# File lib/chef/cookbook_uploader.rb, line 122
    def uploader_function_for(file, checksum, url, checksums_to_upload)
      lambda do
        # Checksum is the hexadecimal representation of the md5,
        # but we need the base64 encoding for the content-md5
        # header
        checksum64 = Base64.encode64([checksum].pack("H*")).strip
        timestamp = Time.now.utc.iso8601
        file_contents = File.open(file, "rb") {|f| f.read}
        # TODO - 5/28/2010, cw: make signing and sending the request streaming
        sign_obj = Mixlib::Authentication::SignedHeaderAuth.signing_object(
                                                                           :http_method => :put,
                                                                           :path        => URI.parse(url).path,
                                                                           :body        => file_contents,
                                                                           :timestamp   => timestamp,
                                                                           :user_id     => rest.client_name
                                                                           )
        headers = { 'content-type' => 'application/x-binary', 'content-md5' => checksum64, :accept => 'application/json' }
        headers.merge!(sign_obj.sign(OpenSSL::PKey::RSA.new(rest.signing_key)))

        begin
          RestClient::Resource.new(url, :headers=>headers, :timeout=>1800, :open_timeout=>1800).put(file_contents)
          checksums_to_upload.delete(checksum)
        rescue RestClient::Exception => e
          Chef::Knife.ui.error("Failed to upload #@cookbook : #{e.message}\n#{e.response.body}")
          raise
        end
      end
    end