Panic fixes (#4214)

 - [ ] Link to issue, e.g. `Resolves #NNN`
 - [ ] Documentation added (if applicable)
 - [ ] Tests added
- [ ] Branch rebased on top of current main (`git pull --rebase origin
main`)
- [ ] Changes squashed to a single commit (described
[here](http://gitready.com/advanced/2009/02/10/squashing-commits-with-rebase.html))
 - [x] Build is green in Travis CI
- [x] You have certified that the contribution is your original work and
that you license the work to the project under the [Apache 2
license](https://github.com/nats-io/nats-server/blob/main/LICENSE)

Resolves panics in the code.

### Changes proposed in this pull request:

 - This PR fixes some of the panics in the code

server/accounts.go

@@ -1429,7 +1429,7 @@ func (a *Account) sendTrackingLatency(si *serviceImport, responder *client) bool
 	}
 	sl.RequestStart = time.Unix(0, si.ts-int64(reqRTT)).UTC()
 	sl.ServiceLatency = serviceRTT - respRTT
-	sl.TotalLatency = sl.Requestor.RTT + serviceRTT
+	sl.TotalLatency = reqRTT + serviceRTT
 	if respRTT > 0 {
 		sl.SystemLatency = time.Since(ts)
 		sl.TotalLatency += sl.SystemLatency
@@ -3784,10 +3784,11 @@ func (ur *URLAccResolver) Fetch(name string) (string, error) {
 		return _EMPTY_, fmt.Errorf("could not fetch <%q>: %v", redactURLString(url), err)
 	} else if resp == nil {
 		return _EMPTY_, fmt.Errorf("could not fetch <%q>: no response", redactURLString(url))
-	} else if resp.StatusCode != http.StatusOK {
-		return _EMPTY_, fmt.Errorf("could not fetch <%q>: %v", redactURLString(url), resp.Status)
 	}
 	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return _EMPTY_, fmt.Errorf("could not fetch <%q>: %v", redactURLString(url), resp.Status)
+	}
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {
 		return _EMPTY_, err

server/client.go

@@ -1989,7 +1989,9 @@ func (c *client) authViolation() {
 			ErrAuthentication.Error(),
 			c.opts.Username)
 	} else {
-		c.Errorf(ErrAuthentication.Error())
+		if c.srv != nil {
+			c.Errorf(ErrAuthentication.Error())
+		}
 	}
 	if c.isMqtt() {
 		c.mqttEnqueueConnAck(mqttConnAckRCNotAuthorized, false)

server/ipqueue.go

@@ -104,6 +104,9 @@ func (q *ipQueue[T]) push(e T) int {
 // emptied the queue. So the caller should never assume that pop() will
 // return a slice of 1 or more, it could return `nil`.
 func (q *ipQueue[T]) pop() []T {
+	if q == nil {
+		return nil
+	}
 	var elts []T
 	q.Lock()
 	if q.pos == 0 {

server/jetstream_cluster.go

@@ -3107,7 +3107,9 @@ func (js *jetStream) processStreamAssignment(sa *streamAssignment) bool {
 		accStreams = make(map[string]*streamAssignment)
 	} else if osa := accStreams[stream]; osa != nil && osa != sa {
 		// Copy over private existing state from former SA.
-		sa.Group.node = osa.Group.node
+		if sa.Group != nil {
+			sa.Group.node = osa.Group.node
+		}
 		sa.consumers = osa.consumers
 		sa.responded = osa.responded
 		sa.err = osa.err
@@ -3198,7 +3200,9 @@ func (js *jetStream) processUpdateStreamAssignment(sa *streamAssignment) {
 	}
 
 	// Copy over private existing state from former SA.
-	sa.Group.node = osa.Group.node
+	if sa.Group != nil {
+		sa.Group.node = osa.Group.node
+	}
 	sa.consumers = osa.consumers
 	sa.err = osa.err
 
@@ -3216,7 +3220,9 @@ func (js *jetStream) processUpdateStreamAssignment(sa *streamAssignment) {
 		sa.responded = false
 	} else {
 		// Make sure to clean up any old node in case this stream moves back here.
-		sa.Group.node = nil
+		if sa.Group != nil {
+			sa.Group.node = nil
+		}
 	}
 	js.mu.Unlock()
 
@@ -3787,7 +3793,9 @@ func (js *jetStream) processConsumerAssignment(ca *consumerAssignment) {
 	} else if oca := sa.consumers[ca.Name]; oca != nil {
 		wasExisting = true
 		// Copy over private existing state from former SA.
-		ca.Group.node = oca.Group.node
+		if ca.Group != nil {
+			ca.Group.node = oca.Group.node
+		}
 		ca.responded = oca.responded
 		ca.err = oca.err
 	}

server/leafnode.go

@@ -1422,7 +1422,7 @@ func (s *Server) addLeafNodeConnection(c *client, srvName, clusterName string, c
 	}
 	// If we have a specified JetStream domain we will want to add a mapping to
 	// allow access cross domain for each non-system account.
-	if opts.JetStreamDomain != _EMPTY_ && acc != sysAcc && opts.JetStream {
+	if opts.JetStreamDomain != _EMPTY_ && opts.JetStream && acc != nil && acc != sysAcc {
 		for src, dest := range generateJSMappingTable(opts.JetStreamDomain) {
 			if err := acc.AddMapping(src, dest); err != nil {
 				c.Debugf("Error adding JetStream domain mapping: %s", err.Error())

server/route.go

@@ -1949,12 +1949,12 @@ func (c *client) processRouteConnect(srv *Server, arg []byte, lang string) error
 		c.closeConnection(WrongGateway)
 		return ErrWrongGateway
 	}
-	var perms *RoutePermissions
-	//TODO this check indicates srv may be nil. see srv usage below
-	if srv != nil {
-		perms = srv.getOpts().Cluster.Permissions
+
+	if srv == nil {
+		return ErrServerNotRunning
 	}
 
+	perms := srv.getOpts().Cluster.Permissions
 	clusterName := srv.ClusterName()
 
 	// If we have a cluster name set, make sure it matches ours.

server/server.go

@@ -3560,7 +3560,10 @@ func (s *Server) lameDuckMode() {
 	numClients := int64(len(s.clients))
 	batch := 1
 	// Sleep interval between each client connection close.
-	si := dur / numClients
+	var si int64
+	if numClients != 0 {
+		si = dur / numClients
+	}
 	if si < 1 {
 		// Should not happen (except in test with very small LD duration), but
 		// if there are too many clients, batch the number of close and

server/stream.go

@@ -1788,7 +1788,9 @@ func gatherSourceMirrorSubjects(subjects []string, cfg *StreamConfig, acc *Accou
 
 // Return the subjects for a stream source.
 func (a *Account) streamSourceSubjects(ss *StreamSource, seen map[string]bool) (subjects []string, hasExt bool) {
-	if ss != nil && ss.External != nil {
+	if ss == nil {
+		return nil, false
+	} else if ss.External != nil {
 		return nil, true
 	}