tstest/natlab: get tailscaled logs from gokrazy via syslog

Using https://github.com/gokrazy/gokrazy/pull/275

This is much lower latency than logcatcher, which is higher latency
and chunkier. And this is better than getting it via 'tailscale debug
daemon-logs', which misses early interesting logs.

Updates #13038

Change-Id: I499ec254c003a9494c0e9910f9c650c8ac44ef33
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tstest/natlab/vnet/conf.go

@@ -73,9 +73,12 @@ func (c *Config) AddNode(opts ...any) *Node {
 		case TailscaledEnv:
 			n.env = append(n.env, o)
 		case NodeOption:
-			if o == HostFirewall {
+			switch o {
+			case HostFirewall:
 				n.hostFW = true
-			} else {
+			case VerboseSyslog:
+				n.verboseSyslog = true
+			default:
 				if n.err == nil {
 					n.err = fmt.Errorf("unknown NodeOption %q", o)
 				}
@@ -93,7 +96,8 @@ func (c *Config) AddNode(opts ...any) *Node {
 type NodeOption string
 
 const (
-	HostFirewall NodeOption = "HostFirewall"
+	HostFirewall  NodeOption = "HostFirewall"
+	VerboseSyslog NodeOption = "VerboseSyslog"
 )
 
 // TailscaledEnv is а option that can be passed to Config.AddNode
@@ -148,8 +152,9 @@ type Node struct {
 	err error
 	n   *node // nil until NewServer called
 
-	env    []TailscaledEnv
-	hostFW bool
+	env           []TailscaledEnv
+	hostFW        bool
+	verboseSyslog bool
 
 	// TODO(bradfitz): this is halfway converted to supporting multiple NICs
 	// but not done. We need a MAC-per-Network.
@@ -171,6 +176,14 @@ func (n *Node) HostFirewall() bool {
 	return n.hostFW
 }
 
+func (n *Node) VerboseSyslog() bool {
+	return n.verboseSyslog
+}
+
+func (n *Node) SetVerboseSyslog(v bool) {
+	n.verboseSyslog = v
+}
+
 // Network returns the first network this node is connected to,
 // or nil if none.
 func (n *Node) Network() *Network {
@@ -277,8 +290,9 @@ func (s *Server) initFromConfig(c *Config) error {
 			return conf.err
 		}
 		n := &node{
-			mac: conf.mac,
-			net: netOfConf[conf.Network()],
+			mac:           conf.mac,
+			net:           netOfConf[conf.Network()],
+			verboseSyslog: conf.VerboseSyslog(),
 		}
 		n.interfaceID = must.Get(s.pcapWriter.AddInterface(pcapgo.NgInterface{
 			Name:     fmt.Sprintf("node%d", i+1),

tstest/natlab/vnet/vnet.go

@@ -397,10 +397,10 @@ func (n *network) serveLogCatcherConn(clientRemoteIP netip.Addr, c net.Conn) {
 		if node != nil {
 			node.logMu.Lock()
 			defer node.logMu.Unlock()
+			node.logCatcherWrites++
 			for _, lg := range logs {
 				tStr := lg.Logtail.Client_Time.Round(time.Millisecond).Format(time.RFC3339Nano)
 				fmt.Fprintf(&node.logBuf, "[%v] %s\n", tStr, lg.Text)
-				log.Printf("LOG %v [%v] %s\n", clientRemoteIP, tStr, lg.Text)
 			}
 		}
 	})
@@ -416,6 +416,7 @@ var (
 	fakeDERP1IP             = netip.AddrFrom4([4]byte{33, 4, 0, 1})  // 3340=DERP; 1=derp 1
 	fakeDERP2IP             = netip.AddrFrom4([4]byte{33, 4, 0, 2})  // 3340=DERP; 1=derp 1
 	fakeLogCatcherIP        = netip.AddrFrom4([4]byte{52, 52, 0, 4})
+	fakeSyslogIP            = netip.AddrFrom4([4]byte{52, 52, 0, 9})
 )
 
 type EthernetPacket struct {
@@ -501,16 +502,18 @@ func (n *network) MACOfIP(ip netip.Addr) (_ MAC, ok bool) {
 }
 
 type node struct {
-	mac         MAC
-	interfaceID int
-	net         *network
-	lanIP       netip.Addr // must be in net.lanIP prefix + unique in net
+	mac           MAC
+	interfaceID   int
+	net           *network
+	lanIP         netip.Addr // must be in net.lanIP prefix + unique in net
+	verboseSyslog bool
 
 	// logMu guards logBuf.
 	// TODO(bradfitz): conditionally write these out to separate files at the end?
 	// Currently they only hold logcatcher logs.
-	logMu  sync.Mutex
-	logBuf bytes.Buffer
+	logMu            sync.Mutex
+	logBuf           bytes.Buffer
+	logCatcherWrites int
 }
 
 type derpServer struct {
@@ -1007,6 +1010,19 @@ func (n *network) HandleEthernetIPv4PacketForRouter(ep EthernetPacket) {
 		return
 	}
 
+	if isUDP && dstIP == fakeSyslogIP {
+		node, ok := n.nodesByIP[srcIP]
+		if !ok {
+			return
+		}
+		if node.verboseSyslog {
+			// TODO(bradfitz): parse this and capture it, structured, into
+			// node's log buffer.
+			log.Printf("syslog from %v: %s", srcIP, udp.Payload)
+		}
+		return
+	}
+
 	if !toForward && isNATPMP(packet) {
 		n.handleNATPMPRequest(UDPPacket{
 			Src:     netip.AddrPortFrom(srcIP, uint16(udp.SrcPort)),