fix: add a dedicated implementation for the watch command, it may be …

…used by the redis gem (#333)

lib/redis_client/cluster/router.rb

@@ -8,6 +8,8 @@
 require 'redis_client/cluster/node'
 require 'redis_client/cluster/node_key'
 require 'redis_client/cluster/normalized_cmd_name'
+require 'redis_client/cluster/transaction'
+require 'redis_client/cluster/optimistic_locking'
 
 class RedisClient
   class Cluster
@@ -44,6 +46,7 @@ def send_command(method, command, *args, &block) # rubocop:disable Metrics/AbcSi
         when 'memory'   then send_memory_command(method, command, args, &block)
         when 'script'   then send_script_command(method, command, args, &block)
         when 'pubsub'   then send_pubsub_command(method, command, args, &block)
+        when 'watch'    then send_watch_command(command, &block)
         when 'acl', 'auth', 'bgrewriteaof', 'bgsave', 'quit', 'save'
           @node.call_all(method, command, args).first.then(&TSF.call(block))
         when 'flushall', 'flushdb'
@@ -308,6 +311,17 @@ def send_pubsub_command(method, command, args, &block) # rubocop:disable Metrics
         end
       end
 
+      # for redis-rb
+      def send_watch_command(command)
+        ::RedisClient::Cluster::OptimisticLocking.new(self).watch(command[1..]) do |c, slot|
+          transaction = ::RedisClient::Cluster::Transaction.new(
+            self, @command_builder, node: c, slot: slot
+          )
+          yield transaction
+          transaction.execute
+        end
+      end
+
       def update_cluster_info!
         @node.reload!
       end

test/redis_client/test_cluster.rb

@@ -363,6 +363,21 @@ def test_transaction_in_race_condition
         assert_equal(%w[3 4], @client.call('MGET', '{key}1', '{key}2'))
       end
 
+      # for redis-rb
+      def test_transaction_with_standalone_watch_command
+        @client.call('MSET', '{key}1', '0', '{key}2', '0')
+
+        got = @client.call('WATCH', '{key}1', '{key}2') do |tx|
+          tx.call('ECHO', 'START')
+          tx.call('SET', '{key}1', '1')
+          tx.call('SET', '{key}2', '2')
+          tx.call('ECHO', 'FINISH')
+        end
+
+        assert_equal(%w[START OK OK FINISH], got)
+        assert_equal(%w[1 2], @client.call('MGET', '{key}1', '{key}2'))
+      end
+
       def test_pubsub_without_subscription
         pubsub = @client.pubsub
         assert_nil(pubsub.next_event(0.01))