up

internal/fingerprint/packet.go

@@ -0,0 +1,38 @@
+package fingerprint
+
+import (
+	"net"
+
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+)
+
+// BuildSYNPacket creates a minimal TCP SYN packet for the given source and destination ports.
+// The packet is not sent; it is used only to demonstrate integration with gopacket.
+func BuildSYNPacket(srcIP string, dstIP string, srcPort, dstPort uint16) ([]byte, error) {
+	ip := &layers.IPv4{
+		SrcIP:    net.ParseIP(srcIP).To4(),
+		DstIP:    net.ParseIP(dstIP).To4(),
+		Version:  4,
+		Protocol: layers.IPProtocolTCP,
+	}
+	tcp := &layers.TCP{
+		SrcPort: layers.TCPPort(srcPort),
+		DstPort: layers.TCPPort(dstPort),
+		SYN:     true,
+		Seq:     1105024978,
+		Window:  14600,
+	}
+	if err := tcp.SetNetworkLayerForChecksum(ip); err != nil {
+		return nil, err
+	}
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{
+		FixLengths:       true,
+		ComputeChecksums: true,
+	}
+	if err := gopacket.SerializeLayers(buf, opts, ip, tcp); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}