Inconsistent timezones in /connz output

[alexbozhenko]

Observed behavior

nats-server -c noauth.conf
Observe that the time zone of last_activity depends on a number of messages processed:

# curl -s  localhost:8222/connz | jq '.connections | .[]  | {cid,port,start,last_activity,in_msgs}  '
{
  "cid": 7,
  "port": 49728,
  "start": "2025-03-19T15:38:53.554328511-07:00",
  "last_activity": "2025-03-19T15:38:53.555454375-07:00",
  "in_msgs": 1
}
{
  "cid": 8,
  "port": 49734,
  "start": "2025-03-19T15:38:53.555259309-07:00",
  "last_activity": "2025-03-19T22:38:53.555779717Z",
  "in_msgs": 0
}

Client code:

func main() {
	nc, err := nats.Connect(nats.DefaultURL)
	if err != nil {
		fmt.Println(err)
		return
	}
	defer nc.Drain()

	fmt.Println(nc.ConnectedServerVersion())
	nc.Publish("yo", []byte("hello"))
	nc.Subscribe("events", func(m *nats.Msg) {
		fmt.Printf("Received a message: %s\n", string(m.Data))
	})
	nc2, err := nats.Connect(nats.DefaultURL)
	fmt.Println(nc2.ConnectedServerVersion())
	for {

		time.Sleep(1 * time.Second)
	}
}

The one in UTC has "in_msgs": 0,, so it is likely was handled by this line:

nats-server/server/client.go

Line 2030 in adb1fcb

c.last = time.Now().UTC()

It was last changed in #1943

The one with the local timezone has in_msgs != 0, so it is likely was handled by this line:

nats-server/server/client.go

Lines 1256 to 1266 in adb1fcb

	last := time.Now()
	// Check pending clients for flush.
	for cp := range c.pcd {
	// TODO(dlc) - Wonder if it makes more sense to create a new map?
	delete(c.pcd, cp)
	// Queue up a flush for those in the set
	cp.mu.Lock()
	// Update last activity for message delivery
	cp.last = last

It was last changed in #4132

Expected behavior

Consistency.

Server and client version

v2.11.0
nats.go v1.39.0

Host environment

No response

Steps to reproduce

No response

[alexbozhenko]

There are other places where time is user-facing, and is not in UTC, e.g.:

nats-server/server/server.go

Lines 3162 to 3170 in 99e836e

	now := time.Now()
	c := &client{
	srv: s,
	nc: conn,
	opts: defaultOpts,
	mpay: maxPay,
	msubs: maxSubs,
	start: now,

@wallyqs that was reverted from UTC in: #4154

Instead of thinking which one is user-facing time and which one is not, can we simply set the timezone to be UTC in the beginning of the nats server run, and use time.Now() everywhere, without ever thinking about which is local, and which has monotonic clock?

func main() {
	fmt.Println(time.Now())
	fmt.Println(time.Local)

	time.Local = time.UTC

	fmt.Println(time.Local)
	fmt.Println("Still has monotonic clock, but in UTC")
	fmt.Println(time.Now())

	fmt.Println("Does not have monotonic clock")
	fmt.Println(time.Now().UTC())
}

2025-03-19 16:11:39.805474167 -0700 PDT m=+0.000727548
Local
UTC
Still has monotonic clock, but in UTC:
2025-03-19 23:11:39.80555561 +0000 UTC m=+0.000808991

Does not have monotonic clock:
2025-03-19 23:11:39.805562743 +0000 UTC

People do it:
https://github.com/search?q=lang%3Ago+%2Ftime.Local+%3D+time.UTC%2F&type=code
so maybe not the craziest idea?

[derekcollison]

Might be a good idea..

[ripienaar]

Would certainly simplify things but I worry about doing that

If someone embeds the server we wouldn’t want to mess with the timezone unconditionally. And if we don’t then there are significant behaviour change between embedded or not.

I suspect best we can do is fix the bugs here

[neilalexander]

I think it's OK if we set time.Local = time.UTC in the main() function in main.go as a catch-all, but I wouldn't do it anywhere else in case of embedding.

[ripienaar]

But then embedded nats will return times different from standalone. This seems like a bad outcome.

[derekcollison]

I agree might not be good. Would also be nice if a request for info could have a header that asked for the TZ for the results.