api: fix panic in conn.NewWatcher()

Before this patch, `conn.c` was not checked for `nil` before calling its
method. This could cause a panic if the connection was lost or closed.

Closes #438

Author: ImeevMA

CHANGELOG.md

@@ -17,6 +17,9 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 
 ### Fixed
 
+- Fixed panic when calling NewWatcher() during reconnection or after
+  connection is closed (#438).
+
 ## [v2.3.2] - 2025-04-14
 
 This release improves the logic of `Connect` and `pool.Connect` in case of a

connection.go

@@ -1461,7 +1461,7 @@ func (conn *Connection) NewWatcher(key string, callback WatchCallback) (Watcher,
 	// That's why we can't just check the Tarantool response for an unsupported
 	// request error.
 	if !isFeatureInSlice(iproto.IPROTO_FEATURE_WATCHERS,
-		conn.c.ProtocolInfo().Features) {
+		conn.serverProtocolInfo.Features) {
 		err := fmt.Errorf("the feature %s must be supported by connection "+
 			"to create a watcher", iproto.IPROTO_FEATURE_WATCHERS)
 		return nil, err

tarantool_test.go

@@ -3550,6 +3550,72 @@ func TestConnection_NewWatcher(t *testing.T) {
 	}
 }
 
+func newWatcherReconnectionPrepareTestConnection(t *testing.T) (*Connection, context.CancelFunc) {
+	t.Helper()
+
+	const server = "127.0.0.1:3015"
+	testDialer := dialer
+	testDialer.Address = server
+
+	inst, err := test_helpers.StartTarantool(test_helpers.StartOpts{
+		Dialer:       testDialer,
+		InitScript:   "config.lua",
+		Listen:       server,
+		WaitStart:    100 * time.Millisecond,
+		ConnectRetry: 10,
+		RetryTimeout: 500 * time.Millisecond,
+	})
+	t.Cleanup(func() { test_helpers.StopTarantoolWithCleanup(inst) })
+	if err != nil {
+		t.Fatalf("Unable to start Tarantool: %s", err)
+	}
+
+	ctx, cancel := test_helpers.GetConnectContext()
+
+	reconnectOpts := opts
+	reconnectOpts.Reconnect = 100 * time.Millisecond
+	reconnectOpts.MaxReconnects = 0
+	reconnectOpts.Notify = make(chan ConnEvent)
+	conn, err := Connect(ctx, testDialer, reconnectOpts)
+	if err != nil {
+		t.Fatalf("Connection was not established: %v", err)
+	}
+
+	test_helpers.StopTarantool(inst)
+
+	// Wait for reconnection process to be started.
+	for conn.ConnectedNow() {
+		time.Sleep(100 * time.Millisecond)
+	}
+
+	return conn, cancel
+}
+
+func TestNewWatcherDuringReconnect(t *testing.T) {
+	test_helpers.SkipIfWatchersUnsupported(t)
+
+	conn, cancel := newWatcherReconnectionPrepareTestConnection(t)
+	defer conn.Close()
+	defer cancel()
+
+	_, err := conn.NewWatcher("one", func(event WatchEvent) {})
+	assert.NotNil(t, err)
+	assert.ErrorContains(t, err, "client connection is not ready")
+}
+
+func TestNewWatcherAfterClose(t *testing.T) {
+	test_helpers.SkipIfWatchersUnsupported(t)
+
+	conn, cancel := newWatcherReconnectionPrepareTestConnection(t)
+	defer cancel()
+
+	_ = conn.Close()
+
+	_, err := conn.NewWatcher("one", func(event WatchEvent) {})
+	assert.NotNil(t, err)
+	assert.ErrorContains(t, err, "using closed connection")
+}
+
 func TestConnection_NewWatcher_noWatchersFeature(t *testing.T) {
 	test_helpers.SkipIfWatchersSupported(t)
 
@@ -4149,13 +4215,13 @@ func runTestMain(m *testing.M) int {
 	startOpts.MemtxUseMvccEngine = !isStreamUnsupported
 
 	inst, err := test_helpers.StartTarantool(startOpts)
-	defer test_helpers.StopTarantoolWithCleanup(inst)
-
 	if err != nil {
 		log.Printf("Failed to prepare test tarantool: %s", err)
 		return 1
 	}
 
+	defer test_helpers.StopTarantoolWithCleanup(inst)
+
 	return m.Run()
 }