Merge changes I1250730c,I7d00848c

* changes:
  Create a wrapper for IpClient
  Move IpClient to NetworkStack

1 files changed, 1075 insertions, 0 deletions

diff --git a/tests/src/android/net/dhcp/DhcpPacketTest.java b/tests/src/android/net/dhcp/DhcpPacketTest.java
new file mode 100644
index 0000000..a592809
--- /dev/null
+++ b/tests/src/android/net/dhcp/DhcpPacketTest.java
@@ -0,0 +1,1075 @@
+/*
+ * 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.dhcp;
+
+import static android.net.NetworkUtils.getBroadcastAddress;
+import static android.net.NetworkUtils.getPrefixMaskAsInet4Address;
+import static android.net.dhcp.DhcpPacket.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import android.annotation.Nullable;
+import android.net.DhcpResults;
+import android.net.LinkAddress;
+import android.net.NetworkUtils;
+import android.net.metrics.DhcpErrorEvent;
+import android.support.test.runner.AndroidJUnit4;
+import android.support.test.filters.SmallTest;
+
+import com.android.internal.util.HexDump;
+
+import java.io.ByteArrayOutputStream;
+import java.net.Inet4Address;
+import java.nio.ByteBuffer;
+import java.nio.charset.Charset;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Random;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+@RunWith(AndroidJUnit4.class)
+@SmallTest
+public class DhcpPacketTest {
+
+    private static final Inet4Address SERVER_ADDR = v4Address("192.0.2.1");
+    private static final Inet4Address CLIENT_ADDR = v4Address("192.0.2.234");
+    private static final int PREFIX_LENGTH = 22;
+    private static final Inet4Address NETMASK = getPrefixMaskAsInet4Address(PREFIX_LENGTH);
+    private static final Inet4Address BROADCAST_ADDR = getBroadcastAddress(
+            SERVER_ADDR, PREFIX_LENGTH);
+    private static final String HOSTNAME = "testhostname";
+    private static final short MTU = 1500;
+    // Use our own empty address instead of Inet4Address.ANY or INADDR_ANY to ensure that the code
+    // doesn't use == instead of equals when comparing addresses.
+    private static final Inet4Address ANY = (Inet4Address) v4Address("0.0.0.0");
+
+    private static final byte[] CLIENT_MAC = new byte[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05 };
+
+    private static final Inet4Address v4Address(String addrString) throws IllegalArgumentException {
+        return (Inet4Address) NetworkUtils.numericToInetAddress(addrString);
+    }
+
+    @Before
+    public void setUp() {
+        DhcpPacket.testOverrideVendorId = "android-dhcp-???";
+        DhcpPacket.testOverrideHostname = "android-01234567890abcde";
+    }
+
+    class TestDhcpPacket extends DhcpPacket {
+        private byte mType;
+        // TODO: Make this a map of option numbers to bytes instead.
+        private byte[] mDomainBytes, mVendorInfoBytes, mLeaseTimeBytes, mNetmaskBytes;
+
+        public TestDhcpPacket(byte type, Inet4Address clientIp, Inet4Address yourIp) {
+            super(0xdeadbeef, (short) 0, clientIp, yourIp, INADDR_ANY, INADDR_ANY,
+                  CLIENT_MAC, true);
+            mType = type;
+        }
+
+        public TestDhcpPacket(byte type) {
+            this(type, INADDR_ANY, CLIENT_ADDR);
+        }
+
+        public TestDhcpPacket setDomainBytes(byte[] domainBytes) {
+            mDomainBytes = domainBytes;
+            return this;
+        }
+
+        public TestDhcpPacket setVendorInfoBytes(byte[] vendorInfoBytes) {
+            mVendorInfoBytes = vendorInfoBytes;
+            return this;
+        }
+
+        public TestDhcpPacket setLeaseTimeBytes(byte[] leaseTimeBytes) {
+            mLeaseTimeBytes = leaseTimeBytes;
+            return this;
+        }
+
+        public TestDhcpPacket setNetmaskBytes(byte[] netmaskBytes) {
+            mNetmaskBytes = netmaskBytes;
+            return this;
+        }
+
+        public ByteBuffer buildPacket(int encap, short unusedDestUdp, short unusedSrcUdp) {
+            ByteBuffer result = ByteBuffer.allocate(MAX_LENGTH);
+            fillInPacket(encap, CLIENT_ADDR, SERVER_ADDR,
+                         DHCP_CLIENT, DHCP_SERVER, result, DHCP_BOOTREPLY, false);
+            return result;
+        }
+
+        public void finishPacket(ByteBuffer buffer) {
+            addTlv(buffer, DHCP_MESSAGE_TYPE, mType);
+            if (mDomainBytes != null) {
+                addTlv(buffer, DHCP_DOMAIN_NAME, mDomainBytes);
+            }
+            if (mVendorInfoBytes != null) {
+                addTlv(buffer, DHCP_VENDOR_INFO, mVendorInfoBytes);
+            }
+            if (mLeaseTimeBytes != null) {
+                addTlv(buffer, DHCP_LEASE_TIME, mLeaseTimeBytes);
+            }
+            if (mNetmaskBytes != null) {
+                addTlv(buffer, DHCP_SUBNET_MASK, mNetmaskBytes);
+            }
+            addTlvEnd(buffer);
+        }
+
+        // Convenience method.
+        public ByteBuffer build() {
+            // ENCAP_BOOTP packets don't contain ports, so just pass in 0.
+            ByteBuffer pkt = buildPacket(ENCAP_BOOTP, (short) 0, (short) 0);
+            pkt.flip();
+            return pkt;
+        }
+    }
+
+    private void assertDomainAndVendorInfoParses(
+            String expectedDomain, byte[] domainBytes,
+            String expectedVendorInfo, byte[] vendorInfoBytes) throws Exception {
+        ByteBuffer packet = new TestDhcpPacket(DHCP_MESSAGE_TYPE_OFFER)
+                .setDomainBytes(domainBytes)
+                .setVendorInfoBytes(vendorInfoBytes)
+                .build();
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_BOOTP);
+        assertEquals(expectedDomain, offerPacket.mDomainName);
+        assertEquals(expectedVendorInfo, offerPacket.mVendorInfo);
+    }
+
+    @Test
+    public void testDomainName() throws Exception {
+        byte[] nullByte = new byte[] { 0x00 };
+        byte[] twoNullBytes = new byte[] { 0x00, 0x00 };
+        byte[] nonNullDomain = new byte[] {
+            (byte) 'g', (byte) 'o', (byte) 'o', (byte) '.', (byte) 'g', (byte) 'l'
+        };
+        byte[] trailingNullDomain = new byte[] {
+            (byte) 'g', (byte) 'o', (byte) 'o', (byte) '.', (byte) 'g', (byte) 'l', 0x00
+        };
+        byte[] embeddedNullsDomain = new byte[] {
+            (byte) 'g', (byte) 'o', (byte) 'o', 0x00, 0x00, (byte) 'g', (byte) 'l'
+        };
+        byte[] metered = "ANDROID_METERED".getBytes("US-ASCII");
+
+        byte[] meteredEmbeddedNull = metered.clone();
+        meteredEmbeddedNull[7] = (char) 0;
+
+        byte[] meteredTrailingNull = metered.clone();
+        meteredTrailingNull[meteredTrailingNull.length - 1] = (char) 0;
+
+        assertDomainAndVendorInfoParses("", nullByte, "\u0000", nullByte);
+        assertDomainAndVendorInfoParses("", twoNullBytes, "\u0000\u0000", twoNullBytes);
+        assertDomainAndVendorInfoParses("goo.gl", nonNullDomain, "ANDROID_METERED", metered);
+        assertDomainAndVendorInfoParses("goo", embeddedNullsDomain,
+                                        "ANDROID\u0000METERED", meteredEmbeddedNull);
+        assertDomainAndVendorInfoParses("goo.gl", trailingNullDomain,
+                                        "ANDROID_METERE\u0000", meteredTrailingNull);
+    }
+
+    private void assertLeaseTimeParses(boolean expectValid, Integer rawLeaseTime,
+            long leaseTimeMillis, byte[] leaseTimeBytes) throws Exception {
+        TestDhcpPacket testPacket = new TestDhcpPacket(DHCP_MESSAGE_TYPE_OFFER);
+        if (leaseTimeBytes != null) {
+            testPacket.setLeaseTimeBytes(leaseTimeBytes);
+        }
+        ByteBuffer packet = testPacket.build();
+        DhcpPacket offerPacket = null;
+
+        if (!expectValid) {
+            try {
+                offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_BOOTP);
+                fail("Invalid packet parsed successfully: " + offerPacket);
+            } catch (ParseException expected) {
+            }
+            return;
+        }
+
+        offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_BOOTP);
+        assertNotNull(offerPacket);
+        assertEquals(rawLeaseTime, offerPacket.mLeaseTime);
+        DhcpResults dhcpResults = offerPacket.toDhcpResults();  // Just check this doesn't crash.
+        assertEquals(leaseTimeMillis, offerPacket.getLeaseTimeMillis());
+    }
+
+    @Test
+    public void testLeaseTime() throws Exception {
+        byte[] noLease = null;
+        byte[] tooShortLease = new byte[] { 0x00, 0x00 };
+        byte[] tooLongLease = new byte[] { 0x00, 0x00, 0x00, 60, 0x01 };
+        byte[] zeroLease = new byte[] { 0x00, 0x00, 0x00, 0x00 };
+        byte[] tenSecondLease = new byte[] { 0x00, 0x00, 0x00, 10 };
+        byte[] oneMinuteLease = new byte[] { 0x00, 0x00, 0x00, 60 };
+        byte[] fiveMinuteLease = new byte[] { 0x00, 0x00, 0x01, 0x2c };
+        byte[] oneDayLease = new byte[] { 0x00, 0x01, 0x51, (byte) 0x80 };
+        byte[] maxIntPlusOneLease = new byte[] { (byte) 0x80, 0x00, 0x00, 0x01 };
+        byte[] infiniteLease = new byte[] { (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff };
+
+        assertLeaseTimeParses(true, null, 0, noLease);
+        assertLeaseTimeParses(false, null, 0, tooShortLease);
+        assertLeaseTimeParses(false, null, 0, tooLongLease);
+        assertLeaseTimeParses(true, 0, 60 * 1000, zeroLease);
+        assertLeaseTimeParses(true, 10, 60 * 1000, tenSecondLease);
+        assertLeaseTimeParses(true, 60, 60 * 1000, oneMinuteLease);
+        assertLeaseTimeParses(true, 300, 300 * 1000, fiveMinuteLease);
+        assertLeaseTimeParses(true, 86400, 86400 * 1000, oneDayLease);
+        assertLeaseTimeParses(true, -2147483647, 2147483649L * 1000, maxIntPlusOneLease);
+        assertLeaseTimeParses(true, DhcpPacket.INFINITE_LEASE, 0, infiniteLease);
+    }
+
+    private void checkIpAddress(String expected, Inet4Address clientIp, Inet4Address yourIp,
+                                byte[] netmaskBytes) throws Exception {
+        checkIpAddress(expected, DHCP_MESSAGE_TYPE_OFFER, clientIp, yourIp, netmaskBytes);
+        checkIpAddress(expected, DHCP_MESSAGE_TYPE_ACK, clientIp, yourIp, netmaskBytes);
+    }
+
+    private void checkIpAddress(String expected, byte type,
+                                Inet4Address clientIp, Inet4Address yourIp,
+                                byte[] netmaskBytes) throws Exception {
+        ByteBuffer packet = new TestDhcpPacket(type, clientIp, yourIp)
+                .setNetmaskBytes(netmaskBytes)
+                .build();
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_BOOTP);
+        DhcpResults results = offerPacket.toDhcpResults();
+
+        if (expected != null) {
+            LinkAddress expectedAddress = new LinkAddress(expected);
+            assertEquals(expectedAddress, results.ipAddress);
+        } else {
+            assertNull(results);
+        }
+    }
+
+    @Test
+    public void testIpAddress() throws Exception {
+        byte[] slash11Netmask = new byte[] { (byte) 0xff, (byte) 0xe0, 0x00, 0x00 };
+        byte[] slash24Netmask = new byte[] { (byte) 0xff, (byte) 0xff, (byte) 0xff, 0x00 };
+        byte[] invalidNetmask = new byte[] { (byte) 0xff, (byte) 0xfb, (byte) 0xff, 0x00 };
+        Inet4Address example1 = v4Address("192.0.2.1");
+        Inet4Address example2 = v4Address("192.0.2.43");
+
+        // A packet without any addresses is not valid.
+        checkIpAddress(null, ANY, ANY, slash24Netmask);
+
+        // ClientIP is used iff YourIP is not present.
+        checkIpAddress("192.0.2.1/24", example2, example1, slash24Netmask);
+        checkIpAddress("192.0.2.43/11", example2, ANY, slash11Netmask);
+        checkIpAddress("192.0.2.43/11", ANY, example2, slash11Netmask);
+
+        // Invalid netmasks are ignored.
+        checkIpAddress(null, example2, ANY, invalidNetmask);
+
+        // If there is no netmask, implicit netmasks are used.
+        checkIpAddress("192.0.2.43/24", ANY, example2, null);
+    }
+
+    private void assertDhcpResults(String ipAddress, String gateway, String dnsServersString,
+            String domains, String serverAddress, String vendorInfo, int leaseDuration,
+            boolean hasMeteredHint, int mtu, DhcpResults dhcpResults) throws Exception {
+        assertEquals(new LinkAddress(ipAddress), dhcpResults.ipAddress);
+        assertEquals(v4Address(gateway), dhcpResults.gateway);
+
+        String[] dnsServerStrings = dnsServersString.split(",");
+        ArrayList dnsServers = new ArrayList();
+        for (String dnsServerString : dnsServerStrings) {
+            dnsServers.add(v4Address(dnsServerString));
+        }
+        assertEquals(dnsServers, dhcpResults.dnsServers);
+
+        assertEquals(domains, dhcpResults.domains);
+        assertEquals(v4Address(serverAddress), dhcpResults.serverAddress);
+        assertEquals(vendorInfo, dhcpResults.vendorInfo);
+        assertEquals(leaseDuration, dhcpResults.leaseDuration);
+        assertEquals(hasMeteredHint, dhcpResults.hasMeteredHint());
+        assertEquals(mtu, dhcpResults.mtu);
+    }
+
+    @Test
+    public void testOffer1() throws Exception {
+        // TODO: Turn all of these into golden files. This will probably require using
+        // android.support.test.InstrumentationRegistry for obtaining a Context object
+        // to read such golden files, along with an appropriate Android.mk.
+        final ByteBuffer packet = ByteBuffer.wrap(HexDump.hexStringToByteArray(
+            // IP header.
+            "451001480000000080118849c0a89003c0a89ff7" +
+            // UDP header.
+            "004300440134dcfa" +
+            // BOOTP header.
+            "02010600c997a63b0000000000000000c0a89ff70000000000000000" +
+            // MAC address.
+            "30766ff2a90c00000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options
+            "638253633501023604c0a89003330400001c200104fffff0000304c0a89ffe06080808080808080404" +
+            "3a0400000e103b040000189cff00000000000000000000"));
+
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L3);
+        assertTrue(offerPacket instanceof DhcpOfferPacket);  // Implicitly checks it's non-null.
+        DhcpResults dhcpResults = offerPacket.toDhcpResults();
+        assertDhcpResults("192.168.159.247/20", "192.168.159.254", "8.8.8.8,8.8.4.4",
+                null, "192.168.144.3", null, 7200, false, 0, dhcpResults);
+    }
+
+    @Test
+    public void testOffer2() throws Exception {
+        final ByteBuffer packet = ByteBuffer.wrap(HexDump.hexStringToByteArray(
+            // IP header.
+            "450001518d0600004011144dc0a82b01c0a82bf7" +
+            // UDP header.
+            "00430044013d9ac7" +
+            // BOOTP header.
+            "02010600dfc23d1f0002000000000000c0a82bf7c0a82b0100000000" +
+            // MAC address.
+            "30766ff2a90c00000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options
+            "638253633501023604c0a82b01330400000e103a04000007083b0400000c4e0104ffffff00" +
+            "1c04c0a82bff0304c0a82b010604c0a82b012b0f414e44524f49445f4d455445524544ff"));
+
+        assertEquals(337, packet.limit());
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L3);
+        assertTrue(offerPacket instanceof DhcpOfferPacket);  // Implicitly checks it's non-null.
+        DhcpResults dhcpResults = offerPacket.toDhcpResults();
+        assertDhcpResults("192.168.43.247/24", "192.168.43.1", "192.168.43.1",
+                null, "192.168.43.1", "ANDROID_METERED", 3600, true, 0, dhcpResults);
+        assertTrue(dhcpResults.hasMeteredHint());
+    }
+
+    @Test
+    public void testBadIpPacket() throws Exception {
+        final byte[] packet = HexDump.hexStringToByteArray(
+            // IP header.
+            "450001518d0600004011144dc0a82b01c0a82bf7");
+
+        try {
+            DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, packet.length, ENCAP_L3);
+        } catch (DhcpPacket.ParseException expected) {
+            assertDhcpErrorCodes(DhcpErrorEvent.L3_TOO_SHORT, expected.errorCode);
+            return;
+        }
+        fail("Dhcp packet parsing should have failed");
+    }
+
+    @Test
+    public void testBadDhcpPacket() throws Exception {
+        final byte[] packet = HexDump.hexStringToByteArray(
+            // IP header.
+            "450001518d0600004011144dc0a82b01c0a82bf7" +
+            // UDP header.
+            "00430044013d9ac7" +
+            // BOOTP header.
+            "02010600dfc23d1f0002000000000000c0a82bf7c0a82b0100000000");
+
+        try {
+            DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, packet.length, ENCAP_L3);
+        } catch (DhcpPacket.ParseException expected) {
+            assertDhcpErrorCodes(DhcpErrorEvent.L3_TOO_SHORT, expected.errorCode);
+            return;
+        }
+        fail("Dhcp packet parsing should have failed");
+    }
+
+    @Test
+    public void testBadTruncatedOffer() throws Exception {
+        final byte[] packet = HexDump.hexStringToByteArray(
+            // IP header.
+            "450001518d0600004011144dc0a82b01c0a82bf7" +
+            // UDP header.
+            "00430044013d9ac7" +
+            // BOOTP header.
+            "02010600dfc23d1f0002000000000000c0a82bf7c0a82b0100000000" +
+            // MAC address.
+            "30766ff2a90c00000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File, missing one byte
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "00000000000000000000000000000000000000000000000000000000000000");
+
+        try {
+            DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, packet.length, ENCAP_L3);
+        } catch (DhcpPacket.ParseException expected) {
+            assertDhcpErrorCodes(DhcpErrorEvent.L3_TOO_SHORT, expected.errorCode);
+            return;
+        }
+        fail("Dhcp packet parsing should have failed");
+    }
+
+    @Test
+    public void testBadOfferWithoutACookie() throws Exception {
+        final byte[] packet = HexDump.hexStringToByteArray(
+            // IP header.
+            "450001518d0600004011144dc0a82b01c0a82bf7" +
+            // UDP header.
+            "00430044013d9ac7" +
+            // BOOTP header.
+            "02010600dfc23d1f0002000000000000c0a82bf7c0a82b0100000000" +
+            // MAC address.
+            "30766ff2a90c00000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000"
+            // No options
+            );
+
+        try {
+            DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, packet.length, ENCAP_L3);
+        } catch (DhcpPacket.ParseException expected) {
+            assertDhcpErrorCodes(DhcpErrorEvent.DHCP_NO_COOKIE, expected.errorCode);
+            return;
+        }
+        fail("Dhcp packet parsing should have failed");
+    }
+
+    @Test
+    public void testOfferWithBadCookie() throws Exception {
+        final byte[] packet = HexDump.hexStringToByteArray(
+            // IP header.
+            "450001518d0600004011144dc0a82b01c0a82bf7" +
+            // UDP header.
+            "00430044013d9ac7" +
+            // BOOTP header.
+            "02010600dfc23d1f0002000000000000c0a82bf7c0a82b0100000000" +
+            // MAC address.
+            "30766ff2a90c00000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Bad cookie
+            "DEADBEEF3501023604c0a82b01330400000e103a04000007083b0400000c4e0104ffffff00" +
+            "1c04c0a82bff0304c0a82b010604c0a82b012b0f414e44524f49445f4d455445524544ff");
+
+        try {
+            DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, packet.length, ENCAP_L3);
+        } catch (DhcpPacket.ParseException expected) {
+            assertDhcpErrorCodes(DhcpErrorEvent.DHCP_BAD_MAGIC_COOKIE, expected.errorCode);
+            return;
+        }
+        fail("Dhcp packet parsing should have failed");
+    }
+
+    private void assertDhcpErrorCodes(int expected, int got) {
+        assertEquals(Integer.toHexString(expected), Integer.toHexString(got));
+    }
+
+    @Test
+    public void testTruncatedOfferPackets() throws Exception {
+        final byte[] packet = HexDump.hexStringToByteArray(
+            // IP header.
+            "450001518d0600004011144dc0a82b01c0a82bf7" +
+            // UDP header.
+            "00430044013d9ac7" +
+            // BOOTP header.
+            "02010600dfc23d1f0002000000000000c0a82bf7c0a82b0100000000" +
+            // MAC address.
+            "30766ff2a90c00000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options
+            "638253633501023604c0a82b01330400000e103a04000007083b0400000c4e0104ffffff00" +
+            "1c04c0a82bff0304c0a82b010604c0a82b012b0f414e44524f49445f4d455445524544ff");
+
+        for (int len = 0; len < packet.length; len++) {
+            try {
+                DhcpPacket.decodeFullPacket(packet, len, ENCAP_L3);
+            } catch (ParseException e) {
+                if (e.errorCode == DhcpErrorEvent.PARSING_ERROR) {
+                    fail(String.format("bad truncated packet of length %d", len));
+                }
+            }
+        }
+    }
+
+    @Test
+    public void testRandomPackets() throws Exception {
+        final int maxRandomPacketSize = 512;
+        final Random r = new Random();
+        for (int i = 0; i < 10000; i++) {
+            byte[] packet = new byte[r.nextInt(maxRandomPacketSize + 1)];
+            r.nextBytes(packet);
+            try {
+                DhcpPacket.decodeFullPacket(packet, packet.length, ENCAP_L3);
+            } catch (ParseException e) {
+                if (e.errorCode == DhcpErrorEvent.PARSING_ERROR) {
+                    fail("bad packet: " + HexDump.toHexString(packet));
+                }
+            }
+        }
+    }
+
+    private byte[] mtuBytes(int mtu) {
+        // 0x1a02: option 26, length 2. 0xff: no more options.
+        if (mtu > Short.MAX_VALUE - Short.MIN_VALUE) {
+            throw new IllegalArgumentException(
+                String.format("Invalid MTU %d, must be 16-bit unsigned", mtu));
+        }
+        String hexString = String.format("1a02%04xff", mtu);
+        return HexDump.hexStringToByteArray(hexString);
+    }
+
+    private void checkMtu(ByteBuffer packet, int expectedMtu, byte[] mtuBytes) throws Exception {
+        if (mtuBytes != null) {
+            packet.position(packet.capacity() - mtuBytes.length);
+            packet.put(mtuBytes);
+            packet.clear();
+        }
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L3);
+        assertTrue(offerPacket instanceof DhcpOfferPacket);  // Implicitly checks it's non-null.
+        DhcpResults dhcpResults = offerPacket.toDhcpResults();
+        assertDhcpResults("192.168.159.247/20", "192.168.159.254", "8.8.8.8,8.8.4.4",
+                null, "192.168.144.3", null, 7200, false, expectedMtu, dhcpResults);
+    }
+
+    @Test
+    public void testMtu() throws Exception {
+        final ByteBuffer packet = ByteBuffer.wrap(HexDump.hexStringToByteArray(
+            // IP header.
+            "451001480000000080118849c0a89003c0a89ff7" +
+            // UDP header.
+            "004300440134dcfa" +
+            // BOOTP header.
+            "02010600c997a63b0000000000000000c0a89ff70000000000000000" +
+            // MAC address.
+            "30766ff2a90c00000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options
+            "638253633501023604c0a89003330400001c200104fffff0000304c0a89ffe06080808080808080404" +
+            "3a0400000e103b040000189cff00000000"));
+
+        checkMtu(packet, 0, null);
+        checkMtu(packet, 0, mtuBytes(1501));
+        checkMtu(packet, 1500, mtuBytes(1500));
+        checkMtu(packet, 1499, mtuBytes(1499));
+        checkMtu(packet, 1280, mtuBytes(1280));
+        checkMtu(packet, 0, mtuBytes(1279));
+        checkMtu(packet, 0, mtuBytes(576));
+        checkMtu(packet, 0, mtuBytes(68));
+        checkMtu(packet, 0, mtuBytes(Short.MIN_VALUE));
+        checkMtu(packet, 0, mtuBytes(Short.MAX_VALUE + 3));
+        checkMtu(packet, 0, mtuBytes(-1));
+    }
+
+    @Test
+    public void testBadHwaddrLength() throws Exception {
+        final ByteBuffer packet = ByteBuffer.wrap(HexDump.hexStringToByteArray(
+            // IP header.
+            "450001518d0600004011144dc0a82b01c0a82bf7" +
+            // UDP header.
+            "00430044013d9ac7" +
+            // BOOTP header.
+            "02010600dfc23d1f0002000000000000c0a82bf7c0a82b0100000000" +
+            // MAC address.
+            "30766ff2a90c00000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options
+            "638253633501023604c0a82b01330400000e103a04000007083b0400000c4e0104ffffff00" +
+            "1c04c0a82bff0304c0a82b010604c0a82b012b0f414e44524f49445f4d455445524544ff"));
+        String expectedClientMac = "30766FF2A90C";
+
+        final int hwAddrLenOffset = 20 + 8 + 2;
+        assertEquals(6, packet.get(hwAddrLenOffset));
+
+        // Expect the expected.
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L3);
+        assertNotNull(offerPacket);
+        assertEquals(6, offerPacket.getClientMac().length);
+        assertEquals(expectedClientMac, HexDump.toHexString(offerPacket.getClientMac()));
+
+        // Reduce the hardware address length and verify that it shortens the client MAC.
+        packet.flip();
+        packet.put(hwAddrLenOffset, (byte) 5);
+        offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L3);
+        assertNotNull(offerPacket);
+        assertEquals(5, offerPacket.getClientMac().length);
+        assertEquals(expectedClientMac.substring(0, 10),
+                HexDump.toHexString(offerPacket.getClientMac()));
+
+        packet.flip();
+        packet.put(hwAddrLenOffset, (byte) 3);
+        offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L3);
+        assertNotNull(offerPacket);
+        assertEquals(3, offerPacket.getClientMac().length);
+        assertEquals(expectedClientMac.substring(0, 6),
+                HexDump.toHexString(offerPacket.getClientMac()));
+
+        // Set the the hardware address length to 0xff and verify that we a) don't treat it as -1
+        // and crash, and b) hardcode it to 6.
+        packet.flip();
+        packet.put(hwAddrLenOffset, (byte) -1);
+        offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L3);
+        assertNotNull(offerPacket);
+        assertEquals(6, offerPacket.getClientMac().length);
+        assertEquals(expectedClientMac, HexDump.toHexString(offerPacket.getClientMac()));
+
+        // Set the the hardware address length to a positive invalid value (> 16) and verify that we
+        // hardcode it to 6.
+        packet.flip();
+        packet.put(hwAddrLenOffset, (byte) 17);
+        offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L3);
+        assertNotNull(offerPacket);
+        assertEquals(6, offerPacket.getClientMac().length);
+        assertEquals(expectedClientMac, HexDump.toHexString(offerPacket.getClientMac()));
+    }
+
+    @Test
+    public void testPadAndOverloadedOptionsOffer() throws Exception {
+        // A packet observed in the real world that is interesting for two reasons:
+        //
+        // 1. It uses pad bytes, which we previously didn't support correctly.
+        // 2. It uses DHCP option overloading, which we don't currently support (but it doesn't
+        //    store any information in the overloaded fields).
+        //
+        // For now, we just check that it parses correctly.
+        final ByteBuffer packet = ByteBuffer.wrap(HexDump.hexStringToByteArray(
+            // Ethernet header.
+            "b4cef6000000e80462236e300800" +
+            // IP header.
+            "4500014c00000000ff11741701010101ac119876" +
+            // UDP header. TODO: fix invalid checksum (due to MAC address obfuscation).
+            "004300440138ae5a" +
+            // BOOTP header.
+            "020106000fa0059f0000000000000000ac1198760000000000000000" +
+            // MAC address.
+            "b4cef600000000000000000000000000" +
+            // Server name.
+            "ff00000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "ff00000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options
+            "638253633501023604010101010104ffff000033040000a8c03401030304ac1101010604ac110101" +
+            "0000000000000000000000000000000000000000000000ff000000"));
+
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L2);
+        assertTrue(offerPacket instanceof DhcpOfferPacket);
+        DhcpResults dhcpResults = offerPacket.toDhcpResults();
+        assertDhcpResults("172.17.152.118/16", "172.17.1.1", "172.17.1.1",
+                null, "1.1.1.1", null, 43200, false, 0, dhcpResults);
+    }
+
+    @Test
+    public void testBug2111() throws Exception {
+        final ByteBuffer packet = ByteBuffer.wrap(HexDump.hexStringToByteArray(
+            // IP header.
+            "4500014c00000000ff119beac3eaf3880a3f5d04" +
+            // UDP header. TODO: fix invalid checksum (due to MAC address obfuscation).
+            "0043004401387464" +
+            // BOOTP header.
+            "0201060002554812000a0000000000000a3f5d040000000000000000" +
+            // MAC address.
+            "00904c00000000000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options.
+            "638253633501023604c00002fe33040000bfc60104fffff00003040a3f50010608c0000201c0000202" +
+            "0f0f646f6d61696e3132332e636f2e756b0000000000ff00000000"));
+
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L3);
+        assertTrue(offerPacket instanceof DhcpOfferPacket);
+        DhcpResults dhcpResults = offerPacket.toDhcpResults();
+        assertDhcpResults("10.63.93.4/20", "10.63.80.1", "192.0.2.1,192.0.2.2",
+                "domain123.co.uk", "192.0.2.254", null, 49094, false, 0, dhcpResults);
+    }
+
+    @Test
+    public void testBug2136() throws Exception {
+        final ByteBuffer packet = ByteBuffer.wrap(HexDump.hexStringToByteArray(
+            // Ethernet header.
+            "bcf5ac000000d0c7890000000800" +
+            // IP header.
+            "4500014c00000000ff119beac3eaf3880a3f5d04" +
+            // UDP header. TODO: fix invalid checksum (due to MAC address obfuscation).
+            "0043004401387574" +
+            // BOOTP header.
+            "0201060163339a3000050000000000000a209ecd0000000000000000" +
+            // MAC address.
+            "bcf5ac00000000000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options.
+            "6382536335010236040a20ff80330400001c200104fffff00003040a20900106089458413494584135" +
+            "0f0b6c616e63732e61632e756b000000000000000000ff00000000"));
+
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L2);
+        assertTrue(offerPacket instanceof DhcpOfferPacket);
+        assertEquals("BCF5AC000000", HexDump.toHexString(offerPacket.getClientMac()));
+        DhcpResults dhcpResults = offerPacket.toDhcpResults();
+        assertDhcpResults("10.32.158.205/20", "10.32.144.1", "148.88.65.52,148.88.65.53",
+                "lancs.ac.uk", "10.32.255.128", null, 7200, false, 0, dhcpResults);
+    }
+
+    @Test
+    public void testUdpServerAnySourcePort() throws Exception {
+        final ByteBuffer packet = ByteBuffer.wrap(HexDump.hexStringToByteArray(
+            // Ethernet header.
+            "9cd917000000001c2e0000000800" +
+            // IP header.
+            "45a00148000040003d115087d18194fb0a0f7af2" +
+            // UDP header. TODO: fix invalid checksum (due to MAC address obfuscation).
+            // NOTE: The server source port is not the canonical port 67.
+            "C29F004401341268" +
+            // BOOTP header.
+            "02010600d628ba8200000000000000000a0f7af2000000000a0fc818" +
+            // MAC address.
+            "9cd91700000000000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options.
+            "6382536335010236040a0169fc3304000151800104ffff000003040a0fc817060cd1818003d1819403" +
+            "d18180060f0777766d2e6564751c040a0fffffff000000"));
+
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L2);
+        assertTrue(offerPacket instanceof DhcpOfferPacket);
+        assertEquals("9CD917000000", HexDump.toHexString(offerPacket.getClientMac()));
+        DhcpResults dhcpResults = offerPacket.toDhcpResults();
+        assertDhcpResults("10.15.122.242/16", "10.15.200.23",
+                "209.129.128.3,209.129.148.3,209.129.128.6",
+                "wvm.edu", "10.1.105.252", null, 86400, false, 0, dhcpResults);
+    }
+
+    @Test
+    public void testUdpInvalidDstPort() throws Exception {
+        final ByteBuffer packet = ByteBuffer.wrap(HexDump.hexStringToByteArray(
+            // Ethernet header.
+            "9cd917000000001c2e0000000800" +
+            // IP header.
+            "45a00148000040003d115087d18194fb0a0f7af2" +
+            // UDP header. TODO: fix invalid checksum (due to MAC address obfuscation).
+            // NOTE: The destination port is a non-DHCP port.
+            "0043aaaa01341268" +
+            // BOOTP header.
+            "02010600d628ba8200000000000000000a0f7af2000000000a0fc818" +
+            // MAC address.
+            "9cd91700000000000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options.
+            "6382536335010236040a0169fc3304000151800104ffff000003040a0fc817060cd1818003d1819403" +
+            "d18180060f0777766d2e6564751c040a0fffffff000000"));
+
+        try {
+            DhcpPacket.decodeFullPacket(packet, ENCAP_L2);
+            fail("Packet with invalid dst port did not throw ParseException");
+        } catch (ParseException expected) {}
+    }
+
+    @Test
+    public void testMultipleRouters() throws Exception {
+        final ByteBuffer packet = ByteBuffer.wrap(HexDump.hexStringToByteArray(
+            // Ethernet header.
+            "fc3d93000000" + "081735000000" + "0800" +
+            // IP header.
+            "45000148c2370000ff117ac2c0a8bd02ffffffff" +
+            // UDP header. TODO: fix invalid checksum (due to MAC address obfuscation).
+            "0043004401343beb" +
+            // BOOTP header.
+            "0201060027f518e20000800000000000c0a8bd310000000000000000" +
+            // MAC address.
+            "fc3d9300000000000000000000000000" +
+            // Server name.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // File.
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            "0000000000000000000000000000000000000000000000000000000000000000" +
+            // Options.
+            "638253633501023604c0abbd023304000070803a04000038403b04000062700104ffffff00" +
+            "0308c0a8bd01ffffff0006080808080808080404ff000000000000"));
+
+        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_L2);
+        assertTrue(offerPacket instanceof DhcpOfferPacket);
+        assertEquals("FC3D93000000", HexDump.toHexString(offerPacket.getClientMac()));
+        DhcpResults dhcpResults = offerPacket.toDhcpResults();
+        assertDhcpResults("192.168.189.49/24", "192.168.189.1", "8.8.8.8,8.8.4.4",
+                null, "192.171.189.2", null, 28800, false, 0, dhcpResults);
+    }
+
+    @Test
+    public void testDiscoverPacket() throws Exception {
+        short secs = 7;
+        int transactionId = 0xdeadbeef;
+        byte[] hwaddr = {
+                (byte) 0xda, (byte) 0x01, (byte) 0x19, (byte) 0x5b, (byte) 0xb1, (byte) 0x7a
+        };
+
+        ByteBuffer packet = DhcpPacket.buildDiscoverPacket(
+                DhcpPacket.ENCAP_L2, transactionId, secs, hwaddr,
+                false /* do unicast */, DhcpClient.REQUESTED_PARAMS);
+
+        byte[] headers = new byte[] {
+            // Ethernet header.
+            (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff,
+            (byte) 0xda, (byte) 0x01, (byte) 0x19, (byte) 0x5b, (byte) 0xb1, (byte) 0x7a,
+            (byte) 0x08, (byte) 0x00,
+            // IP header.
+            (byte) 0x45, (byte) 0x10, (byte) 0x01, (byte) 0x56,
+            (byte) 0x00, (byte) 0x00, (byte) 0x40, (byte) 0x00,
+            (byte) 0x40, (byte) 0x11, (byte) 0x39, (byte) 0x88,
+            (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00,
+            (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff,
+            // UDP header.
+            (byte) 0x00, (byte) 0x44, (byte) 0x00, (byte) 0x43,
+            (byte) 0x01, (byte) 0x42, (byte) 0x6a, (byte) 0x4a,
+            // BOOTP.
+            (byte) 0x01, (byte) 0x01, (byte) 0x06, (byte) 0x00,
+            (byte) 0xde, (byte) 0xad, (byte) 0xbe, (byte) 0xef,
+            (byte) 0x00, (byte) 0x07, (byte) 0x00, (byte) 0x00,
+            (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00,
+            (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00,
+            (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00,
+            (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00,
+            (byte) 0xda, (byte) 0x01, (byte) 0x19, (byte) 0x5b,
+            (byte) 0xb1, (byte) 0x7a
+        };
+        byte[] options = new byte[] {
+            // Magic cookie 0x63825363.
+            (byte) 0x63, (byte) 0x82, (byte) 0x53, (byte) 0x63,
+            // Message type DISCOVER.
+            (byte) 0x35, (byte) 0x01, (byte) 0x01,
+            // Client identifier Ethernet, da:01:19:5b:b1:7a.
+            (byte) 0x3d, (byte) 0x07,
+                    (byte) 0x01,
+                    (byte) 0xda, (byte) 0x01, (byte) 0x19, (byte) 0x5b, (byte) 0xb1, (byte) 0x7a,
+            // Max message size 1500.
+            (byte) 0x39, (byte) 0x02, (byte) 0x05, (byte) 0xdc,
+            // Version "android-dhcp-???".
+            (byte) 0x3c, (byte) 0x10,
+                    'a', 'n', 'd', 'r', 'o', 'i', 'd', '-', 'd', 'h', 'c', 'p', '-', '?', '?', '?',
+            // Hostname "android-01234567890abcde"
+            (byte) 0x0c, (byte) 0x18,
+                    'a', 'n', 'd', 'r', 'o', 'i', 'd', '-',
+                    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', 'a', 'b', 'c', 'd', 'e',
+            // Requested parameter list.
+            (byte) 0x37, (byte) 0x0a,
+                DHCP_SUBNET_MASK,
+                DHCP_ROUTER,
+                DHCP_DNS_SERVER,
+                DHCP_DOMAIN_NAME,
+                DHCP_MTU,
+                DHCP_BROADCAST_ADDRESS,
+                DHCP_LEASE_TIME,
+                DHCP_RENEWAL_TIME,
+                DHCP_REBINDING_TIME,
+                DHCP_VENDOR_INFO,
+            // End options.
+            (byte) 0xff,
+            // Our packets are always of even length. TODO: find out why and possibly fix it.
+            (byte) 0x00
+        };
+        byte[] expected = new byte[DhcpPacket.MIN_PACKET_LENGTH_L2 + options.length];
+        assertTrue((expected.length & 1) == 0);
+        System.arraycopy(headers, 0, expected, 0, headers.length);
+        System.arraycopy(options, 0, expected, DhcpPacket.MIN_PACKET_LENGTH_L2, options.length);
+
+        byte[] actual = new byte[packet.limit()];
+        packet.get(actual);
+        String msg =
+                "Expected:\n  " + Arrays.toString(expected) +
+                "\nActual:\n  " + Arrays.toString(actual);
+        assertTrue(msg, Arrays.equals(expected, actual));
+    }
+
+    public void checkBuildOfferPacket(int leaseTimeSecs, @Nullable String hostname)
+            throws Exception {
+        final int renewalTime = (int) (Integer.toUnsignedLong(leaseTimeSecs) / 2);
+        final int rebindingTime = (int) (Integer.toUnsignedLong(leaseTimeSecs) * 875 / 1000);
+        final int transactionId = 0xdeadbeef;
+
+        final ByteBuffer packet = DhcpPacket.buildOfferPacket(
+                DhcpPacket.ENCAP_BOOTP, transactionId, false /* broadcast */,
+                SERVER_ADDR, INADDR_ANY /* relayIp */, CLIENT_ADDR /* yourIp */,
+                CLIENT_MAC, leaseTimeSecs, NETMASK /* netMask */,
+                BROADCAST_ADDR /* bcAddr */, Collections.singletonList(SERVER_ADDR) /* gateways */,
+                Collections.singletonList(SERVER_ADDR) /* dnsServers */,
+                SERVER_ADDR /* dhcpServerIdentifier */, null /* domainName */, hostname,
+                false /* metered */, MTU);
+
+        ByteArrayOutputStream bos = new ByteArrayOutputStream();
+        // BOOTP headers
+        bos.write(new byte[] {
+                (byte) 0x02, (byte) 0x01, (byte) 0x06, (byte) 0x00,
+                (byte) 0xde, (byte) 0xad, (byte) 0xbe, (byte) 0xef,
+                (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00,
+                // ciaddr
+                (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00,
+        });
+        // yiaddr
+        bos.write(CLIENT_ADDR.getAddress());
+        // siaddr
+        bos.write(SERVER_ADDR.getAddress());
+        // giaddr
+        bos.write(INADDR_ANY.getAddress());
+        // chaddr
+        bos.write(CLIENT_MAC);
+
+        // Padding
+        bos.write(new byte[202]);
+
+        // Options
+        bos.write(new byte[]{
+                // Magic cookie 0x63825363.
+                (byte) 0x63, (byte) 0x82, (byte) 0x53, (byte) 0x63,
+                // Message type OFFER.
+                (byte) 0x35, (byte) 0x01, (byte) 0x02,
+        });
+        // Server ID
+        bos.write(new byte[] { (byte) 0x36, (byte) 0x04 });
+        bos.write(SERVER_ADDR.getAddress());
+        // Lease time
+        bos.write(new byte[] { (byte) 0x33, (byte) 0x04 });
+        bos.write(intToByteArray(leaseTimeSecs));
+        if (leaseTimeSecs != INFINITE_LEASE) {
+            // Renewal time
+            bos.write(new byte[]{(byte) 0x3a, (byte) 0x04});
+            bos.write(intToByteArray(renewalTime));
+            // Rebinding time
+            bos.write(new byte[]{(byte) 0x3b, (byte) 0x04});
+            bos.write(intToByteArray(rebindingTime));
+        }
+        // Subnet mask
+        bos.write(new byte[] { (byte) 0x01, (byte) 0x04 });
+        bos.write(NETMASK.getAddress());
+        // Broadcast address
+        bos.write(new byte[] { (byte) 0x1c, (byte) 0x04 });
+        bos.write(BROADCAST_ADDR.getAddress());
+        // Router
+        bos.write(new byte[] { (byte) 0x03, (byte) 0x04 });
+        bos.write(SERVER_ADDR.getAddress());
+        // Nameserver
+        bos.write(new byte[] { (byte) 0x06, (byte) 0x04 });
+        bos.write(SERVER_ADDR.getAddress());
+        // Hostname
+        if (hostname != null) {
+            bos.write(new byte[]{(byte) 0x0c, (byte) hostname.length()});
+            bos.write(hostname.getBytes(Charset.forName("US-ASCII")));
+        }
+        // MTU
+        bos.write(new byte[] { (byte) 0x1a, (byte) 0x02 });
+        bos.write(shortToByteArray(MTU));
+        // End options.
+        bos.write(0xff);
+
+        if ((bos.size() & 1) != 0) {
+            bos.write(0x00);
+        }
+
+        final byte[] expected = bos.toByteArray();
+        final byte[] actual = new byte[packet.limit()];
+        packet.get(actual);
+        final String msg = "Expected:\n  " + HexDump.dumpHexString(expected) +
+                "\nActual:\n  " + HexDump.dumpHexString(actual);
+        assertTrue(msg, Arrays.equals(expected, actual));
+    }
+
+    @Test
+    public void testOfferPacket() throws Exception {
+        checkBuildOfferPacket(3600, HOSTNAME);
+        checkBuildOfferPacket(Integer.MAX_VALUE, HOSTNAME);
+        checkBuildOfferPacket(0x80000000, HOSTNAME);
+        checkBuildOfferPacket(INFINITE_LEASE, HOSTNAME);
+        checkBuildOfferPacket(3600, null);
+    }
+
+    private static byte[] intToByteArray(int val) {
+        return ByteBuffer.allocate(4).putInt(val).array();
+    }
+
+    private static byte[] shortToByteArray(short val) {
+        return ByteBuffer.allocate(2).putShort(val).array();
+    }
+}