fix(embedded/store): handle replication of empty values

Signed-off-by: Jeronimo Irazabal <jeronimo.irazabal@gmail.com>

embedded/store/immustore.go

@@ -2868,10 +2868,6 @@ func (s *ImmuStore) ReadValue(entry *TxEntry) ([]byte, error) {
 func (s *ImmuStore) readValueAt(b []byte, off int64, hvalue [sha256.Size]byte, skipIntegrityCheck bool) (n int, err error) {
 	vLogID, offset := decodeOffset(off)
 
-	if len(b) == 0 && vLogID > 0 {
-		return 0, fmt.Errorf("%w: attempt to read empty value from a non-embedded vlog", ErrCorruptedTxData)
-	}
-
 	if !s.embeddedValues && vLogID == 0 && len(b) > 0 {
 		// it means value was not stored on any vlog i.e. a truncated transaction was replicated
 		return 0, io.EOF
@@ -2922,7 +2918,7 @@ func (s *ImmuStore) readValueAt(b []byte, off int64, hvalue [sha256.Size]byte, s
 		}
 	}
 
-	// either value was empty (n == 0 && vLogID == 0)
+	// either value was empty (n == 0)
 	// or a non-empty value (n > 0) was read from cache or disk
 
 	if !skipIntegrityCheck && (len(b) != n || hvalue != sha256.Sum256(b[:n])) {

embedded/store/immustore_test.go

@@ -4937,3 +4937,30 @@ func TestCommitOfEmptyTxWithMetadata(t *testing.T) {
 	require.NoError(t, err)
 	require.Empty(t, txholder.Entries())
 }
+
+func TestImmudbStore_ExportTxWithEmptyValues(t *testing.T) {
+	opts := DefaultOptions().WithEmbeddedValues(false)
+
+	st, err := Open(t.TempDir(), opts)
+	require.NoError(t, err)
+	require.NotNil(t, st)
+
+	defer immustoreClose(t, st)
+
+	tx, err := st.NewWriteOnlyTx(context.Background())
+	require.NoError(t, err)
+
+	err = tx.Set([]byte("my-key"), nil, nil)
+	require.NoError(t, err)
+
+	hdr, err := tx.Commit(context.Background())
+	require.NoError(t, err)
+
+	txholder, err := st.fetchAllocTx()
+	require.NoError(t, err)
+
+	defer st.releaseAllocTx(txholder)
+
+	_, err = st.ExportTx(hdr.ID, false, false, txholder)
+	require.NoError(t, err)
+}