fix(pcap): add pcap filters

internal/qol/capture/pcap.go

@@ -3,7 +3,9 @@ package capture
 import (
 	"context"
 	"fmt"
+	"net"
 	"os"
+	"strings"
 	"sync"
 
 	"github.com/google/gopacket"
@@ -19,12 +21,91 @@ type PacketCapture struct {
 	err    error
 }
 
-func NewPacketCapture(iface, outputPath string) (*PacketCapture, error) {
+func getLocalIPs() ([]string, error) {
+	var localIPs []string
+	
+	addrs, err := net.InterfaceAddrs()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get network interfaces: %w", err)
+	}
+	
+	for _, addr := range addrs {
+		var ip net.IP
+		switch v := addr.(type) {
+		case *net.IPNet:
+			ip = v.IP
+		case *net.IPAddr:
+			ip = v.IP
+		}
+		
+		// Skip loopback
+		if ip == nil || ip.IsLoopback() {
+			continue
+		}
+		
+		localIPs = append(localIPs, ip.String())
+	}
+	
+	if len(localIPs) == 0 {
+		return nil, fmt.Errorf("no non-loopback IPs found")
+	}
+	
+	return localIPs, nil
+}
+
+func buildBPFFilter(protocol string, localIPs []string) string {
+	// Build filter for this machine's IPs
+	var hostFilters []string
+	for _, ip := range localIPs {
+		hostFilters = append(hostFilters, fmt.Sprintf("host %s", ip))
+	}
+	testMachineFilter := "(" + strings.Join(hostFilters, " or ") + ")"
+	
+	// Protocol-specific ports
+	var portFilter string
+	switch strings.ToLower(protocol) {
+	case "udp":
+		portFilter = "(port 53)"
+	case "tls", "dot":
+		portFilter = "(port 53 or port 853)"
+	case "https", "doh":
+		portFilter = "(port 53 or port 443)"
+	case "doq":
+		portFilter = "(port 53 or port 853)"
+	case "doh3":
+		portFilter = "(port 53 or port 443)"
+	default:
+		portFilter = "(port 53 or port 443 or port 853)"
+	}
+	
+	// Exclude private-to-private traffic (LAN-to-LAN, includes Docker ranges)
+	privateExclude := "not (src net (10.0.0.0/8 or 172.16.0.0/12 or 192.168.0.0/16) and dst net (10.0.0.0/8 or 172.16.0.0/12 or 192.168.0.0/16))"
+	
+	// Combine: test machine AND protocol ports AND NOT (private to private)
+	return testMachineFilter + " and " + portFilter + " and " + privateExclude
+}
+
+func NewPacketCapture(iface, outputPath, protocol string) (*PacketCapture, error) {
 	handle, err := pcap.OpenLive(iface, 65535, true, pcap.BlockForever)
 	if err != nil {
 		return nil, fmt.Errorf("pcap open (try running as root): %w", err)
 	}
 
+	// Get local IPs dynamically
+	localIPs, err := getLocalIPs()
+	if err != nil {
+		handle.Close()
+		return nil, fmt.Errorf("failed to get local IPs: %w", err)
+	}
+
+	// Build and apply BPF filter
+	bpfFilter := buildBPFFilter(protocol, localIPs)
+	
+	if err := handle.SetBPFFilter(bpfFilter); err != nil {
+		handle.Close()
+		return nil, fmt.Errorf("failed to set BPF filter '%s': %w", bpfFilter, err)
+	}
+
 	file, err := os.Create(outputPath)
 	if err != nil {
 		handle.Close()