Revert "Remove providesRoutesToMostDestinations."

This reverts commit 92bd90fa0b.

Reason for revert: multiple build breakages b/137069068

Change-Id: I60a4f71e13fe82f970b177a07c0b58439cbc64ff

core/java/android/net/NetworkUtils.java

@@ -29,6 +29,7 @@ import android.util.Log;
 import android.util.Pair;
 
 import java.io.FileDescriptor;
+import java.math.BigInteger;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
 import java.net.InetAddress;
@@ -36,6 +37,7 @@ import java.net.SocketException;
 import java.net.UnknownHostException;
 import java.util.Collection;
 import java.util.Locale;
+import java.util.TreeSet;
 
 /**
  * Native methods for managing network interfaces.
@@ -390,6 +392,74 @@ public class NetworkUtils {
         return result;
     }
 
+    /**
+     * Returns a prefix set without overlaps.
+     *
+     * This expects the src set to be sorted from shorter to longer. Results are undefined
+     * failing this condition. The returned prefix set is sorted in the same order as the
+     * passed set, with the same comparator.
+     */
+    private static TreeSet<IpPrefix> deduplicatePrefixSet(final TreeSet<IpPrefix> src) {
+        final TreeSet<IpPrefix> dst = new TreeSet<>(src.comparator());
+        // Prefixes match addresses that share their upper part up to their length, therefore
+        // the only kind of possible overlap in two prefixes is strict inclusion of the longer
+        // (more restrictive) in the shorter (including equivalence if they have the same
+        // length).
+        // Because prefixes in the src set are sorted from shorter to longer, deduplicating
+        // is done by simply iterating in order, and not adding any longer prefix that is
+        // already covered by a shorter one.
+        newPrefixes:
+        for (IpPrefix newPrefix : src) {
+            for (IpPrefix existingPrefix : dst) {
+                if (existingPrefix.containsPrefix(newPrefix)) {
+                    continue newPrefixes;
+                }
+            }
+            dst.add(newPrefix);
+        }
+        return dst;
+    }
+
+    /**
+     * Returns how many IPv4 addresses match any of the prefixes in the passed ordered set.
+     *
+     * Obviously this returns an integral value between 0 and 2**32.
+     * The behavior is undefined if any of the prefixes is not an IPv4 prefix or if the
+     * set is not ordered smallest prefix to longer prefix.
+     *
+     * @param prefixes the set of prefixes, ordered by length
+     */
+    public static long routedIPv4AddressCount(final TreeSet<IpPrefix> prefixes) {
+        long routedIPCount = 0;
+        for (final IpPrefix prefix : deduplicatePrefixSet(prefixes)) {
+            if (!prefix.isIPv4()) {
+                Log.wtf(TAG, "Non-IPv4 prefix in routedIPv4AddressCount");
+            }
+            int rank = 32 - prefix.getPrefixLength();
+            routedIPCount += 1L << rank;
+        }
+        return routedIPCount;
+    }
+
+    /**
+     * Returns how many IPv6 addresses match any of the prefixes in the passed ordered set.
+     *
+     * This returns a BigInteger between 0 and 2**128.
+     * The behavior is undefined if any of the prefixes is not an IPv6 prefix or if the
+     * set is not ordered smallest prefix to longer prefix.
+     */
+    public static BigInteger routedIPv6AddressCount(final TreeSet<IpPrefix> prefixes) {
+        BigInteger routedIPCount = BigInteger.ZERO;
+        for (final IpPrefix prefix : deduplicatePrefixSet(prefixes)) {
+            if (!prefix.isIPv6()) {
+                Log.wtf(TAG, "Non-IPv6 prefix in routedIPv6AddressCount");
+            }
+            int rank = 128 - prefix.getPrefixLength();
+            routedIPCount = routedIPCount.add(BigInteger.ONE.shiftLeft(rank));
+        }
+        return routedIPCount;
+    }
+
     private static final int[] ADDRESS_FAMILIES = new int[] {AF_INET, AF_INET6};
 
     /**

tests/net/java/android/net/NetworkUtilsTest.java

@@ -0,0 +1,128 @@
+/*
+ * Copyright (C) 2015 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 android.net;
+
+import static junit.framework.Assert.assertEquals;
+
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import java.math.BigInteger;
+import java.util.TreeSet;
+
+@RunWith(AndroidJUnit4.class)
+@androidx.test.filters.SmallTest
+public class NetworkUtilsTest {
+    @Test
+    public void testRoutedIPv4AddressCount() {
+        final TreeSet<IpPrefix> set = new TreeSet<>(IpPrefix.lengthComparator());
+        // No routes routes to no addresses.
+        assertEquals(0, NetworkUtils.routedIPv4AddressCount(set));
+
+        set.add(new IpPrefix("0.0.0.0/0"));
+        assertEquals(1l << 32, NetworkUtils.routedIPv4AddressCount(set));
+
+        set.add(new IpPrefix("20.18.0.0/16"));
+        set.add(new IpPrefix("20.18.0.0/24"));
+        set.add(new IpPrefix("20.18.0.0/8"));
+        // There is a default route, still covers everything
+        assertEquals(1l << 32, NetworkUtils.routedIPv4AddressCount(set));
+
+        set.clear();
+        set.add(new IpPrefix("20.18.0.0/24"));
+        set.add(new IpPrefix("20.18.0.0/8"));
+        // The 8-length includes the 24-length prefix
+        assertEquals(1l << 24, NetworkUtils.routedIPv4AddressCount(set));
+
+        set.add(new IpPrefix("10.10.10.126/25"));
+        // The 8-length does not include this 25-length prefix
+        assertEquals((1l << 24) + (1 << 7), NetworkUtils.routedIPv4AddressCount(set));
+
+        set.clear();
+        set.add(new IpPrefix("1.2.3.4/32"));
+        set.add(new IpPrefix("1.2.3.4/32"));
+        set.add(new IpPrefix("1.2.3.4/32"));
+        set.add(new IpPrefix("1.2.3.4/32"));
+        assertEquals(1l, NetworkUtils.routedIPv4AddressCount(set));
+
+        set.add(new IpPrefix("1.2.3.5/32"));
+        set.add(new IpPrefix("1.2.3.6/32"));
+
+        set.add(new IpPrefix("1.2.3.7/32"));
+        set.add(new IpPrefix("1.2.3.8/32"));
+        set.add(new IpPrefix("1.2.3.9/32"));
+        set.add(new IpPrefix("1.2.3.0/32"));
+        assertEquals(7l, NetworkUtils.routedIPv4AddressCount(set));
+
+        // 1.2.3.4/30 eats 1.2.3.{4-7}/32
+        set.add(new IpPrefix("1.2.3.4/30"));
+        set.add(new IpPrefix("6.2.3.4/28"));
+        set.add(new IpPrefix("120.2.3.4/16"));
+        assertEquals(7l - 4 + 4 + 16 + 65536, NetworkUtils.routedIPv4AddressCount(set));
+    }
+
+    @Test
+    public void testRoutedIPv6AddressCount() {
+        final TreeSet<IpPrefix> set = new TreeSet<>(IpPrefix.lengthComparator());
+        // No routes routes to no addresses.
+        assertEquals(BigInteger.ZERO, NetworkUtils.routedIPv6AddressCount(set));
+
+        set.add(new IpPrefix("::/0"));
+        assertEquals(BigInteger.ONE.shiftLeft(128), NetworkUtils.routedIPv6AddressCount(set));
+
+        set.add(new IpPrefix("1234:622a::18/64"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6adb/96"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6adb/8"));
+        // There is a default route, still covers everything
+        assertEquals(BigInteger.ONE.shiftLeft(128), NetworkUtils.routedIPv6AddressCount(set));
+
+        set.clear();
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6adb/96"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6adb/8"));
+        // The 8-length includes the 96-length prefix
+        assertEquals(BigInteger.ONE.shiftLeft(120), NetworkUtils.routedIPv6AddressCount(set));
+
+        set.add(new IpPrefix("10::26/64"));
+        // The 8-length does not include this 64-length prefix
+        assertEquals(BigInteger.ONE.shiftLeft(120).add(BigInteger.ONE.shiftLeft(64)),
+                NetworkUtils.routedIPv6AddressCount(set));
+
+        set.clear();
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad4/128"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad4/128"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad4/128"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad4/128"));
+        assertEquals(BigInteger.ONE, NetworkUtils.routedIPv6AddressCount(set));
+
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad5/128"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad6/128"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad7/128"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad8/128"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad9/128"));
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad0/128"));
+        assertEquals(BigInteger.valueOf(7), NetworkUtils.routedIPv6AddressCount(set));
+
+        // add4:f00:80:f7:1111::6ad4/126 eats add4:f00:8[:f7:1111::6ad{4-7}/128
+        set.add(new IpPrefix("add4:f00:80:f7:1111::6ad4/126"));
+        set.add(new IpPrefix("d00d:f00:80:f7:1111::6ade/124"));
+        set.add(new IpPrefix("f00b:a33::/112"));
+        assertEquals(BigInteger.valueOf(7l - 4 + 4 + 16 + 65536),
+                NetworkUtils.routedIPv6AddressCount(set));
+    }
+}