lexi: Avoid generating key when reading (#3159)

When looking up a key that did not exist in the db, it would attempt to
generate a new one, and a nil error would be returned instead of
ErrKeyNotFound.

dex/lexi/lexi.go

@@ -26,7 +26,7 @@ func convertError(err error) error {
 	case errors.Is(err, badger.ErrKeyNotFound):
 		return ErrKeyNotFound
 	}
-	return nil
+	return err
 }
 
 // DB is the Lexi DB. The Lexi DB wraps a badger key-value database and provides
@@ -177,13 +177,13 @@ func (db *DB) nextID() (dbID DBID, _ error) {
 // method is provided as a tool to keep database index entries short.
 func (db *DB) KeyID(kB []byte) (dbID DBID, err error) {
 	err = db.View(func(txn *badger.Txn) error {
-		dbID, err = db.keyID(txn, kB)
+		dbID, err = db.keyID(txn, kB, true)
 		return err
 	})
 	return
 }
 
-func (db *DB) keyID(txn *badger.Txn, kB []byte) (dbID DBID, err error) {
+func (db *DB) keyID(txn *badger.Txn, kB []byte, readOnly bool) (dbID DBID, err error) {
 	item, err := txn.Get(prefixedKey(keyToIDPrefix, kB))
 	if err == nil {
 		err = item.Value(func(v []byte) error {
@@ -192,7 +192,7 @@ func (db *DB) keyID(txn *badger.Txn, kB []byte) (dbID DBID, err error) {
 		})
 		return
 	}
-	if errors.Is(err, ErrKeyNotFound) {
+	if !readOnly && errors.Is(err, ErrKeyNotFound) {
 		if dbID, err = db.nextID(); err != nil {
 			return
 		}

dex/lexi/table.go

@@ -42,7 +42,7 @@ func (t *Table) Get(k encoding.BinaryMarshaler, v encoding.BinaryUnmarshaler) er
 		return fmt.Errorf("error marshaling key: %w", err)
 	}
 	return t.View(func(txn *badger.Txn) error {
-		dbID, err := t.keyID(txn, kB)
+		dbID, err := t.keyID(txn, kB, true)
 		if err != nil {
 			return convertError(err)
 		}
@@ -122,7 +122,7 @@ func (t *Table) Set(k, v encoding.BinaryMarshaler, setOpts ...SetOption) error {
 	}
 	d := &datum{v: vB, indexes: make([][]byte, len(t.indexes))}
 	return t.Update(func(txn *badger.Txn) error {
-		dbID, err := t.keyID(txn, kB)
+		dbID, err := t.keyID(txn, kB, false)
 		if err != nil {
 			return convertError(err)
 		}
@@ -160,7 +160,7 @@ func (t *Table) Set(k, v encoding.BinaryMarshaler, setOpts ...SetOption) error {
 // and the id<->key mappings.
 func (t *Table) Delete(kB []byte) error {
 	return t.Update(func(txn *badger.Txn) error {
-		dbID, err := t.keyID(txn, kB)
+		dbID, err := t.keyID(txn, kB, true)
 		if err != nil {
 			return convertError(err)
 		}