Default to localhost when no host is found, as per IANA spec.

Author: djanowski

lib/redis/client.rb

@@ -392,11 +392,8 @@ def _parse_options(options)
         if uri.scheme == "unix"
           defaults[:path]   = uri.path
         elsif uri.scheme == "redis"
-          # Require the URL to have at least a host
-          raise ArgumentError, "invalid url: #{uri}" unless uri.host
-
           defaults[:scheme]   = uri.scheme
-          defaults[:host]     = uri.host
+          defaults[:host]     = uri.host if uri.host
           defaults[:port]     = uri.port if uri.port
           defaults[:password] = CGI.unescape(uri.password) if uri.password
           defaults[:db]       = uri.path[1..-1].to_i if uri.path

test/url_param_test.rb

@@ -129,4 +129,10 @@ def test_uses_redis_url_over_default_if_available
 
     ENV.delete("REDIS_URL")
   end
+
+  def test_defaults_to_localhost
+    redis = Redis.new(:url => "redis:///")
+
+    assert_equal "127.0.0.1", redis.client.host
+  end
 end