net/sockstats: remove explicit dependency on wgengine/monitor

Followup to #7177 to avoid adding extra dependencies to the CLI. We
instead declare an interface for the link monitor.

Signed-off-by: Mihai Parparita <mihai@tailscale.com>

cmd/derper/depaware.txt

@@ -12,7 +12,7 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
         github.com/golang/groupcache/lru                             from tailscale.com/net/dnscache
         github.com/hdevalence/ed25519consensus                       from tailscale.com/tka
    L    github.com/josharian/native                                  from github.com/mdlayher/netlink+
-   L 💣 github.com/jsimonetti/rtnetlink                              from tailscale.com/net/interfaces+
+   L 💣 github.com/jsimonetti/rtnetlink                              from tailscale.com/net/interfaces
    L    github.com/jsimonetti/rtnetlink/internal/unix                from github.com/jsimonetti/rtnetlink
         github.com/klauspost/compress/flate                          from nhooyr.io/websocket
    L 💣 github.com/mdlayher/netlink                                  from github.com/jsimonetti/rtnetlink+
@@ -85,14 +85,13 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
         tailscale.com/util/lineread                                  from tailscale.com/hostinfo+
         tailscale.com/util/mak                                       from tailscale.com/syncs+
         tailscale.com/util/multierr                                  from tailscale.com/health
-        tailscale.com/util/set                                       from tailscale.com/health+
+        tailscale.com/util/set                                       from tailscale.com/health
         tailscale.com/util/singleflight                              from tailscale.com/net/dnscache
         tailscale.com/util/vizerror                                  from tailscale.com/tsweb
    W 💣 tailscale.com/util/winutil                                   from tailscale.com/hostinfo+
         tailscale.com/version                                        from tailscale.com/derp+
         tailscale.com/version/distro                                 from tailscale.com/hostinfo+
         tailscale.com/wgengine/filter                                from tailscale.com/types/netmap
-        tailscale.com/wgengine/monitor                               from tailscale.com/net/sockstats
         golang.org/x/crypto/acme                                     from golang.org/x/crypto/acme/autocert
         golang.org/x/crypto/acme/autocert                            from tailscale.com/cmd/derper
         golang.org/x/crypto/argon2                                   from tailscale.com/tka

cmd/tailscale/depaware.txt

@@ -13,7 +13,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         github.com/google/uuid                                       from tailscale.com/util/quarantine+
         github.com/hdevalence/ed25519consensus                       from tailscale.com/tka
    L    github.com/josharian/native                                  from github.com/mdlayher/netlink+
-   L 💣 github.com/jsimonetti/rtnetlink                              from tailscale.com/net/interfaces+
+   L 💣 github.com/jsimonetti/rtnetlink                              from tailscale.com/net/interfaces
    L    github.com/jsimonetti/rtnetlink/internal/unix                from github.com/jsimonetti/rtnetlink
         github.com/kballard/go-shellquote                            from tailscale.com/cmd/tailscale/cli
         github.com/klauspost/compress/flate                          from nhooyr.io/websocket
@@ -127,7 +127,6 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/version/distro                                 from tailscale.com/cmd/tailscale/cli+
         tailscale.com/wgengine/capture                               from tailscale.com/cmd/tailscale/cli
         tailscale.com/wgengine/filter                                from tailscale.com/types/netmap
-        tailscale.com/wgengine/monitor                               from tailscale.com/net/sockstats
         golang.org/x/crypto/argon2                                   from tailscale.com/tka
         golang.org/x/crypto/blake2b                                  from golang.org/x/crypto/nacl/box+
         golang.org/x/crypto/blake2s                                  from tailscale.com/control/controlbase+

net/interfaces/interfaces.go

@@ -353,6 +353,12 @@ func (s *State) String() string {
 	return sb.String()
 }
 
+// ChangeFunc is a callback function (usually registered with
+// wgengine/monitor's Mon) that's called when the network
+// changed. The changed parameter is whether the network changed
+// enough for State to have changed since the last callback.
+type ChangeFunc func(changed bool, state *State)
+
 // An InterfaceFilter indicates whether EqualFiltered should use i when deciding whether two States are equal.
 // ips are all the IPPrefixes associated with i.
 type InterfaceFilter func(i Interface, ips []netip.Prefix) bool

net/sockstats/sockstats.go

@@ -11,7 +11,7 @@
 import (
 	"context"
 
-	"tailscale.com/wgengine/monitor"
+	"tailscale.com/net/interfaces"
 )
 
 type SockStats struct {
@@ -34,6 +34,13 @@ func Get() *SockStats {
 	return get()
 }
 
-func SetLinkMonitor(lm *monitor.Mon) {
+// LinkMonitor is the interface for the parts of wgengine/mointor's Mon that we
+// need, to avoid the dependency.
+type LinkMonitor interface {
+	InterfaceState() *interfaces.State
+	RegisterChangeCallback(interfaces.ChangeFunc) (unregister func())
+}
+
+func SetLinkMonitor(lm LinkMonitor) {
 	setLinkMonitor(lm)
 }

net/sockstats/sockstats_noop.go

@@ -7,8 +7,6 @@
 
 import (
 	"context"
-
-	"tailscale.com/wgengine/monitor"
 )
 
 func withSockStats(ctx context.Context, label string) context.Context {
@@ -19,5 +17,5 @@ func get() *SockStats {
 	return nil
 }
 
-func setLinkMonitor(lm *monitor.Mon) {
+func setLinkMonitor(lm LinkMonitor) {
 }

net/sockstats/sockstats_tsgo.go

@@ -13,7 +13,6 @@
 	"sync/atomic"
 
 	"tailscale.com/net/interfaces"
-	"tailscale.com/wgengine/monitor"
 )
 
 type sockStatCounters struct {
@@ -113,7 +112,7 @@ func get() *SockStats {
 	return r
 }
 
-func setLinkMonitor(lm *monitor.Mon) {
+func setLinkMonitor(lm LinkMonitor) {
 	sockStats.mu.Lock()
 	defer sockStats.mu.Unlock()
 

wgengine/monitor/monitor.go

@@ -48,12 +48,6 @@ type osMon interface {
 	IsInterestingInterface(iface string) bool
 }
 
-// ChangeFunc is a callback function that's called when the network
-// changed. The changed parameter is whether the network changed
-// enough for interfaces.State to have changed since the last
-// callback.
-type ChangeFunc func(changed bool, state *interfaces.State)
-
 // Mon represents a monitoring instance.
 type Mon struct {
 	logf   logger.Logf
@@ -62,7 +56,7 @@ type Mon struct {
 	stop   chan struct{} // closed on Stop
 
 	mu         sync.Mutex // guards all following fields
-	cbs        set.HandleSet[ChangeFunc]
+	cbs        set.HandleSet[interfaces.ChangeFunc]
 	ruleDelCB  set.HandleSet[RuleDeleteCallback]
 	ifState    *interfaces.State
 	gwValid    bool       // whether gw and gwSelfIP are valid
@@ -139,7 +133,7 @@ func (m *Mon) GatewayAndSelfIP() (gw, myIP netip.Addr, ok bool) {
 // RegisterChangeCallback adds callback to the set of parties to be
 // notified (in their own goroutine) when the network state changes.
 // To remove this callback, call unregister (or close the monitor).
-func (m *Mon) RegisterChangeCallback(callback ChangeFunc) (unregister func()) {
+func (m *Mon) RegisterChangeCallback(callback interfaces.ChangeFunc) (unregister func()) {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 	handle := m.cbs.Add(callback)