Allow writing null when "AllowNulls" Property is true

fixes #1254

opc-ua-sdk/integration-tests/src/test/java/org/eclipse/milo/opcua/sdk/server/api/util/AttributeWriterTest.java

@@ -0,0 +1,100 @@
+package org.eclipse.milo.opcua.sdk.server.api.util;
+
+import org.eclipse.milo.opcua.sdk.core.AccessLevel;
+import org.eclipse.milo.opcua.sdk.server.nodes.UaVariableNode;
+import org.eclipse.milo.opcua.sdk.test.AbstractClientServerTest;
+import org.eclipse.milo.opcua.stack.core.Identifiers;
+import org.eclipse.milo.opcua.stack.core.StatusCodes;
+import org.eclipse.milo.opcua.stack.core.types.builtin.DataValue;
+import org.eclipse.milo.opcua.stack.core.types.builtin.LocalizedText;
+import org.eclipse.milo.opcua.stack.core.types.builtin.NodeId;
+import org.eclipse.milo.opcua.stack.core.types.builtin.QualifiedName;
+import org.eclipse.milo.opcua.stack.core.types.builtin.StatusCode;
+import org.eclipse.milo.opcua.stack.core.types.builtin.Variant;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class AttributeWriterTest extends AbstractClientServerTest {
+
+    @Test
+    void writeNullAllowed() throws Exception {
+        StatusCode statusCode = client.writeValue(
+            new NodeId(2, "AllowNulls"),
+            DataValue.valueOnly(Variant.NULL_VALUE)
+        ).get();
+
+        assertEquals(StatusCode.GOOD, statusCode);
+    }
+
+    @Test
+    void writeNullDisallowed() throws Exception {
+        StatusCode statusCode = client.writeValue(
+            new NodeId(2, "DisallowNulls"),
+            DataValue.valueOnly(Variant.NULL_VALUE)
+        ).get();
+
+        assertEquals(new StatusCode(StatusCodes.Bad_TypeMismatch), statusCode);
+    }
+
+    @Test
+    void writeNullNotConfigured() throws Exception {
+        // Default behavior when AllowNulls property is not configured is to reject null values.
+        StatusCode statusCode = client.writeValue(
+            new NodeId(2, "AllowNullsNotConfigured"),
+            DataValue.valueOnly(Variant.NULL_VALUE)
+        ).get();
+
+        assertEquals(new StatusCode(StatusCodes.Bad_TypeMismatch), statusCode);
+    }
+
+    @BeforeAll
+    void configure() {
+        testNamespace.configureNode((context, nodeManager) -> {
+            UaVariableNode allowNulls = UaVariableNode.build(
+                context,
+                b -> {
+                    b.setNodeId(new NodeId(2, "AllowNulls"));
+                    b.setBrowseName(new QualifiedName(2, "AllowNulls"));
+                    b.setDisplayName(LocalizedText.english("AllowNulls"));
+                    b.setDataType(Identifiers.String);
+                    b.setAccessLevel(AccessLevel.READ_WRITE);
+                    b.setUserAccessLevel(AccessLevel.READ_WRITE);
+                    return b.buildAndAdd();
+                }
+            );
+
+            allowNulls.setAllowNulls(true);
+
+            UaVariableNode disallowNulls = UaVariableNode.build(
+                context,
+                b -> {
+                    b.setNodeId(new NodeId(2, "DisallowNulls"));
+                    b.setBrowseName(new QualifiedName(2, "DisallowNulls"));
+                    b.setDisplayName(LocalizedText.english("DisallowNulls"));
+                    b.setDataType(Identifiers.String);
+                    b.setAccessLevel(AccessLevel.READ_WRITE);
+                    b.setUserAccessLevel(AccessLevel.READ_WRITE);
+                    return b.buildAndAdd();
+                }
+            );
+
+            disallowNulls.setAllowNulls(false);
+
+            UaVariableNode.build(
+                context,
+                b -> {
+                    b.setNodeId(new NodeId(2, "AllowNullsNotConfigured"));
+                    b.setBrowseName(new QualifiedName(2, "AllowNullsNotConfigured"));
+                    b.setDisplayName(LocalizedText.english("AllowNullsNotConfigured"));
+                    b.setDataType(Identifiers.String);
+                    b.setAccessLevel(AccessLevel.READ_WRITE);
+                    b.setUserAccessLevel(AccessLevel.READ_WRITE);
+                    return b.buildAndAdd();
+                }
+            );
+        });
+    }
+
+}

opc-ua-sdk/sdk-server/src/main/java/org/eclipse/milo/opcua/sdk/server/util/AttributeWriter.java

@@ -23,6 +23,7 @@
 import org.eclipse.milo.opcua.sdk.server.nodes.AttributeContext;
 import org.eclipse.milo.opcua.sdk.server.nodes.UaNode;
 import org.eclipse.milo.opcua.sdk.server.nodes.UaServerNode;
+import org.eclipse.milo.opcua.sdk.server.nodes.UaVariableNode;
 import org.eclipse.milo.opcua.stack.core.AttributeId;
 import org.eclipse.milo.opcua.stack.core.Identifiers;
 import org.eclipse.milo.opcua.stack.core.StatusCodes;
@@ -119,14 +120,20 @@ public static void writeAttribute(AttributeContext context,
         );
 
         if (attributeId == AttributeId.Value) {
+            boolean allowNulls = false;
+            if (node instanceof UaVariableNode) {
+                Boolean b = ((UaVariableNode) node).getAllowNulls();
+                allowNulls = b != null ? b : false;
+            }
+
             NodeId dataType = extract(
                 node.getAttribute(
                     internalContext,
                     AttributeId.DataType)
             );
 
             if (dataType != null) {
-                value = validateDataType(context.getServer(), dataType, value);
+                value = validateDataType(context.getServer(), dataType, value, allowNulls);
             }
 
             Integer valueRank = extract(
@@ -206,13 +213,20 @@ private static WriteMask writeMaskForAttribute(AttributeId attributeId) {
     private static DataValue validateDataType(
         OpcUaServer server,
         NodeId dataType,
-        DataValue value) throws UaException {
+        DataValue value,
+        boolean allowNulls
+    ) throws UaException {
 
         Variant variant = value.getValue();
-        if (variant == null) return value;
 
         Object o = variant.getValue();
-        if (o == null) throw new UaException(StatusCodes.Bad_TypeMismatch);
+        if (o == null) {
+            if (allowNulls) {
+                return value;
+            } else {
+                throw new UaException(StatusCodes.Bad_TypeMismatch);
+            }
+        }
 
         Class<?> valueClass = o.getClass().isArray() ?
             ArrayUtil.getType(o) : o.getClass();