rlp: added pooling of streams using sync (#19044)

Prevents reallocation, improves performance

rlp/decode.go

@@ -26,6 +26,7 @@ import (
 	"math/big"
 	"reflect"
 	"strings"
+	"sync"
 )
 
 var (
@@ -48,6 +49,10 @@ var (
 	errUintOverflow  = errors.New("rlp: uint overflow")
 	errNoPointer     = errors.New("rlp: interface given to Decode must be a pointer")
 	errDecodeIntoNil = errors.New("rlp: pointer given to Decode must not be nil")
+
+	streamPool = sync.Pool{
+		New: func() interface{} { return new(Stream) },
+	}
 )
 
 // Decoder is implemented by types that require custom RLP
@@ -126,17 +131,24 @@ type Decoder interface {
 //
 //     NewStream(r, limit).Decode(val)
 func Decode(r io.Reader, val interface{}) error {
-	// TODO: this could use a Stream from a pool.
-	return NewStream(r, 0).Decode(val)
+	stream := streamPool.Get().(*Stream)
+	defer streamPool.Put(stream)
+
+	stream.Reset(r, 0)
+	return stream.Decode(val)
 }
 
 // DecodeBytes parses RLP data from b into val.
 // Please see the documentation of Decode for the decoding rules.
 // The input must contain exactly one value and no trailing data.
 func DecodeBytes(b []byte, val interface{}) error {
-	// TODO: this could use a Stream from a pool.
 	r := bytes.NewReader(b)
-	if err := NewStream(r, uint64(len(b))).Decode(val); err != nil {
+
+	stream := streamPool.Get().(*Stream)
+	defer streamPool.Put(stream)
+
+	stream.Reset(r, uint64(len(b)))
+	if err := stream.Decode(val); err != nil {
 		return err
 	}
 	if r.Len() > 0 {
@@ -853,6 +865,7 @@ func (s *Stream) Reset(r io.Reader, inputLimit uint64) {
 	if s.uintbuf == nil {
 		s.uintbuf = make([]byte, 8)
 	}
+	s.byteval = 0
 }
 
 // Kind returns the kind and size of the next value in the