appc,ipn/ipnlocal: Add split DNS entries for conn25 peers

If conn25 config is sent in the netmap: add split DNS entries to use appropriately tagged peers' PeerAPI to resolve DNS requests for those domains. This will enable future work where we use the peers as connectors for the configured domains. Updates tailscale/corp#34252 Signed-off-by: Fran Bull <fran@tailscale.com>
2026-01-14 11:53:14 -08:00
parent 1183f7a191
commit 9d13a6df9c
4 changed files with 298 additions and 0 deletions
@@ -4,10 +4,14 @@
 package appc

 import (
+	"encoding/json"
 	"net/netip"
+	"reflect"
 	"testing"

 	"tailscale.com/tailcfg"
+	"tailscale.com/types/appctype"
+	"tailscale.com/types/opt"
 )

 // TestHandleConnectorTransitIPRequestZeroLength tests that if sent a
@@ -186,3 +190,122 @@ func TestTransitIPTargetUnknownTIP(t *testing.T) {
 		t.Fatalf("Unknown transit addr, want: %v, got %v", want, got)
 	}
 }
+
+func TestPickSplitDNSPeers(t *testing.T) {
+	getBytesForAttr := func(name string, domains []string, tags []string) []byte {
+		attr := appctype.AppConnectorAttr{
+			Name:       name,
+			Domains:    domains,
+			Connectors: tags,
+		}
+		bs, err := json.Marshal(attr)
+		if err != nil {
+			t.Fatalf("test setup: %v", err)
+		}
+		return bs
+	}
+	appOneBytes := getBytesForAttr("app1", []string{"example.com"}, []string{"tag:one"})
+	appTwoBytes := getBytesForAttr("app2", []string{"a.example.com"}, []string{"tag:two"})
+	appThreeBytes := getBytesForAttr("app3", []string{"woo.b.example.com", "hoo.b.example.com"}, []string{"tag:three1", "tag:three2"})
+	appFourBytes := getBytesForAttr("app4", []string{"woo.b.example.com", "c.example.com"}, []string{"tag:four1", "tag:four2"})
+
+	makeNodeView := func(id tailcfg.NodeID, name string, tags []string) tailcfg.NodeView {
+		return (&tailcfg.Node{
+			ID:       id,
+			Name:     name,
+			Tags:     tags,
+			Hostinfo: (&tailcfg.Hostinfo{AppConnector: opt.NewBool(true)}).View(),
+		}).View()
+	}
+	nvp1 := makeNodeView(1, "p1", []string{"tag:one"})
+	nvp2 := makeNodeView(2, "p2", []string{"tag:four1", "tag:four2"})
+	nvp3 := makeNodeView(3, "p3", []string{"tag:two", "tag:three1"})
+	nvp4 := makeNodeView(4, "p4", []string{"tag:two", "tag:three2", "tag:four2"})
+
+	for _, tt := range []struct {
+		name   string
+		want   map[string][]tailcfg.NodeView
+		peers  []tailcfg.NodeView
+		config []tailcfg.RawMessage
+	}{
+		{
+			name: "empty",
+		},
+		{
+			name:   "bad-config", // bad config should return a nil map rather than error.
+			config: []tailcfg.RawMessage{tailcfg.RawMessage(`hey`)},
+		},
+		{
+			name:   "no-peers",
+			config: []tailcfg.RawMessage{tailcfg.RawMessage(appOneBytes)},
+		},
+		{
+			name:   "peers-that-are-not-connectors",
+			config: []tailcfg.RawMessage{tailcfg.RawMessage(appOneBytes)},
+			peers: []tailcfg.NodeView{
+				(&tailcfg.Node{
+					ID:   5,
+					Name: "p5",
+					Tags: []string{"tag:one"},
+				}).View(),
+				(&tailcfg.Node{
+					ID:   6,
+					Name: "p6",
+					Tags: []string{"tag:one"},
+				}).View(),
+			},
+		},
+		{
+			name:   "peers-that-dont-match-tags",
+			config: []tailcfg.RawMessage{tailcfg.RawMessage(appOneBytes)},
+			peers: []tailcfg.NodeView{
+				makeNodeView(5, "p5", []string{"tag:seven"}),
+				makeNodeView(6, "p6", nil),
+			},
+		},
+		{
+			name: "matching-tagged-connector-peers",
+			config: []tailcfg.RawMessage{
+				tailcfg.RawMessage(appOneBytes),
+				tailcfg.RawMessage(appTwoBytes),
+				tailcfg.RawMessage(appThreeBytes),
+				tailcfg.RawMessage(appFourBytes),
+			},
+			peers: []tailcfg.NodeView{
+				nvp1,
+				nvp2,
+				nvp3,
+				nvp4,
+				makeNodeView(5, "p5", nil),
+			},
+			want: map[string][]tailcfg.NodeView{
+				// p5 has no matching tags and so doesn't appear
+				"example.com":       {nvp1},
+				"a.example.com":     {nvp3, nvp4},
+				"woo.b.example.com": {nvp2, nvp3, nvp4},
+				"hoo.b.example.com": {nvp3, nvp4},
+				"c.example.com":     {nvp2, nvp4},
+			},
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			selfNode := &tailcfg.Node{}
+			if tt.config != nil {
+				selfNode.CapMap = tailcfg.NodeCapMap{
+					tailcfg.NodeCapability(AppConnectorsExperimentalAttrName): tt.config,
+				}
+			}
+			selfView := selfNode.View()
+			peers := map[tailcfg.NodeID]tailcfg.NodeView{}
+			for _, p := range tt.peers {
+				peers[p.ID()] = p
+			}
+			got := PickSplitDNSPeers(func(_ tailcfg.NodeCapability) bool {
+				return true
+			}, selfView, peers)
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Fatalf("got %v, want %v", got, tt.want)
+			}
+		})
+	}
+}