stream: add jitter to retry backoff in accordance with gRFC A6 (#7869)

Author: isgj

service_config.go

@@ -168,6 +168,7 @@ func init() {
 		return parseServiceConfig(js, defaultMaxCallAttempts)
 	}
 }
+
 func parseServiceConfig(js string, maxAttempts int) *serviceconfig.ParseResult {
 	if len(js) == 0 {
 		return &serviceconfig.ParseResult{Err: fmt.Errorf("no JSON service config provided")}
@@ -297,7 +298,7 @@ func convertRetryPolicy(jrp *jsonRetryPolicy, maxAttempts int) (p *internalservi
 	return rp, nil
 }
 
-func min(a, b *int) *int {
+func minPointers(a, b *int) *int {
 	if *a < *b {
 		return a
 	}
@@ -309,7 +310,7 @@ func getMaxSize(mcMax, doptMax *int, defaultVal int) *int {
 		return &defaultVal
 	}
 	if mcMax != nil && doptMax != nil {
-		return min(mcMax, doptMax)
+		return minPointers(mcMax, doptMax)
 	}
 	if mcMax != nil {
 		return mcMax

stream.go

@@ -218,7 +218,7 @@ func newClientStream(ctx context.Context, desc *StreamDesc, cc *ClientConn, meth
 
 	var mc serviceconfig.MethodConfig
 	var onCommit func()
-	var newStream = func(ctx context.Context, done func()) (iresolver.ClientStream, error) {
+	newStream := func(ctx context.Context, done func()) (iresolver.ClientStream, error) {
 		return newClientStreamWithParams(ctx, desc, cc, method, mc, onCommit, done, opts...)
 	}
 
@@ -708,11 +708,10 @@ func (a *csAttempt) shouldRetry(err error) (bool, error) {
 		cs.numRetriesSincePushback = 0
 	} else {
 		fact := math.Pow(rp.BackoffMultiplier, float64(cs.numRetriesSincePushback))
-		cur := float64(rp.InitialBackoff) * fact
-		if max := float64(rp.MaxBackoff); cur > max {
-			cur = max
-		}
-		dur = time.Duration(rand.Int64N(int64(cur)))
+		cur := min(float64(rp.InitialBackoff)*fact, float64(rp.MaxBackoff))
+		// Apply jitter by multiplying with a random factor between 0.8 and 1.2
+		cur *= 0.8 + 0.4*rand.Float64()
+		dur = time.Duration(int64(cur))
 		cs.numRetriesSincePushback++
 	}