reset buffer if its average use size smaller than quater of capacity

closes #95

Author: funny-falcon

connection.go

@@ -442,7 +442,7 @@ func (conn *Connection) writeAuthRequest(w *bufio.Writer, scramble []byte) (err
 	if err != nil {
 		return errors.New("auth: pack error " + err.Error())
 	}
-	if err := write(w, packet); err != nil {
+	if err := write(w, packet.b); err != nil {
 		return errors.New("auth: write error " + err.Error())
 	}
 	if err = w.Flush(); err != nil {
@@ -521,7 +521,7 @@ func (conn *Connection) closeConnection(neterr error, forever bool) (err error)
 		conn.c = nil
 	}
 	for i := range conn.shard {
-		conn.shard[i].buf = conn.shard[i].buf[:0]
+		conn.shard[i].buf.Reset()
 		requests := &conn.shard[i].requests
 		for pos := range requests {
 			fut := requests[pos].first
@@ -621,14 +621,14 @@ func (conn *Connection) writer(w *bufio.Writer, c net.Conn) {
 		}
 		packet, shard.buf = shard.buf, packet
 		shard.bufmut.Unlock()
-		if len(packet) == 0 {
+		if packet.Len() == 0 {
 			continue
 		}
-		if err := write(w, packet); err != nil {
+		if err := write(w, packet.b); err != nil {
 			conn.reconnect(err, c)
 			return
 		}
-		packet = packet[0:0]
+		packet.Reset()
 	}
 }
 
@@ -717,14 +717,14 @@ func (conn *Connection) putFuture(fut *Future, body func(*msgpack.Encoder) error
 		return
 	default:
 	}
-	firstWritten := len(shard.buf) == 0
-	if cap(shard.buf) == 0 {
-		shard.buf = make(smallWBuf, 0, 128)
+	firstWritten := shard.buf.Len() == 0
+	if shard.buf.Cap() == 0 {
+		shard.buf.b = make([]byte, 0, 128)
 		shard.enc = msgpack.NewEncoder(&shard.buf)
 	}
-	blen := len(shard.buf)
+	blen := shard.buf.Len()
 	if err := fut.pack(&shard.buf, shard.enc, body); err != nil {
-		shard.buf = shard.buf[:blen]
+		shard.buf.Trunc(blen)
 		shard.bufmut.Unlock()
 		if f := conn.fetchFuture(fut.requestId); f == fut {
 			fut.markReady(conn)

request.go

@@ -352,25 +352,25 @@ func (conn *Connection) EvalAsync(expr string, args interface{}) *Future {
 
 func (fut *Future) pack(h *smallWBuf, enc *msgpack.Encoder, body func(*msgpack.Encoder) error) (err error) {
 	rid := fut.requestId
-	hl := len(*h)
-	*h = append(*h, smallWBuf{
+	hl := h.Len()
+	h.Write([]byte{
 		0xce, 0, 0, 0, 0, // length
 		0x82,                           // 2 element map
 		KeyCode, byte(fut.requestCode), // request code
 		KeySync, 0xce,
 		byte(rid >> 24), byte(rid >> 16),
 		byte(rid >> 8), byte(rid),
-	}...)
+	})
 
 	if err = body(enc); err != nil {
 		return
 	}
 
-	l := uint32(len(*h) - 5 - hl)
-	(*h)[hl+1] = byte(l >> 24)
-	(*h)[hl+2] = byte(l >> 16)
-	(*h)[hl+3] = byte(l >> 8)
-	(*h)[hl+4] = byte(l)
+	l := uint32(h.Len() - 5 - hl)
+	h.b[hl+1] = byte(l >> 24)
+	h.b[hl+2] = byte(l >> 16)
+	h.b[hl+3] = byte(l >> 8)
+	h.b[hl+4] = byte(l)
 
 	return
 }

smallbuf.go

@@ -51,19 +51,47 @@ func (s *smallBuf) Bytes() []byte {
 	return nil
 }
 
-type smallWBuf []byte
+type smallWBuf struct {
+	b []byte
+	sum uint
+	n uint
+}
 
 func (s *smallWBuf) Write(b []byte) (int, error) {
-	*s = append(*s, b...)
-	return len(b), nil
+	s.b = append(s.b, b...)
+	return len(s.b), nil
 }
 
 func (s *smallWBuf) WriteByte(b byte) error {
-	*s = append(*s, b)
+	s.b = append(s.b, b)
 	return nil
 }
 
 func (s *smallWBuf) WriteString(ss string) (int, error) {
-	*s = append(*s, ss...)
+	s.b = append(s.b, ss...)
 	return len(ss), nil
 }
+
+func (s smallWBuf) Len() int {
+	return len(s.b)
+}
+
+func (s smallWBuf) Cap() int {
+	return cap(s.b)
+}
+
+func (s *smallWBuf) Trunc(n int) {
+	s.b = s.b[:n]
+}
+
+func (s *smallWBuf) Reset() {
+	s.sum = uint(uint64(s.sum) * 15 / 16) + uint(len(s.b))
+	if s.n < 16 {
+		s.n++
+	}
+	if cap(s.b) > 1024 && s.sum / s.n < uint(cap(s.b))/4 {
+		s.b = make([]byte, 0, s.sum/s.n)
+	} else {
+		s.b = s.b[:0]
+	}
+}