initial commit

waterutil/tap.go

@@ -0,0 +1,40 @@
+package waterutil
+
+import (
+	"net"
+)
+
+type Tagging int
+
+// Indicating whether/how a MAC frame is tagged. The value is number of bytes taken by tagging.
+const (
+	NotTagged    Tagging = 0
+	Tagged       Tagging = 4
+	DoubleTagged Tagging = 8
+)
+
+func MACDestination(macFrame []byte) net.HardwareAddr {
+	return net.HardwareAddr(macFrame[:6])
+}
+
+func MACSource(macFrame []byte) net.HardwareAddr {
+	return net.HardwareAddr(macFrame[6:12])
+}
+
+func MACTagging(macFrame []byte) Tagging {
+	if macFrame[12] == 0x81 && macFrame[13] == 0x00 {
+		return Tagged
+	} else if macFrame[12] == 0x88 && macFrame[13] == 0xa8 {
+		return DoubleTagged
+	}
+	return NotTagged
+}
+
+func MACEthertype(macFrame []byte) Ethertype {
+	ethertypePos := 12 + MACTagging(macFrame)
+	return Ethertype{macFrame[ethertypePos], macFrame[ethertypePos+1]}
+}
+
+func MACPayload(macFrame []byte) []byte {
+	return macFrame[12+MACTagging(macFrame)+2:]
+}