Allow for URI Adapter as an optional paperclip io adapter

This PR allows you to assign a URI object to an attachment. The
attachment is downloaded and saved with a proper content type and
filename based on the path of the URL.

lib/paperclip.rb

@@ -223,3 +223,4 @@ require 'paperclip/io_adapters/stringio_adapter'
 require 'paperclip/io_adapters/nil_adapter'
 require 'paperclip/io_adapters/attachment_adapter'
 require 'paperclip/io_adapters/uploaded_file_adapter'
+require 'paperclip/io_adapters/uri_adapter'

lib/paperclip/io_adapters/uri_adapter.rb

+require 'open-uri'
+
+module Paperclip
+  class UriAdapter < AbstractAdapter
+    def initialize(target)
+      @target = target
+      @content = download_content
+      cache_current_values
+      @tempfile = copy_to_tempfile(@content)
+    end
+
+    attr_writer :original_filename, :content_type
+    private
+
+    def download_content
+      open(@target)
+    end
+
+    def cache_current_values
+      @original_filename = @target.path.split("/").last
+      @original_filename ||= "index.html"
+      @original_filename = @original_filename.strip
+
+      @content_type = @content.content_type if @content.respond_to?(:content_type)
+      @content_type ||= "text/html"
+
+      @size = @content.size
+    end
+
+    def copy_to_tempfile(src)
+      while data = src.read(16*1024)
+        destination.write(data)
+      end
+      destination.rewind
+      destination
+    end
+  end
+end
+
+Paperclip.io_adapters.register Paperclip::UriAdapter do |target|
+  target.kind_of?(URI)
+end

test/io_adapters/uri_adapter_test.rb

+require './test/helper'
+
+class UriProxyTest < Test::Unit::TestCase
+  context "a new instance" do
+    setup do
+      @open_return = StringIO.new("xxx")
+      @open_return.stubs(:content_type).returns("image/png")
+      Paperclip::UriAdapter.any_instance.stubs(:download_content).returns(@open_return)
+      @uri = URI.parse("http://thoughtbot.com/images/thoughtbot-logo.png")
+      @subject = Paperclip.io_adapters.for(@uri)
+    end
+
+    should "return a file name" do
+      assert_equal "thoughtbot-logo.png", @subject.original_filename
+    end
+
+    should "return a content type" do
+      assert_equal "image/png", @subject.content_type
+    end
+
+    should "return the size of the data" do
+      assert_equal @open_return.size, @subject.size
+    end
+
+    should "generate an MD5 hash of the contents" do
+      assert_equal Digest::MD5.hexdigest("xxx"), @subject.fingerprint
+    end
+
+    should "generate correct fingerprint after read" do
+      fingerprint = Digest::MD5.hexdigest(@subject.read)
+      assert_equal fingerprint, @subject.fingerprint
+    end
+
+    should "generate same fingerprint" do
+      assert_equal @subject.fingerprint, @subject.fingerprint
+    end
+
+    should "return the data contained in the StringIO" do
+      assert_equal "xxx", @subject.read
+    end
+
+    should 'accept a content_type' do
+      @subject.content_type = 'image/png'
+      assert_equal 'image/png', @subject.content_type
+    end
+
+    should 'accept an orgiginal_filename' do
+      @subject.original_filename = 'image.png'
+      assert_equal 'image.png', @subject.original_filename
+    end
+
+  end
+
+  context "a directory index url" do
+    setup do
+      Paperclip::UriAdapter.any_instance.stubs(:download_content).returns(StringIO.new("xxx"))
+      @uri = URI.parse("http://thoughtbot.com")
+      @subject = Paperclip.io_adapters.for(@uri)
+    end
+
+    should "return a file name" do
+      assert_equal "index.html", @subject.original_filename
+    end
+
+    should "return a content type" do
+      assert_equal "text/html", @subject.content_type
+    end
+  end
+
+  context "a url with query params" do
+    setup do
+      Paperclip::UriAdapter.any_instance.stubs(:download_content).returns(StringIO.new("xxx"))
+      @uri = URI.parse("https://github.com/thoughtbot/paperclip?file=test")
+      @subject = Paperclip.io_adapters.for(@uri)
+    end
+
+    should "return a file name" do
+      assert_equal "paperclip", @subject.original_filename
+    end
+  end
+
+end