reduce allocations (also pulls in updated ironwood to do the same)

src/core/core.go

@@ -183,7 +183,8 @@ func (c *Core) MTU() uint64 {
 }
 
 func (c *Core) ReadFrom(p []byte) (n int, from net.Addr, err error) {
-	buf := make([]byte, c.PacketConn.MTU())
+	buf := allocBytes(int(c.PacketConn.MTU()))
+	defer freeBytes(buf)
 	for {
 		bs := buf
 		n, from, err = c.PacketConn.ReadFrom(bs)
@@ -217,7 +218,8 @@ func (c *Core) ReadFrom(p []byte) (n int, from net.Addr, err error) {
 }
 
 func (c *Core) WriteTo(p []byte, addr net.Addr) (n int, err error) {
-	buf := make([]byte, 0, 65535)
+	buf := allocBytes(0)
+	defer freeBytes(buf)
 	buf = append(buf, typeSessionTraffic)
 	buf = append(buf, p...)
 	n, err = c.PacketConn.WriteTo(buf, addr)

src/core/pool.go

@@ -0,0 +1,17 @@
+package core
+
+import "sync"
+
+var bytePool = sync.Pool{New: func() interface{} { return []byte(nil) }}
+
+func allocBytes(size int) []byte {
+	bs := bytePool.Get().([]byte)
+	if cap(bs) < size {
+		bs = make([]byte, size)
+	}
+	return bs[:size]
+}
+
+func freeBytes(bs []byte) {
+	bytePool.Put(bs[:0])
+}