Improve writeCheckpoint in MySQL storage implementation (#82)

* Improve `writeCheckpoint` in MySQL storage implementation

* Remove unused `WriteCheckpointFunc`

* Use `rfc6962.DefaultHasher.EmptyRoot()` as the initial checkpoint root hash

cmd/example-mysql/main.go

@@ -23,12 +23,14 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"os"
 	"strconv"
 	"strings"
 	"time"
 
 	tessera "github.com/transparency-dev/trillian-tessera"
 	"github.com/transparency-dev/trillian-tessera/storage/mysql"
+	"golang.org/x/mod/sumdb/note"
 	"k8s.io/klog/v2"
 )
 
@@ -38,6 +40,7 @@ var (
 	dbMaxOpenConns    = flag.Int("db_max_open_conns", 64, "")
 	dbMaxIdleConns    = flag.Int("db_max_idle_conns", 64, "")
 	listen            = flag.String("listen", ":2024", "Address:port to listen on")
+	privateKeyPath    = flag.String("private_key_path", "", "Location of private key file")
 )
 
 func main() {
@@ -53,7 +56,16 @@ func main() {
 	db.SetMaxOpenConns(*dbMaxOpenConns)
 	db.SetMaxIdleConns(*dbMaxIdleConns)
 
-	storage, err := mysql.New(ctx, db)
+	rawPrivateKey, err := os.ReadFile(*privateKeyPath)
+	if err != nil {
+		klog.Exitf("Failed to read private key file %q: %v", *privateKeyPath, err)
+	}
+	noteSigner, err := note.NewSigner(string(rawPrivateKey))
+	if err != nil {
+		klog.Exitf("Failed to create new signer: %v", err)
+	}
+
+	storage, err := mysql.New(ctx, db, tessera.WithCheckpointSigner(noteSigner))
 	if err != nil {
 		klog.Exitf("Failed to create new MySQL storage: %v", err)
 	}

go.mod

@@ -56,7 +56,7 @@ require (
 	go.opentelemetry.io/otel v1.24.0 // indirect
 	go.opentelemetry.io/otel/metric v1.24.0 // indirect
 	go.opentelemetry.io/otel/trace v1.24.0 // indirect
-	golang.org/x/crypto v0.25.0 // indirect
+	golang.org/x/crypto v0.25.0
 	golang.org/x/net v0.27.0 // indirect
 	golang.org/x/oauth2 v0.21.0 // indirect
 	golang.org/x/sync v0.7.0

storage/mysql/mysql.go

@@ -20,6 +20,8 @@ import (
 	"database/sql"
 
 	_ "github.com/go-sql-driver/mysql"
+	"github.com/transparency-dev/merkle/rfc6962"
+	tessera "github.com/transparency-dev/trillian-tessera"
 	"k8s.io/klog/v2"
 )
 
@@ -35,12 +37,16 @@ const (
 // Storage is a MySQL-based storage implementation for Tessera.
 type Storage struct {
 	db *sql.DB
+
+	newCheckpoint tessera.NewCPFunc
 }
 
 // New creates a new instance of the MySQL-based Storage.
-func New(ctx context.Context, db *sql.DB) (*Storage, error) {
+func New(ctx context.Context, db *sql.DB, opts ...func(*tessera.StorageOptions)) (*Storage, error) {
+	opt := tessera.ResolveStorageOptions(nil, opts...)
 	s := &Storage{
-		db: db,
+		db:            db,
+		newCheckpoint: opt.NewCP,
 	}
 	if err := s.db.Ping(); err != nil {
 		klog.Errorf("Failed to ping database: %v", err)
@@ -55,10 +61,25 @@ func New(ctx context.Context, db *sql.DB) (*Storage, error) {
 		}
 
 		klog.Infof("Initializing checkpoint")
-		if err := s.writeCheckpoint(ctx, []byte("")); err != nil {
+		// Get a Tx for making transaction requests.
+		tx, err := s.db.BeginTx(ctx, nil)
+		if err != nil {
+			return nil, err
+		}
+		// Defer a rollback in case anything fails.
+		defer func() {
+			if err := tx.Rollback(); err != nil && err != sql.ErrTxDone {
+				klog.Errorf("Failed to rollback in write initial checkpoint: %v", err)
+			}
+		}()
+		if err := s.writeCheckpoint(ctx, tx, 0, rfc6962.DefaultHasher.EmptyRoot()); err != nil {
 			klog.Errorf("Failed to write initial checkpoint: %v", err)
 			return nil, err
 		}
+		// Commit the transaction.
+		if err := tx.Commit(); err != nil {
+			return nil, err
+		}
 	}
 
 	return s, nil
@@ -75,27 +96,19 @@ func (s *Storage) ReadCheckpoint(ctx context.Context) ([]byte, error) {
 	return checkpoint, row.Scan(&checkpoint)
 }
 
-// writeCheckpoint stores a raw log checkpoint.
-func (s *Storage) writeCheckpoint(ctx context.Context, rawCheckpoint []byte) error {
-	// Get a Tx for making transaction requests.
-	tx, err := s.db.BeginTx(ctx, nil)
+// writeCheckpoint stores the log signed checkpoint.
+func (s *Storage) writeCheckpoint(ctx context.Context, tx *sql.Tx, size uint64, rootHash []byte) error {
+	rawCheckpoint, err := s.newCheckpoint(size, rootHash)
 	if err != nil {
 		return err
 	}
-	// Defer a rollback in case anything fails.
-	defer func() {
-		if err := tx.Rollback(); err != nil && err != sql.ErrTxDone {
-			klog.Errorf("Failed to rollback in writeCheckpoint: %v", err)
-		}
-	}()
 
 	if _, err := tx.ExecContext(ctx, replaceCheckpointSQL, checkpointID, rawCheckpoint); err != nil {
 		klog.Errorf("Failed to execute replaceCheckpointSQL: %v", err)
 		return err
 	}
 
-	// Commit the transaction.
-	return tx.Commit()
+	return nil
 }
 
 // ReadTile returns a full tile or a partial tile at the given level and index.