Add packet capture to debug bundle and CLI

client/firewall/uspfilter/filter.go

@@ -115,12 +115,13 @@ type Manager struct {
 
 	localipmanager *localIPManager
 
-	udpTracker  *conntrack.UDPTracker
-	icmpTracker *conntrack.ICMPTracker
-	tcpTracker  *conntrack.TCPTracker
-	forwarder   atomic.Pointer[forwarder.Forwarder]
-	logger      *nblog.Logger
-	flowLogger  nftypes.FlowLogger
+	udpTracker     *conntrack.UDPTracker
+	icmpTracker    *conntrack.ICMPTracker
+	tcpTracker     *conntrack.TCPTracker
+	forwarder      atomic.Pointer[forwarder.Forwarder]
+	pendingCapture atomic.Pointer[forwarder.PacketCapture]
+	logger         *nblog.Logger
+	flowLogger     nftypes.FlowLogger
 
 	blockRule firewall.Rule
 
@@ -351,6 +352,19 @@ func (m *Manager) determineRouting() error {
 	return nil
 }
 
+// SetPacketCapture sets or clears packet capture on the forwarder endpoint.
+// This captures outbound response packets that bypass the FilteredDevice in netstack mode.
+func (m *Manager) SetPacketCapture(pc forwarder.PacketCapture) {
+	if pc == nil {
+		m.pendingCapture.Store(nil)
+	} else {
+		m.pendingCapture.Store(&pc)
+	}
+	if fwder := m.forwarder.Load(); fwder != nil {
+		fwder.SetCapture(pc)
+	}
+}
+
 // initForwarder initializes the forwarder, it disables routing on errors
 func (m *Manager) initForwarder() error {
 	if m.forwarder.Load() != nil {
@@ -370,6 +384,10 @@ func (m *Manager) initForwarder() error {
 		return fmt.Errorf("create forwarder: %w", err)
 	}
 
+	if pc := m.pendingCapture.Load(); pc != nil {
+		forwarder.SetCapture(*pc)
+	}
+
 	m.forwarder.Store(forwarder)
 
 	log.Debug("forwarder initialized")
@@ -614,6 +632,7 @@ func (m *Manager) resetState() {
 	}
 
 	if fwder := m.forwarder.Load(); fwder != nil {
+		fwder.SetCapture(nil)
 		fwder.Stop()
 	}
 

client/firewall/uspfilter/forwarder/endpoint.go

@@ -12,12 +12,19 @@ import (
 	nblog "github.com/netbirdio/netbird/client/firewall/uspfilter/log"
 )
 
+// PacketCapture captures raw packets for debugging. Implementations must be
+// safe for concurrent use and must not block.
+type PacketCapture interface {
+	Offer(data []byte, outbound bool)
+}
+
 // endpoint implements stack.LinkEndpoint and handles integration with the wireguard device
 type endpoint struct {
 	logger     *nblog.Logger
 	dispatcher stack.NetworkDispatcher
 	device     *wgdevice.Device
 	mtu        atomic.Uint32
+	capture    atomic.Pointer[PacketCapture]
 }
 
 func (e *endpoint) Attach(dispatcher stack.NetworkDispatcher) {
@@ -54,13 +61,17 @@ func (e *endpoint) WritePackets(pkts stack.PacketBufferList) (int, tcpip.Error)
 			continue
 		}
 
-		// Send the packet through WireGuard
+		pktBytes := data.AsSlice()
+
 		address := netHeader.DestinationAddress()
-		err := e.device.CreateOutboundPacket(data.AsSlice(), address.AsSlice())
-		if err != nil {
+		if err := e.device.CreateOutboundPacket(pktBytes, address.AsSlice()); err != nil {
 			e.logger.Error1("CreateOutboundPacket: %v", err)
 			continue
 		}
+
+		if pc := e.capture.Load(); pc != nil {
+			(*pc).Offer(pktBytes, true)
+		}
 		written++
 	}
 

client/firewall/uspfilter/forwarder/forwarder.go

@@ -139,6 +139,16 @@ func New(iface common.IFaceMapper, logger *nblog.Logger, flowLogger nftypes.Flow
 	return f, nil
 }
 
+// SetCapture sets or clears the packet capture on the forwarder endpoint.
+// This captures outbound packets that bypass the FilteredDevice (netstack forwarding).
+func (f *Forwarder) SetCapture(pc PacketCapture) {
+	if pc == nil {
+		f.endpoint.capture.Store(nil)
+		return
+	}
+	f.endpoint.capture.Store(&pc)
+}
+
 func (f *Forwarder) InjectIncomingPacket(payload []byte) error {
 	if len(payload) < header.IPv4MinimumSize {
 		return fmt.Errorf("packet too small: %d bytes", len(payload))

client/firewall/uspfilter/forwarder/icmp.go

@@ -270,5 +270,9 @@ func (f *Forwarder) injectICMPReply(id stack.TransportEndpointID, icmpPayload []
 		return 0
 	}
 
+	if pc := f.endpoint.capture.Load(); pc != nil {
+		(*pc).Offer(fullPacket, true)
+	}
+
 	return len(fullPacket)
 }