package timesource import ( "bytes" "errors" "sort" "sync" "time" "github.com/beevik/ntp" "github.com/ethereum/go-ethereum/log" "github.com/ethereum/go-ethereum/p2p" "github.com/ethereum/go-ethereum/rpc" ) const ( // DefaultMaxAllowedFailures defines how many failures will be tolerated. DefaultMaxAllowedFailures = 1 // FastNTPSyncPeriod period between ntp synchronizations before the first // successful connection. FastNTPSyncPeriod = 2 * time.Minute // SlowNTPSyncPeriod period between ntp synchronizations after the first // successful connection. SlowNTPSyncPeriod = 1 * time.Hour // DefaultRPCTimeout defines write deadline for single ntp server request. DefaultRPCTimeout = 2 * time.Second ) // defaultServers will be resolved to the closest available, // and with high probability resolved to the different IPs var defaultServers = []string{ "0.pool.ntp.org", "1.pool.ntp.org", "2.pool.ntp.org", "3.pool.ntp.org", } var errUpdateOffset = errors.New("failed to compute offset") type ntpQuery func(string, ntp.QueryOptions) (*ntp.Response, error) type queryResponse struct { Offset time.Duration Error error } type multiRPCError []error func (e multiRPCError) Error() string { var b bytes.Buffer b.WriteString("RPC failed: ") more := false for _, err := range e { if more { b.WriteString("; ") } b.WriteString(err.Error()) more = true } b.WriteString(".") return b.String() } func computeOffset(timeQuery ntpQuery, servers []string, allowedFailures int) (time.Duration, error) { if len(servers) == 0 { return 0, nil } responses := make(chan queryResponse, len(servers)) for _, server := range servers { go func(server string) { response, err := timeQuery(server, ntp.QueryOptions{ Timeout: DefaultRPCTimeout, }) if err == nil { err = response.Validate() } if err != nil { responses <- queryResponse{Error: err} return } responses <- queryResponse{Offset: response.ClockOffset} }(server) } var ( rpcErrors multiRPCError offsets []time.Duration collected int ) for response := range responses { if response.Error != nil { rpcErrors = append(rpcErrors, response.Error) } else { offsets = append(offsets, response.Offset) } collected++ if collected == len(servers) { break } } if lth := len(rpcErrors); lth > allowedFailures { return 0, rpcErrors } else if lth == len(servers) { return 0, rpcErrors } sort.SliceStable(offsets, func(i, j int) bool { return offsets[i] > offsets[j] }) mid := len(offsets) / 2 if len(offsets)%2 == 0 { return (offsets[mid-1] + offsets[mid]) / 2, nil } return offsets[mid], nil } // Default initializes time source with default config values. func Default() *NTPTimeSource { return &NTPTimeSource{ servers: defaultServers, allowedFailures: DefaultMaxAllowedFailures, fastNTPSyncPeriod: FastNTPSyncPeriod, slowNTPSyncPeriod: SlowNTPSyncPeriod, timeQuery: ntp.QueryWithOptions, } } // NTPTimeSource provides source of time that tries to be resistant to time skews. // It does so by periodically querying time offset from ntp servers. type NTPTimeSource struct { servers []string allowedFailures int fastNTPSyncPeriod time.Duration slowNTPSyncPeriod time.Duration timeQuery ntpQuery // for ease of testing quit chan struct{} wg sync.WaitGroup mu sync.RWMutex latestOffset time.Duration } // Now returns time adjusted by latest known offset func (s *NTPTimeSource) Now() time.Time { s.mu.RLock() defer s.mu.RUnlock() return time.Now().Add(s.latestOffset) } func (s *NTPTimeSource) updateOffset() error { offset, err := computeOffset(s.timeQuery, s.servers, s.allowedFailures) if err != nil { log.Error("failed to compute offset", "error", err) return errUpdateOffset } log.Info("Difference with ntp servers", "offset", offset) s.mu.Lock() s.latestOffset = offset s.mu.Unlock() return nil } // runPeriodically runs periodically the given function based on NTPTimeSource // synchronization limits (fastNTPSyncPeriod / slowNTPSyncPeriod) func (s *NTPTimeSource) runPeriodically(fn func() error) error { var period time.Duration s.quit = make(chan struct{}) // we try to do it synchronously so that user can have reliable messages right away s.wg.Add(1) go func() { for { select { case <-time.After(period): if err := fn(); err == nil { period = s.slowNTPSyncPeriod } else if period != s.slowNTPSyncPeriod { period = s.fastNTPSyncPeriod } case <-s.quit: s.wg.Done() return } } }() return nil } // Start runs a goroutine that updates local offset every updatePeriod. func (s *NTPTimeSource) Start(*p2p.Server) error { return s.runPeriodically(s.updateOffset) } // Stop goroutine that updates time source. func (s *NTPTimeSource) Stop() error { if s.quit == nil { return nil } close(s.quit) s.wg.Wait() return nil } // APIs used to be conformant with service interface func (s *NTPTimeSource) APIs() []rpc.API { return nil } // Protocols used to conformant with service interface func (s *NTPTimeSource) Protocols() []p2p.Protocol { return nil }