fix small Read() big rate for slow.Reader

src/slow/reader.go

@@ -9,30 +9,36 @@ import (
 
 type Reader struct {
 	ctx     context.Context
-	limiter *rate.Limiter
+	limiter rate.Limiter
 	r       io.Reader
 }
 
-var _ io.Reader = Reader{}
+var _ io.Reader = &Reader{}
 
-func NewReader(ctx context.Context, bps rate.Limit, r io.Reader) Reader {
-	return Reader{
+func NewReader(ctx context.Context, bps rate.Limit, r io.Reader) *Reader {
+	return &Reader{
 		ctx:     ctx,
-		limiter: rate.NewLimiter(bps, int(bps)),
+		limiter: *rate.NewLimiter(bps, int(bps)),
 		r:       r,
 	}
 }
 
-func (r Reader) Read(b []byte) (int, error) {
+func (r *Reader) Read(b []byte) (int, error) {
 	n, err := r.r.Read(b)
 
 	m := 0
 	burst := r.limiter.Burst()
 	for m < n {
-		if err := r.limiter.WaitN(r.ctx, burst); err != nil {
+		page := burst
+		if left := n - m; page > left {
+			page = left
+		}
+
+		if err := r.limiter.WaitN(r.ctx, page); err != nil {
 			return n, err
 		}
-		m += burst
+
+		m += page
 	}
 
 	return n, err