func (m mysqlTimeWriter) Now(b builder, cl clockwork.Clock) {
	if cl == nil {
		b.Build("NOW()")
	} else {
		b.Build("?", cl.Now())
	}
}

func nextSyncAfter(exp time.Time, clock clockwork.Clock) time.Duration {
	if exp.IsZero() {
		return MaximumProviderConfigSyncInterval
	}

	t := exp.Sub(clock.Now()) / 2
	if t > MaximumProviderConfigSyncInterval {
		t = MaximumProviderConfigSyncInterval
	} else if t < minimumProviderConfigSyncInterval {
		t = minimumProviderConfigSyncInterval
	}

	return t
}

func nextSyncAfter(exp time.Time, clock clockwork.Clock) time.Duration {
	if exp.IsZero() {
		return MaximumTokenRefreshInterval
	}

	t := exp.Sub(clock.Now()) / 2
	if t > MaximumTokenRefreshInterval {
		t = MaximumTokenRefreshInterval
	} else if t < MinimumTokenRefreshInterval {
		t = MinimumTokenRefreshInterval
	}

	return t
}

func (n *node) expirationAndTTL(clock clockwork.Clock) (*time.Time, int64) {
	if !n.IsPermanent() {
		/* compute ttl as:
		   ceiling( (expireTime - timeNow) / nanosecondsPerSecond )
		   which ranges from 1..n
		   rather than as:
		   ( (expireTime - timeNow) / nanosecondsPerSecond ) + 1
		   which ranges 1..n+1
		*/
		ttlN := n.ExpireTime.Sub(clock.Now())
		ttl := ttlN / time.Second
		if (ttlN % time.Second) > 0 {
			ttl++
		}
		t := n.ExpireTime.UTC()
		return &t, int64(ttl)
	}
	return nil, 0
}

// sync copies the keyset from r to the KeySet at w and returns the duration in which the KeySet will expire.
// If keyset has already expired, returns a zero duration.
func sync(r ReadableKeySetRepo, w WritableKeySetRepo, clock clockwork.Clock) (exp time.Duration, err error) {
	var ks KeySet
	ks, err = r.Get()
	if err != nil {
		return
	}

	if ks == nil {
		err = errors.New("no source KeySet")
		return
	}

	if err = w.Set(ks); err != nil {
		return
	}

	now := clock.Now()
	if ks.ExpiresAt().After(now) {
		exp = ks.ExpiresAt().Sub(now)
	}
	return
}

func handleKeysFunc(km key.PrivateKeyManager, clock clockwork.Clock) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != "GET" {
			w.Header().Set("Allow", "GET")
			phttp.WriteError(w, http.StatusMethodNotAllowed, "GET only acceptable method")
			return
		}

		jwks, err := km.JWKs()
		if err != nil {
			log.Errorf("Failed to get JWKs while serving HTTP request: %v", err)
			phttp.WriteError(w, http.StatusInternalServerError, "")
			return
		}

		keys := struct {
			Keys []jose.JWK `json:"keys"`
		}{
			Keys: jwks,
		}

		b, err := json.Marshal(keys)
		if err != nil {
			log.Errorf("Unable to marshal signing key to JSON: %v", err)
		}

		exp := km.ExpiresAt()
		w.Header().Set("Expires", exp.Format(time.RFC1123))

		ttl := int(exp.Sub(clock.Now()).Seconds())
		w.Header().Set("Cache-Control", fmt.Sprintf("public, max-age=%d", ttl))

		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusOK)
		w.Write(b)
	}
}

// parseKeyRequest converts a received http.Request on keysPrefix to
// a server Request, performing validation of supplied fields as appropriate.
// If any validation fails, an empty Request and non-nil error is returned.
func parseKeyRequest(r *http.Request, clock clockwork.Clock) (etcdserverpb.Request, error) {
	emptyReq := etcdserverpb.Request{}

	err := r.ParseForm()
	if err != nil {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeInvalidForm,
			err.Error(),
		)
	}

	if !strings.HasPrefix(r.URL.Path, keysPrefix) {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeInvalidForm,
			"incorrect key prefix",
		)
	}
	p := path.Join(etcdserver.StoreKeysPrefix, r.URL.Path[len(keysPrefix):])

	var pIdx, wIdx uint64
	if pIdx, err = getUint64(r.Form, "prevIndex"); err != nil {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeIndexNaN,
			`invalid value for "prevIndex"`,
		)
	}
	if wIdx, err = getUint64(r.Form, "waitIndex"); err != nil {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeIndexNaN,
			`invalid value for "waitIndex"`,
		)
	}

	var rec, sort, wait, dir, quorum, stream bool
	if rec, err = getBool(r.Form, "recursive"); err != nil {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeInvalidField,
			`invalid value for "recursive"`,
		)
	}
	if sort, err = getBool(r.Form, "sorted"); err != nil {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeInvalidField,
			`invalid value for "sorted"`,
		)
	}
	if wait, err = getBool(r.Form, "wait"); err != nil {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeInvalidField,
			`invalid value for "wait"`,
		)
	}
	// TODO(jonboulle): define what parameters dir is/isn't compatible with?
	if dir, err = getBool(r.Form, "dir"); err != nil {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeInvalidField,
			`invalid value for "dir"`,
		)
	}
	if quorum, err = getBool(r.Form, "quorum"); err != nil {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeInvalidField,
			`invalid value for "quorum"`,
		)
	}
	if stream, err = getBool(r.Form, "stream"); err != nil {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeInvalidField,
			`invalid value for "stream"`,
		)
	}

	if wait && r.Method != "GET" {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodeInvalidField,
			`"wait" can only be used with GET requests`,
		)
	}

	pV := r.FormValue("prevValue")
	if _, ok := r.Form["prevValue"]; ok && pV == "" {
		return emptyReq, etcdErr.NewRequestError(
			etcdErr.EcodePrevValueRequired,
			`"prevValue" cannot be empty`,
		)
	}

	// TTL is nullable, so leave it null if not specified
	// or an empty string
	var ttl *uint64
	if len(r.FormValue("ttl")) > 0 {
		i, err := getUint64(r.Form, "ttl")
		if err != nil {
			return emptyReq, etcdErr.NewRequestError(
				etcdErr.EcodeTTLNaN,
				`invalid value for "ttl"`,
			)
//.........这里部分代码省略.........

func nowTime(cl clockwork.Clock) time.Time {
	if cl == nil {
		return time.Now()
	}
	return cl.Now()
}