Added expiring_url method to Fog Storage

IMPORTANT: There is a bug in the current release of Fog (1.3.1) that will
return a broken expiring URL when the bucket name is valid for a subdomain.
This is fixed per https://github.com/fog/fog/pull/857 but not released
in the gem yet. I have added currently FAILING tests for these cases that
should pass when a new Fog is released.

lib/paperclip/storage/fog.rb

@@ -108,26 +108,25 @@ module Paperclip
 
       def public_url(style = default_style)
         if @options[:fog_host]
-          host = if @options[:fog_host].respond_to?(:call)
-            @options[:fog_host].call(self)
-          else
-            (@options[:fog_host] =~ /%d/) ? @options[:fog_host] % (path(style).hash % 4) : @options[:fog_host]
-          end
-
-          "#{host}/#{path(style)}"
+          "#{dynamic_fog_host_for_style(style)}/#{path(style)}"
         else
           if fog_credentials[:provider] == 'AWS'
-            if @options[:fog_directory].to_s =~ Fog::AWS_BUCKET_SUBDOMAIN_RESTRICTON_REGEX
-              "https://#{@options[:fog_directory]}.s3.amazonaws.com/#{path(style)}"
-            else
-              # directory is not a valid subdomain, so use path style for access
-              "https://s3.amazonaws.com/#{@options[:fog_directory]}/#{path(style)}"
-            end
+            "https://#{host_name_for_directory}/#{path(style)}"
           else
             directory.files.new(:key => path(style)).public_url
           end
         end
       end
+      
+      def expiring_url(time = 3600, style = default_style)
+        expiring_url = directory.files.get_http_url(path(style), time)
+        
+        if @options[:fog_host]
+          expiring_url[host_name_for_directory] = dynamic_fog_host_for_style(style)
+        end
+        
+        return expiring_url
+      end
 
       def parse_credentials(creds)
         creds = find_credentials(creds).stringify_keys
@@ -147,6 +146,22 @@ module Paperclip
       end
 
       private
+      
+      def dynamic_fog_host_for_style(style)
+        if @options[:fog_host].respond_to?(:call)
+          @options[:fog_host].call(self)
+        else
+          (@options[:fog_host] =~ /%d/) ? @options[:fog_host] % (path(style).hash % 4) : @options[:fog_host]
+        end
+      end
+      
+      def host_name_for_directory
+        if @options[:fog_directory].to_s =~ Fog::AWS_BUCKET_SUBDOMAIN_RESTRICTON_REGEX
+          "#{@options[:fog_directory]}.s3.amazonaws.com"
+        else
+          "s3.amazonaws.com/#{@options[:fog_directory]}"
+        end
+      end
 
       def find_credentials(creds)
         case creds

test/storage/fog_test.rb

@@ -198,6 +198,10 @@ class FogTest < Test::Unit::TestCase
         should "provide an url in subdomain style" do
           assert_match /^https:\/\/papercliptests.s3.amazonaws.com\/avatars\/5k.png\?\d*$/, @dummy.avatar.url
         end
+        
+        should "provide an url that expires in subdomain style" do
+          assert_match /^http:\/\/papercliptests.s3.amazonaws.com\/avatars\/5k.png\?AWSAccessKeyId=.+$/, @dummy.avatar.expiring_url
+        end
       end
 
       context "with an invalid bucket name for a subdomain" do
@@ -218,6 +222,10 @@ class FogTest < Test::Unit::TestCase
         should "provide an url in folder style" do
           assert_match /^https:\/\/s3.amazonaws.com\/this_is_invalid\/avatars\/5k.png\?\d*$/, @dummy.avatar.url
         end
+        
+        should "provide a url that expires in folder style" do
+          assert_match /^http:\/\/s3.amazonaws.com\/this_is_invalid\/avatars\/5k.png\?AWSAccessKeyId=.+$/, @dummy.avatar.expiring_url
+        end
 
       end
 
@@ -249,6 +257,38 @@ class FogTest < Test::Unit::TestCase
         should "provide a public url" do
           assert_match /http:\/\/dynamicfoghost\.com/, @dummy.avatar.url
         end
+        
+      end
+      
+      context "with a custom fog_host" do
+        setup do
+          rebuild_model(@options.merge(:fog_host => "http://dynamicfoghost.com"))
+          @dummy = Dummy.new
+          @dummy.avatar = @file
+          @dummy.save
+        end
+        
+        should "provide a public url" do
+          assert_match /http:\/\/dynamicfoghost\.com/, @dummy.avatar.url
+        end
+        
+        should "provide an expiring url" do
+          assert_match /http:\/\/dynamicfoghost\.com/, @dummy.avatar.expiring_url
+        end
+        
+        context "with an invalid bucket name for a subdomain" do
+          setup do
+            rebuild_model(@options.merge({:fog_directory => "this_is_invalid", :fog_host => "http://dynamicfoghost.com"}))
+            @dummy = Dummy.new
+            @dummy.avatar = @file
+            @dummy.save
+          end
+          
+          should "provide an expiring url" do
+            assert_match /http:\/\/dynamicfoghost\.com/, @dummy.avatar.expiring_url
+          end
+        end
+        
       end
 
       context "with a proc for the fog_credentials evaluating a model method" do