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Add new MPUBLISH command #1657

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merged 2 commits into from
Aug 11, 2023
Merged

Add new MPUBLISH command #1657

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cd3a26e
Add new command MPUBLISH to publish one or more messages to a channel.
torwig Aug 8, 2023
d2810cb
Merge branch 'unstable' into pub_multi_msg
PragmaTwice Aug 11, 2023
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39 changes: 34 additions & 5 deletions src/commands/cmd_pubsub.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -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()) {
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Seems that Publish will be likely to success?

return {Status::RedisExecErr, s.ToString()};
}
}

int receivers = svr->PublishMessage(args_[1], args_[i]);
total_receivers += receivers;
}

*output = redis::Integer(total_receivers);
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Would an array of int be better here?

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@mapleFU Possibly, yes. However, according to this PR (redis/redis#12267) it's likely that MPUBLISH will have a single integer as a response.

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Oh this LGTM. Seems this is not stable. Maybe we can mark "mpublish" as "experimental" or something, and make it able to change the syntax of it.

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In general, I think it's not easy to utilize the return value of the PUBLISH command, except to check whether it is 0 or more. The actual goal of Pub/Sub pattern is to decouple publishers from subscribers and if I want to check the number of receivers I should know the exact number of them. And for example, if I know that there should be 5 subscribers but I received only 4 in response to the PUBLISH command, what should I do?

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Sounds ok. It's ok to leave it like this


return Status::OK();
}
};
Expand Down Expand Up @@ -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 {
Expand Down Expand Up @@ -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:
Expand All @@ -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),
Expand Down
1 change: 1 addition & 0 deletions src/commands/error_constants.h
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Expand Up @@ -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
57 changes: 57 additions & 0 deletions tests/gocase/unit/pubsub/pubsub_test.go
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Expand Up @@ -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)
Expand Down