Add DhcpServingParams

Those parameters will be used to start DhcpServer or update its
configuration.

Test: runtest DhcpServingParamsTest.java
Bug: b/109584964
Change-Id: Id8d3dcf62d66dcb02accffa8d8500e30f07af452
diff --git a/core/java/android/net/NetworkUtils.java b/core/java/android/net/NetworkUtils.java
index 451435c..34e9476 100644
--- a/core/java/android/net/NetworkUtils.java
+++ b/core/java/android/net/NetworkUtils.java
@@ -161,7 +161,7 @@
      * @param hostAddress an int coding for an IPv4 address, where higher-order int byte is
      *                    lower-order IPv4 address byte
      */
-    public static InetAddress intToInet4AddressHTL(int hostAddress) {
+    public static Inet4Address intToInet4AddressHTL(int hostAddress) {
         return intToInet4AddressHTH(Integer.reverseBytes(hostAddress));
     }
 
@@ -169,14 +169,14 @@
      * Convert a IPv4 address from an integer to an InetAddress (0x01020304 -> 1.2.3.4)
      * @param hostAddress an int coding for an IPv4 address
      */
-    public static InetAddress intToInet4AddressHTH(int hostAddress) {
+    public static Inet4Address intToInet4AddressHTH(int hostAddress) {
         byte[] addressBytes = { (byte) (0xff & (hostAddress >> 24)),
                 (byte) (0xff & (hostAddress >> 16)),
                 (byte) (0xff & (hostAddress >> 8)),
                 (byte) (0xff & hostAddress) };
 
         try {
-            return InetAddress.getByAddress(addressBytes);
+            return (Inet4Address) InetAddress.getByAddress(addressBytes);
         } catch (UnknownHostException e) {
             throw new AssertionError();
         }
@@ -409,6 +409,28 @@
     }
 
     /**
+     * Get a prefix mask as Inet4Address for a given prefix length.
+     *
+     * <p>For example 20 -> 255.255.240.0
+     */
+    public static Inet4Address getPrefixMaskAsInet4Address(int prefixLength)
+            throws IllegalArgumentException {
+        return intToInet4AddressHTH(prefixLengthToV4NetmaskIntHTH(prefixLength));
+    }
+
+    /**
+     * Get the broadcast address for a given prefix.
+     *
+     * <p>For example 192.168.0.1/24 -> 192.168.0.255
+     */
+    public static Inet4Address getBroadcastAddress(Inet4Address addr, int prefixLength)
+            throws IllegalArgumentException {
+        final int intBroadcastAddr = inet4AddressToIntHTH(addr)
+                | ~prefixLengthToV4NetmaskIntHTH(prefixLength);
+        return intToInet4AddressHTH(intBroadcastAddr);
+    }
+
+    /**
      * Check if IP address type is consistent between two InetAddress.
      * @return true if both are the same type.  False otherwise.
      */
diff --git a/services/net/java/android/net/dhcp/DhcpLeaseRepository.java b/services/net/java/android/net/dhcp/DhcpLeaseRepository.java
index b7a55a4..7e57c9f 100644
--- a/services/net/java/android/net/dhcp/DhcpLeaseRepository.java
+++ b/services/net/java/android/net/dhcp/DhcpLeaseRepository.java
@@ -512,7 +512,7 @@
         // Loop until a free address is found, or there are no more addresses.
         // There is slightly less than this many usable addresses, but some extra looping is OK
         for (int i = 0; i < mNumAddresses; i++) {
-            final Inet4Address addr = (Inet4Address) intToInet4AddressHTH(intAddr);
+            final Inet4Address addr = intToInet4AddressHTH(intAddr);
             if (isAvailable(addr) && !mDeclinedAddrs.containsKey(addr)) {
                 return new DhcpLease(clientId, hwAddr, addr, expTime, hostname);
             }
diff --git a/services/net/java/android/net/dhcp/DhcpServingParams.java b/services/net/java/android/net/dhcp/DhcpServingParams.java
new file mode 100644
index 0000000..ba9d116
--- /dev/null
+++ b/services/net/java/android/net/dhcp/DhcpServingParams.java
@@ -0,0 +1,262 @@
+/*
+ * Copyright (C) 2018 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.dhcp;
+
+import static android.net.NetworkUtils.getPrefixMaskAsInet4Address;
+import static android.net.dhcp.DhcpPacket.INFINITE_LEASE;
+import static android.net.util.NetworkConstants.IPV4_MAX_MTU;
+import static android.net.util.NetworkConstants.IPV4_MIN_MTU;
+
+import static java.lang.Integer.toUnsignedLong;
+
+import android.annotation.NonNull;
+import android.net.IpPrefix;
+import android.net.LinkAddress;
+import android.net.NetworkUtils;
+
+import java.net.Inet4Address;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Parameters used by the DhcpServer to serve requests.
+ *
+ * <p>Instances are immutable. Use {@link DhcpServingParams.Builder} to instantiate.
+ * @hide
+ */
+public class DhcpServingParams {
+    public static final int MTU_UNSET = 0;
+    public static final int MIN_PREFIX_LENGTH = 16;
+    public static final int MAX_PREFIX_LENGTH = 30;
+
+    /** Server inet address and prefix to serve */
+    @NonNull
+    public final LinkAddress serverAddr;
+
+    /**
+     * Default routers to be advertised to DHCP clients. May be empty.
+     * This set is provided by {@link DhcpServingParams.Builder} and is immutable.
+     */
+    @NonNull
+    public final Set<Inet4Address> defaultRouters;
+
+    /**
+     * DNS servers to be advertised to DHCP clients. May be empty.
+     * This set is provided by {@link DhcpServingParams.Builder} and is immutable.
+     */
+    @NonNull
+    public final Set<Inet4Address> dnsServers;
+
+    /**
+     * Excluded addresses that the DHCP server is not allowed to assign to clients.
+     * This set is provided by {@link DhcpServingParams.Builder} and is immutable.
+     */
+    @NonNull
+    public final Set<Inet4Address> excludedAddrs;
+
+    // DHCP uses uint32. Use long for clearer code, and check range when building.
+    public final long dhcpLeaseTimeSecs;
+    public final int linkMtu;
+
+    /**
+     * Checked exception thrown when some parameters used to build {@link DhcpServingParams} are
+     * missing or invalid.
+     */
+    public static class InvalidParameterException extends Exception {
+        public InvalidParameterException(String message) {
+            super(message);
+        }
+    }
+
+    private DhcpServingParams(@NonNull LinkAddress serverAddr,
+            @NonNull Set<Inet4Address> defaultRouters,
+            @NonNull Set<Inet4Address> dnsServers, @NonNull Set<Inet4Address> excludedAddrs,
+            long dhcpLeaseTimeSecs, int linkMtu) {
+        this.serverAddr = serverAddr;
+        this.defaultRouters = defaultRouters;
+        this.dnsServers = dnsServers;
+        this.excludedAddrs = excludedAddrs;
+        this.dhcpLeaseTimeSecs = dhcpLeaseTimeSecs;
+        this.linkMtu = linkMtu;
+    }
+
+    @NonNull
+    public Inet4Address getServerInet4Addr() {
+        return (Inet4Address) serverAddr.getAddress();
+    }
+
+    /**
+     * Get the served prefix mask as an IPv4 address.
+     *
+     * <p>For example, if the served prefix is 192.168.42.0/24, this will return 255.255.255.0.
+     */
+    @NonNull
+    public Inet4Address getPrefixMaskAsAddress() {
+        return getPrefixMaskAsInet4Address(serverAddr.getPrefixLength());
+    }
+
+    /**
+     * Get the server broadcast address.
+     *
+     * <p>For example, if the server {@link LinkAddress} is 192.168.42.1/24, this will return
+     * 192.168.42.255.
+     */
+    @NonNull
+    public Inet4Address getBroadcastAddress() {
+        return NetworkUtils.getBroadcastAddress(getServerInet4Addr(), serverAddr.getPrefixLength());
+    }
+
+    /**
+     * Utility class to create new instances of {@link DhcpServingParams} while checking validity
+     * of the parameters.
+     */
+    public static class Builder {
+        private LinkAddress serverAddr;
+        private Set<Inet4Address> defaultRouters;
+        private Set<Inet4Address> dnsServers;
+        private Set<Inet4Address> excludedAddrs;
+        private long dhcpLeaseTimeSecs;
+        private int linkMtu = MTU_UNSET;
+
+        /**
+         * Set the server address and served prefix for the DHCP server.
+         *
+         * <p>This parameter is required.
+         */
+        public Builder setServerAddr(@NonNull LinkAddress serverAddr) {
+            this.serverAddr = serverAddr;
+            return this;
+        }
+
+        /**
+         * Set the default routers to be advertised to DHCP clients.
+         *
+         * <p>Each router must be inside the served prefix. This may be an empty set, but it must
+         * always be set explicitly before building the {@link DhcpServingParams}.
+         */
+        public Builder setDefaultRouters(@NonNull Set<Inet4Address> defaultRouters) {
+            this.defaultRouters = defaultRouters;
+            return this;
+        }
+
+        /**
+         * Set the DNS servers to be advertised to DHCP clients.
+         *
+         * <p>This may be an empty set, but it must always be set explicitly before building the
+         * {@link DhcpServingParams}.
+         */
+        public Builder setDnsServers(@NonNull Set<Inet4Address> dnsServers) {
+            this.dnsServers = dnsServers;
+            return this;
+        }
+
+        /**
+         * Set excluded addresses that the DHCP server is not allowed to assign to clients.
+         *
+         * <p>This parameter is optional. DNS servers and default routers are always excluded
+         * and do not need to be set here.
+         */
+        public Builder setExcludedAddrs(@NonNull Set<Inet4Address> excludedAddrs) {
+            this.excludedAddrs = excludedAddrs;
+            return this;
+        }
+
+        /**
+         * Set the lease time for leases assigned by the DHCP server.
+         *
+         * <p>This parameter is required.
+         */
+        public Builder setDhcpLeaseTimeSecs(long dhcpLeaseTimeSecs) {
+            this.dhcpLeaseTimeSecs = dhcpLeaseTimeSecs;
+            return this;
+        }
+
+        /**
+         * Set the link MTU to be advertised to DHCP clients.
+         *
+         * <p>If set to {@link #MTU_UNSET}, no MTU will be advertised to clients. This parameter
+         * is optional and defaults to {@link #MTU_UNSET}.
+         */
+        public Builder setLinkMtu(int linkMtu) {
+            this.linkMtu = linkMtu;
+            return this;
+        }
+
+        /**
+         * Create a new {@link DhcpServingParams} instance based on parameters set in the builder.
+         *
+         * <p>This method has no side-effects. If it does not throw, a valid
+         * {@link DhcpServingParams} is returned.
+         * @return The constructed parameters.
+         * @throws InvalidParameterException At least one parameter is missing or invalid.
+         */
+        @NonNull
+        public DhcpServingParams build() throws InvalidParameterException {
+            if (serverAddr == null) {
+                throw new InvalidParameterException("Missing serverAddr");
+            }
+            if (defaultRouters == null) {
+                throw new InvalidParameterException("Missing defaultRouters");
+            }
+            if (dnsServers == null) {
+                // Empty set is OK, but enforce explicitly setting it
+                throw new InvalidParameterException("Missing dnsServers");
+            }
+            if (dhcpLeaseTimeSecs <= 0 || dhcpLeaseTimeSecs > toUnsignedLong(INFINITE_LEASE)) {
+                throw new InvalidParameterException("Invalid lease time: " + dhcpLeaseTimeSecs);
+            }
+            if (linkMtu != MTU_UNSET && (linkMtu < IPV4_MIN_MTU || linkMtu > IPV4_MAX_MTU)) {
+                throw new InvalidParameterException("Invalid link MTU: " + linkMtu);
+            }
+            if (!serverAddr.isIPv4()) {
+                throw new InvalidParameterException("serverAddr must be IPv4");
+            }
+            if (serverAddr.getPrefixLength() < MIN_PREFIX_LENGTH
+                    || serverAddr.getPrefixLength() > MAX_PREFIX_LENGTH) {
+                throw new InvalidParameterException("Prefix length is not in supported range");
+            }
+
+            final IpPrefix prefix = makeIpPrefix(serverAddr);
+            for (Inet4Address addr : defaultRouters) {
+                if (!prefix.contains(addr)) {
+                    throw new InvalidParameterException(String.format(
+                            "Default router %s is not in server prefix %s", addr, serverAddr));
+                }
+            }
+
+            final Set<Inet4Address> excl = new HashSet<>();
+            if (excludedAddrs != null) {
+                excl.addAll(excludedAddrs);
+            }
+            excl.add((Inet4Address) serverAddr.getAddress());
+            excl.addAll(defaultRouters);
+            excl.addAll(dnsServers);
+
+            return new DhcpServingParams(serverAddr,
+                    Collections.unmodifiableSet(new HashSet<>(defaultRouters)),
+                    Collections.unmodifiableSet(new HashSet<>(dnsServers)),
+                    Collections.unmodifiableSet(excl),
+                    dhcpLeaseTimeSecs, linkMtu);
+        }
+    }
+
+    @NonNull
+    static IpPrefix makeIpPrefix(@NonNull LinkAddress addr) {
+        return new IpPrefix(addr.getAddress(), addr.getPrefixLength());
+    }
+}
diff --git a/services/net/java/android/net/util/NetworkConstants.java b/services/net/java/android/net/util/NetworkConstants.java
index de04fd0..3defe56 100644
--- a/services/net/java/android/net/util/NetworkConstants.java
+++ b/services/net/java/android/net/util/NetworkConstants.java
@@ -77,10 +77,12 @@
     /**
      * IPv4 constants.
      *
-     * See als:
+     * See also:
      *     - https://tools.ietf.org/html/rfc791
      */
     public static final int IPV4_HEADER_MIN_LEN = 20;
+    public static final int IPV4_MIN_MTU = 68;
+    public static final int IPV4_MAX_MTU = 65_535;
     public static final int IPV4_IHL_MASK = 0xf;
     public static final int IPV4_FLAGS_OFFSET = 6;
     public static final int IPV4_FRAGMENT_MASK = 0x1fff;
diff --git a/tests/net/java/android/net/NetworkUtilsTest.java b/tests/net/java/android/net/NetworkUtilsTest.java
index 2b172da..3452819 100644
--- a/tests/net/java/android/net/NetworkUtilsTest.java
+++ b/tests/net/java/android/net/NetworkUtilsTest.java
@@ -24,6 +24,8 @@
 import static android.net.NetworkUtils.netmaskToPrefixLength;
 import static android.net.NetworkUtils.prefixLengthToV4NetmaskIntHTH;
 import static android.net.NetworkUtils.prefixLengthToV4NetmaskIntHTL;
+import static android.net.NetworkUtils.getBroadcastAddress;
+import static android.net.NetworkUtils.getPrefixMaskAsInet4Address;
 
 import static junit.framework.Assert.assertEquals;
 
@@ -125,7 +127,6 @@
         assertInvalidNetworkMask(IPv4Address("255.255.0.255"));
     }
 
-
     @Test
     public void testPrefixLengthToV4NetmaskIntHTL() {
         assertEquals(0, prefixLengthToV4NetmaskIntHTL(0));
@@ -266,4 +267,44 @@
         assertEquals(BigInteger.valueOf(7l - 4 + 4 + 16 + 65536),
                 NetworkUtils.routedIPv6AddressCount(set));
     }
+
+    @Test
+    public void testGetPrefixMaskAsAddress() {
+        assertEquals("255.255.240.0", getPrefixMaskAsInet4Address(20).getHostAddress());
+        assertEquals("255.0.0.0", getPrefixMaskAsInet4Address(8).getHostAddress());
+        assertEquals("0.0.0.0", getPrefixMaskAsInet4Address(0).getHostAddress());
+        assertEquals("255.255.255.255", getPrefixMaskAsInet4Address(32).getHostAddress());
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testGetPrefixMaskAsAddress_PrefixTooLarge() {
+        getPrefixMaskAsInet4Address(33);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testGetPrefixMaskAsAddress_NegativePrefix() {
+        getPrefixMaskAsInet4Address(-1);
+    }
+
+    @Test
+    public void testGetBroadcastAddress() {
+        assertEquals("192.168.15.255",
+                getBroadcastAddress(IPv4Address("192.168.0.123"), 20).getHostAddress());
+        assertEquals("192.255.255.255",
+                getBroadcastAddress(IPv4Address("192.168.0.123"), 8).getHostAddress());
+        assertEquals("192.168.0.123",
+                getBroadcastAddress(IPv4Address("192.168.0.123"), 32).getHostAddress());
+        assertEquals("255.255.255.255",
+                getBroadcastAddress(IPv4Address("192.168.0.123"), 0).getHostAddress());
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testGetBroadcastAddress_PrefixTooLarge() {
+        getBroadcastAddress(IPv4Address("192.168.0.123"), 33);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testGetBroadcastAddress_NegativePrefix() {
+        getBroadcastAddress(IPv4Address("192.168.0.123"), -1);
+    }
 }
diff --git a/tests/net/java/android/net/dhcp/DhcpServingParamsTest.java b/tests/net/java/android/net/dhcp/DhcpServingParamsTest.java
new file mode 100644
index 0000000..dfa09a9
--- /dev/null
+++ b/tests/net/java/android/net/dhcp/DhcpServingParamsTest.java
@@ -0,0 +1,177 @@
+/*
+ * Copyright (C) 2018 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.dhcp;
+
+import static android.net.dhcp.DhcpServingParams.MTU_UNSET;
+
+import static junit.framework.Assert.assertEquals;
+import static junit.framework.Assert.assertFalse;
+import static junit.framework.Assert.assertTrue;
+
+import static java.net.InetAddress.parseNumericAddress;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.net.LinkAddress;
+import android.net.dhcp.DhcpServingParams.InvalidParameterException;
+import android.support.test.filters.SmallTest;
+import android.support.test.runner.AndroidJUnit4;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import java.net.Inet4Address;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+@RunWith(AndroidJUnit4.class)
+@SmallTest
+public class DhcpServingParamsTest {
+    @NonNull
+    private DhcpServingParams.Builder mBuilder;
+
+    private static final Set<Inet4Address> TEST_DEFAULT_ROUTERS = new HashSet<>(
+            Arrays.asList(parseAddr("192.168.0.123"), parseAddr("192.168.0.124")));
+    private static final long TEST_LEASE_TIME_SECS = 3600L;
+    private static final Set<Inet4Address> TEST_DNS_SERVERS = new HashSet<>(
+            Arrays.asList(parseAddr("192.168.0.126"), parseAddr("192.168.0.127")));
+    private static final Inet4Address TEST_SERVER_ADDR = parseAddr("192.168.0.2");
+    private static final LinkAddress TEST_LINKADDR = new LinkAddress(TEST_SERVER_ADDR, 20);
+    private static final int TEST_MTU = 1500;
+    private static final Set<Inet4Address> TEST_EXCLUDED_ADDRS = new HashSet<>(
+            Arrays.asList(parseAddr("192.168.0.200"), parseAddr("192.168.0.201")));
+
+    @Before
+    public void setUp() {
+        mBuilder = new DhcpServingParams.Builder()
+                .setDefaultRouters(TEST_DEFAULT_ROUTERS)
+                .setDhcpLeaseTimeSecs(TEST_LEASE_TIME_SECS)
+                .setDnsServers(TEST_DNS_SERVERS)
+                .setServerAddr(TEST_LINKADDR)
+                .setLinkMtu(TEST_MTU)
+                .setExcludedAddrs(TEST_EXCLUDED_ADDRS);
+    }
+
+    @Test
+    public void testBuild_Immutable() throws InvalidParameterException {
+        final Set<Inet4Address> routers = new HashSet<>(TEST_DEFAULT_ROUTERS);
+        final Set<Inet4Address> dnsServers = new HashSet<>(TEST_DNS_SERVERS);
+        final Set<Inet4Address> excludedAddrs = new HashSet<>(TEST_EXCLUDED_ADDRS);
+
+        final DhcpServingParams params = mBuilder
+                .setDefaultRouters(routers)
+                .setDnsServers(dnsServers)
+                .setExcludedAddrs(excludedAddrs)
+                .build();
+
+        // Modifications to source objects should not affect builder or final parameters
+        final Inet4Address addedAddr = parseAddr("192.168.0.223");
+        routers.add(addedAddr);
+        dnsServers.add(addedAddr);
+        excludedAddrs.add(addedAddr);
+
+        assertEquals(TEST_DEFAULT_ROUTERS, params.defaultRouters);
+        assertEquals(TEST_LEASE_TIME_SECS, params.dhcpLeaseTimeSecs);
+        assertEquals(TEST_DNS_SERVERS, params.dnsServers);
+        assertEquals(TEST_LINKADDR, params.serverAddr);
+        assertEquals(TEST_MTU, params.linkMtu);
+
+        assertContains(params.excludedAddrs, TEST_EXCLUDED_ADDRS);
+        assertContains(params.excludedAddrs, TEST_DEFAULT_ROUTERS);
+        assertContains(params.excludedAddrs, TEST_DNS_SERVERS);
+        assertContains(params.excludedAddrs, TEST_SERVER_ADDR);
+
+        assertFalse("excludedAddrs should not contain " + addedAddr,
+                params.excludedAddrs.contains(addedAddr));
+    }
+
+    @Test(expected = InvalidParameterException.class)
+    public void testBuild_NegativeLeaseTime() throws InvalidParameterException {
+        mBuilder.setDhcpLeaseTimeSecs(-1).build();
+    }
+
+    @Test(expected = InvalidParameterException.class)
+    public void testBuild_LeaseTimeTooLarge() throws InvalidParameterException {
+        // Set lease time larger than max value for uint32
+        mBuilder.setDhcpLeaseTimeSecs(1L << 32).build();
+    }
+
+    @Test
+    public void testBuild_InfiniteLeaseTime() throws InvalidParameterException {
+        final long infiniteLeaseTime = 0xffffffffL;
+        final DhcpServingParams params = mBuilder
+                .setDhcpLeaseTimeSecs(infiniteLeaseTime).build();
+        assertEquals(infiniteLeaseTime, params.dhcpLeaseTimeSecs);
+        assertTrue(params.dhcpLeaseTimeSecs > 0L);
+    }
+
+    @Test
+    public void testBuild_UnsetMtu() throws InvalidParameterException {
+        final DhcpServingParams params = mBuilder.setLinkMtu(MTU_UNSET).build();
+        assertEquals(MTU_UNSET, params.linkMtu);
+    }
+
+    @Test(expected = InvalidParameterException.class)
+    public void testBuild_MtuTooSmall() throws InvalidParameterException {
+        mBuilder.setLinkMtu(20).build();
+    }
+
+    @Test(expected = InvalidParameterException.class)
+    public void testBuild_MtuTooLarge() throws InvalidParameterException {
+        mBuilder.setLinkMtu(65_536).build();
+    }
+
+    @Test(expected = InvalidParameterException.class)
+    public void testBuild_IPv6Addr() throws InvalidParameterException {
+        mBuilder.setServerAddr(new LinkAddress(parseNumericAddress("fe80::1111"), 120)).build();
+    }
+
+    @Test(expected = InvalidParameterException.class)
+    public void testBuild_PrefixTooLarge() throws InvalidParameterException {
+        mBuilder.setServerAddr(new LinkAddress(TEST_SERVER_ADDR, 15)).build();
+    }
+
+    @Test(expected = InvalidParameterException.class)
+    public void testBuild_PrefixTooSmall() throws InvalidParameterException {
+        mBuilder.setDefaultRouters(Collections.singleton(parseAddr("192.168.0.254")))
+                .setServerAddr(new LinkAddress(TEST_SERVER_ADDR, 31))
+                .build();
+    }
+
+    @Test(expected = InvalidParameterException.class)
+    public void testBuild_RouterNotInPrefix() throws InvalidParameterException {
+        mBuilder.setDefaultRouters(Collections.singleton(parseAddr("192.168.254.254"))).build();
+    }
+
+    private static <T> void assertContains(@NonNull Set<T> set, @NonNull Set<T> subset) {
+        for (final T elem : subset) {
+            assertContains(set, elem);
+        }
+    }
+
+    private static <T> void assertContains(@NonNull Set<T> set, @Nullable T elem) {
+        assertTrue("Set does not contain " + elem, set.contains(elem));
+    }
+
+    @NonNull
+    private static Inet4Address parseAddr(@NonNull String inet4Addr) {
+        return (Inet4Address) parseNumericAddress(inet4Addr);
+    }
+}