Add loop to analyze ethernet packets further; add basic DNS packet analyzer

src/ethernet/dns.go

@@ -0,0 +1,50 @@
+package ethernet
+
+import (
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+	"log"
+)
+
+var (
+	numQuestions int
+	numAnswers int
+)
+
+// Called on every DNS packet
+func processDNSPacket(packet gopacket.Packet) error {
+	var dnspacket layers.DNS
+
+	// Decode raw packet into DNS
+	decodeErr := dnspacket.DecodeFromBytes(packet.ApplicationLayer().LayerContents(), gopacket.NilDecodeFeedback)
+	if decodeErr != nil {
+		// Encountered an error during decoding, most likely a broken packet
+		return decodeErr
+	}
+
+	// Further process the packet
+	processDNSQuestion(dnspacket.Questions)
+	processDNSAnswers(dnspacket.Answers)
+
+	// No error encountered, return clean
+	return nil
+}
+
+// Called on every DNS packet to process questions
+func processDNSQuestion(questions []layers.DNSQuestion) {
+	for _, _ = range questions {
+		numQuestions++
+	}
+}
+
+// Called on every DNS packet to process response(s)
+func processDNSAnswers(answers []layers.DNSResourceRecord) {
+	for _, _ = range answers {
+		numAnswers++
+	}
+}
+
+// Print a summary after all packets were processed
+func printDNSSummary() {
+	log.Printf("%d DNS Questions, %d DNS Answers in total", numQuestions, numAnswers)
+}

src/ethernet/ethernet.go

@@ -1,8 +1,42 @@
 package ethernet
 
-import "github.com/google/gopacket"
+import (
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+	"log"
+)
 
 func Analyze(source *gopacket.PacketSource) error {
-	// Dummy
+	// Loop over all packets now
+	for {
+		packet, packetErr := source.NextPacket()
+		if packet == nil {
+			// We iterated over all packets, we're done here
+			break
+		} else if packetErr != nil {
+			// encountered some problem, report it
+			log.Printf("Encountered a problem with a packet: %s", packetErr.Error())
+			continue
+		}
+
+		// Check if we can do some Application Layer statistics with this packet
+		if packet.ApplicationLayer() != nil {
+			// We can, switch over the type
+			switch packet.ApplicationLayer().LayerType() {
+			case layers.LayerTypeDNS:
+				// Handle DNS packet
+				processDNSPacket(packet)
+			}
+		}
+	}
+
+	// After processing all packets, print summary
+	printSummary()
+
 	return nil
 }
+
+// Prints all the summaries.
+func printSummary() {
+	printDNSSummary()
+}