Jetstream Sequence Number and/or Last Sequence Number in Subject

[FerdinandvHagen]

The Jetstream "RePublish" functionality provides Nats-Sequence and Nats-Last-Sequence headers among others.

Example:

map[Nats-Last-Sequence:[0] Nats-Sequence:[1] Nats-Stream:[TEST] Nats-Subject:[msg.1]]

When using a "normal" consumer no such information is provided:

sub, err := js.Subscribe("msg.1", func(msg *nats.Msg) {
		fmt.Println(msg.Header) ***--> yields map[]***
})

Is there any way to receive the Sequence Number of a message when receiving messages from a Subscriber - or even better the Last Sequence Number?

I'm building an event sourcing setup where I have a large number of ephemeral consumers (devices) that need to catch up and then process messages. Jetstream would act as a event stream that will be limited in length.
From the other discussions I have gathered that using a large number of durable consumers (e.g. bound to a device id) is not advisable. Using Republish and a temporary consumer to catch up old messages seems like a good solution - however without knowing the sequence ids of the messages received from the temporary consumer I'm going to have a hard time sorting messages properly.

[derekcollison]

You want to use the messages metadata which has everything you want.

  meta, err := msg.Metadata()

The struct from the Go client.

// MsgMetadata is the JetStream metadata associated with received messages.
type MsgMetadata struct {
	Sequence     SequencePair
	NumDelivered uint64
	NumPending   uint64
	Timestamp    time.Time
	Stream       string
	Consumer     string
	Domain       string
}

[FerdinandvHagen]

Thank you very much! Sorry for that easy question - it was apparently too well hidden for me.

[alifengineer]

I want to know what is the difference of count fields,

count, err := msg.Sub.Delivered()

and with metadata.sub.NumDelivered

sub, err := msg.Metadata()
sub.NumDelivered

Now i am checking as a number of redelivery messages as a first. I need to get info about how much time this message not processed because if this count more than 3 i want to manual ack this message for this queue.

@derekcollison

[derekcollison]

This is more a question for the client team. /cc @piotrpio

[Jarema]

Hey!

msg.Sub.Delivered() is the count of messages delivered to this subsription (Core NATS subscription that is used internallly by the consumer). I would not use it in this case. This is mostly useful in Core NATS when you use AutoUnsubscribe and is not relevant for what you need.

sub.NumDelivered is the delivery attempt for this message for given consumer.
This will be incremented if you miss an ack and consumer redelivers the message.