Add PubSub support to Ring

ring.go

@@ -177,6 +177,34 @@ func (c *Ring) PoolStats() *PoolStats {
 	return &acc
 }
 
+// Subscribe subscribes the client to the specified channels.
+func (c *Ring) Subscribe(channels ...string) *PubSub {
+	if len(channels) == 0 {
+		panic("at least one channel is required")
+	}
+
+	shard, err := c.shardByKey(channels[0])
+	if err != nil {
+		// TODO: return PubSub with sticky error
+		panic(err)
+	}
+	return shard.Client.Subscribe(channels...)
+}
+
+// PSubscribe subscribes the client to the given patterns.
+func (c *Ring) PSubscribe(channels ...string) *PubSub {
+	if len(channels) == 0 {
+		panic("at least one channel is required")
+	}
+
+	shard, err := c.shardByKey(channels[0])
+	if err != nil {
+		// TODO: return PubSub with sticky error
+		panic(err)
+	}
+	return shard.Client.PSubscribe(channels...)
+}
+
 // ForEachShard concurrently calls the fn on each live shard in the ring.
 // It returns the first error if any.
 func (c *Ring) ForEachShard(fn func(client *Client) error) error {