Extract test utilities for ConnectivityService

The utilities help using ConnectivityService in tests, and will be used
to write integration tests for ConnectivityService.

Test: atest FrameworksNetTests
Change-Id: Ie895ad05139cd5768d3d8a9bd5589d72571f47e6

services/core/java/com/android/server/NetIdManager.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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 com.android.server;
+
+import android.annotation.NonNull;
+import android.util.SparseBooleanArray;
+
+import com.android.internal.annotations.GuardedBy;
+
+/**
+ * Class used to reserve and release net IDs.
+ *
+ * <p>Instances of this class are thread-safe.
+ */
+public class NetIdManager {
+    // Sequence number for Networks; keep in sync with system/netd/NetworkController.cpp
+    public static final int MIN_NET_ID = 100; // some reserved marks
+    // Top IDs reserved by IpSecService
+    public static final int MAX_NET_ID = 65535 - IpSecService.TUN_INTF_NETID_RANGE;
+
+    @GuardedBy("mNetIdInUse")
+    private final SparseBooleanArray mNetIdInUse = new SparseBooleanArray();
+
+    @GuardedBy("mNetIdInUse")
+    private int mLastNetId = MIN_NET_ID - 1;
+
+    /**
+     * Get the first netId that follows the provided lastId and is available.
+     */
+    private static int getNextAvailableNetIdLocked(
+            int lastId, @NonNull SparseBooleanArray netIdInUse) {
+        int netId = lastId;
+        for (int i = MIN_NET_ID; i <= MAX_NET_ID; i++) {
+            netId = netId < MAX_NET_ID ? netId + 1 : MIN_NET_ID;
+            if (!netIdInUse.get(netId)) {
+                return netId;
+            }
+        }
+        throw new IllegalStateException("No free netIds");
+    }
+
+    /**
+     * Reserve a new ID for a network.
+     */
+    public int reserveNetId() {
+        synchronized (mNetIdInUse) {
+            mLastNetId = getNextAvailableNetIdLocked(mLastNetId, mNetIdInUse);
+            // Make sure NetID unused.  http://b/16815182
+            mNetIdInUse.put(mLastNetId, true);
+            return mLastNetId;
+        }
+    }
+
+    /**
+     * Clear a previously reserved ID for a network.
+     */
+    public void releaseNetId(int id) {
+        synchronized (mNetIdInUse) {
+            mNetIdInUse.delete(id);
+        }
+    }
+}