feat(ring): add GetShardClients and GetShardClientForKey methods to Ring for shard access (#3388)

* feat: expose shard information in redis.Ring

- Add GetShards() method to retrieve a list of active shard clients.
- Add GetShardByKey(key string) method to get the shard client for a specific key.
- These methods enable users to manage Pub/Sub operations more effectively by accessing shard-specific clients.

* rename GetShardClients and GetShardClientForKey

---------

Co-authored-by: DengY11 <212294929@qq.com>
Co-authored-by: Nedyalko Dyakov <1547186+ndyakov@users.noreply.github.com>

ring_test.go

@@ -782,3 +782,82 @@ var _ = Describe("Ring Tx timeout", func() {
 		testTimeout()
 	})
 })
+
+var _ = Describe("Ring GetShardClients and GetShardClientForKey", func() {
+	var ring *redis.Ring
+
+	BeforeEach(func() {
+		ring = redis.NewRing(&redis.RingOptions{
+			Addrs: map[string]string{
+				"shard1": ":6379",
+				"shard2": ":6380",
+			},
+		})
+	})
+
+	AfterEach(func() {
+		Expect(ring.Close()).NotTo(HaveOccurred())
+	})
+
+	It("GetShardClients returns active shard clients", func() {
+		shards := ring.GetShardClients()
+		// Note: This test will pass even if Redis servers are not running,
+		// because GetShardClients only returns clients that are marked as "up",
+		// and newly created shards start as "up" until the first health check fails.
+
+		if len(shards) == 0 {
+			// Expected if Redis servers are not running
+			Skip("No active shards found (Redis servers not running)")
+		} else {
+			Expect(len(shards)).To(BeNumerically(">", 0))
+			for _, client := range shards {
+				Expect(client).NotTo(BeNil())
+			}
+		}
+	})
+
+	It("GetShardClientForKey returns correct shard for keys", func() {
+		testKeys := []string{"key1", "key2", "user:123", "channel:test"}
+
+		for _, key := range testKeys {
+			client, err := ring.GetShardClientForKey(key)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(client).NotTo(BeNil())
+		}
+	})
+
+	It("GetShardClientForKey is consistent for same key", func() {
+		key := "test:consistency"
+
+		// Call GetShardClientForKey multiple times with the same key
+		// Should always return the same shard
+		var firstClient *redis.Client
+		for i := 0; i < 5; i++ {
+			client, err := ring.GetShardClientForKey(key)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(client).NotTo(BeNil())
+
+			if i == 0 {
+				firstClient = client
+			} else {
+				Expect(client.String()).To(Equal(firstClient.String()))
+			}
+		}
+	})
+
+	It("GetShardClientForKey distributes keys across shards", func() {
+		testKeys := []string{"key1", "key2", "key3", "key4", "key5"}
+		shardMap := make(map[string]int)
+
+		for _, key := range testKeys {
+			client, err := ring.GetShardClientForKey(key)
+			Expect(err).NotTo(HaveOccurred())
+			shardMap[client.String()]++
+		}
+
+		// Should have at least 1 shard (could be all keys go to same shard due to hashing)
+		Expect(len(shardMap)).To(BeNumerically(">=", 1))
+		// But with multiple keys, we expect some distribution
+		Expect(len(shardMap)).To(BeNumerically("<=", 2)) // At most 2 shards (our setup)
+	})
+})