tka: implement Chonk type & an in-memory implementation

Chonks are responsible for efficient storage of AUMs and other TKA state.

For testing/prototyping I've implemented an in-memory version, but once we
start to use this from tailscaled we'll need a file-based version.

Signed-off-by: Tom DNetto <tom@tailscale.com>

tka/tailchonk_test.go

@@ -0,0 +1,128 @@
+// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tka
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"golang.org/x/crypto/blake2s"
+)
+
+// randHash derives a fake blake2s hash from the test name
+// and the given seed.
+func randHash(t *testing.T, seed int64) [blake2s.Size]byte {
+	var out [blake2s.Size]byte
+	testingRand(t, seed).Read(out[:])
+	return out
+}
+
+func TestImplementsChonk(t *testing.T) {
+	impls := []Chonk{&Mem{}}
+	t.Logf("chonks: %v", impls)
+}
+
+func TestTailchonkMem_ChildAUMs(t *testing.T) {
+	chonk := Mem{}
+	parentHash := randHash(t, 1)
+	data := []AUM{
+		{
+			MessageKind: AUMRemoveKey,
+			KeyID:       []byte{1, 2},
+			PrevAUMHash: parentHash[:],
+		},
+		{
+			MessageKind: AUMRemoveKey,
+			KeyID:       []byte{3, 4},
+			PrevAUMHash: parentHash[:],
+		},
+	}
+
+	if err := chonk.CommitVerifiedAUMs(data); err != nil {
+		t.Fatalf("CommitVerifiedAUMs failed: %v", err)
+	}
+	stored, err := chonk.ChildAUMs(parentHash)
+	if err != nil {
+		t.Fatalf("ChildAUMs failed: %v", err)
+	}
+	if diff := cmp.Diff(data, stored); diff != "" {
+		t.Errorf("stored AUM differs (-want, +got):\n%s", diff)
+	}
+}
+
+func TestTailchonkMem_Orphans(t *testing.T) {
+	chonk := Mem{}
+
+	parentHash := randHash(t, 1)
+	orphan := AUM{MessageKind: AUMNoOp}
+	aums := []AUM{
+		orphan,
+		// A parent is specified, so we shouldnt see it in GetOrphans()
+		{
+			MessageKind: AUMRemoveKey,
+			KeyID:       []byte{3, 4},
+			PrevAUMHash: parentHash[:],
+		},
+	}
+	if err := chonk.CommitVerifiedAUMs(aums); err != nil {
+		t.Fatalf("CommitVerifiedAUMs failed: %v", err)
+	}
+
+	stored, err := chonk.Orphans()
+	if err != nil {
+		t.Fatalf("Orphans failed: %v", err)
+	}
+	if diff := cmp.Diff([]AUM{orphan}, stored); diff != "" {
+		t.Errorf("stored AUM differs (-want, +got):\n%s", diff)
+	}
+}
+
+func TestTailchonkMem_ReadChainFromHead(t *testing.T) {
+	chonk := Mem{}
+	genesis := AUM{MessageKind: AUMRemoveKey, KeyID: []byte{1, 2}}
+	gHash := genesis.Hash()
+	intermediate := AUM{PrevAUMHash: gHash[:]}
+	iHash := intermediate.Hash()
+	leaf := AUM{PrevAUMHash: iHash[:]}
+
+	commitSet := []AUM{
+		genesis,
+		intermediate,
+		leaf,
+	}
+	if err := chonk.CommitVerifiedAUMs(commitSet); err != nil {
+		t.Fatalf("CommitVerifiedAUMs failed: %v", err)
+	}
+	// t.Logf("genesis hash = %X", genesis.Hash())
+	// t.Logf("intermediate hash = %X", intermediate.Hash())
+	// t.Logf("leaf hash = %X", leaf.Hash())
+
+	// Read the chain from the leaf backwards.
+	gotLeafs, err := chonk.Heads()
+	if err != nil {
+		t.Fatalf("Heads failed: %v", err)
+	}
+	if diff := cmp.Diff([]AUM{leaf}, gotLeafs); diff != "" {
+		t.Fatalf("leaf AUM differs (-want, +got):\n%s", diff)
+	}
+
+	parent, _ := gotLeafs[0].Parent()
+	gotIntermediate, err := chonk.AUM(parent)
+	if err != nil {
+		t.Fatalf("AUM(<intermediate>) failed: %v", err)
+	}
+	if diff := cmp.Diff(intermediate, gotIntermediate); diff != "" {
+		t.Errorf("intermediate AUM differs (-want, +got):\n%s", diff)
+	}
+
+	parent, _ = gotIntermediate.Parent()
+	gotGenesis, err := chonk.AUM(parent)
+	if err != nil {
+		t.Fatalf("AUM(<genesis>) failed: %v", err)
+	}
+	if diff := cmp.Diff(genesis, gotGenesis); diff != "" {
+		t.Errorf("genesis AUM differs (-want, +got):\n%s", diff)
+	}
+}