chore: add nodeUpdater to tailnet (#11539)

Adds a nodeUpdater component, which serves a similar role to configMaps, but tracks information from tailscale going out to the coordinator as node updates.  This first PR just handles netInfo, subsequent PRs will
handle DERP forced websockets, endpoints, and addresses.

tailnet/node_internal_test.go

@@ -0,0 +1,110 @@
+package tailnet
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/exp/maps"
+	"tailscale.com/tailcfg"
+	"tailscale.com/types/key"
+
+	"cdr.dev/slog"
+	"cdr.dev/slog/sloggers/slogtest"
+	"github.com/coder/coder/v2/testutil"
+)
+
+func TestNodeUpdater_setNetInfo_different(t *testing.T) {
+	t.Parallel()
+	ctx := testutil.Context(t, testutil.WaitShort)
+	logger := slogtest.Make(t, nil).Leveled(slog.LevelDebug)
+	id := tailcfg.NodeID(1)
+	nodeKey := key.NewNode().Public()
+	discoKey := key.NewDisco().Public()
+	nodeCh := make(chan *Node)
+	goCh := make(chan struct{})
+	uut := newNodeUpdater(
+		logger,
+		func(n *Node) {
+			nodeCh <- n
+			<-goCh
+		},
+		id, nodeKey, discoKey,
+	)
+	defer uut.close()
+
+	dl := map[string]float64{"1": 0.025}
+	uut.setNetInfo(&tailcfg.NetInfo{
+		PreferredDERP: 1,
+		DERPLatency:   dl,
+	})
+
+	node := testutil.RequireRecvCtx(ctx, t, nodeCh)
+	require.Equal(t, nodeKey, node.Key)
+	require.Equal(t, discoKey, node.DiscoKey)
+	require.Equal(t, 1, node.PreferredDERP)
+	require.True(t, maps.Equal(dl, node.DERPLatency))
+
+	// Send in second update to test getting updates in the middle of the
+	// callback
+	uut.setNetInfo(&tailcfg.NetInfo{
+		PreferredDERP: 2,
+		DERPLatency:   dl,
+	})
+	close(goCh) // allows callback to complete
+
+	node = testutil.RequireRecvCtx(ctx, t, nodeCh)
+	require.Equal(t, nodeKey, node.Key)
+	require.Equal(t, discoKey, node.DiscoKey)
+	require.Equal(t, 2, node.PreferredDERP)
+	require.True(t, maps.Equal(dl, node.DERPLatency))
+
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		uut.close()
+	}()
+	_ = testutil.RequireRecvCtx(ctx, t, done)
+}
+
+func TestNodeUpdater_setNetInfo_same(t *testing.T) {
+	t.Parallel()
+	ctx := testutil.Context(t, testutil.WaitShort)
+	logger := slogtest.Make(t, nil).Leveled(slog.LevelDebug)
+	id := tailcfg.NodeID(1)
+	nodeKey := key.NewNode().Public()
+	discoKey := key.NewDisco().Public()
+	nodeCh := make(chan *Node)
+	goCh := make(chan struct{})
+	uut := newNodeUpdater(
+		logger,
+		func(n *Node) {
+			nodeCh <- n
+			<-goCh
+		},
+		id, nodeKey, discoKey,
+	)
+	defer uut.close()
+
+	// Then: we don't configure
+	requireNeverConfigures(ctx, t, &uut.phased)
+
+	// Given: preferred DERP and latency already set
+	dl := map[string]float64{"1": 0.025}
+	uut.L.Lock()
+	uut.preferredDERP = 1
+	uut.derpLatency = maps.Clone(dl)
+	uut.L.Unlock()
+
+	// When: new update with same info
+	uut.setNetInfo(&tailcfg.NetInfo{
+		PreferredDERP: 1,
+		DERPLatency:   dl,
+	})
+
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		uut.close()
+	}()
+	_ = testutil.RequireRecvCtx(ctx, t, done)
+}