wgengine: log connection metrics

Adds counter for connection types, which aren't currently bubbled up anywhere but can be easily
in the future.

Signed-off-by: julianknodt <julianknodt@gmail.com>

wgengine/magicsock/magicsock.go

@@ -190,6 +190,9 @@ type Conn struct {
 	// havePrivateKey is whether privateKey is non-zero.
 	havePrivateKey syncs.AtomicBool
 
+	// DERPCount is the number of DERP connections created.
+	DERPCount uint32
+
 	// port is the preferred port from opts.Port; 0 means auto.
 	port syncs.AtomicUint32
 
@@ -350,6 +353,7 @@ func (c *Conn) addDerpPeerRoute(peer key.Public, derpID int, dc *derphttp.Client
 	if c.derpRoute == nil {
 		c.derpRoute = make(map[key.Public]derpRoute)
 	}
+	atomic.AddUint32(&c.DERPCount, 1)
 	r := derpRoute{derpID, dc}
 	c.derpRoute[peer] = r
 }

wgengine/pendopen.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"runtime"
 	"strconv"
+	"sync/atomic"
 	"time"
 
 	"tailscale.com/ipn/ipnstate"
@@ -122,6 +123,9 @@ func (e *userspaceEngine) trackOpenPostFilterOut(pp *packet.Parsed, t *tstun.Wra
 		}
 	}
 
+	// Accepted a flow, log the flow kind
+	atomic.AddUint32(&e.connMetrics.direct, 1)
+
 	timer := time.AfterFunc(tcpTimeoutBeforeDebug, func() {
 		e.onOpenTimeout(flow)
 	})
@@ -153,6 +157,7 @@ func (e *userspaceEngine) onOpenTimeout(flow flowtrack.Tuple) {
 	e.mu.Unlock()
 
 	if !problem.IsZero() {
+		atomic.AddUint32(&e.connMetrics.unreachable, 1)
 		e.logf("open-conn-track: timeout opening %v; peer reported problem: %v", flow, problem)
 	}
 
@@ -160,14 +165,17 @@ func (e *userspaceEngine) onOpenTimeout(flow flowtrack.Tuple) {
 	n, err := e.peerForIP(flow.Dst.IP())
 	if err != nil {
 		e.logf("open-conn-track: timeout opening %v; peerForIP: %v", flow, err)
+		atomic.AddUint32(&e.connMetrics.unreachable, 1)
 		return
 	}
 	if n == nil {
 		e.logf("open-conn-track: timeout opening %v; no associated peer node", flow)
+		atomic.AddUint32(&e.connMetrics.unreachable, 1)
 		return
 	}
 	if n.DiscoKey.IsZero() {
 		e.logf("open-conn-track: timeout opening %v; peer node %v running pre-0.100", flow, n.Key.ShortString())
+		atomic.AddUint32(&e.connMetrics.unreachable, 1)
 		return
 	}
 	if n.DERP == "" {

wgengine/userspace.go

@@ -119,6 +119,8 @@ type userspaceEngine struct {
 	statusBufioReader   *bufio.Reader // reusable for UAPI
 	lastStatusPollTime  mono.Time     // last time we polled the engine status
 
+	connMetrics metrics // counts for success/failure/kinds of connections.
+
 	mu                  sync.Mutex         // guards following; see lock order comment below
 	netMap              *netmap.NetworkMap // or nil
 	closing             bool               // Close was called (even if we're still closing)
@@ -133,6 +135,19 @@ type userspaceEngine struct {
 	// Lock ordering: magicsock.Conn.mu, wgLock, then mu.
 }
 
+type metrics struct {
+	// offline is the number of flows magicsock attempted to connect to which are offline.
+	offline uint32
+	// relayed is the number of flows magicsock connected thru over DERP.
+	relayed uint32
+	// direct is the number of flows connected to directly.
+	direct uint32
+	// unreachable is the number of flows which were expected to be online but could not be
+	// connected to. This is expected to be small, as there is only a brief window where flows are
+	// offline but have not yet notified control.
+	unreachable uint32
+}
+
 // InternalsGetter is implemented by Engines that can export their internals.
 type InternalsGetter interface {
 	GetInternals() (_ *tstun.Wrapper, _ *magicsock.Conn, ok bool)