Rewind the file after reading it for fingerprinting

lib/paperclip/upfile.rb

@@ -35,7 +35,9 @@ module Paperclip
 
     # Returns the hash of the file.
     def fingerprint
-      Digest::MD5.hexdigest(self.read)
+      data = self.read
+      self.rewind
+      Digest::MD5.hexdigest(data)
     end
   end
 end

test/upfile_test.rb

@@ -33,4 +33,21 @@ class UpfileTest < Test::Unit::TestCase
     end
     assert_equal 'text/plain', file.content_type
   end
+
+  should "return a MD5 fingerprint of the file" do
+    file = StringIO.new("1234567890")
+    class << file
+      include Paperclip::Upfile
+    end
+    assert_equal "e807f1fcf82d132f9bb018ca6738a19f", file.fingerprint
+  end
+
+  should "still be readable after the file fingerprints itself" do
+    file = StringIO.new("1234567890")
+    class << file
+      include Paperclip::Upfile
+    end
+    file.fingerprint
+    assert_equal "1234567890", file.read
+  end
 end