ONOS-5218 protected Link related changes.

Change-Id: I0163a2c4ec3c32b5aaf320a71d5ab5929ad3c73a

@@ -145,6 +145,13 @@ public final class AnnotationKeys {
     public static final String PASSWORD = "password";
 
     /**
+     * Link annotation key to express that a Link
+     * is backed by underlying protection mechanism.
+     */
+    // value is undefined at the moment, only using key existence
+    public static final String PROTECTED = "protected";
+
+    /**
      * Returns the value annotated object for the specified annotation key.
      * The annotated value is expected to be String that can be parsed as double.
      * If parsing fails, the returned value will be 1.0.

+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.net.intent.constraint;
+
+import org.onosproject.net.AnnotationKeys;
+import org.onosproject.net.Link;
+import org.onosproject.net.intent.ResourceContext;
+
+/**
+ * Constraint to request using only {@link AnnotationKeys#PROTECTED protected}
+ * Links.
+ */
+public class ProtectedConstraint extends BooleanConstraint {
+
+    private static final ProtectedConstraint PROTECTED_CONSTRAINT
+            = new ProtectedConstraint();
+
+    /**
+     * Returns {@link ProtectedConstraint} instance.
+     *
+     * @return {@link ProtectedConstraint} instance
+     */
+    public static ProtectedConstraint useProtectedLink() {
+        return PROTECTED_CONSTRAINT;
+    }
+
+    @Override
+    public boolean isValid(Link link, ResourceContext context) {
+        return link.annotations().keys().contains(AnnotationKeys.PROTECTED);
+    }
+
+    @Override
+    public String toString() {
+        return "Protected";
+    }
+
+}