// verifierLogAppend censors an entry and prepares the commands to:
// 1) store it to local persistent storage
// 2) mark the log entry as used
// 3) share the new log entry with verifiers
// called from step: no io
func (ks *Keyserver) verifierLogAppend(m *proto.VerifierStep, rs *proto.ReplicaState, wb kv.Batch) func() {
	// m : *mut // RECURSIVE transfer of ownership
	// ks : &const // read-only
	// rs, wb : &mut
	wb.Put(tableVerifierLog(rs.NextIndexVerifier), proto.MustMarshal(m))
	rs.NextIndexVerifier++
	return func() {
		ks.sb.Send(m)
	}
}

// Flush returns a newly usable Snapshot
func (snapshot *NewSnapshot) Flush(wb kv.Batch) (flushed *Snapshot) {
	if snapshot.root == nil {
		flushed = &Snapshot{snapshot.tree, 0}
	} else {
		rootId, _ := snapshot.tree.flushNode([]bool{}, snapshot.root, wb)
		flushed = &Snapshot{snapshot.tree, rootId}
	}
	allocCountVal := make([]byte, 8)
	binary.LittleEndian.PutUint64(allocCountVal, snapshot.tree.allocCounter)
	wb.Put(snapshot.tree.allocCounterKey, allocCountVal)
	return
}

// step is called by run and changes the in-memory state. No i/o allowed.
func (vr *Verifier) step(step *proto.VerifierStep, vs *proto.VerifierState, wb kv.Batch) (deferredIO func()) {
	// vr: &const
	// step, vs, wb: &mut
	switch step.Type.(type) {
	case *proto.VerifierStep_Update:
		index := step.GetUpdate().NewEntry.Index
		prevEntry, err := vr.getEntry(index, vs.NextEpoch)
		if err := coname.VerifyUpdate(prevEntry, step.GetUpdate()); err != nil {
			// the keyserver should filter all bad updates
			log.Panicf("%d: bad update %v: %s", vs.NextIndex, *step, err)
		}
		var entryHash [32]byte
		sha3.ShakeSum256(entryHash[:], step.GetUpdate().NewEntry.Encoding)
		latestTree := vr.merkletree.GetSnapshot(vs.LatestTreeSnapshot)
		newTree, err := latestTree.BeginModification()
		if err != nil {
			log.Panicf("%d: BeginModification(): %s", vs.NextIndex, err)
		}
		if err := newTree.Set(index, entryHash[:]); err != nil {
			log.Panicf("%d: Set(%x,%x): %s", vs.NextIndex, index, entryHash[:], err)
		}
		vs.LatestTreeSnapshot = newTree.Flush(wb).Nr
		wb.Put(tableEntries(index, vs.NextEpoch), step.GetUpdate().NewEntry.Encoding)

	case *proto.VerifierStep_Epoch:
		ok := coname.VerifyPolicy(vr.vs.KeyserverAuth, step.GetEpoch().Head.Encoding, step.GetEpoch().Signatures)
		// the bad steps here will not get persisted to disk right now. do we want them to?
		if !ok {
			log.Panicf("%d: keyserver signature verification failed: %#v", vs.NextIndex, *step)
		}
		r := step.GetEpoch().Head
		if r.Head.Realm != vr.realm {
			log.Panicf("%d: seh for realm %q, expected %q: %#v", vs.NextEpoch, r.Head.Realm, vr.realm, *step)
		}
		if r.Head.Epoch != vs.NextEpoch {
			log.Panicf("%d: got epoch %d instead: %#v", vs.NextEpoch, r.Head.Epoch, *step)
		}
		s := r.Head
		if !bytes.Equal(s.PreviousSummaryHash, vs.PreviousSummaryHash) {
			log.Panicf("%d: seh with previous summary hash %q, expected %q: %#v", vs.NextEpoch, s.PreviousSummaryHash, vs.PreviousSummaryHash, *step)
		}
		latestTree := vr.merkletree.GetSnapshot(vs.LatestTreeSnapshot)
		rootHash, err := latestTree.GetRootHash()
		if err != nil {
			log.Panicf("GetRootHash() failed: %s", err)
		}
		if !bytes.Equal(s.RootHash, rootHash) {
			log.Panicf("%d: seh with root hash %q, expected %q: %#v", vs.NextEpoch, s.RootHash, rootHash, *step)
		}
		seh := &proto.SignedEpochHead{
			Head: proto.EncodedTimestampedEpochHead{TimestampedEpochHead: proto.TimestampedEpochHead{
				Head:      s,
				Timestamp: proto.Time(time.Now()),
			}, Encoding: nil},
			Signatures: make(map[uint64][]byte, 1),
		}
		if vs.PreviousSummaryHash == nil {
			vs.PreviousSummaryHash = make([]byte, 64)
		}
		sha3.ShakeSum256(vs.PreviousSummaryHash[:], seh.Head.Head.Encoding)
		seh.Head.UpdateEncoding()
		seh.Signatures[vr.id] = ed25519.Sign(vr.signingKey, proto.MustMarshal(&seh.Head))[:]
		wb.Put(tableRatifications(vs.NextEpoch, vr.id), proto.MustMarshal(seh))
		vs.NextEpoch++
		return func() {
			_, err := vr.keyserver.PushRatification(vr.ctx, seh)
			if err != nil {
				log.Printf("PushRatification: %s", err)
			}
		}
	default:
		log.Panicf("%d: unknown step: %#v", vs.NextIndex, *step)
	}
	return
}

// step is called by run and changes the in-memory state. No i/o allowed.
func (ks *Keyserver) step(step *proto.KeyserverStep, rs *proto.ReplicaState, wb kv.Batch) (deferredIO func()) {
	// ks: &const
	// step, rs, wb: &mut
	switch step.Type.(type) {
	case *proto.KeyserverStep_Update:
		index := step.GetUpdate().Update.NewEntry.Index
		prevUpdate, err := ks.getUpdate(index, math.MaxUint64)
		if err != nil {
			log.Printf("getUpdate: %s", err)
			ks.wr.Notify(step.UID, updateOutput{Error: fmt.Errorf("internal error")})
			return
		}
		if err := ks.verifyUpdateDeterministic(prevUpdate, step.GetUpdate()); err != nil {
			ks.wr.Notify(step.UID, updateOutput{Error: err})
			return
		}
		latestTree := ks.merkletree.GetSnapshot(rs.LatestTreeSnapshot)

		// sanity check: compare previous version in Merkle tree vs in updates table
		prevEntryHashTree, _, err := latestTree.Lookup(index)
		if err != nil {
			ks.wr.Notify(step.UID, updateOutput{Error: fmt.Errorf("internal error")})
			return
		}
		var prevEntryHash []byte
		if prevUpdate != nil {
			prevEntryHash = make([]byte, 32)
			sha3.ShakeSum256(prevEntryHash, prevUpdate.Update.NewEntry.Encoding)
		}
		if !bytes.Equal(prevEntryHashTree, prevEntryHash) {
			log.Fatalf("ERROR: merkle tree and DB inconsistent for index %x: %x vs %x", index, prevEntryHashTree, prevEntryHash)
		}

		var entryHash [32]byte
		sha3.ShakeSum256(entryHash[:], step.GetUpdate().Update.NewEntry.Encoding)
		newTree, err := latestTree.BeginModification()
		if err != nil {
			ks.wr.Notify(step.UID, updateOutput{Error: fmt.Errorf("internal error")})
			return
		}
		if err := newTree.Set(index, entryHash[:]); err != nil {
			log.Printf("setting index '%x' gave error: %s", index, err)
			ks.wr.Notify(step.UID, updateOutput{Error: fmt.Errorf("internal error")})
			return
		}
		rs.LatestTreeSnapshot = newTree.Flush(wb).Nr
		epochNr := rs.LastEpochDelimiter.EpochNumber + 1
		wb.Put(tableUpdateRequests(index, epochNr), proto.MustMarshal(step.GetUpdate()))
		ks.wr.Notify(step.UID, updateOutput{Epoch: epochNr})

		rs.PendingUpdates = true
		ks.updateEpochProposer()

		if rs.LastEpochNeedsRatification {
			// We need to wait for the last epoch to appear in the verifier log before
			// inserting this update.
			wb.Put(tableUpdatesPendingRatification(rs.NextIndexLog), proto.MustMarshal(step.GetUpdate().Update))
		} else {
			// We can deliver the update to verifiers right away.
			return ks.verifierLogAppend(&proto.VerifierStep{Type: &proto.VerifierStep_Update{Update: step.GetUpdate().Update}}, rs, wb)
		}

	case *proto.KeyserverStep_EpochDelimiter:
		if step.GetEpochDelimiter().EpochNumber <= rs.LastEpochDelimiter.EpochNumber {
			return // a duplicate of this step has already been handled
		}
		rs.LastEpochDelimiter = *step.GetEpochDelimiter()
		log.Printf("epoch %d", step.GetEpochDelimiter().EpochNumber)

		rs.PendingUpdates = false
		ks.resetEpochTimers(rs.LastEpochDelimiter.Timestamp.Time())
		// rs.ThisReplicaNeedsToSignLastEpoch might already be true, if a majority
		// signed that did not include us. This will make us skip signing the last
		// epoch, but that's fine.
		rs.ThisReplicaNeedsToSignLastEpoch = true
		// However, it's not okay to see a new epoch delimiter before the previous
		// epoch has been ratified.
		if rs.LastEpochNeedsRatification {
			log.Panicf("new epoch delimiter but last epoch not ratified")
		}
		rs.LastEpochNeedsRatification = true
		ks.updateEpochProposer()
		deferredIO = ks.updateSignatureProposer

		snapshotNumberBytes := make([]byte, 8)
		binary.BigEndian.PutUint64(snapshotNumberBytes, rs.LatestTreeSnapshot)
		wb.Put(tableMerkleTreeSnapshot(step.GetEpochDelimiter().EpochNumber), snapshotNumberBytes)

		latestTree := ks.merkletree.GetSnapshot(rs.LatestTreeSnapshot)
		rootHash, err := latestTree.GetRootHash()
		if err != nil {
			log.Panicf("ks.latestTree.GetRootHash() failed: %s", err)
		}
		teh := &proto.EncodedTimestampedEpochHead{TimestampedEpochHead: proto.TimestampedEpochHead{
			Head: proto.EncodedEpochHead{EpochHead: proto.EpochHead{
				RootHash:            rootHash,
				PreviousSummaryHash: rs.PreviousSummaryHash,
				Realm:               ks.realm,
				Epoch:               step.GetEpochDelimiter().EpochNumber,
//.........这里部分代码省略.........

func (t *MerkleTree) storeNode(id uint64, n *node, wb kv.Batch) {
	wb.Put(t.serializeKey(id, n.prefixBits), n.serialize())
}