ipn,net,tsnet,wgengine: make an eventbus mandatory where it is used (#16594)

In the components where an event bus is already plumbed through, remove the
exceptions that allow it to be omitted, and update all the tests that relied on
those workarounds execute properly.

This change applies only to the places where we're already using the bus; it
does not enforce the existence of a bus in other components (yet),

Updates #15160

Change-Id: Iebb92243caba82b5eb420c49fc3e089a77454f65
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>

net/portmapper/igd_test.go

@@ -263,16 +263,21 @@ func (d *TestIGD) handlePCPQuery(pkt []byte, src netip.AddrPort) {
 }
 
 // newTestClient configures a new test client connected to igd for mapping updates.
-// If bus != nil, update events are published to it.
-// A cleanup for the resulting client is added to t.
+// If bus == nil, a new empty event bus is constructed that is cleaned up when t exits.
+// A cleanup for the resulting client is also added to t.
 func newTestClient(t *testing.T, igd *TestIGD, bus *eventbus.Bus) *Client {
+	if bus == nil {
+		bus = eventbus.New()
+		t.Log("Created empty event bus for test client")
+		t.Cleanup(bus.Close)
+	}
 	var c *Client
 	c = NewClient(Config{
 		Logf:         tstest.WhileTestRunningLogger(t),
 		NetMon:       netmon.NewStatic(),
 		ControlKnobs: new(controlknobs.Knobs),
 		EventBus:     bus,
-		OnChange: func() {
+		OnChange: func() { // TODO(creachadair): Remove.
 			t.Logf("port map changed")
 			t.Logf("have mapping: %v", c.HaveMapping())
 		},

net/portmapper/portmapper.go

@@ -85,7 +85,7 @@ const trustServiceStillAvailableDuration = 10 * time.Minute
 
 // Client is a port mapping client.
 type Client struct {
-	// The following two fields must either both be nil, or both non-nil.
+	// The following two fields must both be non-nil.
 	// Both are immutable after construction.
 	pubClient *eventbus.Client
 	updates   *eventbus.Publisher[Mapping]
@@ -238,8 +238,11 @@ type Config struct {
 // NewClient constructs a new portmapping [Client] from c. It will panic if any
 // required parameters are omitted.
 func NewClient(c Config) *Client {
-	if c.NetMon == nil {
-		panic("nil netMon")
+	switch {
+	case c.NetMon == nil:
+		panic("nil NetMon")
+	case c.EventBus == nil:
+		panic("nil EventBus")
 	}
 	ret := &Client{
 		logf:         c.Logf,
@@ -248,10 +251,8 @@ func NewClient(c Config) *Client {
 		onChange:     c.OnChange,
 		controlKnobs: c.ControlKnobs,
 	}
-	if c.EventBus != nil {
-		ret.pubClient = c.EventBus.Client("portmapper")
-		ret.updates = eventbus.Publish[Mapping](ret.pubClient)
-	}
+	ret.pubClient = c.EventBus.Client("portmapper")
+	ret.updates = eventbus.Publish[Mapping](ret.pubClient)
 	if ret.logf == nil {
 		ret.logf = logger.Discard
 	}
@@ -286,10 +287,9 @@ func (c *Client) Close() error {
 	}
 	c.closed = true
 	c.invalidateMappingsLocked(true)
-	if c.updates != nil {
-		c.updates.Close()
-		c.pubClient.Close()
-	}
+	c.updates.Close()
+	c.pubClient.Close()
+
 	// TODO: close some future ever-listening UDP socket(s),
 	// waiting for multicast announcements from router.
 	return nil
@@ -515,14 +515,14 @@ func (c *Client) createMapping() {
 		// the control flow to eliminate that possibility. Meanwhile, this
 		// mitigates a panic downstream, cf. #16662.
 	}
-	if c.updates != nil {
-		c.updates.Publish(Mapping{
-			External:  mapping.External(),
-			Type:      mapping.MappingType(),
-			GoodUntil: mapping.GoodUntil(),
-		})
-	}
-	if c.onChange != nil && c.pubClient == nil {
+	c.updates.Publish(Mapping{
+		External:  mapping.External(),
+		Type:      mapping.MappingType(),
+		GoodUntil: mapping.GoodUntil(),
+	})
+	// TODO(creachadair): Remove this entirely once there are no longer any
+	// places where the callback is set.
+	if c.onChange != nil {
 		go c.onChange()
 	}
 }

net/udprelay/server.go

@@ -291,6 +291,9 @@ func NewServer(logf logger.Logf, port int, overrideAddrs []netip.Addr) (s *Serve
 		s.vniPool = append(s.vniPool, uint32(i))
 	}
 
+	// TODO(creachadair): Find a way to plumb this in during initialization.
+	// As-written, messages published here will not be seen by other components
+	// in a running client.
 	bus := eventbus.New()
 	s.bus = bus
 	netMon, err := netmon.New(s.bus, logf)