config: add jitter interval for watcher to avoid dos

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

config/config.go

@@ -10,8 +10,11 @@ import (
 // DefaultConfig default config
 var DefaultConfig Config = NewConfig()
 
-// DefaultWatcherInterval default interval for poll changes
-var DefaultWatcherInterval = 5 * time.Second
+// DefaultWatcherMinInterval default min interval for poll changes
+var DefaultWatcherMinInterval = 5 * time.Second
+
+// DefaultWatcherMinInterval default max interval for poll changes
+var DefaultWatcherMaxInterval = 9 * time.Second
 
 var (
 	// ErrCodecMissing is returned when codec needed and not specified

config/default.go

@@ -5,9 +5,9 @@ import (
 	"reflect"
 	"strconv"
 	"strings"
-	"time"
 
 	"github.com/imdario/mergo"
+	"github.com/unistack-org/micro/v3/util/jitter"
 	rutil "github.com/unistack-org/micro/v3/util/reflect"
 )
 
@@ -302,7 +302,7 @@ type defaultWatcher struct {
 }
 
 func (w *defaultWatcher) run() {
-	ticker := time.NewTicker(w.wopts.Interval)
+	ticker := jitter.NewTicker(w.wopts.MinInterval, w.wopts.MaxInterval)
 	defer ticker.Stop()
 
 	src := w.opts.Struct

config/default_test.go

@@ -31,7 +31,7 @@ func TestWatch(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	w, err := cfg.Watch(ctx, config.WatchInterval(500*time.Millisecond))
+	w, err := cfg.Watch(ctx, config.WatchInterval(200*time.Millisecond, 500*time.Millisecond))
 	if err != nil {
 		t.Fatal(err)
 	}

config/options.go

@@ -211,8 +211,10 @@ type WatchOptions struct {
 	Context context.Context
 	// Coalesce multiple events to one
 	Coalesce bool
-	// Interval to periodically pull changes if config source not supports async notify
-	Interval time.Duration
+	// MinInterval specifies the min time.Duration interval for poll changes
+	MinInterval time.Duration
+	// MaxInterval specifies the max time.Duration interval for poll changes
+	MaxInterval time.Duration
 	// Struct for filling
 	Struct interface{}
 }
@@ -221,8 +223,9 @@ type WatchOption func(*WatchOptions)
 
 func NewWatchOptions(opts ...WatchOption) WatchOptions {
 	options := WatchOptions{
-		Context:  context.Background(),
-		Interval: DefaultWatcherInterval,
+		Context:     context.Background(),
+		MinInterval: DefaultWatcherMinInterval,
+		MaxInterval: DefaultWatcherMaxInterval,
 	}
 	for _, o := range opts {
 		o(&options)
@@ -244,10 +247,11 @@ func WatchCoalesce(b bool) WatchOption {
 	}
 }
 
-// WatchInterval specifies time.Duration for pulling changes
-func WatchInterval(td time.Duration) WatchOption {
+// WatchInterval specifies min and max time.Duration for pulling changes
+func WatchInterval(min, max time.Duration) WatchOption {
 	return func(o *WatchOptions) {
-		o.Interval = td
+		o.MinInterval = min
+		o.MaxInterval = max
 	}
 }
 

util/jitter/random.go

@@ -7,8 +7,8 @@ import (
 	"github.com/unistack-org/micro/v3/util/rand"
 )
 
-// Do returns a random time to jitter with max cap specified
-func Do(d time.Duration) time.Duration {
+// Random returns a random time to jitter with max cap specified
+func Random(d time.Duration) time.Duration {
 	var rng rand.Rand
 	v := rng.Float64() * float64(d.Nanoseconds())
 	return time.Duration(v)

util/jitter/ticker.go

@@ -0,0 +1,65 @@
+package jitter
+
+import (
+	"time"
+
+	"github.com/unistack-org/micro/v3/util/rand"
+)
+
+// Ticker is similar to time.Ticker but ticks at random intervals between
+// the min and max duration values (stored internally as int64 nanosecond
+// counts).
+type Ticker struct {
+	C    chan time.Time
+	done chan chan struct{}
+	min  int64
+	max  int64
+	rng  rand.Rand
+}
+
+// NewTicker returns a pointer to an initialized instance of the Ticker.
+// Min and max are durations of the shortest and longest allowed
+// ticks. Ticker will run in a goroutine until explicitly stopped.
+func NewTicker(min, max time.Duration) *Ticker {
+	ticker := &Ticker{
+		C:    make(chan time.Time),
+		done: make(chan chan struct{}),
+		min:  min.Nanoseconds(),
+		max:  max.Nanoseconds(),
+	}
+	go ticker.run()
+	return ticker
+}
+
+// Stop terminates the ticker goroutine and closes the C channel.
+func (ticker *Ticker) Stop() {
+	c := make(chan struct{})
+	ticker.done <- c
+	<-c
+}
+
+func (ticker *Ticker) run() {
+	defer close(ticker.C)
+	t := time.NewTimer(ticker.nextInterval())
+	for {
+		// either a stop signal or a timeout
+		select {
+		case c := <-ticker.done:
+			t.Stop()
+			close(c)
+			return
+		case <-t.C:
+			select {
+			case ticker.C <- time.Now():
+				t.Stop()
+				t = time.NewTimer(ticker.nextInterval())
+			default:
+				// there could be noone receiving...
+			}
+		}
+	}
+}
+
+func (ticker *Ticker) nextInterval() time.Duration {
+	return time.Duration(ticker.rng.Int63n(ticker.max-ticker.min)+ticker.min) * time.Nanosecond
+}