Don't enable ReadOnly in custom cluster mode

cluster.go

@@ -82,7 +82,7 @@ func (opt *ClusterOptions) init() {
 		opt.MaxRedirects = 8
 	}
 
-	if opt.RouteByLatency || opt.RouteRandomly {
+	if (opt.RouteByLatency || opt.RouteRandomly) && opt.ClusterSlots == nil {
 		opt.ReadOnly = true
 	}
 
@@ -831,7 +831,7 @@ func (c *ClusterClient) cmdSlotAndNode(cmd Cmder) (int, *clusterNode, error) {
 	cmdInfo := c.cmdInfo(cmd.Name())
 	slot := cmdSlot(cmd, cmdFirstKeyPos(cmd, cmdInfo))
 
-	if cmdInfo != nil && cmdInfo.ReadOnly && c.opt.ReadOnly {
+	if c.opt.ReadOnly && cmdInfo != nil && cmdInfo.ReadOnly {
 		if c.opt.RouteByLatency {
 			node, err := state.slotClosestNode(slot)
 			return slot, node, err

cluster_test.go

@@ -846,6 +846,60 @@ var _ = Describe("ClusterClient", func() {
 
 		assertClusterClient()
 	})
+
+	Describe("ClusterClient with RouteRandomly and ClusterSlots", func() {
+		BeforeEach(func() {
+			failover = true
+
+			opt = redisClusterOptions()
+			opt.RouteRandomly = true
+			opt.ClusterSlots = func() ([]redis.ClusterSlot, error) {
+				slots := []redis.ClusterSlot{{
+					Start: 0,
+					End:   4999,
+					Nodes: []redis.ClusterNode{{
+						Addr: ":" + ringShard1Port,
+					}},
+				}, {
+					Start: 5000,
+					End:   9999,
+					Nodes: []redis.ClusterNode{{
+						Addr: ":" + ringShard2Port,
+					}},
+				}, {
+					Start: 10000,
+					End:   16383,
+					Nodes: []redis.ClusterNode{{
+						Addr: ":" + ringShard3Port,
+					}},
+				}}
+				return slots, nil
+			}
+			client = cluster.clusterClient(opt)
+
+			err := client.ForEachMaster(func(master *redis.Client) error {
+				return master.FlushDB().Err()
+			})
+			Expect(err).NotTo(HaveOccurred())
+
+			err = client.ForEachSlave(func(slave *redis.Client) error {
+				Eventually(func() int64 {
+					return client.DBSize().Val()
+				}, 30*time.Second).Should(Equal(int64(0)))
+				return nil
+			})
+			Expect(err).NotTo(HaveOccurred())
+		})
+
+		AfterEach(func() {
+			failover = false
+
+			err := client.Close()
+			Expect(err).NotTo(HaveOccurred())
+		})
+
+		assertClusterClient()
+	})
 })
 
 var _ = Describe("ClusterClient without nodes", func() {