wintun: Auto-calculate TUN exchange buffer size

Signed-off-by: Simon Rozman <simon@rozman.si>

diff --git a/tun/tun_windows.go b/tun/tun_windows.go
index 57be3dcccff55591be43bb39172d7a11efc3be2d..0bfd8472033791586b7dee904a5f5281dbd0d185 100644 (file)
--- a/tun/tun_windows.go
+++ b/tun/tun_windows.go
@@ -18,7 +18,6 @@ import (
 const (
        packetSizeMax      = 1600
        packetExchangeMax  = 256 // Number of packets that can be exchanged at a time
-       exchangeBufferSize = 410632
 )
 
 const (
@@ -252,10 +251,10 @@ func (tun *nativeTun) Read(buff []byte, offset int) (int, error) {
                }
 
                // Fill queue.
-               data := (*[exchangeBufferSize]byte)(unsafe.Pointer(&tun.rdBuff))
-               n, err := tun.tunFile.Read(data[:])
+               const bufSize = int(unsafe.Sizeof(tun.rdBuff))
+               n, err := tun.tunFile.Read((*[bufSize]byte)(unsafe.Pointer(&tun.rdBuff))[:])
                tun.rdNextPacket = 0
-               if n != exchangeBufferSize || err != nil {
+               if n != bufSize || err != nil {
                        // TUN interface stopped, returned incomplete data, etc.
                        // Retry.
                        tun.rdBuff.numPackets = 0
@@ -269,14 +268,14 @@ func (tun *nativeTun) Read(buff []byte, offset int) (int, error) {
 
 func (tun *nativeTun) flush() error {
        // Flush write buffer.
-       data := (*[exchangeBufferSize]byte)(unsafe.Pointer(&tun.wrBuff))
-       n, err := tun.tunFile.Write(data[:])
+       const bufSize = int(unsafe.Sizeof(tun.wrBuff))
+       n, err := tun.tunFile.Write((*[bufSize]byte)(unsafe.Pointer(&tun.wrBuff))[:])
        tun.wrBuff.numPackets = 0
        if err != nil {
                return err
        }
-       if n != exchangeBufferSize {
-               return fmt.Errorf("%d byte(s) written, %d byte(s) expected", n, exchangeBufferSize)
+       if n != bufSize {
+               return fmt.Errorf("%d byte(s) written, %d byte(s) expected", n, bufSize)
        }
 
        return nil