wgengine/magicsock: support self as candidate peer relay (#16499)

Updates tailscale/corp#30247

Signed-off-by: Jordan Whited <jordan@tailscale.com>

wgengine/magicsock/magicsock.go

@@ -2618,8 +2618,8 @@ func (c *Conn) onFilterUpdate(f FilterUpdate) {
 	c.updateRelayServersSet(f.Filter, self, peers)
 }
 
-// updateRelayServersSet iterates all peers, evaluating filt for each one in
-// order to determine which peers are relay server candidates. filt, self, and
+// updateRelayServersSet iterates all peers and self, evaluating filt for each
+// one in order to determine which are relay server candidates. filt, self, and
 // peers are passed as args (vs c.mu-guarded fields) to enable callers to
 // release c.mu before calling as this is O(m * n) (we iterate all cap rules 'm'
 // in filt for every peer 'n').
@@ -2631,8 +2631,9 @@ func (c *Conn) onFilterUpdate(f FilterUpdate) {
 //     the computed result over the eventbus instead.
 func (c *Conn) updateRelayServersSet(filt *filter.Filter, self tailcfg.NodeView, peers views.Slice[tailcfg.NodeView]) {
 	relayServers := make(set.Set[netip.AddrPort])
-	for _, peer := range peers.All() {
-		peerAPI := peerAPIIfCandidateRelayServer(filt, self, peer)
+	nodes := append(peers.AsSlice(), self)
+	for _, maybeCandidate := range nodes {
+		peerAPI := peerAPIIfCandidateRelayServer(filt, self, maybeCandidate)
 		if peerAPI.IsValid() {
 			relayServers.Add(peerAPI)
 		}
@@ -2640,33 +2641,34 @@ func (c *Conn) updateRelayServersSet(filt *filter.Filter, self tailcfg.NodeView,
 	c.relayManager.handleRelayServersSet(relayServers)
 }
 
-// peerAPIIfCandidateRelayServer returns the peer API address of peer if it
-// is considered to be a candidate relay server upon evaluation against filt and
-// self, otherwise it returns a zero value.
-func peerAPIIfCandidateRelayServer(filt *filter.Filter, self, peer tailcfg.NodeView) netip.AddrPort {
+// peerAPIIfCandidateRelayServer returns the peer API address of maybeCandidate
+// if it is considered to be a candidate relay server upon evaluation against
+// filt and self, otherwise it returns a zero value. self and maybeCandidate
+// may be equal.
+func peerAPIIfCandidateRelayServer(filt *filter.Filter, self, maybeCandidate tailcfg.NodeView) netip.AddrPort {
 	if filt == nil ||
 		!self.Valid() ||
-		!peer.Valid() ||
-		!capVerIsRelayServerCapable(peer.Cap()) ||
-		!peer.Hostinfo().Valid() {
+		!maybeCandidate.Valid() ||
+		!capVerIsRelayServerCapable(maybeCandidate.Cap()) ||
+		!maybeCandidate.Hostinfo().Valid() {
 		return netip.AddrPort{}
 	}
-	for _, peerPrefix := range peer.Addresses().All() {
-		if !peerPrefix.IsSingleIP() {
+	for _, maybeCandidatePrefix := range maybeCandidate.Addresses().All() {
+		if !maybeCandidatePrefix.IsSingleIP() {
 			continue
 		}
-		peerAddr := peerPrefix.Addr()
+		maybeCandidateAddr := maybeCandidatePrefix.Addr()
 		for _, selfPrefix := range self.Addresses().All() {
 			if !selfPrefix.IsSingleIP() {
 				continue
 			}
 			selfAddr := selfPrefix.Addr()
-			if selfAddr.BitLen() == peerAddr.BitLen() { // same address family
-				if filt.CapsWithValues(peerAddr, selfAddr).HasCapability(tailcfg.PeerCapabilityRelayTarget) {
-					for _, s := range peer.Hostinfo().Services().All() {
-						if peerAddr.Is4() && s.Proto == tailcfg.PeerAPI4 ||
-							peerAddr.Is6() && s.Proto == tailcfg.PeerAPI6 {
-							return netip.AddrPortFrom(peerAddr, s.Port)
+			if selfAddr.BitLen() == maybeCandidateAddr.BitLen() { // same address family
+				if filt.CapsWithValues(maybeCandidateAddr, selfAddr).HasCapability(tailcfg.PeerCapabilityRelayTarget) {
+					for _, s := range maybeCandidate.Hostinfo().Services().All() {
+						if maybeCandidateAddr.Is4() && s.Proto == tailcfg.PeerAPI4 ||
+							maybeCandidateAddr.Is6() && s.Proto == tailcfg.PeerAPI6 {
+							return netip.AddrPortFrom(maybeCandidateAddr, s.Port)
 						}
 					}
 					return netip.AddrPort{} // no peerAPI
@@ -2674,10 +2676,11 @@ func peerAPIIfCandidateRelayServer(filt *filter.Filter, self, peer tailcfg.NodeV
 					// [nodeBackend.peerCapsLocked] only returns/considers the
 					// [tailcfg.PeerCapMap] between the passed src and the
 					// _first_ host (/32 or /128) address for self. We are
-					// consistent with that behavior here. If self and peer
-					// host addresses are of the same address family they either
-					// have the capability or not. We do not check against
-					// additional host addresses of the same address family.
+					// consistent with that behavior here. If self and
+					// maybeCandidate host addresses are of the same address
+					// family they either have the capability or not. We do not
+					// check against additional host addresses of the same
+					// address family.
 					return netip.AddrPort{}
 				}
 			}

wgengine/magicsock/magicsock_test.go

@@ -3385,16 +3385,7 @@ func Test_virtualNetworkID(t *testing.T) {
 }
 
 func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
-	selfOnlyIPv4 := &tailcfg.Node{
-		Cap: math.MinInt32,
-		Addresses: []netip.Prefix{
-			netip.MustParsePrefix("1.1.1.1/32"),
-		},
-	}
-	selfOnlyIPv6 := selfOnlyIPv4.Clone()
-	selfOnlyIPv6.Addresses[0] = netip.MustParsePrefix("::1/128")
-
-	peerHostinfo := &tailcfg.Hostinfo{
+	hostInfo := &tailcfg.Hostinfo{
 		Services: []tailcfg.Service{
 			{
 				Proto: tailcfg.PeerAPI4,
@@ -3406,12 +3397,23 @@ func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
 			},
 		},
 	}
+
+	selfOnlyIPv4 := &tailcfg.Node{
+		Cap: math.MinInt32,
+		Addresses: []netip.Prefix{
+			netip.MustParsePrefix("1.1.1.1/32"),
+		},
+		Hostinfo: hostInfo.View(),
+	}
+	selfOnlyIPv6 := selfOnlyIPv4.Clone()
+	selfOnlyIPv6.Addresses[0] = netip.MustParsePrefix("::1/128")
+
 	peerOnlyIPv4 := &tailcfg.Node{
 		Cap: math.MinInt32,
 		Addresses: []netip.Prefix{
 			netip.MustParsePrefix("2.2.2.2/32"),
 		},
-		Hostinfo: peerHostinfo.View(),
+		Hostinfo: hostInfo.View(),
 	}
 
 	peerOnlyIPv6 := peerOnlyIPv4.Clone()
@@ -3424,11 +3426,11 @@ func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
 	peerOnlyIPv4NilHostinfo.Hostinfo = tailcfg.HostinfoView{}
 
 	tests := []struct {
-		name string
-		filt *filter.Filter
-		self tailcfg.NodeView
-		peer tailcfg.NodeView
-		want netip.AddrPort
+		name           string
+		filt           *filter.Filter
+		self           tailcfg.NodeView
+		maybeCandidate tailcfg.NodeView
+		want           netip.AddrPort
 	}{
 		{
 			name: "match v4",
@@ -3443,9 +3445,26 @@ func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
 					},
 				},
 			}, nil, nil, nil, nil, nil),
-			self: selfOnlyIPv4.View(),
-			peer: peerOnlyIPv4.View(),
-			want: netip.MustParseAddrPort("2.2.2.2:4"),
+			self:           selfOnlyIPv4.View(),
+			maybeCandidate: peerOnlyIPv4.View(),
+			want:           netip.MustParseAddrPort("2.2.2.2:4"),
+		},
+		{
+			name: "match v4 self",
+			filt: filter.New([]filtertype.Match{
+				{
+					Srcs: []netip.Prefix{selfOnlyIPv4.Addresses[0]},
+					Caps: []filtertype.CapMatch{
+						{
+							Dst: selfOnlyIPv4.Addresses[0],
+							Cap: tailcfg.PeerCapabilityRelayTarget,
+						},
+					},
+				},
+			}, nil, nil, nil, nil, nil),
+			self:           selfOnlyIPv4.View(),
+			maybeCandidate: selfOnlyIPv4.View(),
+			want:           netip.AddrPortFrom(selfOnlyIPv4.Addresses[0].Addr(), 4),
 		},
 		{
 			name: "match v6",
@@ -3460,9 +3479,26 @@ func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
 					},
 				},
 			}, nil, nil, nil, nil, nil),
-			self: selfOnlyIPv6.View(),
-			peer: peerOnlyIPv6.View(),
-			want: netip.MustParseAddrPort("[::2]:6"),
+			self:           selfOnlyIPv6.View(),
+			maybeCandidate: peerOnlyIPv6.View(),
+			want:           netip.MustParseAddrPort("[::2]:6"),
+		},
+		{
+			name: "match v6 self",
+			filt: filter.New([]filtertype.Match{
+				{
+					Srcs: []netip.Prefix{selfOnlyIPv6.Addresses[0]},
+					Caps: []filtertype.CapMatch{
+						{
+							Dst: selfOnlyIPv6.Addresses[0],
+							Cap: tailcfg.PeerCapabilityRelayTarget,
+						},
+					},
+				},
+			}, nil, nil, nil, nil, nil),
+			self:           selfOnlyIPv6.View(),
+			maybeCandidate: selfOnlyIPv6.View(),
+			want:           netip.AddrPortFrom(selfOnlyIPv6.Addresses[0].Addr(), 6),
 		},
 		{
 			name: "no match dst",
@@ -3477,8 +3513,8 @@ func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
 					},
 				},
 			}, nil, nil, nil, nil, nil),
-			self: selfOnlyIPv6.View(),
-			peer: peerOnlyIPv6.View(),
+			self:           selfOnlyIPv6.View(),
+			maybeCandidate: peerOnlyIPv6.View(),
 		},
 		{
 			name: "no match peer cap",
@@ -3493,8 +3529,8 @@ func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
 					},
 				},
 			}, nil, nil, nil, nil, nil),
-			self: selfOnlyIPv6.View(),
-			peer: peerOnlyIPv6.View(),
+			self:           selfOnlyIPv6.View(),
+			maybeCandidate: peerOnlyIPv6.View(),
 		},
 		{
 			name: "cap ver not relay capable",
@@ -3509,14 +3545,14 @@ func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
 					},
 				},
 			}, nil, nil, nil, nil, nil),
-			self: peerOnlyIPv4.View(),
-			peer: peerOnlyIPv4ZeroCapVer.View(),
+			self:           peerOnlyIPv4.View(),
+			maybeCandidate: peerOnlyIPv4ZeroCapVer.View(),
 		},
 		{
-			name: "nil filt",
-			filt: nil,
-			self: selfOnlyIPv4.View(),
-			peer: peerOnlyIPv4.View(),
+			name:           "nil filt",
+			filt:           nil,
+			self:           selfOnlyIPv4.View(),
+			maybeCandidate: peerOnlyIPv4.View(),
 		},
 		{
 			name: "nil self",
@@ -3531,8 +3567,8 @@ func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
 					},
 				},
 			}, nil, nil, nil, nil, nil),
-			self: tailcfg.NodeView{},
-			peer: peerOnlyIPv4.View(),
+			self:           tailcfg.NodeView{},
+			maybeCandidate: peerOnlyIPv4.View(),
 		},
 		{
 			name: "nil peer",
@@ -3547,8 +3583,8 @@ func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
 					},
 				},
 			}, nil, nil, nil, nil, nil),
-			self: selfOnlyIPv4.View(),
-			peer: tailcfg.NodeView{},
+			self:           selfOnlyIPv4.View(),
+			maybeCandidate: tailcfg.NodeView{},
 		},
 		{
 			name: "nil peer hostinfo",
@@ -3563,13 +3599,13 @@ func Test_peerAPIIfCandidateRelayServer(t *testing.T) {
 					},
 				},
 			}, nil, nil, nil, nil, nil),
-			self: selfOnlyIPv4.View(),
-			peer: peerOnlyIPv4NilHostinfo.View(),
+			self:           selfOnlyIPv4.View(),
+			maybeCandidate: peerOnlyIPv4NilHostinfo.View(),
 		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			if got := peerAPIIfCandidateRelayServer(tt.filt, tt.self, tt.peer); !reflect.DeepEqual(got, tt.want) {
+			if got := peerAPIIfCandidateRelayServer(tt.filt, tt.self, tt.maybeCandidate); !reflect.DeepEqual(got, tt.want) {
 				t.Errorf("peerAPIIfCandidateRelayServer() = %v, want %v", got, tt.want)
 			}
 		})