Build out a URI Adapter to allow uploading an avatar via a url

Currently only really accessible via the API. The UriAdapter creates a
tempfile from a url and gives a ActionDispatch::HTTP::UploadedFile back
to the controller to process as normal.
This will help a lot in being able to transfer avatar urls from another
app without monkey patching a lot of discourse code.

spec/services/uri_adapter_spec.rb

@@ -0,0 +1,51 @@
+require 'spec_helper'
+
+describe UriAdapter do
+  let(:target) { "http://cdn.discourse.org/assets/logo.png" }
+  let(:response) { StringIO.new(fixture_file("images/logo.png")) }
+
+  before :each do
+    response.stubs(:content_type).returns("image/png")
+    UriAdapter.any_instance.stubs(:open).returns(response)
+  end
+
+  subject { UriAdapter.new(target) }
+
+  describe "#initialize" do
+
+    it "has a target" do
+      subject.target.should be_instance_of(URI::HTTP)
+    end
+
+    it "has content" do
+      subject.content.should == response
+    end
+
+    it "has an original_filename" do
+      subject.original_filename.should == "logo.png"
+    end
+
+    it "has a tempfile" do
+      subject.tempfile.should be_instance_of Tempfile
+    end
+
+  end
+
+  describe "#copy_to_tempfile" do
+    it "does not allow files bigger then max_image_size_kb" do
+      SiteSetting.stubs(:max_image_size_kb).returns(1)
+      subject.build_uploaded_file.should == nil
+    end
+  end
+
+  describe "#build_uploaded_file" do
+    it "returns an uploaded file" do
+      file = subject.build_uploaded_file
+      file.should be_instance_of(ActionDispatch::Http::UploadedFile)
+      file.content_type.should == "image/png"
+      file.original_filename.should == "logo.png"
+      file.tempfile.should be_instance_of Tempfile
+    end
+  end
+
+end