Add new MPUBLISH command (#1657)

The new `MPUBLISH` command allows publishing one or more messages to a channel. 
Syntax: `MPUBLISH channel-name message1 message2 ... messageN`

src/commands/cmd_pubsub.cc

@@ -27,20 +27,48 @@ namespace redis {
 
 class CommandPublish : public Commander {
  public:
-  // mark is_write as false here because slave should be able to execute publish command
   Status Execute(Server *svr, Connection *conn, std::string *output) override {
     if (!svr->IsSlave()) {
-      // Compromise: can't replicate message to sub-replicas in a cascading-like structure.
-      // Replication relies on WAL seq, increase the seq on slave will break the replication, hence the compromise
+      // Compromise: can't replicate a message to sub-replicas in a cascading-like structure.
+      // Replication relies on WAL seq; increasing the seq on a replica will break the replication process,
+      // hence the compromise solution
       redis::PubSub pubsub_db(svr->storage);
+
       auto s = pubsub_db.Publish(args_[1], args_[2]);
       if (!s.ok()) {
         return {Status::RedisExecErr, s.ToString()};
       }
     }
 
     int receivers = svr->PublishMessage(args_[1], args_[2]);
+
     *output = redis::Integer(receivers);
+
+    return Status::OK();
+  }
+};
+
+class CommandMPublish : public Commander {
+ public:
+  Status Execute(Server *svr, Connection *conn, std::string *output) override {
+    int total_receivers = 0;
+
+    for (size_t i = 2; i < args_.size(); i++) {
+      if (!svr->IsSlave()) {
+        redis::PubSub pubsub_db(svr->storage);
+
+        auto s = pubsub_db.Publish(args_[1], args_[i]);
+        if (!s.ok()) {
+          return {Status::RedisExecErr, s.ToString()};
+        }
+      }
+
+      int receivers = svr->PublishMessage(args_[1], args_[i]);
+      total_receivers += receivers;
+    }
+
+    *output = redis::Integer(total_receivers);
+
     return Status::OK();
   }
 };
@@ -132,7 +160,7 @@ class CommandPubSub : public Commander {
       return Status::OK();
     }
 
-    return {Status::RedisInvalidCmd, "Unknown subcommand or wrong number of arguments"};
+    return {Status::RedisInvalidCmd, errUnknownSubcommandOrWrongArguments};
   }
 
   Status Execute(Server *srv, Connection *conn, std::string *output) override {
@@ -161,7 +189,7 @@ class CommandPubSub : public Commander {
       return Status::OK();
     }
 
-    return {Status::RedisInvalidCmd, "Unknown subcommand or wrong number of arguments"};
+    return {Status::RedisInvalidCmd, errUnknownSubcommandOrWrongArguments};
   }
 
  private:
@@ -172,6 +200,7 @@ class CommandPubSub : public Commander {
 
 REDIS_REGISTER_COMMANDS(
     MakeCmdAttr<CommandPublish>("publish", 3, "read-only pub-sub", 0, 0, 0),
+    MakeCmdAttr<CommandMPublish>("mpublish", -3, "read-only pub-sub", 0, 0, 0),
     MakeCmdAttr<CommandSubscribe>("subscribe", -2, "read-only pub-sub no-multi no-script", 0, 0, 0),
     MakeCmdAttr<CommandUnSubscribe>("unsubscribe", -1, "read-only pub-sub no-multi no-script", 0, 0, 0),
     MakeCmdAttr<CommandPSubscribe>("psubscribe", -2, "read-only pub-sub no-multi no-script", 0, 0, 0),

src/commands/error_constants.h

@@ -41,5 +41,6 @@ inline constexpr const char *errScoreIsNotValidFloat = "score is not a valid flo
 inline constexpr const char *errValueIsNotFloat = "value is not a valid float";
 inline constexpr const char *errNoMatchingScript = "NOSCRIPT No matching script. Please use EVAL";
 inline constexpr const char *errUnknownOption = "unknown option";
+inline constexpr const char *errUnknownSubcommandOrWrongArguments = "Unknown subcommand or wrong number of arguments";
 
 }  // namespace redis

tests/gocase/unit/pubsub/pubsub_test.go

@@ -115,6 +115,63 @@ func TestPubSub(t *testing.T) {
 		require.Equal(t, "hello", msg.Payload)
 	})
 
+	t.Run("MPUBLISH basics", func(t *testing.T) {
+		var (
+			channelName = "channel1"
+			msg1        = "hello"
+			msg2        = "world"
+			msg3        = "!"
+			msg4        = "foo-bar"
+		)
+
+		c1 := srv.NewClient()
+		defer func() { require.NoError(t, c1.Close()) }()
+		c2 := srv.NewClient()
+		defer func() { require.NoError(t, c2.Close()) }()
+
+		pubsub1 := c1.Subscribe(ctx, channelName)
+		pubsub2 := c2.Subscribe(ctx, channelName)
+
+		require.EqualValues(t, 1, receiveType(t, pubsub1, &redis.Subscription{}).Count)
+		require.EqualValues(t, 1, receiveType(t, pubsub2, &redis.Subscription{}).Count)
+
+		require.EqualValues(t, 6, rdb.Do(ctx, "MPUBLISH", channelName, msg1, msg2, msg3).Val())
+
+		msg := receiveType(t, pubsub1, &redis.Message{})
+		require.Equal(t, channelName, msg.Channel)
+		require.Equal(t, msg1, msg.Payload)
+
+		msg = receiveType(t, pubsub2, &redis.Message{})
+		require.Equal(t, channelName, msg.Channel)
+		require.Equal(t, msg1, msg.Payload)
+
+		msg = receiveType(t, pubsub1, &redis.Message{})
+		require.Equal(t, channelName, msg.Channel)
+		require.Equal(t, msg2, msg.Payload)
+
+		msg = receiveType(t, pubsub2, &redis.Message{})
+		require.Equal(t, channelName, msg.Channel)
+		require.Equal(t, msg2, msg.Payload)
+
+		msg = receiveType(t, pubsub1, &redis.Message{})
+		require.Equal(t, channelName, msg.Channel)
+		require.Equal(t, msg3, msg.Payload)
+
+		msg = receiveType(t, pubsub2, &redis.Message{})
+		require.Equal(t, channelName, msg.Channel)
+		require.Equal(t, msg3, msg.Payload)
+
+		require.EqualValues(t, 2, rdb.Do(ctx, "MPUBLISH", channelName, msg4).Val())
+
+		msg = receiveType(t, pubsub1, &redis.Message{})
+		require.Equal(t, channelName, msg.Channel)
+		require.Equal(t, msg4, msg.Payload)
+
+		msg = receiveType(t, pubsub2, &redis.Message{})
+		require.Equal(t, channelName, msg.Channel)
+		require.Equal(t, msg4, msg.Payload)
+	})
+
 	t.Run("PUBLISH/SUBSCRIBE after UNSUBSCRIBE without arguments", func(t *testing.T) {
 		pubsub := rdb.Subscribe(ctx, "chan1", "chan2", "chan3")
 		require.EqualValues(t, 1, receiveType(t, pubsub, &redis.Subscription{}).Count)