1 files changed, 265 insertions, 0 deletions
diff --git a/internal/state/single.go b/internal/state/single.go
new file mode 100644
index 0000000..fd73b3f
--- /dev/null
+++ b/internal/state/single.go
@@ -0,0 +1,265 @@
+package state
+
+import (
+	"context"
+	"crypto"
+	"crypto/ed25519"
+	"fmt"
+	"sync"
+	"time"
+
+	"git.sigsum.org/log-go/internal/db"
+	"git.sigsum.org/sigsum-go/pkg/client"
+	"git.sigsum.org/sigsum-go/pkg/log"
+	"git.sigsum.org/sigsum-go/pkg/merkle"
+	"git.sigsum.org/sigsum-go/pkg/requests"
+	"git.sigsum.org/sigsum-go/pkg/types"
+)
+
+// StateManagerSingle implements a single-instance StateManagerPrimary for primary nodes
+type StateManagerSingle struct {
+	client    db.Client
+	signer    crypto.Signer
+	namespace merkle.Hash
+	interval  time.Duration
+	deadline  time.Duration
+	secondary client.Client
+
+	// Lock-protected access to pointers.  A write lock is only obtained once
+	// per interval when doing pointer rotation.  All endpoints are readers.
+	sync.RWMutex
+	signedTreeHead   *types.SignedTreeHead
+	cosignedTreeHead *types.CosignedTreeHead
+
+	// Syncronized and deduplicated witness cosignatures for signedTreeHead
+	events       chan *event
+	cosignatures map[merkle.Hash]*types.Signature
+}
+
+// NewStateManagerSingle() sets up a new state manager, in particular its
+// signedTreeHead.  An optional secondary node can be used to ensure that
+// a newer primary tree is not signed unless it has been replicated.
+func NewStateManagerSingle(dbcli db.Client, signer crypto.Signer, interval, deadline time.Duration, secondary client.Client) (*StateManagerSingle, error) {
+	sm := &StateManagerSingle{
+		client:    dbcli,
+		signer:    signer,
+		namespace: *merkle.HashFn(signer.Public().(ed25519.PublicKey)),
+		interval:  interval,
+		deadline:  deadline,
+		secondary: secondary,
+	}
+	sth, err := sm.restoreTreeHead()
+	if err != nil {
+		return nil, fmt.Errorf("restore signed tree head: %v", err)
+	}
+	sm.signedTreeHead = sth
+
+	ictx, cancel := context.WithTimeout(context.Background(), sm.deadline)
+	defer cancel()
+	return sm, sm.tryRotate(ictx)
+}
+
+func (sm *StateManagerSingle) ToCosignTreeHead() *types.SignedTreeHead {
+	sm.RLock()
+	defer sm.RUnlock()
+	return sm.signedTreeHead
+}
+
+func (sm *StateManagerSingle) CosignedTreeHead(_ context.Context) (*types.CosignedTreeHead, error) {
+	sm.RLock()
+	defer sm.RUnlock()
+	if sm.cosignedTreeHead == nil {
+		return nil, fmt.Errorf("no cosignatures available")
+	}
+	return sm.cosignedTreeHead, nil
+}
+
+func (sm *StateManagerSingle) AddCosignature(ctx context.Context, pub *types.PublicKey, sig *types.Signature) error {
+	sm.RLock()
+	defer sm.RUnlock()
+
+	msg := sm.signedTreeHead.TreeHead.ToBinary(&sm.namespace)
+	if !ed25519.Verify(ed25519.PublicKey(pub[:]), msg, sig[:]) {
+		return fmt.Errorf("invalid cosignature")
+	}
+	select {
+	case sm.events <- &event{merkle.HashFn(pub[:]), sig}:
+		return nil
+	case <-ctx.Done():
+		return fmt.Errorf("request timeout")
+	}
+}
+
+func (sm *StateManagerSingle) Run(ctx context.Context) {
+	sm.events = make(chan *event, 4096)
+	defer close(sm.events)
+	ticker := time.NewTicker(sm.interval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			ictx, cancel := context.WithTimeout(ctx, sm.deadline)
+			defer cancel()
+			if err := sm.tryRotate(ictx); err != nil {
+				log.Warning("failed rotating tree heads: %v", err)
+			}
+		case ev := <-sm.events:
+			sm.handleEvent(ev)
+		case <-ctx.Done():
+			return
+		}
+	}
+}
+
+func (sm *StateManagerSingle) tryRotate(ctx context.Context) error {
+	th, err := sm.client.GetTreeHead(ctx)
+	if err != nil {
+		return fmt.Errorf("get tree head: %v", err)
+	}
+	nextSTH, err := sm.chooseTree(ctx, th).Sign(sm.signer, &sm.namespace)
+	if err != nil {
+		return fmt.Errorf("sign tree head: %v", err)
+	}
+	log.Debug("wanted to advance to size %d, chose size %d", th.TreeSize, nextSTH.TreeSize)
+
+	sm.rotate(nextSTH)
+	return nil
+}
+
+// chooseTree picks a tree to publish, taking the state of a possible secondary node into account.
+func (sm *StateManagerSingle) chooseTree(ctx context.Context, proposedTreeHead *types.TreeHead) *types.TreeHead {
+	if !sm.secondary.Initiated() {
+		return proposedTreeHead
+	}
+
+	secSTH, err := sm.secondary.GetToCosignTreeHead(ctx)
+	if err != nil {
+		log.Warning("failed fetching tree head from secondary: %v", err)
+		return refreshTreeHead(sm.signedTreeHead.TreeHead)
+	}
+	if secSTH.TreeSize > proposedTreeHead.TreeSize {
+		log.Error("secondary is ahead of us: %d > %d", secSTH.TreeSize, proposedTreeHead.TreeSize)
+		return refreshTreeHead(sm.signedTreeHead.TreeHead)
+	}
+
+	if secSTH.TreeSize == proposedTreeHead.TreeSize {
+		if secSTH.RootHash != proposedTreeHead.RootHash {
+			log.Error("secondary root hash doesn't match our root hash at tree size %d", secSTH.TreeSize)
+			return refreshTreeHead(sm.signedTreeHead.TreeHead)
+		}
+		log.Debug("secondary is up-to-date with matching tree head, using proposed tree, size %d", proposedTreeHead.TreeSize)
+		return proposedTreeHead
+	}
+	//
+	// Now we know that the proposed tree size is larger than the secondary's tree size.
+	// We also now that the secondary's minimum tree size is 0.
+	// This means that the proposed tree size is at least 1.
+	//
+	// Case 1: secondary tree size is 0, primary tree size is >0 --> return based on what we signed before
+	// Case 2: secondary tree size is 1, primary tree size is >1 --> fetch consistency proof, if ok ->
+	//   2a) secondary tree size is smaller than or equal to what we than signed before -> return whatever we signed before
+	//   2b) secondary tree size is larger than what we signed before -> return secondary tree head
+	//
+	// (If not ok in case 2, return based on what we signed before)
+	//
+	if secSTH.TreeSize == 0 {
+		return refreshTreeHead(sm.signedTreeHead.TreeHead)
+	}
+	if err := sm.verifyConsistencyWithLatest(ctx, secSTH.TreeHead); err != nil {
+		log.Error("secondaries tree not consistent with ours: %v", err)
+		return refreshTreeHead(sm.signedTreeHead.TreeHead)
+	}
+	if secSTH.TreeSize <= sm.signedTreeHead.TreeSize {
+		log.Warning("secondary is behind what primary already signed: %d <= %d", secSTH.TreeSize, sm.signedTreeHead.TreeSize)
+		return refreshTreeHead(sm.signedTreeHead.TreeHead)
+	}
+
+	log.Debug("using latest tree head from secondary: size %d", secSTH.TreeSize)
+	return refreshTreeHead(secSTH.TreeHead)
+}
+
+func (sm *StateManagerSingle) verifyConsistencyWithLatest(ctx context.Context, to types.TreeHead) error {
+	from := sm.signedTreeHead.TreeHead
+	req := &requests.ConsistencyProof{
+		OldSize: from.TreeSize,
+		NewSize: to.TreeSize,
+	}
+	proof, err := sm.client.GetConsistencyProof(ctx, req)
+	if err != nil {
+		return fmt.Errorf("unable to get consistency proof from %d to %d: %w", req.OldSize, req.NewSize, err)
+	}
+	if err := proof.Verify(&from.RootHash, &to.RootHash); err != nil {
+		return fmt.Errorf("invalid consistency proof from %d to %d: %v", req.OldSize, req.NewSize, err)
+	}
+	log.Debug("consistency proof from %d to %d verified", req.OldSize, req.NewSize)
+	return nil
+}
+
+func (sm *StateManagerSingle) rotate(nextSTH *types.SignedTreeHead) {
+	sm.Lock()
+	defer sm.Unlock()
+
+	log.Debug("about to rotate tree heads, next at %d: %s", nextSTH.TreeSize, sm.treeStatusString())
+	sm.handleEvents()
+	sm.setCosignedTreeHead()
+	sm.setToCosignTreeHead(nextSTH)
+	log.Debug("tree heads rotated: %s", sm.treeStatusString())
+}
+
+func (sm *StateManagerSingle) handleEvents() {
+	log.Debug("handling any outstanding events")
+	for i, n := 0, len(sm.events); i < n; i++ {
+		sm.handleEvent(<-sm.events)
+	}
+}
+
+func (sm *StateManagerSingle) handleEvent(ev *event) {
+	log.Debug("handling event from witness %x", ev.keyHash[:])
+	sm.cosignatures[*ev.keyHash] = ev.cosignature
+}
+
+func (sm *StateManagerSingle) setCosignedTreeHead() {
+	n := len(sm.cosignatures)
+	if n == 0 {
+		sm.cosignedTreeHead = nil
+		return
+	}
+
+	var cth types.CosignedTreeHead
+	cth.SignedTreeHead = *sm.signedTreeHead
+	cth.Cosignature = make([]types.Signature, 0, n)
+	cth.KeyHash = make([]merkle.Hash, 0, n)
+	for keyHash, cosignature := range sm.cosignatures {
+		cth.KeyHash = append(cth.KeyHash, keyHash)
+		cth.Cosignature = append(cth.Cosignature, *cosignature)
+	}
+	sm.cosignedTreeHead = &cth
+}
+
+func (sm *StateManagerSingle) setToCosignTreeHead(nextSTH *types.SignedTreeHead) {
+	sm.cosignatures = make(map[merkle.Hash]*types.Signature)
+	sm.signedTreeHead = nextSTH
+}
+
+func (sm *StateManagerSingle) treeStatusString() string {
+	var cosigned uint64
+	if sm.cosignedTreeHead != nil {
+		cosigned = sm.cosignedTreeHead.TreeSize
+	}
+	return fmt.Sprintf("signed at %d, cosigned at %d", sm.signedTreeHead.TreeSize, cosigned)
+}
+
+func (sm *StateManagerSingle) restoreTreeHead() (*types.SignedTreeHead, error) {
+	th := zeroTreeHead() // TODO: restore from disk, stored when advanced the tree; zero tree head if "bootstrap"
+	return refreshTreeHead(*th).Sign(sm.signer, &sm.namespace)
+}
+
+func zeroTreeHead() *types.TreeHead {
+	return refreshTreeHead(types.TreeHead{RootHash: *merkle.HashFn([]byte(""))})
+}
+
+func refreshTreeHead(th types.TreeHead) *types.TreeHead {
+	th.Timestamp = uint64(time.Now().Unix())
+	return &th
+}