S3 headers can be set as a proc now

lib/paperclip/storage/s3.rb

@@ -98,7 +98,9 @@ module Paperclip
               (permission == :public_read) ? 'http' : 'https'
             end
           @s3_metadata = @options[:s3_metadata] || {}
-          @s3_headers = (@options[:s3_headers] || {}).inject({}) do |headers,(name,value)|
+          @s3_headers = @options[:s3_headers] || {}
+          @s3_headers = @s3_headers.call(instance) if @s3_headers.is_a?(Proc)
+          @s3_headers = (@s3_headers).inject({}) do |headers,(name,value)|
             case name.to_s
             when /^x-amz-meta-(.*)/i
               @s3_metadata[$1.downcase] = value

test/storage/s3_test.rb

@@ -940,4 +940,53 @@ class S3Test < Test::Unit::TestCase
 
     end
   end
+
+  context "An attachment with S3 storage and metadata set using a proc as headers" do
+    setup do
+      rebuild_model(
+        :storage => :s3,
+        :bucket => "testing",
+        :path => ":attachment/:style/:basename.:extension",
+        :styles => {
+          :thumb => "80x80>"
+        },
+        :s3_credentials => {
+          'access_key_id' => "12345",
+          'secret_access_key' => "54321"
+        },
+        :s3_headers => lambda {|attachment|
+          {'Content-Disposition' => "attachment; filename=\"#{attachment.name}\""}
+        }
+      )
+    end
+
+    context "when assigned" do
+      setup do
+        @file = File.new(fixture_file('5k.png'), 'rb')
+        @dummy = Dummy.new
+        @dummy.stubs(:name => 'Custom Avatar Name.png')
+        @dummy.avatar = @file
+      end
+
+      teardown { @file.close }
+
+      context "and saved" do
+        setup do
+          [:thumb, :original].each do |style|
+            object = stub
+            @dummy.avatar.stubs(:s3_object).with(style).returns(object)
+            object.expects(:write).with(anything,
+                                        :content_type => "image/png",
+                                        :acl => :public_read,
+                                        :content_disposition => 'attachment; filename="Custom Avatar Name.png"')
+          end
+          @dummy.save
+        end
+
+        should "succeed" do
+          assert true
+        end
+      end
+    end
+  end
 end