add lneto.Validator type for frame validation

examples/stack/main.go

@@ -0,0 +1,77 @@
+package main
+
+import (
+	"errors"
+	"io"
+
+	"github.com/soypat/lneto"
+)
+
+func main() {
+
+}
+
+type LinkStack struct {
+	mac [6]byte
+	mtu uint16
+}
+
+func (ls *LinkStack) RecvEth(ethFrame []byte) (err error) {
+	eframe, err := lneto.NewEthFrame(ethFrame)
+	if err != nil {
+		return err
+	}
+	if !eframe.IsBroadcast() && ls.mac != *eframe.DestinationHardwareAddr() {
+		return errors.New("packet MAC mismatch")
+	}
+
+	// Convert to dynamic handling.
+	etype := eframe.EtherTypeOrSize()
+	if etype != lneto.EtherTypeARP && etype != lneto.EtherTypeIPv4 && etype != lneto.EtherTypeIPv6 {
+		return nil
+	}
+
+	return nil
+}
+
+func (ls *LinkStack) HandleEth(dst []byte) (n int, err error) {
+	if len(dst) < int(ls.mtu) {
+		return 0, io.ErrShortBuffer
+	}
+	n, addr, etype, err := ls.handleUpper(dst[14:])
+	if err != nil || n == 0 {
+		return 0, err
+	}
+	eframe, _ := lneto.NewEthFrame(dst[:14])
+	*eframe.DestinationHardwareAddr() = addr
+	*eframe.SourceHardwareAddr() = ls.mac
+	eframe.SetEtherType(etype)
+	return 14 + n, nil
+}
+
+func (ls *LinkStack) handleUpper(dst []byte) (n int, dstAddr [6]byte, etype lneto.EtherType, err error) {
+	return
+}
+
+type IPv4Stack struct {
+	ip        [4]byte
+	mtu       uint16
+	validator lneto.Validator
+}
+
+func (is *IPv4Stack) Recv(ipframe []byte) error {
+	iframe, err := lneto.NewIPv4Frame(ipframe)
+	if err != nil {
+		return err
+	}
+	if *iframe.DestinationAddr() != is.ip {
+		return errors.New("packet not for us")
+	}
+	iframe.Validate(&is.validator)
+	err = is.validator.Err()
+	if err != nil {
+		return err
+	}
+	return nil
+
+}