1 files changed, 154 insertions, 0 deletions
diff --git a/pkg/state/state_manager.go b/pkg/state/state_manager.go
new file mode 100644
index 0000000..dfa73f4
--- /dev/null
+++ b/pkg/state/state_manager.go
@@ -0,0 +1,154 @@
+package state
+
+import (
+	"context"
+	"crypto"
+	"fmt"
+	"reflect"
+	"sync"
+	"time"
+
+	"github.com/golang/glog"
+	"github.com/google/certificate-transparency-go/schedule"
+	"github.com/system-transparency/stfe/pkg/trillian"
+	"github.com/system-transparency/stfe/pkg/types"
+)
+
+// StateManager coordinates access to the log's tree heads and (co)signatures
+type StateManager interface {
+	Latest(context.Context) (*types.SignedTreeHead, error)
+	ToSign(context.Context) (*types.SignedTreeHead, error)
+	Cosigned(context.Context) (*types.SignedTreeHead, error)
+	AddCosignature(context.Context, *[types.VerificationKeySize]byte, *[types.SignatureSize]byte) error
+	Run(context.Context)
+}
+
+// StateManagerSingle implements the StateManager interface.  It is assumed that
+// the log server is running on a single-instance machine.  So, no coordination.
+type StateManagerSingle struct {
+	client   trillian.Client
+	signer   crypto.Signer
+	interval time.Duration
+	deadline time.Duration
+	sync.RWMutex
+
+	// cosigned is the current cosigned tree head that is being served
+	cosigned types.SignedTreeHead
+
+	// tosign is the current tree head that is being cosigned by witnesses
+	tosign types.SignedTreeHead
+
+	// cosignature keeps track of all cosignatures for the tosign tree head
+	cosignature map[[types.HashSize]byte]*types.SigIdent
+}
+
+func NewStateManagerSingle(client trillian.Client, signer crypto.Signer, interval, deadline time.Duration) (*StateManagerSingle, error) {
+	sm := &StateManagerSingle{
+		client:   client,
+		signer:   signer,
+		interval: interval,
+		deadline: deadline,
+	}
+
+	ctx, _ := context.WithTimeout(context.Background(), sm.deadline)
+	sth, err := sm.Latest(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("Latest: %v", err)
+	}
+
+	sm.cosigned = *sth
+	sm.tosign = *sth
+	sm.cosignature = map[[types.HashSize]byte]*types.SigIdent{
+		*sth.SigIdent[0].KeyHash: sth.SigIdent[0], // log signature
+	}
+	return sm, nil
+}
+
+func (sm *StateManagerSingle) Run(ctx context.Context) {
+	schedule.Every(ctx, sm.interval, func(ctx context.Context) {
+		ictx, _ := context.WithTimeout(ctx, sm.deadline)
+		nextTreeHead, err := sm.Latest(ictx)
+		if err != nil {
+			glog.Warningf("rotate failed: Latest: %v", err)
+			return
+		}
+
+		sm.Lock()
+		defer sm.Unlock()
+		sm.rotate(nextTreeHead)
+	})
+}
+
+func (sm *StateManagerSingle) Latest(ctx context.Context) (*types.SignedTreeHead, error) {
+	th, err := sm.client.GetTreeHead(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("LatestTreeHead: %v", err)
+	}
+	sth, err := th.Sign(sm.signer)
+	if err != nil {
+		return nil, fmt.Errorf("sign: %v", err)
+	}
+	return sth, nil
+}
+
+func (sm *StateManagerSingle) ToSign(_ context.Context) (*types.SignedTreeHead, error) {
+	sm.RLock()
+	defer sm.RUnlock()
+	return &sm.tosign, nil
+}
+
+func (sm *StateManagerSingle) Cosigned(_ context.Context) (*types.SignedTreeHead, error) {
+	sm.RLock()
+	defer sm.RUnlock()
+	return &sm.cosigned, nil
+}
+
+func (sm *StateManagerSingle) AddCosignature(_ context.Context, vk *[types.VerificationKeySize]byte, sig *[types.SignatureSize]byte) error {
+	sm.Lock()
+	defer sm.Unlock()
+
+	if err := sm.tosign.TreeHead.Verify(vk, sig); err != nil {
+		return fmt.Errorf("Verify: %v", err)
+	}
+	witness := types.Hash(vk[:])
+	if _, ok := sm.cosignature[*witness]; ok {
+		return fmt.Errorf("signature-signer pair is a duplicate")
+	}
+	sm.cosignature[*witness] = &types.SigIdent{
+		Signature: sig,
+		KeyHash:   witness,
+	}
+
+	glog.V(3).Infof("accepted new cosignature from witness: %x", *witness)
+	return nil
+}
+
+// rotate rotates the log's cosigned and stable STH.  The caller must aquire the
+// source's read-write lock if there are concurrent reads and/or writes.
+func (sm *StateManagerSingle) rotate(next *types.SignedTreeHead) {
+	if reflect.DeepEqual(sm.cosigned.TreeHead, sm.tosign.TreeHead) {
+		// cosigned and tosign are the same.  So, we need to merge all
+		// cosignatures that we already had with the new collected ones.
+		for _, sigident := range sm.cosigned.SigIdent {
+			if _, ok := sm.cosignature[*sigident.KeyHash]; !ok {
+				sm.cosignature[*sigident.KeyHash] = sigident
+			}
+		}
+		glog.V(3).Infof("cosigned tree head repeated, merged signatures")
+	}
+	var cosignatures []*types.SigIdent
+	for _, sigident := range sm.cosignature {
+		cosignatures = append(cosignatures, sigident)
+	}
+
+	// Update cosigned tree head
+	sm.cosigned.TreeHead = sm.tosign.TreeHead
+	sm.cosigned.SigIdent = cosignatures
+
+	// Update to-sign tree head
+	sm.tosign = *next
+	sm.cosignature = map[[types.HashSize]byte]*types.SigIdent{
+		*next.SigIdent[0].KeyHash: next.SigIdent[0], // log signature
+	}
+	glog.V(3).Infof("rotated tree heads")
+}