figure out the api version from HTTP_ACCEPT

lib/travis/api/app/endpoint.rb

@@ -9,7 +9,7 @@ class Travis::Api::App
     set(:prefix) { "/" << name[/[^:]+$/].underscore }
     set disable_root_endpoint: false
     register :scoping
-    helpers :current_user # :services
+    helpers :current_user
 
     before { content_type :json }
     error(ActiveRecord::RecordNotFound, Sinatra::NotFound) { not_found }

lib/travis/api/app/helpers/json_renderer.rb

@@ -6,6 +6,9 @@ class Travis::Api::App
     # convert (in addition to the return values supported by Sinatra, of
     # course). These values will be encoded in JSON.
     module JsonRenderer
+      ACCEPT_VERSION  = /vnd\.travis-ci\.(\d+)\+/
+      DEFAULT_VERSION = 'v1'
+
       def respond_with(resource, options = {})
         halt render_json(resource, options)
       end
@@ -18,7 +21,7 @@ class Travis::Api::App
       private
 
         def render_json(resource, options = {})
-          options[:version] ||= 'v2' # TODO: Content negotiation
+          options[:version] ||= api_version
           options[:params]  ||= params
 
           builder  = Travis::Api.builder(resource, options)
@@ -27,6 +30,11 @@ class Travis::Api::App
 
           resource
         end
+
+        def api_version
+          accept = request.env['HTTP_ACCEPT'] || ''
+          accept =~ ACCEPT_VERSION && "v#{$1}" || DEFAULT_VERSION
+        end
     end
   end
 end