2 files changed, 57 insertions, 13 deletions

diff --git a/internal/state/single.go b/internal/state/single.go
index fd73b3f..2c6bb4b 100644
--- a/internal/state/single.go
+++ b/internal/state/single.go
@@ -1,10 +1,12 @@
 package state
 
 import (
+	"bytes"
 	"context"
 	"crypto"
 	"crypto/ed25519"
 	"fmt"
+	"os"
 	"sync"
 	"time"
 
@@ -24,6 +26,7 @@ type StateManagerSingle struct {
 	interval  time.Duration
 	deadline  time.Duration
 	secondary client.Client
+	sthFile   *os.File
 
 	// Lock-protected access to pointers.  A write lock is only obtained once
 	// per interval when doing pointer rotation.  All endpoints are readers.
@@ -39,7 +42,7 @@ type StateManagerSingle struct {
 // 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) {
+func NewStateManagerSingle(dbcli db.Client, signer crypto.Signer, interval, deadline time.Duration, secondary client.Client, sthFile *os.File) (*StateManagerSingle, error) {
 	sm := &StateManagerSingle{
 		client:    dbcli,
 		signer:    signer,
@@ -47,16 +50,22 @@ func NewStateManagerSingle(dbcli db.Client, signer crypto.Signer, interval, dead
 		interval:  interval,
 		deadline:  deadline,
 		secondary: secondary,
+		sthFile:   sthFile,
 	}
-	sth, err := sm.restoreTreeHead()
-	if err != nil {
-		return nil, fmt.Errorf("restore signed tree head: %v", err)
+	var err error
+	if sm.signedTreeHead, err = sm.restoreSTH(); err != nil {
+		return nil, err
 	}
-	sm.signedTreeHead = sth
-
-	ictx, cancel := context.WithTimeout(context.Background(), sm.deadline)
-	defer cancel()
-	return sm, sm.tryRotate(ictx)
+	ctx := context.Background()
+	for {
+		err := sm.tryRotate(ctx)
+		if err == nil {
+			break
+		}
+		log.Warning("restore signed tree head: %v", err)
+		time.Sleep(time.Second * 3)
+	}
+	return sm, nil
 }
 
 func (sm *StateManagerSingle) ToCosignTreeHead() *types.SignedTreeHead {
@@ -123,6 +132,10 @@ func (sm *StateManagerSingle) tryRotate(ctx context.Context) error {
 	}
 	log.Debug("wanted to advance to size %d, chose size %d", th.TreeSize, nextSTH.TreeSize)
 
+	if err := sm.storeSTH(nextSTH); err != nil {
+		return err
+	}
+
 	sm.rotate(nextSTH)
 	return nil
 }
@@ -250,9 +263,34 @@ func (sm *StateManagerSingle) treeStatusString() string {
 	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 (sm *StateManagerSingle) restoreSTH() (*types.SignedTreeHead, error) {
+	var th types.TreeHead
+	b := make([]byte, 1024)
+	n, err := sm.sthFile.Read(b)
+	if err != nil {
+		th = *zeroTreeHead()
+	} else if err := th.FromASCII(bytes.NewBuffer(b[:n])); err != nil {
+		th = *zeroTreeHead()
+	}
+	th = *refreshTreeHead(th)
+	return th.Sign(sm.signer, &sm.namespace)
+}
+
+func (sm *StateManagerSingle) storeSTH(sth *types.SignedTreeHead) error {
+	buf := bytes.NewBuffer(nil)
+	if err := sth.ToASCII(buf); err != nil {
+		return err
+	}
+	if err := sm.sthFile.Truncate(int64(buf.Len())); err != nil {
+		return err
+	}
+	if _, err := sm.sthFile.WriteAt(buf.Bytes(), 0); err != nil {
+		return err
+	}
+	if err := sm.sthFile.Sync(); err != nil {
+		return err
+	}
+	return nil
 }
 
 func zeroTreeHead() *types.TreeHead {
diff --git a/internal/state/single_test.go b/internal/state/single_test.go
index 9442fdc..a60795c 100644
--- a/internal/state/single_test.go
+++ b/internal/state/single_test.go
@@ -8,6 +8,7 @@ import (
 	"crypto/rand"
 	"fmt"
 	"io"
+	"os"
 	"reflect"
 	"testing"
 	"time"
@@ -65,7 +66,12 @@ func TestNewStateManagerSingle(t *testing.T) {
 				secondary.EXPECT().Initiated().Return(false)
 			}
 
-			sm, err := NewStateManagerSingle(trillianClient, table.signer, time.Duration(0), time.Duration(0), secondary)
+			tmpFile, err := os.CreateTemp("", "sigsum-log-test-sth")
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer os.Remove(tmpFile.Name())
+			sm, err := NewStateManagerSingle(trillianClient, table.signer, time.Duration(0), time.Duration(0), secondary, tmpFile)
 			if got, want := err != nil, table.description != "valid"; got != want {
 				t.Errorf("got error %v but wanted %v in test %q: %v", got, want, table.description, err)
 			}