Binary iidm: distinction between null and empty string

commons/src/main/java/com/powsybl/commons/binary/BinReader.java

@@ -71,7 +71,7 @@ private void readDictionary() throws IOException {
     private String readString() {
         try {
             int stringNbBytes = dis.readShort();
-            if (stringNbBytes == 0) {
+            if (stringNbBytes == -1) {
                 return null;
             }
             byte[] stringBytes = dis.readNBytes(stringNbBytes);

commons/src/main/java/com/powsybl/commons/binary/BinWriter.java

@@ -52,7 +52,7 @@ private static void writeIndex(int index, DataOutputStream dataOutputStream) {
     private static void writeString(String value, DataOutputStream dataOutputStream) {
         try {
             if (value == null) {
-                writeIndex(0, dataOutputStream);
+                writeIndex(-1, dataOutputStream);
             } else {
                 byte[] bytes = value.getBytes(StandardCharsets.UTF_8);
                 writeIndex(bytes.length, dataOutputStream);

iidm/iidm-serde/src/test/java/com/powsybl/iidm/serde/BinaryTest.java

@@ -0,0 +1,51 @@
+/**
+ * Copyright (c) 2024, RTE (http://www.rte-france.com)
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ * SPDX-License-Identifier: MPL-2.0
+ */
+package com.powsybl.iidm.serde;
+
+import com.powsybl.commons.io.TreeDataFormat;
+import com.powsybl.iidm.network.Line;
+import com.powsybl.iidm.network.Network;
+import com.powsybl.iidm.network.TopologyKind;
+import org.junit.jupiter.api.Test;
+
+import java.nio.file.Path;
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * @author Florian Dupuy {@literal <florian.dupuy at rte-france.com>}
+ */
+class BinaryTest extends AbstractIidmSerDeTest {
+
+    @Test
+    void testEmptyNullStringAttributes() {
+        Network n0 = Network.create("test", "test");
+        n0.setProperty("property", "");
+        n0.newVoltageLevel().setId("vl1").setNominalV(220).setTopologyKind(TopologyKind.NODE_BREAKER).add();
+        n0.newVoltageLevel().setId("vl2").setNominalV(220).setTopologyKind(TopologyKind.NODE_BREAKER).add();
+        Line l0 = n0.newLine().setId("line").setName("")
+                .setVoltageLevel1("vl1").setNode1(0)
+                .setVoltageLevel2("vl2").setNode2(0)
+                .setR(0.1).setX(10)
+                .add();
+        l0.newCurrentLimits1().add();
+        l0.cancelSelectedOperationalLimitsGroup1(); // selected group id is now null on side 1
+        l0.newOperationalLimitsGroup2("").newCurrentLimits().add();
+        l0.setSelectedOperationalLimitsGroup2(""); // selected group id is now "" on side 2
+
+        Path binFile = fileSystem.getPath("/work/test");
+        NetworkSerDe.write(n0, new ExportOptions().setFormat(TreeDataFormat.BIN), binFile);
+        Network n1 = NetworkSerDe.read(binFile, new ImportOptions().setFormat(TreeDataFormat.BIN));
+        Line s = n1.getLine("line");
+        assertEquals("", n1.getProperty("property"));
+        assertEquals(Optional.of(""), s.getOptionalName());
+        assertEquals(Optional.empty(), l0.getSelectedOperationalLimitsGroupId1());
+        assertEquals(Optional.of(""), l0.getSelectedOperationalLimitsGroupId2());
+    }
+}

iidm/iidm-serde/src/test/java/com/powsybl/iidm/serde/EurostagBinaryTest.java

@@ -1,8 +1,9 @@
 /**
- * Copyright (c) 2019, RTE (http://www.rte-france.com)
+ * Copyright (c) 2024, RTE (http://www.rte-france.com)
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ * SPDX-License-Identifier: MPL-2.0
  */
 package com.powsybl.iidm.serde;
 
@@ -23,7 +24,7 @@
 import static com.powsybl.iidm.serde.IidmSerDeConstants.CURRENT_IIDM_VERSION;
 
 /**
- * @author Geoffroy Jamgotchian {@literal <geoffroy.jamgotchian at rte-france.com>}
+ * @author Florian Dupuy {@literal <florian.dupuy at rte-france.com>}
  */
 class EurostagBinaryTest extends AbstractIidmSerDeTest {