wgengine/magicsock,all: allocate peer relay over disco instead of PeerAPI (#16603)

Updates tailscale/corp#30583
Updates tailscale/corp#30534
Updates tailscale/corp#30557

Signed-off-by: Dylan Bargatze <dylan@tailscale.com>
Signed-off-by: Jordan Whited <jordan@tailscale.com>
Co-authored-by: Dylan Bargatze <dylan@tailscale.com>

types/key/disco.go

@@ -73,6 +73,44 @@ func (k DiscoPrivate) Shared(p DiscoPublic) DiscoShared {
 	return ret
 }
 
+// SortedPairOfDiscoPublic is a lexicographically sorted container of two
+// [DiscoPublic] keys.
+type SortedPairOfDiscoPublic struct {
+	k [2]DiscoPublic
+}
+
+// Get returns the underlying keys.
+func (s SortedPairOfDiscoPublic) Get() [2]DiscoPublic {
+	return s.k
+}
+
+// NewSortedPairOfDiscoPublic returns a SortedPairOfDiscoPublic from a and b.
+func NewSortedPairOfDiscoPublic(a, b DiscoPublic) SortedPairOfDiscoPublic {
+	s := SortedPairOfDiscoPublic{}
+	if a.Compare(b) < 0 {
+		s.k[0] = a
+		s.k[1] = b
+	} else {
+		s.k[0] = b
+		s.k[1] = a
+	}
+	return s
+}
+
+func (s SortedPairOfDiscoPublic) String() string {
+	return fmt.Sprintf("%s <=> %s", s.k[0].ShortString(), s.k[1].ShortString())
+}
+
+// Equal returns true if s and b are equal, otherwise it returns false.
+func (s SortedPairOfDiscoPublic) Equal(b SortedPairOfDiscoPublic) bool {
+	for i := range s.k {
+		if s.k[i].Compare(b.k[i]) != 0 {
+			return false
+		}
+	}
+	return true
+}
+
 // DiscoPublic is the public portion of a DiscoPrivate.
 type DiscoPublic struct {
 	k [32]byte

types/key/disco_test.go

@@ -81,3 +81,21 @@ func TestDiscoShared(t *testing.T) {
 		t.Error("k1.Shared(k2) != k2.Shared(k1)")
 	}
 }
+
+func TestSortedPairOfDiscoPublic(t *testing.T) {
+	pubA := DiscoPublic{}
+	pubA.k[0] = 0x01
+	pubB := DiscoPublic{}
+	pubB.k[0] = 0x02
+	sortedInput := NewSortedPairOfDiscoPublic(pubA, pubB)
+	unsortedInput := NewSortedPairOfDiscoPublic(pubB, pubA)
+	if sortedInput.Get() != unsortedInput.Get() {
+		t.Fatal("sortedInput.Get() != unsortedInput.Get()")
+	}
+	if unsortedInput.Get()[0] != pubA {
+		t.Fatal("unsortedInput.Get()[0] != pubA")
+	}
+	if unsortedInput.Get()[1] != pubB {
+		t.Fatal("unsortedInput.Get()[1] != pubB")
+	}
+}