add support for alternate file sources for image size analysis

lib/compass/configuration.rb

@@ -40,7 +40,8 @@ module Compass
       :preferred_syntax,
       :disable_warnings,
       :sprite_engine,
-      :chunky_png_options
+      :chunky_png_options,
+      :images_file_source
     ].flatten
 
     ARRAY_ATTRIBUTES = [

lib/compass/sass_extensions/functions/image_size.rb

@@ -24,12 +24,22 @@ module Compass::SassExtensions::Functions::ImageSize
     end
 
     private
+    def open_file_source
+      source = Compass.configuration.images_file_source || lambda { |file| File.open(file, 'rb') }
+
+      io = source.call(@file)
+      result = yield io
+      io.close
+
+      result
+    end
+
     def get_size_for_png
-      File.open(@file, "rb") {|io| io.read}[0x10..0x18].unpack('NN')
+      open_file_source {|io| io.read}[0x10..0x18].unpack('NN')
     end
 
     def get_size_for_gif
-      File.open(@file, "rb") {|io| io.read}[6..10].unpack('SS')
+      open_file_source {|io| io.read}[6..10].unpack('SS')
     end
 
     def get_size_for_jpg
@@ -37,10 +47,12 @@ module Compass::SassExtensions::Functions::ImageSize
     end
 
     def get_size_for_jpeg
-      jpeg = JPEG.new(@file)
+      open_file_source do |io|
+        jpeg = JPEG.new(io)
         [ jpeg.width, jpeg.height ]
       end
     end
+  end
 
   private
 
@@ -69,12 +81,8 @@ private
   class JPEG
     attr_reader :width, :height, :bits
 
-    def initialize(file)
-      if file.kind_of? IO
-        examine(file)
-      else
-        File.open(file, 'rb') { |io| examine(io) }
-      end
+    def initialize(io)
+      examine(io)
     end
 
     private

test/units/sass_extensions_test.rb

@@ -167,7 +167,6 @@ class SassExtensionsTest < Test::Unit::TestCase
     assert_equal "url('data:font/truetype;base64,#{base64_string}') format('truetype')", evaluate("inline_font_files('bgrove.ttf', truetype)")
   end
 
-  
   def test_image_size_should_respond_to_to_path
     object = mock()
     object.expects(:to_path).returns('foo.jpg')
@@ -176,6 +175,20 @@ class SassExtensionsTest < Test::Unit::TestCase
     Compass::SassExtensions::Functions::ImageSize::ImageProperties.new(object)
   end
 
+  def test_image_properites_should_be_able_to_use_file_like_object
+    source = Class.new do
+      def self.open(*args, &block)
+        File.open(*args, &block)
+      end
+    end
+
+    Compass.configuration.images_file_source = lambda { |file| source.open(file) }
+
+    properties = Compass::SassExtensions::Functions::ImageSize::ImageProperties.new('test/fixtures/sprites/public/images/colors/blue.png')
+
+    assert_equal [ 10, 10 ], properties.size
+  end
+
   def test_reject
     assert_equal "b d", evaluate("reject(a b c d, a, c)")
     assert_equal "a b c d", evaluate("reject(a b c d, e)")