always use etag for caching when cache_key or updated_at are present, add the deploy_sha as a cache buster

lib/travis/api/app.rb

@@ -51,6 +51,10 @@ module Travis::Api
       super()
     end
 
+    def self.deploy_sha
+      @deploy_sha ||= File.exist?('.deploy_sha') ? File.read('.deploy-sha')[0..7] : 'deploy-sha'
+    end
+
     attr_accessor :app
 
     def initialize
@@ -64,11 +68,10 @@ module Travis::Api
 
         memcache_servers = ENV['MEMCACHE_SERVERS']
         if Travis::Features.feature_active?(:use_rack_cache) && memcache_server
-          namespace = File.read('.deploy-sha')[0..7]
           use Rack::Cache,
             verbose: true,
-            metastore:   "memcached://#{memcache_servers}/#{namespace}",
-            entitystore: "memcached://#{memcache_servers}/#{namespace}"
+            metastore:   "memcached://#{memcache_servers}/#{self.class.deploy_sha}",
+            entitystore: "memcached://#{memcache_servers}/#{self.class.deploy_sha}"
         end
 
         use Rack::Deflater
@@ -115,7 +118,7 @@ module Travis::Api
         Raven.configure do |config|
           config.dsn = Travis.config.sentry.dsn
         end if Travis.config.sentry
-        
+
         Travis::LogSubscriber::ActiveRecordMetrics.attach
         $metriks_reporter = Metriks::Reporter::Logger.new
       end

lib/travis/api/app/responders/service.rb

@@ -1,54 +1,68 @@
-module Travis::Api::App::Responders
-  class Service < Base
-    def apply?
-      resource.respond_to?(:run)
-    end
+require 'digest/md5'
 
-    def apply
-      cache_control
-      result = normalize(resource.run)
-      result[:flash] = resource.messages if result && resource.respond_to?(:messages) # TODO should rather happen in the JSON responder, no?
-      result
-    end
+module Travis::Api
+  class App
+    module Responders
+      class Service < Base
+        include Helpers::Accept
 
-    private
-
-      def cache_control
-        if final?
-          mode = endpoint.public? ? :public : :private
-          endpoint.expires(31536000, mode) # 1 year
-        else
-          # FIXME: Chrome WTF?
-          endpoint.cache_control :no_cache
+        def apply?
+          resource.respond_to?(:run)
         end
 
-        endpoint.etag resource.cache_key           if cache_key?
-        endpoint.last_modified resource.updated_at if updated_at?
-      end
-
-      def final?
-        resource.respond_to?(:final?) && resource.final?
-      end
-
-      def updated_at?
-        resource.respond_to?(:updated_at) && resource.updated_at
-      end
-
-      def cache_key?
-        resource.respond_to?(:cache_key) && resource.cache_key
-      end
-
-      # Services potentially return all sorts of things
-      # If it's a string, true or false we'll wrap it into a hash.
-      # If it's an active record or scope we just pass so it can be processed by the json responder.
-      # If it's nil we also pass it but yield not_found.
-      def normalize(result)
-        case result
-        when String, true, false
-          { result: result }
-        else
+        def apply
+          cache_control
+          result = normalize(resource.run)
+          result[:flash] = resource.messages if result && resource.respond_to?(:messages) # TODO should rather happen in the JSON responder, no?
           result
         end
+
+        private
+
+          def cache_control
+            if final?
+              mode = endpoint.public? ? :public : :private
+              endpoint.expires(31536000, mode) # 1 year
+            else
+              # FIXME: Chrome WTF?
+              endpoint.cache_control :no_cache
+            end
+
+            endpoint.etag cache_key if cache_key
+          end
+
+          def final?
+            resource.respond_to?(:final?) && resource.final?
+          end
+
+          def cache_key
+            cache_key ||= begin
+              key = resource_cache_key || resource_updated_at
+              Digest::MD5.hexdigest([App.deploy_sha, key].join('-')) if key
+            end
+          end
+
+          def resource_cache_key
+            resource.respond_to?(:updated_at) && resource.updated_at
+          end
+
+          def resource_updated_at
+            resource.respond_to?(:updated_at) && resource.updated_at.try(:strftime, '%FT%T%:z')
+          end
+
+          # Services potentially return all sorts of things
+          # If it's a string, true or false we'll wrap it into a hash.
+          # If it's an active record or scope we just pass so it can be processed by the json responder.
+          # If it's nil we also pass it but yield not_found.
+          def normalize(result)
+            case result
+            when String, true, false
+              { result: result }
+            else
+              result
+            end
+          end
       end
+    end
   end
 end