1 files changed, 27 insertions, 15 deletions

diff --git a/actionpack/lib/action_dispatch/http/cache.rb b/actionpack/lib/action_dispatch/http/cache.rb
index aaed0d750f..bea62b94d2 100644
--- a/actionpack/lib/action_dispatch/http/cache.rb
+++ b/actionpack/lib/action_dispatch/http/cache.rb
@@ -4,14 +4,18 @@ module ActionDispatch
   module Http
     module Cache
       module Request
+
+        HTTP_IF_MODIFIED_SINCE = 'HTTP_IF_MODIFIED_SINCE'.freeze
+        HTTP_IF_NONE_MATCH     = 'HTTP_IF_NONE_MATCH'.freeze
+
         def if_modified_since
-          if since = env['HTTP_IF_MODIFIED_SINCE']
+          if since = env[HTTP_IF_MODIFIED_SINCE]
             Time.rfc2822(since) rescue nil
           end
         end
 
         def if_none_match
-          env['HTTP_IF_NONE_MATCH']
+          env[HTTP_IF_NONE_MATCH]
         end
 
         def not_modified?(modified_at)
@@ -43,31 +47,35 @@ module ActionDispatch
         alias :etag? :etag
 
         def last_modified
-          if last = headers['Last-Modified']
+          if last = headers[LAST_MODIFIED]
             Time.httpdate(last)
           end
         end
 
         def last_modified?
-          headers.include?('Last-Modified')
+          headers.include?(LAST_MODIFIED)
         end
 
         def last_modified=(utc_time)
-          headers['Last-Modified'] = utc_time.httpdate
+          headers[LAST_MODIFIED] = utc_time.httpdate
         end
 
         def etag=(etag)
           key = ActiveSupport::Cache.expand_cache_key(etag)
-          @etag = self["ETag"] = %("#{Digest::MD5.hexdigest(key)}")
+          @etag = self[ETAG] = %("#{Digest::MD5.hexdigest(key)}")
         end
 
       private
 
+        LAST_MODIFIED = "Last-Modified".freeze
+        ETAG          = "ETag".freeze
+        CACHE_CONTROL = "Cache-Control".freeze
+
         def prepare_cache_control!
           @cache_control = {}
-          @etag = self["ETag"]
+          @etag = self[ETAG]
 
-          if cache_control = self["Cache-Control"]
+          if cache_control = self[CACHE_CONTROL]
             cache_control.split(/,\s*/).each do |segment|
               first, last = segment.split("=")
               @cache_control[first.to_sym] = last || true
@@ -81,28 +89,32 @@ module ActionDispatch
           end
         end
 
-        DEFAULT_CACHE_CONTROL = "max-age=0, private, must-revalidate"
+        DEFAULT_CACHE_CONTROL = "max-age=0, private, must-revalidate".freeze
+        NO_CACHE              = "no-cache".freeze
+        PUBLIC                = "public".freeze
+        PRIVATE               = "private".freeze
+        MUST_REVALIDATE       = "must-revalidate".freeze
 
         def set_conditional_cache_control!
-          return if self["Cache-Control"].present?
+          return if self[CACHE_CONTROL].present?
 
           control = @cache_control
 
           if control.empty?
-            headers["Cache-Control"] = DEFAULT_CACHE_CONTROL
+            headers[CACHE_CONTROL] = DEFAULT_CACHE_CONTROL
           elsif control[:no_cache]
-            headers["Cache-Control"] = "no-cache"
+            headers[CACHE_CONTROL] = NO_CACHE
           else
             extras  = control[:extras]
             max_age = control[:max_age]
 
             options = []
             options << "max-age=#{max_age.to_i}" if max_age
-            options << (control[:public] ? "public" : "private")
-            options << "must-revalidate" if control[:must_revalidate]
+            options << (control[:public] ? PUBLIC : PRIVATE)
+            options << MUST_REVALIDATE if control[:must_revalidate]
             options.concat(extras) if extras
 
-            headers["Cache-Control"] = options.join(", ")
+            headers[CACHE_CONTROL] = options.join(", ")
           end
         end
       end