Class: DescribedRoutes::Middleware::Base

Inherits:
Object
  • Object
show all
Includes:
Rack::RespondTo
Defined in:
lib/described_routes/middleware/base.rb

Overview

Abstract Rack middleware for described_routes. It serves ResourceTemplate data at the configured descrbed_routes path and adds link headers to regular requests whose routing matches a ResourceTemplate.

It must be customised to the web framework in use - override #get_resource_templates and #get_resource_routing.

Direct Known Subclasses

Rails

Constant Summary collapse

DEFAULT_OPTIONS =

The default options parameter to #link_headers; controls which links appear in html link elements

{
  :describedby           => true,
  :self                  => false,
  :up                    => false,
  :related               => false,
  :registered_rels       => {'edit' => 'edit', 'up' => 'up'},
  :described_routes_path => '/described_routes'
}

Instance Method Summary collapse

Constructor Details

#initialize(app, options = {}) ⇒ Base

Returns a new instance of Base.



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# File 'lib/described_routes/middleware/base.rb', line 27

def initialize(app, options={})
  @app = app

  @options = DEFAULT_OPTIONS.merge(options)
  DEFAULT_OPTIONS.keys.each do |option|
    instance_variable_set("@option_#{option}", @options[option])
  end
  
  @inited = false
end

Instance Method Details

#call(env) ⇒ Object

Process a Rack request, either returning ResourceTemplate data fif the request matches the described_routes path, otherwise passing on the request the application and adding a link header to the response.



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# File 'lib/described_routes/middleware/base.rb', line 75

def call(env)
  # puts "\n", "-" * 80, "\n", env.map{|k, v| "#{k} => #{v.inspect}"}

  req = Rack::Request.new(env)
  
  init_from_first_req(req) unless @inited

  if req.path =~ %r(^#{@option_described_routes_path}(/([^/.]+)?)?(\.([a-z]+))?)
    serve_resource_template_data(req, $2, $3)
  else
    call_with_link_header(req)
  end
end

#call_with_link_header(req) ⇒ Object

Passes on a request to the application and adds a link header to the response



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# File 'lib/described_routes/middleware/base.rb', line 140

def call_with_link_header(req)
  status, headers, body = @app.call(req.env)
  
  resource_template, params = get_resource_routing(req)
  if resource_template
    headers = headers.merge("Link" => make_link_header(resource_template, params, @root + req.fullpath).to_s)
  end
  
  [status, headers, body]
end

#get_resource_routing(req) ⇒ Object

Does nothing - override in framwork-specific middleware to return the ResourceTemplate and params hash matching the request, otherwise a pair of nils



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# File 'lib/described_routes/middleware/base.rb', line 67

def get_resource_routing(req)
  [nil, nil]
end

#get_resource_templates ⇒ Object

Does nothing - override in framework-specific middleware to return the top level ResourceTemplates object



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# File 'lib/described_routes/middleware/base.rb', line 59

def get_resource_templates
  nil
end

#init_from_first_req(req) ⇒ Object

From the first request, initialize @root, @described_routes_uri and @resource_templates



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# File 'lib/described_routes/middleware/base.rb', line 41

def init_from_first_req(req)
  raise "no request host" unless req.host
  
  @root = "http://#{req.host}"
  @root += ":#{req.port}" if req.port && req.port != 80
  @root += "#{script_name}" if req.script_name && !req.script_name.empty?

  @described_routes_uri = @root + @option_described_routes_path

  @resource_templates = get_resource_templates(@root)
  raise "get_resource_templates(#{@root.inspect}) failed; no resource templates!" unless @resource_templates

  @inited = true
end

#make_link_header(resource_template, params, request_uri) ⇒ Object

Returns a LinkHeader object that represents the required links.

Link relation types (“rel” attributes) will contain a standard type (‘self’, ‘up’, ‘describedby’) &/or an extension type in the form “described_route_url(name)#rel”, using the name and rel of the resource template.

The output is filtered by the options hash, with members :self, :describedby, :up, :related.

TODO move this to ResourceTemplate



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# File 'lib/described_routes/middleware/base.rb', line 160

def make_link_header(resource_template, params, request_uri)
  links = []

  type_prefix = @described_routes_uri + '#'
  #
  # For the application's root, the link with rel="describedby" has meta="ResourceTemplates" and it refers to a list of all
  # top level resource templates. Otherwise, rel="describedby" has meta="ResourceTemplate" and it refers to a single resource
  # template (together with any descendants).
  #
  if resource_template.name == 'root'
    described_by = @described_routes_uri
    related = @resource_templates
    meta = "ResourceTemplates"
  else
    described_by = @described_routes_uri + "/" + resource_template.name
    related = resource_template.resource_templates
    meta = "ResourceTemplate"
  end

  #
  # Add any query parameters to the rel="describedby" link
  #
  if params.empty?
    described_by_with_params = described_by
  else
    described_by_with_params = described_by + '?' + params.to_query
  end

  # data for rel="self"
  links << LinkHeader::Link.new(request_uri, [['rel', 'self'], ['role', type_prefix + resource_template.name]]) if @option_self

  # data for rel="described_by"
  links << LinkHeader::Link.new(described_by_with_params, [['rel', 'describedby'], ['meta', meta]]) if @option_describedby

  # data for rel="up"
  # TODO move this to ResourceTemplate
  if @option_up
    if resource_template.parent
      links << LinkHeader::Link.new(
                  resource_template.parent.uri_for(params),
                  [['rel', 'up'], ['role', type_prefix + resource_template.parent.name]])
    elsif resource_template.name != 'root'
      links << LinkHeader::Link.new(@root + '/', [['rel', 'up'], ['role', type_prefix + 'root']])
    end
  end

  # data for rel="related"
  if @option_related
    related.expand_links(params).each do |l|
      if l.name != resource_template.name
        rel = l.rel || l.name
        rels = [['rel', described_by + '#' + rel]]
        if l.rel
          registered_rel = @option_registered_rels[rel]
          if registered_rel
            rels.unshift(['rel', registered_rel])
          end
        end
        links << LinkHeader::Link.new(l.uri, rels + [['role', type_prefix + l.name]])
      end
    end
  end
  LinkHeader.new(links)
end

#serve_resource_template_data(req, route_name, format) ⇒ Object

Handles requests for ResourceTemplate data



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# File 'lib/described_routes/middleware/base.rb', line 92

def serve_resource_template_data(req, route_name, format)
  if route_name   # /described_routes/{route_name}
    resource_template = @resource_templates.all_by_name[route_name]
    unless resource_template
      return [404, {'Content-Type' => 'text/plain'}, ["No ResourceTemplate named #{route_name.inspect}"]]
    end
    target = resource_template
    rel = "index" # link header will point to the site ResourceTemplates description
  else
    rel = "self"  # this is the site ResourceTemplates description
    target = @resource_templates
  end
  expanded = target.partial_expand(req.GET)
  
  Rack::RespondTo.env = req.env
  if format
    # Format extension overrides any accept header
    Rack::RespondTo.media_types = [Rack::Mime::MIME_TYPES[format]]
  else
    # Supported formats, .text preferred.  No html yet!
    supported_media_types = %w(.text .json .yaml .xml).map{|format| Rack::Mime::MIME_TYPES[format]}
    # not sure why this is needed - thought Rack::RespondTo would choose for us
    http_accept = req.env['HTTP_ACCEPT']
    if supported_media_types.grep(http_accept).empty?
      Rack::RespondTo.media_types = supported_media_types
    else
      Rack::RespondTo.media_types = [http_accept]
    end
  end

  body = respond_to do |format|
    format.text {expanded.to_text}
    format.json {expanded.to_json}
    format.yaml {expanded.to_yaml}
    format.xml  {expanded.to_xml(Builder::XmlMarkup.new(:indent => 2)).target!}
  end

  headers = {
    'Link' => %Q(<#{@described_routes_uri}>; rel="#{rel}"; meta="ResourceTemplates"),
    'Content-Type' => Rack::RespondTo.selected_media_type
  }
  
  [200, headers, [body]]
end