Fix t3c update when fallback occurs

CHANGELOG.md

@@ -104,6 +104,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - [#6027](https://github.com/apache/trafficcontrol/issues/6027) - Collapsed DB migrations
 - [#6091](https://github.com/apache/trafficcontrol/issues/6091) - Fixed cache config of internal cache communication for https origins
 - [#6066](https://github.com/apache/trafficcontrol/issues/6066) - Fixed missing/incorrect indices on some tables
+- [#6169](https://github.com/apache/trafficcontrol/issues/6169) - Fixed t3c-update not updating server status when a fallback to a previous Traffic Ops API version occurred
 - [#5576](https://github.com/apache/trafficcontrol/issues/5576) - Inconsistent Profile Name restrictions
 - Fixed Federations IMS so TR federations watcher will get updates.
 

cache-config/t3cutil/toreq/client.go

@@ -104,6 +104,11 @@ func New(url *url.URL, user string, pass string, insecure bool, timeout time.Dur
 		}
 		client.c = nil
 		client.old = oldClient
+
+		{
+			newClient := toclient.NewNoAuthSession("", false, "", false, 0) // only used for the version, because toClient could be nil if it had an error
+			log.Infof("cache-config Traffic Ops client: %v not supported, falling back to %v\n", newClient.APIVersion(), oldClient.APIVersion())
+		}
 	}
 
 	return client, nil

cache-config/t3cutil/toreq/toreqold/client.go

@@ -49,6 +49,10 @@ func (cl *TOClient) SetURL(newURL string) {
 	cl.c.URL = newURL
 }
 
+func (cl *TOClient) APIVersion() string {
+	return cl.c.APIVersion()
+}
+
 // New logs into Traffic Ops, returning the TOClient which contains the logged-in client.
 func New(url *url.URL, user string, pass string, insecure bool, timeout time.Duration, userAgent string) (*TOClient, error) {
 	log.Infoln("URL: '" + url.String() + "' User: '" + user + "' Pass len: '" + strconv.Itoa(len(pass)) + "'")

cache-config/t3cutil/toreq/toreqold/clientfuncs.go

@@ -570,7 +570,7 @@ func (cl *TOClient) GetServerUpdateStatus(cacheHostName tc.CacheName) (tc.Server
 func (cl *TOClient) SetServerUpdateStatus(cacheHostName tc.CacheName, updateStatus *bool, revalStatus *bool) (toclientlib.ReqInf, error) {
 	reqInf := toclientlib.ReqInf{}
 	err := torequtil.GetRetry(cl.NumRetries, "server_update_status_"+string(cacheHostName), nil, func(obj interface{}) error {
-		_, toReqInf, err := cl.c.GetServerUpdateStatus(string(cacheHostName))
+		toReqInf, err := cl.c.SetUpdateServerStatuses(string(cacheHostName), updateStatus, revalStatus)
 		if err != nil {
 			return errors.New("setting server update status from Traffic Ops '" + torequtil.MaybeIPStr(reqInf.RemoteAddr) + "': " + err.Error())
 		}