feat(ntp): add delay between sync attempts and support NTP servers from DHCP (#162)

* feat(ntp): use ntp server from dhcp info

* feat(ntp): use ntp server from dhcp info

* feat(ntp): add delay between time sync attempts

* chore(ntp): more logging

ntp.go

@@ -11,20 +11,56 @@ import (
 	"github.com/beevik/ntp"
 )
 
-var timeSynced = false
+const (
+	timeSyncRetryStep     = 5 * time.Second
+	timeSyncRetryMaxInt   = 1 * time.Minute
+	timeSyncWaitNetChkInt = 100 * time.Millisecond
+	timeSyncWaitNetUpInt  = 3 * time.Second
+	timeSyncInterval      = 1 * time.Hour
+	timeSyncTimeout       = 2 * time.Second
+)
+
+var (
+	timeSynced            = false
+	timeSyncRetryInterval = 0 * time.Second
+	defaultNTPServers     = []string{
+		"time.cloudflare.com",
+		"time.apple.com",
+	}
+)
 
 func TimeSyncLoop() {
 	for {
-		fmt.Println("Syncing system time")
+		if !networkState.checked {
+			time.Sleep(timeSyncWaitNetChkInt)
+			continue
+		}
+
+		if !networkState.Up {
+			log.Printf("Waiting for network to come up")
+			time.Sleep(timeSyncWaitNetUpInt)
+			continue
+		}
+
+		log.Printf("Syncing system time")
 		start := time.Now()
 		err := SyncSystemTime()
 		if err != nil {
 			log.Printf("Failed to sync system time: %v", err)
+
+			// retry after a delay
+			timeSyncRetryInterval += timeSyncRetryStep
+			time.Sleep(timeSyncRetryInterval)
+			// reset the retry interval if it exceeds the max interval
+			if timeSyncRetryInterval > timeSyncRetryMaxInt {
+				timeSyncRetryInterval = 0
+			}
+
 			continue
 		}
 		log.Printf("Time sync successful, now is: %v, time taken: %v", time.Now(), time.Since(start))
 		timeSynced = true
-		time.Sleep(1 * time.Hour) //once the first sync is done, sync every hour
+		time.Sleep(timeSyncInterval) // after the first sync is done
 	}
 }
 
@@ -41,13 +77,22 @@ func SyncSystemTime() (err error) {
 }
 
 func queryNetworkTime() (*time.Time, error) {
-	ntpServers := []string{
-		"time.cloudflare.com",
-		"time.apple.com",
+	ntpServers, err := getNTPServersFromDHCPInfo()
+	if err != nil {
+		log.Printf("failed to get NTP servers from DHCP info: %v\n", err)
 	}
+
+	if ntpServers == nil {
+		ntpServers = defaultNTPServers
+		log.Printf("Using default NTP servers: %v\n", ntpServers)
+	} else {
+		log.Printf("Using NTP servers from DHCP: %v\n", ntpServers)
+	}
+
 	for _, server := range ntpServers {
-		now, err := queryNtpServer(server, 2*time.Second)
+		now, err := queryNtpServer(server, timeSyncTimeout)
 		if err == nil {
+			log.Printf("NTP server [%s] returned time: %v\n", server, now)
 			return now, nil
 		}
 	}
@@ -56,7 +101,7 @@ func queryNetworkTime() (*time.Time, error) {
 		"http://cloudflare.com",
 	}
 	for _, url := range httpUrls {
-		now, err := queryHttpTime(url, 2*time.Second)
+		now, err := queryHttpTime(url, timeSyncTimeout)
 		if err == nil {
 			return now, nil
 		}