[ONOS-3478] Add the implementation of SnatService interface.

Change-Id: Idae0300b8254a01e8e49abd77f9abd13c4b357fe

+/*
+ * Copyright 2015 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.vtn.table.impl;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.slf4j.LoggerFactory.getLogger;
+
+import org.onlab.osgi.DefaultServiceDirectory;
+import org.onlab.osgi.ServiceDirectory;
+import org.onlab.packet.Ethernet;
+import org.onlab.packet.IpAddress;
+import org.onlab.packet.IpPrefix;
+import org.onlab.packet.MacAddress;
+import org.onosproject.core.ApplicationId;
+import org.onosproject.net.DeviceId;
+import org.onosproject.net.flow.DefaultTrafficSelector;
+import org.onosproject.net.flow.DefaultTrafficTreatment;
+import org.onosproject.net.flow.TrafficSelector;
+import org.onosproject.net.flow.TrafficTreatment;
+import org.onosproject.net.flowobjective.DefaultForwardingObjective;
+import org.onosproject.net.flowobjective.FlowObjectiveService;
+import org.onosproject.net.flowobjective.ForwardingObjective;
+import org.onosproject.net.flowobjective.ForwardingObjective.Flag;
+import org.onosproject.net.flowobjective.Objective;
+import org.onosproject.vtn.table.SnatService;
+import org.onosproject.vtnrsc.SegmentationId;
+import org.slf4j.Logger;
+
+/**
+ * Provides implementation of SnatService.
+ */
+public class SnatServiceImpl implements SnatService {
+    private final Logger log = getLogger(getClass());
+
+    private static final int SNAT_PRIORITY = 0xffff;
+    private static final int PREFIC_LENGTH = 32;
+
+    private final FlowObjectiveService flowObjectiveService;
+    private final ApplicationId appId;
+
+    /**
+     * Construct a SnatServiceImpl object.
+     *
+     * @param appId the application id of vtn
+     */
+    public SnatServiceImpl(ApplicationId appId) {
+        this.appId = checkNotNull(appId, "ApplicationId can not be null");
+        ServiceDirectory serviceDirectory = new DefaultServiceDirectory();
+        this.flowObjectiveService = serviceDirectory.get(FlowObjectiveService.class);
+    }
+
+    @Override
+    public void programRules(DeviceId deviceId, SegmentationId matchVni,
+                             IpAddress srcIP, MacAddress ethDst,
+                             MacAddress ethSrc, IpAddress ipSrc,
+                             SegmentationId actionVni, Objective.Operation type) {
+        TrafficSelector selector = DefaultTrafficSelector.builder()
+                .matchEthType(Ethernet.TYPE_IPV4)
+                .matchTunnelId(Long.parseLong(matchVni.segmentationId()))
+                .matchIPSrc(IpPrefix.valueOf(srcIP, PREFIC_LENGTH)).build();
+
+        TrafficTreatment.Builder treatment = DefaultTrafficTreatment.builder();
+        treatment.setEthDst(ethDst).setEthSrc(ethSrc).setIpSrc(ipSrc)
+                .setTunnelId(Long.parseLong(actionVni.segmentationId()));
+        ForwardingObjective.Builder objective = DefaultForwardingObjective
+                .builder().withTreatment(treatment.build())
+                .withSelector(selector).fromApp(appId).withFlag(Flag.SPECIFIC)
+                .withPriority(SNAT_PRIORITY);
+        if (type.equals(Objective.Operation.ADD)) {
+            log.debug("RouteRules-->ADD");
+            flowObjectiveService.forward(deviceId, objective.add());
+        } else {
+            log.debug("RouteRules-->REMOVE");
+            flowObjectiveService.forward(deviceId, objective.remove());
+        }
+    }
+}