[ONOS-7584] Adding Capability of re-connecting to a P4Runtime Device.
Also addresses ONOS-7359

Change-Id: I47ec4ed429af82feb225ab5ac180b94c91366a53
diff --git a/core/api/src/main/java/org/onosproject/net/device/ChannelEvent.java b/core/api/src/main/java/org/onosproject/net/device/ChannelEvent.java
new file mode 100644
index 0000000..98ea5cb
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/device/ChannelEvent.java
@@ -0,0 +1,108 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * 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.device;
+
+import org.onlab.util.Tools;
+import org.onosproject.event.AbstractEvent;
+import org.onosproject.net.DeviceId;
+
+import static com.google.common.base.MoreObjects.toStringHelper;
+
+/**
+ * Describes event related to a channel established by ONOS with a device.
+ */
+public class ChannelEvent extends AbstractEvent<ChannelEvent.Type, DeviceId> {
+
+    private final Throwable throwable;
+
+    /**
+     * Type of device events.
+     */
+    public enum Type {
+        /**
+         * Signifies that the channel has properly connected.
+         */
+        CHANNEL_CONNECTED,
+
+        /**
+         * Signifies that the channel has disconnected.
+         */
+        CHANNEL_DISCONNECTED,
+
+        /**
+         * Signifies that an error happened on the channel with the given device.
+         */
+        CHANNEL_ERROR
+
+    }
+
+    /**
+     * Creates an event of a given type and for the specified device.
+     *
+     * @param type     device event type
+     * @param deviceId event device subject
+     */
+    public ChannelEvent(Type type, DeviceId deviceId) {
+        this(type, deviceId, null);
+    }
+
+    /**
+     * Creates an event of a given type and for the specified device, given a certain throwable.
+     *
+     * @param type      device event type
+     * @param deviceId  event device subject
+     * @param throwable exception happened on the channel
+     */
+    public ChannelEvent(Type type, DeviceId deviceId, Throwable throwable) {
+        super(type, deviceId);
+        this.throwable = throwable;
+    }
+
+    /**
+     * Creates an event of a given type and for the specified device and the current time.
+     *
+     * @param type      device event type
+     * @param deviceId  event device subject
+     * @param throwable exception happened on the channel
+     * @param time      occurrence time
+     */
+    public ChannelEvent(Type type, DeviceId deviceId, Throwable throwable, long time) {
+        super(type, deviceId, time);
+        this.throwable = throwable;
+    }
+
+    /**
+     * Returns the exception that happened on the channel.
+     *
+     * @return a throwable if associated to the event, otherwise null.
+     */
+    public Throwable throwable() {
+        return throwable;
+    }
+
+    @Override
+    public String toString() {
+        if (throwable == null) {
+            return super.toString();
+        }
+        return toStringHelper(this)
+                .add("time", Tools.defaultOffsetDataTime(time()))
+                .add("type", type())
+                .add("subject", subject())
+                .add("throwable", throwable)
+                .toString();
+    }
+}
diff --git a/core/api/src/main/java/org/onosproject/net/device/ChannelListener.java b/core/api/src/main/java/org/onosproject/net/device/ChannelListener.java
new file mode 100644
index 0000000..cdc90bf70
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/device/ChannelListener.java
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * 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.device;
+
+import org.onosproject.event.EventListener;
+
+/**
+ * A listener to receive events related to a transport channel established with a device.
+ */
+public interface ChannelListener extends EventListener<ChannelEvent> {
+}
diff --git a/core/api/src/main/java/org/onosproject/net/device/DeviceHandshaker.java b/core/api/src/main/java/org/onosproject/net/device/DeviceHandshaker.java
index eb3c19c..606248a 100644
--- a/core/api/src/main/java/org/onosproject/net/device/DeviceHandshaker.java
+++ b/core/api/src/main/java/org/onosproject/net/device/DeviceHandshaker.java
@@ -46,4 +46,22 @@
      */
     CompletableFuture<MastershipRole> roleChanged(MastershipRole newRole);
 
+    /**
+     * Applies a listener to a channel established with the device.
+     *
+     * @param listener the channel listener
+     */
+    default void addChannelListener(ChannelListener listener) {
+        throw new UnsupportedOperationException("Listener Registration not supported");
+    }
+
+    /**
+     * Removes a listener to a channel established with the device.
+     *
+     * @param listener the channel listener
+     */
+    default void removeChannelListener(ChannelListener listener) {
+        throw new UnsupportedOperationException("Listener Removal not supported");
+    }
+
 }