Add support for (optional) population of packet type in afpacket via …

…ancillary data (#1)

afpacket/afpacket.go

@@ -57,6 +57,13 @@ type AncillaryVLAN struct {
 	VLAN int
 }
 
+// AncillaryPktType structures are used to pass the packet type
+// as ancillary data via CaptureInfo.
+type AncillaryPktType struct {
+	// The packet type provided by the kernel.
+	Type uint8
+}
+
 // Stats is a set of counters detailing the work TPacket has done so far.
 type Stats struct {
 	// Packets is the total number of packets returned to the caller.
@@ -293,10 +300,11 @@ func (h *TPacket) releaseCurrentPacket() error {
 // to old bytes when using ZeroCopyReadPacketData... if you need to keep data past
 // the next time you call ZeroCopyReadPacketData, use ReadPacketData, which copies
 // the bytes into a new buffer for you.
-//  tp, _ := NewTPacket(...)
-//  data1, _, _ := tp.ZeroCopyReadPacketData()
-//  // do everything you want with data1 here, copying bytes out of it if you'd like to keep them around.
-//  data2, _, _ := tp.ZeroCopyReadPacketData()  // invalidates bytes in data1
+//
+//	tp, _ := NewTPacket(...)
+//	data1, _, _ := tp.ZeroCopyReadPacketData()
+//	// do everything you want with data1 here, copying bytes out of it if you'd like to keep them around.
+//	data2, _, _ := tp.ZeroCopyReadPacketData()  // invalidates bytes in data1
 func (h *TPacket) ZeroCopyReadPacketData() (data []byte, ci gopacket.CaptureInfo, err error) {
 	h.mu.Lock()
 retry:
@@ -324,6 +332,9 @@ retry:
 	if vlan >= 0 {
 		ci.AncillaryData = append(ci.AncillaryData, AncillaryVLAN{vlan})
 	}
+	if h.opts.addPktType {
+		ci.AncillaryData = append(ci.AncillaryData, AncillaryPktType{h.current.getPktType()})
+	}
 	atomic.AddInt64(&h.stats.Packets, 1)
 	h.headerNextNeeded = true
 	h.mu.Unlock()

afpacket/header.go

@@ -4,6 +4,7 @@
 // that can be found in the LICENSE file in the root of the source
 // tree.
 
+//go:build linux
 // +build linux
 
 package afpacket
@@ -45,6 +46,8 @@ type header interface {
 	// getIfaceIndex returns the index of the network interface
 	// where the packet was seen. The index can later be translated to a name.
 	getIfaceIndex() int
+	// getPktType returns the packet type
+	getPktType() uint8
 	// getVLAN returns the VLAN of a packet if it was provided out-of-band
 	getVLAN() int
 	// next moves this header to point to the next packet it contains,
@@ -103,6 +106,10 @@ func (h *v1header) getIfaceIndex() int {
 	ll := (*C.struct_sockaddr_ll)(unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(tpAlign(int(C.sizeof_struct_tpacket_hdr)))))
 	return int(ll.sll_ifindex)
 }
+func (h *v1header) getPktType() uint8 {
+	ll := (*C.struct_sockaddr_ll)(unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(tpAlign(int(C.sizeof_struct_tpacket_hdr)))))
+	return uint8(ll.sll_pkttype)
+}
 func (h *v1header) next() bool {
 	return false
 }
@@ -130,6 +137,10 @@ func (h *v2header) getIfaceIndex() int {
 	ll := (*C.struct_sockaddr_ll)(unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(tpAlign(int(C.sizeof_struct_tpacket2_hdr)))))
 	return int(ll.sll_ifindex)
 }
+func (h *v2header) getPktType() uint8 {
+	ll := (*C.struct_sockaddr_ll)(unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(tpAlign(int(C.sizeof_struct_tpacket2_hdr)))))
+	return uint8(ll.sll_pkttype)
+}
 func (h *v2header) next() bool {
 	return false
 }
@@ -178,6 +189,10 @@ func (w *v3wrapper) getIfaceIndex() int {
 	ll := (*C.struct_sockaddr_ll)(unsafe.Pointer(uintptr(unsafe.Pointer(w.packet)) + uintptr(tpAlign(int(C.sizeof_struct_tpacket3_hdr)))))
 	return int(ll.sll_ifindex)
 }
+func (w *v3wrapper) getPktType() uint8 {
+	ll := (*C.struct_sockaddr_ll)(unsafe.Pointer(uintptr(unsafe.Pointer(w.packet)) + uintptr(tpAlign(int(C.sizeof_struct_tpacket3_hdr)))))
+	return uint8(ll.sll_pkttype)
+}
 func (w *v3wrapper) next() bool {
 	w.used++
 	if w.used >= w.blockhdr.num_pkts {

afpacket/options.go

@@ -4,6 +4,7 @@
 // that can be found in the LICENSE file in the root of the source
 // tree.
 
+//go:build linux
 // +build linux
 
 package afpacket
@@ -106,6 +107,10 @@ type OptPollTimeout time.Duration
 // be provided if available.
 type OptAddVLANHeader bool
 
+// OptAddPktType enables extraction / population of the packet type as reported by the
+// kernel via the AncillaryPktType struct in CaptureInfo.AncillaryData
+type OptAddPktType bool
+
 // Default constants used by options.
 const (
 	DefaultFrameSize    = 4096                   // Default value for OptFrameSize.
@@ -121,6 +126,7 @@ type options struct {
 	blockSize      int
 	numBlocks      int
 	addVLANHeader  bool
+	addPktType     bool
 	blockTimeout   time.Duration
 	pollTimeout    time.Duration
 	version        OptTPacketVersion
@@ -160,6 +166,8 @@ func parseOptions(opts ...interface{}) (ret options, err error) {
 			ret.socktype = v
 		case OptAddVLANHeader:
 			ret.addVLANHeader = bool(v)
+		case OptAddPktType:
+			ret.addPktType = bool(v)
 		default:
 			err = errors.New("unknown type in options")
 			return