Fix UriReference issue in MixedLwM2mLink when rootpath is not null.

leshan-core/src/main/java/org/eclipse/leshan/core/link/lwm2m/MixedLwM2mLink.java

@@ -43,15 +43,27 @@ public MixedLwM2mLink(String rootPath, LwM2mPath path, Collection<? extends Attr
     }
 
     public MixedLwM2mLink(String rootPath, LwM2mPath path, MixedLwM2mAttributeSet attributes) {
-        super(rootPath == null || rootPath.equals("/") ? path.toString() : rootPath + path.toString(), attributes);
+        super(getUriReference(rootPath, path), attributes);
 
-        Validate.notNull(path);
         Validate.notNull(attributes);
 
         this.path = path;
         this.rootPath = rootPath == null ? "/" : rootPath;
     }
 
+    private static String getUriReference(String rootPath, LwM2mPath path) {
+        Validate.notNull(path);
+
+        if (rootPath == null || rootPath.equals("/")) {
+            return path.toString();
+        } else if (path.isRoot()) {
+            // rootpath can not be null because we check this before
+            return rootPath;
+        } else {
+            return rootPath + path.toString();
+        }
+    }
+
     public LwM2mPath getPath() {
         return path;
     }

leshan-core/src/test/java/org/eclipse/leshan/core/link/MixedLwM2mLinkTest.java

@@ -0,0 +1,44 @@
+/*******************************************************************************
+ * Copyright (c) 2022 Sierra Wireless and others.
+ * 
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v2.0
+ * and Eclipse Distribution License v1.0 which accompany this distribution.
+ * 
+ * The Eclipse Public License is available at
+ *    http://www.eclipse.org/legal/epl-v20.html
+ * and the Eclipse Distribution License is available at
+ *    http://www.eclipse.org/org/documents/edl-v10.html.
+ * 
+ * Contributors:
+ *     Sierra Wireless - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.leshan.core.link;
+
+import static org.junit.Assert.assertEquals;
+
+import org.eclipse.leshan.core.link.attributes.ResourceTypeAttribute;
+import org.eclipse.leshan.core.link.lwm2m.MixedLwM2mLink;
+import org.eclipse.leshan.core.node.LwM2mPath;
+import org.junit.Test;
+
+public class MixedLwM2mLinkTest {
+
+    @Test
+    public void check_uri_reference() {
+        Link link = new MixedLwM2mLink("/root", LwM2mPath.ROOTPATH, new ResourceTypeAttribute("oma.lwm2m"));
+        assertEquals("/root", link.getUriReference());
+
+        link = new MixedLwM2mLink("/root", new LwM2mPath(2));
+        assertEquals("/root/2", link.getUriReference());
+
+        link = new MixedLwM2mLink("/root/", new LwM2mPath(2));
+        assertEquals("/root//2", link.getUriReference());
+
+        link = new MixedLwM2mLink("/", new LwM2mPath(2));
+        assertEquals("/2", link.getUriReference());
+
+        link = new MixedLwM2mLink(null, new LwM2mPath(2));
+        assertEquals("/2", link.getUriReference());
+    }
+}