Refactors McastHandler to optimize network failures

Changes:
- Introduces a paths store
- Optimizes SINKS_ADDED, SINKS_REMOVED
- Uses SINKS_REMOVED to handle egress failures
- Optimizes SOURCES_ADDED, SOURCES_REMOVED
- Leverages SOURCES_REMOVED to handle ingress failures
- Optimizes infra failures

Change-Id: I16d264f58d6fe11cfce4a546f7b4ab82a9fcc21b
diff --git a/app/src/main/java/org/onosproject/segmentrouting/mcast/McastPathStoreKeySerializer.java b/app/src/main/java/org/onosproject/segmentrouting/mcast/McastPathStoreKeySerializer.java
new file mode 100644
index 0000000..4ef0194
--- /dev/null
+++ b/app/src/main/java/org/onosproject/segmentrouting/mcast/McastPathStoreKeySerializer.java
@@ -0,0 +1,52 @@
+/*
+ * Copyright 2020-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.segmentrouting.mcast;
+
+
+import com.esotericsoftware.kryo.Kryo;
+import com.esotericsoftware.kryo.Serializer;
+import com.esotericsoftware.kryo.io.Input;
+import com.esotericsoftware.kryo.io.Output;
+import org.onlab.packet.IpAddress;
+import org.onosproject.net.ConnectPoint;
+
+/**
+ * Custom serializer for {@link McastPathStoreKey}.
+ */
+class McastPathStoreKeySerializer extends Serializer<McastPathStoreKey> {
+
+    /**
+     * Creates {@link McastPathStoreKeySerializer} serializer instance.
+     */
+    McastPathStoreKeySerializer() {
+        // non-null, immutable
+        super(false, true);
+    }
+
+    @Override
+    public void write(Kryo kryo, Output output, McastPathStoreKey object) {
+        kryo.writeClassAndObject(output, object.mcastIp());
+        kryo.writeClassAndObject(output, object.source());
+    }
+
+    @Override
+    public McastPathStoreKey read(Kryo kryo, Input input, Class<McastPathStoreKey> type) {
+        IpAddress mcastIp = (IpAddress) kryo.readClassAndObject(input);
+        ConnectPoint source = (ConnectPoint) kryo.readClassAndObject(input);
+        return new McastPathStoreKey(mcastIp, source);
+    }
+}