add a sync.Pool of byte buffers with maximum packet size as cap

ref #217

buffer_pool.go

@@ -0,0 +1,23 @@
+package quic
+
+import (
+	"sync"
+
+	"github.com/lucas-clemente/quic-go/protocol"
+)
+
+var bufferPool sync.Pool
+
+func getPacketBuffer() []byte {
+	return bufferPool.Get().([]byte)
+}
+
+func putPacketBuffer(buf []byte) {
+	bufferPool.Put(buf[:0])
+}
+
+func init() {
+	bufferPool.New = func() interface{} {
+		return make([]byte, 0, protocol.MaxPacketSize)
+	}
+}