tailcfg: add DNS address list for IsWireGuardOnly nodes

Tailscale exit nodes provide DNS service over the peer API, however
IsWireGuardOnly nodes do not have a peer API, and instead need client
DNS parameters passed in their node description.

For Mullvad nodes this will contain the in network 10.64.0.1 address.

Updates #9377

Signed-off-by: James Tucker <james@tailscale.com>

types/dnstype/dnstype.go

@@ -8,6 +8,7 @@ package dnstype
 
 import (
 	"net/netip"
+	"slices"
 )
 
 // Resolver is the configuration for one DNS resolver.
@@ -51,3 +52,15 @@ func (r *Resolver) IPPort() (ipp netip.AddrPort, ok bool) {
 	}
 	return
 }
+
+// Equal reports whether r and other are equal.
+func (r *Resolver) Equal(other *Resolver) bool {
+	if r == nil || other == nil {
+		return r == other
+	}
+	if r == other {
+		return true
+	}
+
+	return r.Addr == other.Addr && slices.Equal(r.BootstrapResolution, other.BootstrapResolution)
+}

types/dnstype/dnstype_test.go

@@ -0,0 +1,81 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package dnstype
+
+import (
+	"net/netip"
+	"reflect"
+	"slices"
+	"sort"
+	"testing"
+)
+
+func TestResolverEqual(t *testing.T) {
+	var fieldNames []string
+	for _, field := range reflect.VisibleFields(reflect.TypeOf(Resolver{})) {
+		fieldNames = append(fieldNames, field.Name)
+	}
+	sort.Strings(fieldNames)
+	if !slices.Equal(fieldNames, []string{"Addr", "BootstrapResolution"}) {
+		t.Errorf("Resolver fields changed; update test")
+	}
+
+	tests := []struct {
+		name string
+		a, b *Resolver
+		want bool
+	}{
+		{
+			name: "nil",
+			a:    nil,
+			b:    nil,
+			want: true,
+		},
+		{
+			name: "nil vs non-nil",
+			a:    nil,
+			b:    &Resolver{},
+			want: false,
+		},
+		{
+			name: "non-nil vs nil",
+			a:    &Resolver{},
+			b:    nil,
+			want: false,
+		},
+		{
+			name: "equal",
+			a:    &Resolver{Addr: "dns.example.com"},
+			b:    &Resolver{Addr: "dns.example.com"},
+			want: true,
+		},
+		{
+			name: "not equal addrs",
+			a:    &Resolver{Addr: "dns.example.com"},
+			b:    &Resolver{Addr: "dns2.example.com"},
+			want: false,
+		},
+		{
+			name: "not equal bootstrap",
+			a: &Resolver{
+				Addr:                "dns.example.com",
+				BootstrapResolution: []netip.Addr{netip.MustParseAddr("8.8.8.8")},
+			},
+			b: &Resolver{
+				Addr:                "dns.example.com",
+				BootstrapResolution: []netip.Addr{netip.MustParseAddr("8.8.4.4")},
+			},
+			want: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := tt.a.Equal(tt.b)
+			if got != tt.want {
+				t.Errorf("got %v; want %v", got, tt.want)
+			}
+		})
+	}
+}

types/dnstype/dnstype_view.go

@@ -64,6 +64,7 @@ func (v ResolverView) Addr() string { return v.ж.Addr }
 func (v ResolverView) BootstrapResolution() views.Slice[netip.Addr] {
 	return views.SliceOf(v.ж.BootstrapResolution)
 }
+func (v ResolverView) Equal(v2 ResolverView) bool { return v.ж.Equal(v2.ж) }
 
 // A compilation failure here means this code must be regenerated, with the command at the top of this file.
 var _ResolverViewNeedsRegeneration = Resolver(struct {