`KeyValue.Watch()` blocks forever for certain values of the `keys` parameter about nats.go

[Jarema]

Thanks for the detailed report!

We will take a look soon.

[piotrpio]

@mihaitodor there were 2 issues:

• The Watch("\"001.>\"") was a server issue, fixed here: nats-io/nats-server#5318
• Watch("") returned wrong error due to lacking client-side validation: #1613

Both will now return an error since both are essentially invalid arguments: nats: invalid key: keys cannot be empty and must be a valid NATS subject.

[mihaitodor]

That's awesome, thank you very much for the quick fixes!

[piotrpio]

Both PRs are merged and will be included in the next releases of nats-server and nats.go.

[mihaitodor]

Update: I also investigated switching to the new github.com/nats-io/nats.go/jetstream API and I can still reproduce the issue with the following code:

package main

import (
	"context"
	"log"
	"time"

	"github.com/nats-io/nats.go"
	"github.com/nats-io/nats.go/jetstream"
)

func main() {
	conn, err := nats.Connect("localhost:4222")
	if err != nil {
		log.Fatal(err)
	}

	js, err := jetstream.New(conn)
	if err != nil {
		log.Fatal(err)
	}

	kv, err := js.KeyValue(context.Background(), "foobar")
	if err != nil {
		log.Fatal(err)
	}

	// watcher, err := kv.Watch(ctx, "001.>")
	watcher, err := kv.Watch(context.Background(), "\"001.>\"")
	if err != nil {
		log.Fatal(err)
	}
	defer func() {
		if err := watcher.Stop(); err != nil {
			log.Fatal(err)
		}
	}()

	var keys []any
	ctx, done := context.WithTimeout(context.Background(), 3*time.Second)
	defer done()
loop:
	for {
		select {
		case entry := <-watcher.Updates():
			if entry == nil {
				break loop
			}
			keys = append(keys, entry.Key())
		case <-ctx.Done():
			log.Fatal("timeout")
		}
	}
	log.Printf("%v", keys)
}

I can, however, now pass a context to kv.Watch() which makes it easier to abort after a while, but I still think the kv.Watch() call should reject invalid keys.

Also, the nats: jetstream not enabled error is still returned for kv.Watch(context.Background(), "").