContentTypeAlreadySet

Constants

 Dictionary.new
 {}
 Mutex.new
 {}

Public Class methods

included(base)

Parameters

base<Module>:

The module that ResponderMixin was mixed into

:api: private

[Source]

     # File merb-core/lib/merb-core/controller/mixins/responder.rb, line 111
111:     def self.included(base)
112:       base.extend(ClassMethods)
113:       base.class_eval do
114:         class_inheritable_accessor :class_provided_formats
115:         self.class_provided_formats = []
116:       end
117:       base.reset_provides
118:     end

Public Instance methods

_accept_types()

[Source]

     # File merb-core/lib/merb-core/controller/mixins/responder.rb, line 262
262:     def _accept_types
263:       accept = request.accept
264:       
265:       MIME_MUTEX.synchronize do
266:         return ACCEPT_RESULTS[accept] if ACCEPT_RESULTS[accept]
267:       end
268:       
269:       types = request.accept.split(Merb::Const::ACCEPT_SPLIT).map do |entry|
270:         entry =~ Merb::Const::MEDIA_RANGE
271:         media_range, quality = $1, $3
272:         
273:         kind, sub_type = media_range.split(Merb::Const::SLASH_SPLIT)
274:         mime_sym = Merb.available_accepts[media_range]
275:         mime = Merb.available_mime_types[mime_sym]
276:         (quality ||= 0.0) if media_range == "*/*"          
277:         quality = quality ? (quality.to_f * 100).to_i : 100
278:         quality *= (mime && mime[:default_quality] || 1)
279:         [quality, mime_sym, media_range, kind, sub_type, mime]
280:       end
281:     
282:       accepts = types.sort_by {|x| x.first }.reverse!.map! {|x| x[1]}      
283:       
284:       MIME_MUTEX.synchronize do
285:         ACCEPT_RESULTS[accept] = accepts.freeze
286:       end
287:       
288:       accepts
289:     end

_perform_content_negotiation()

Do the content negotiation:

if params[:format] is there, and provided, use it
Parse the Accept header
If it‘s */*, use the first provided format
Look for one that is provided, in order of request
Raise 406 if none found

:api: private

[Source]

     # File merb-core/lib/merb-core/controller/mixins/responder.rb, line 299
299:     def _perform_content_negotiation
300:       if fmt = params[:format]
301:         accepts = [fmt.to_sym]
302:       else
303:         accepts = _accept_types
304:       end
305: 
306:       provided_formats = _provided_formats
307:       
308:       specifics = accepts & provided_formats
309:       return specifics.first unless specifics.length == 0
310:       return provided_formats.first if accepts.include?(:all) && !provided_formats.empty?
311:       
312:       message  = "A format (%s) that isn't provided (%s) has been requested. "
313:       message += "Make sure the action provides the format, and be "
314:       message += "careful of before filters which won't recognize "
315:       message += "formats provided within actions."
316:       raise Merb::ControllerExceptions::NotAcceptable,
317:         (message % [accepts.join(', '), provided_formats.join(', ')])
318:     end

_provided_formats()

Returns

Array[Symbol]:

The current list of formats provided for this instance of the controller. It starts with what has been set in the controller (or :html by default) but can be modifed on a per-action basis.

:api: private

[Source]

     # File merb-core/lib/merb-core/controller/mixins/responder.rb, line 201
201:     def _provided_formats
202:       @_provided_formats ||= class_provided_formats.dup
203:     end

content_type(fmt = nil)

Returns the output format for this request, based on the provided formats, params[:format] and the client‘s HTTP Accept header.

The first time this is called, it triggers content negotiation and caches the value. Once you call content_type you can not set or change the list of provided formats.

Called automatically by render, so you should only call it if you need the value, not to trigger content negotiation.

Parameters

fmt<String>:

An optional format to use instead of performing content negotiation. This can be used to pass in the values of opts[:format] from the render function to short-circuit content-negotiation when it‘s not necessary. This optional parameter should not be considered part of the public API.

Returns

Symbol:

The content-type that will be used for this controller.

:api: public

[Source]

     # File merb-core/lib/merb-core/controller/mixins/responder.rb, line 345
345:     def content_type(fmt = nil)
346:       self.content_type = (fmt || _perform_content_negotiation) unless @_content_type
347:       @_content_type
348:     end

content_type=(type)

Sets the content type of the current response to a value based on a passed in key. The Content-Type header will be set to the first registered header for the mime-type.

Parameters

type<Symbol>:

The content type.

Raises

ArgumentError:

type is not in the list of registered mime-types.

Returns

Symbol:

The content-type that was passed in.

:api: plugin

[Source]

     # File merb-core/lib/merb-core/controller/mixins/responder.rb, line 364
364:     def content_type=(type)
365:       unless Merb.available_mime_types.has_key?(type)
366:         raise Merb::ControllerExceptions::NotAcceptable.new("Unknown content_type for response: #{type}") 
367:       end
368: 
369:       @_content_type = type
370: 
371:       mime = Merb.available_mime_types[type]
372:       
373:       headers["Content-Type"] = mime[:content_type]
374:       
375:       # merge any format specific response headers
376:       mime[:response_headers].each { |k,v| headers[k] ||= v }
377:       
378:       # if given, use a block to finetune any runtime headers
379:       mime[:response_block].call(self) if mime[:response_block]
380: 
381:       @_content_type
382:     end

does_not_provide(*formats)

Removes formats from the list of provided formats for this particular request. Usually used to remove formats from a single action. See also the controller-level does_not_provide that affects all actions in a controller.

Parameters

*formats<Symbol>:

Registered mime-type

Returns

Array[Symbol]:

List of formats that remain after removing the ones not to provide.

:api: public

[Source]

     # File merb-core/lib/merb-core/controller/mixins/responder.rb, line 258
258:     def does_not_provide(*formats)
259:       @_provided_formats -= formats.flatten
260:     end

only_provides(*formats)

Sets list of provided formats for this particular request. Usually used to limit formats to a single action. See also the controller-level only_provides that affects all actions in a controller.

Parameters

*formats<Symbol>:

A list of formats to use as the per-action list of provided formats.

Returns

Array[Symbol]:

List of formats passed in.

:api: public

[Source]

     # File merb-core/lib/merb-core/controller/mixins/responder.rb, line 240
240:     def only_provides(*formats)
241:       @_provided_formats = []
242:       provides(*formats)
243:     end

provides(*formats)

Adds formats to the list of provided formats for this particular request. Usually used to add formats to a single action. See also the controller-level provides that affects all actions in a controller.

Parameters

*formats<Symbol>:

A list of formats to add to the per-action list of provided formats.

Raises

Merb::ResponderMixin::ContentTypeAlreadySet:

Content negotiation already occured, and the content_type is set.

Returns

Array[Symbol]:

List of formats passed in.

:api: public

[Source]

     # File merb-core/lib/merb-core/controller/mixins/responder.rb, line 221
221:     def provides(*formats)
222:       if @_content_type
223:         raise ContentTypeAlreadySet, "Cannot modify provided_formats because content_type has already been set"
224:       end
225:       @_provided_formats = self._provided_formats | formats # merges with class_provided_formats if not already
226:     end