Don't check for unnecessary flags, fix potential bottleneck

pndp/NDPRequest.go

@@ -13,7 +13,7 @@ type ndpRequest struct {
 	answeringForIP []byte
 	dstIP          []byte
 	sourceIface    string
-	rawPacket      []byte
+	payload        []byte
 }
 
 type ndpQuestion struct {

pndp/listener.go

@@ -75,8 +75,8 @@ func listen(iface string, responder chan *ndpRequest, requestType ndpType, stopW
 		bpf.LoadAbsolute{Off: 54, Size: 1},
 		// Jump to the drop packet instruction if Type is not Neighbor Solicitation / Advertisement.
 		bpf.JumpIf{Cond: bpf.JumpNotEqual, Val: protocolNo, SkipTrue: 1},
-		// Verdict is: send up to 4096 bytes of the packet to userspace.
-		bpf.RetConstant{Val: 4096},
+		// Verdict is: send up to 86 bytes of the packet to userspace.
+		bpf.RetConstant{Val: 86},
 		// Verdict is: "ignore packet."
 		bpf.RetConstant{Val: 0},
 	}
@@ -87,12 +87,12 @@ func listen(iface string, responder chan *ndpRequest, requestType ndpType, stopW
 	}
 
 	for {
-		buf := make([]byte, 4096)
+		buf := make([]byte, 86)
 		numRead, err := syscall.Read(fd, buf)
 		if err != nil {
 			panic(err)
 		}
-		if numRead < 86 {
+		if numRead < 78 {
 			if GlobalDebug {
 				fmt.Println("Dropping packet since it does not meet the minimum length requirement")
 				fmt.Printf("% X\n", buf[:numRead])
@@ -115,8 +115,6 @@ func listen(iface string, responder chan *ndpRequest, requestType ndpType, stopW
 				fmt.Println("NDP Flags")
 				fmt.Printf("% X\n", buf[58])
 			}
-			fmt.Println("NDP MAC:")
-			fmt.Printf("% X\n", buf[80:86])
 			fmt.Println()
 		}
 
@@ -127,13 +125,22 @@ func listen(iface string, responder chan *ndpRequest, requestType ndpType, stopW
 			continue
 		}
 
+		if requestType == ndp_ADV {
+			if buf[58] == 0x0 {
+				if GlobalDebug {
+					fmt.Println("Dropping Advertisement packet without any NDP flags set")
+				}
+				continue
+			}
+		}
+
 		responder <- &ndpRequest{
 			requestType:    requestType,
 			srcIP:          buf[22:38],
 			dstIP:          buf[38:54],
 			answeringForIP: buf[62:78],
+			payload:        buf[54:],
 			sourceIface:    iface,
-			rawPacket:      buf[:numRead],
 		}
 	}
 }

pndp/packet.go

@@ -135,7 +135,7 @@ func checksumAddition(b []byte) uint32 {
 	for i := 0; i < len(b); i++ {
 		if i%2 == 0 {
 			if len(b)-1 == i {
-				sum += uint32(uint16(b[i])<<8 | uint16(0x0))
+				sum += uint32(uint16(b[i])<<8 | uint16(0x00))
 			} else {
 				sum += uint32(uint16(b[i])<<8 | uint16(b[i+1]))
 			}

pndp/responder.go

@@ -84,36 +84,11 @@ func respond(iface string, requests chan *ndpRequest, respondType ndpType, ndpQu
 			continue
 		}
 
-		if req.requestType == ndp_ADV {
-			if (req.rawPacket[78] != 0x02) || (req.rawPacket[79] != 0x01) {
-				if GlobalDebug {
-					fmt.Println("Dropping Advertisement packet without target Source address set")
-				}
-				continue
-			}
-			if req.rawPacket[58] == 0x0 {
-				if GlobalDebug {
-					fmt.Println("Dropping Advertisement packet without any NDP flags set")
-				}
-				continue
-			}
-		} else {
-			if (req.rawPacket[78] != 0x01) || (req.rawPacket[79] != 0x01) {
-				if GlobalDebug {
-					fmt.Println("Dropping Solicitation packet without Source address set")
-				}
-				continue
-			}
-		}
-
 		v6Header, err := newIpv6Header(req.srcIP, req.dstIP)
 		if err != nil {
 			continue
 		}
-		if !checkPacketChecksum(v6Header, req.rawPacket[54:]) {
-			if GlobalDebug {
-				fmt.Println("Dropping packet because of invalid checksum")
-			}
+		if !checkPacketChecksum(v6Header, req.payload) {
 			continue
 		}
 
@@ -216,23 +191,19 @@ func getAddressFromQuestionListRetry(targetIP []byte, ndpQuestionChan chan *ndpQ
 		return result, true
 	}
 
-	hasBuffered := true
 	gotBuffered := false
-	for hasBuffered {
-		select {
-		case q := <-ndpQuestionChan:
-			ndpQuestionsList = append(ndpQuestionsList, q)
-			gotBuffered = true
-		default:
-			hasBuffered = false
-		}
+	select {
+	case q := <-ndpQuestionChan:
+		ndpQuestionsList = append(ndpQuestionsList, q)
+		gotBuffered = true
+	default:
 	}
 
 	if gotBuffered {
 		result, success = getAddressFromQuestionList(targetIP, ndpQuestionsList)
 	}
 
-	return result, success
+	return nil, false
 }
 
 func getAddressFromQuestionList(targetIP []byte, ndpQuestionsList []*ndpQuestion) ([]byte, bool) {