Keep rate limited reader reads to within the burst capacity

ratelimitreader.go

@@ -1,6 +1,7 @@
 package torrent
 
 import (
+	"fmt"
 	"io"
 	"time"
 
@@ -14,12 +15,18 @@ type rateLimitedReader struct {
 }
 
 func (me rateLimitedReader) Read(b []byte) (n int, err error) {
+	// Wait until we can read at all.
 	if err := me.l.WaitN(context.Background(), 1); err != nil {
 		panic(err)
 	}
+	// Limit the read to within the burst.
+	if me.l.Limit() != rate.Inf && len(b) > me.l.Burst() {
+		b = b[:me.l.Burst()]
+	}
 	n, err = me.r.Read(b)
+	// Pay the piper.
 	if !me.l.ReserveN(time.Now(), n-1).OK() {
-		panic(n - 1)
+		panic(fmt.Sprintf("burst exceeded?: %d", n-1))
 	}
 	return
 }