Migrate netlink-client to net-utils-device-common-netlink.

Move netlink stuff to frameworks/libs/net/common/device, and build the
source files as an individual libraray. NetworkStack module just depends
on the net-utils-device-common-netlink.

Besides, also fix the incorrect format detected by checkstyle_hook script
such as missing java doc and make some public function as private, rename
the variable and etc.

Bug: 192535368
Test: atest NetworkStaticlibTests
Change-Id: I00e7f30be1bc9ebc2e24d7cd53efc403d6ba3daa

22 files changed, 3329 insertions, 4 deletions

diff --git a/common/device/com/android/net/module/util/HexDump.java b/common/device/com/android/net/module/util/HexDump.java
index 6d36487b..a27c0a3c 100644
--- a/common/device/com/android/net/module/util/HexDump.java
+++ b/common/device/com/android/net/module/util/HexDump.java
@@ -16,7 +16,7 @@
 
 package com.android.net.module.util;
 
-import android.annotation.Nullable;
+import androidx.annotation.Nullable;
 
 /**
  * Hex utility functions.
diff --git a/common/device/com/android/net/module/util/Struct.java b/common/device/com/android/net/module/util/Struct.java
index d95c3037..b43e2c45 100644
--- a/common/device/com/android/net/module/util/Struct.java
+++ b/common/device/com/android/net/module/util/Struct.java
@@ -16,10 +16,11 @@
 
 package com.android.net.module.util;
 
-import android.annotation.NonNull;
-import android.annotation.Nullable;
 import android.net.MacAddress;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
diff --git a/common/device/com/android/net/module/util/netlink/ConntrackMessage.java b/common/device/com/android/net/module/util/netlink/ConntrackMessage.java
new file mode 100644
index 00000000..1763c04b
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/ConntrackMessage.java
@@ -0,0 +1,558 @@
+/*
+ * Copyright (C) 2017 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.net.module.util.netlink;
+
+import static android.system.OsConstants.IPPROTO_TCP;
+import static android.system.OsConstants.IPPROTO_UDP;
+
+import static com.android.net.module.util.netlink.StructNlAttr.findNextAttrOfType;
+import static com.android.net.module.util.netlink.StructNlAttr.makeNestedType;
+import static com.android.net.module.util.netlink.StructNlMsgHdr.NLM_F_ACK;
+import static com.android.net.module.util.netlink.StructNlMsgHdr.NLM_F_REPLACE;
+import static com.android.net.module.util.netlink.StructNlMsgHdr.NLM_F_REQUEST;
+
+import static java.nio.ByteOrder.BIG_ENDIAN;
+
+import android.system.OsConstants;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.VisibleForTesting;
+
+import java.net.Inet4Address;
+import java.net.InetAddress;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.util.Objects;
+
+/**
+ * A NetlinkMessage subclass for netlink conntrack messages.
+ *
+ * see also: <linux_src>/include/uapi/linux/netfilter/nfnetlink_conntrack.h
+ *
+ * @hide
+ */
+public class ConntrackMessage extends NetlinkMessage {
+    public static final int STRUCT_SIZE = StructNlMsgHdr.STRUCT_SIZE + StructNfGenMsg.STRUCT_SIZE;
+
+    // enum ctattr_type
+    public static final short CTA_TUPLE_ORIG  = 1;
+    public static final short CTA_TUPLE_REPLY = 2;
+    public static final short CTA_STATUS      = 3;
+    public static final short CTA_TIMEOUT     = 7;
+
+    // enum ctattr_tuple
+    public static final short CTA_TUPLE_IP    = 1;
+    public static final short CTA_TUPLE_PROTO = 2;
+
+    // enum ctattr_ip
+    public static final short CTA_IP_V4_SRC = 1;
+    public static final short CTA_IP_V4_DST = 2;
+
+    // enum ctattr_l4proto
+    public static final short CTA_PROTO_NUM      = 1;
+    public static final short CTA_PROTO_SRC_PORT = 2;
+    public static final short CTA_PROTO_DST_PORT = 3;
+
+    // enum ip_conntrack_status
+    public static final int IPS_EXPECTED      = 0x00000001;
+    public static final int IPS_SEEN_REPLY    = 0x00000002;
+    public static final int IPS_ASSURED       = 0x00000004;
+    public static final int IPS_CONFIRMED     = 0x00000008;
+    public static final int IPS_SRC_NAT       = 0x00000010;
+    public static final int IPS_DST_NAT       = 0x00000020;
+    public static final int IPS_SEQ_ADJUST    = 0x00000040;
+    public static final int IPS_SRC_NAT_DONE  = 0x00000080;
+    public static final int IPS_DST_NAT_DONE  = 0x00000100;
+    public static final int IPS_DYING         = 0x00000200;
+    public static final int IPS_FIXED_TIMEOUT = 0x00000400;
+    public static final int IPS_TEMPLATE      = 0x00000800;
+    public static final int IPS_UNTRACKED     = 0x00001000;
+    public static final int IPS_HELPER        = 0x00002000;
+    public static final int IPS_OFFLOAD       = 0x00004000;
+    public static final int IPS_HW_OFFLOAD    = 0x00008000;
+
+    // ip_conntrack_status mask
+    // Interesting on the NAT conntrack session which has already seen two direction traffic.
+    // TODO: Probably IPS_{SRC, DST}_NAT_DONE are also interesting.
+    public static final int ESTABLISHED_MASK = IPS_CONFIRMED | IPS_ASSURED | IPS_SEEN_REPLY
+            | IPS_SRC_NAT;
+    // Interesting on the established NAT conntrack session which is dying.
+    public static final int DYING_MASK = ESTABLISHED_MASK | IPS_DYING;
+
+    /**
+     * A tuple for the conntrack connection information.
+     *
+     * see also CTA_TUPLE_ORIG and CTA_TUPLE_REPLY.
+     */
+    public static class Tuple {
+        public final Inet4Address srcIp;
+        public final Inet4Address dstIp;
+
+        // Both port and protocol number are unsigned numbers stored in signed integers, and that
+        // callers that want to compare them to integers should either cast those integers, or
+        // convert them to unsigned using Byte.toUnsignedInt() and Short.toUnsignedInt().
+        public final short srcPort;
+        public final short dstPort;
+        public final byte protoNum;
+
+        public Tuple(TupleIpv4 ip, TupleProto proto) {
+            this.srcIp = ip.src;
+            this.dstIp = ip.dst;
+            this.srcPort = proto.srcPort;
+            this.dstPort = proto.dstPort;
+            this.protoNum = proto.protoNum;
+        }
+
+        @Override
+        @VisibleForTesting
+        public boolean equals(Object o) {
+            if (!(o instanceof Tuple)) return false;
+            Tuple that = (Tuple) o;
+            return Objects.equals(this.srcIp, that.srcIp)
+                    && Objects.equals(this.dstIp, that.dstIp)
+                    && this.srcPort == that.srcPort
+                    && this.dstPort == that.dstPort
+                    && this.protoNum == that.protoNum;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(srcIp, dstIp, srcPort, dstPort, protoNum);
+        }
+
+        @Override
+        public String toString() {
+            final String srcIpStr = (srcIp == null) ? "null" : srcIp.getHostAddress();
+            final String dstIpStr = (dstIp == null) ? "null" : dstIp.getHostAddress();
+            final String protoStr = NetlinkConstants.stringForProtocol(protoNum);
+
+            return "Tuple{"
+                    + protoStr + ": "
+                    + srcIpStr + ":" + Short.toUnsignedInt(srcPort) + " -> "
+                    + dstIpStr + ":" + Short.toUnsignedInt(dstPort)
+                    + "}";
+        }
+    }
+
+    /**
+     * A tuple for the conntrack connection address.
+     *
+     * see also CTA_TUPLE_IP.
+     */
+    public static class TupleIpv4 {
+        public final Inet4Address src;
+        public final Inet4Address dst;
+
+        public TupleIpv4(Inet4Address src, Inet4Address dst) {
+            this.src = src;
+            this.dst = dst;
+        }
+    }
+
+    /**
+     * A tuple for the conntrack connection protocol.
+     *
+     * see also CTA_TUPLE_PROTO.
+     */
+    public static class TupleProto {
+        public final byte protoNum;
+        public final short srcPort;
+        public final short dstPort;
+
+        public TupleProto(byte protoNum, short srcPort, short dstPort) {
+            this.protoNum = protoNum;
+            this.srcPort = srcPort;
+            this.dstPort = dstPort;
+        }
+    }
+
+    /**
+     * Create a netlink message to refresh IPv4 conntrack entry timeout.
+     */
+    public static byte[] newIPv4TimeoutUpdateRequest(
+            int proto, Inet4Address src, int sport, Inet4Address dst, int dport, int timeoutSec) {
+        // *** STYLE WARNING ***
+        //
+        // Code below this point uses extra block indentation to highlight the
+        // packing of nested tuple netlink attribute types.
+        final StructNlAttr ctaTupleOrig = new StructNlAttr(CTA_TUPLE_ORIG,
+                new StructNlAttr(CTA_TUPLE_IP,
+                        new StructNlAttr(CTA_IP_V4_SRC, src),
+                        new StructNlAttr(CTA_IP_V4_DST, dst)),
+                new StructNlAttr(CTA_TUPLE_PROTO,
+                        new StructNlAttr(CTA_PROTO_NUM, (byte) proto),
+                        new StructNlAttr(CTA_PROTO_SRC_PORT, (short) sport, BIG_ENDIAN),
+                        new StructNlAttr(CTA_PROTO_DST_PORT, (short) dport, BIG_ENDIAN)));
+
+        final StructNlAttr ctaTimeout = new StructNlAttr(CTA_TIMEOUT, timeoutSec, BIG_ENDIAN);
+
+        final int payloadLength = ctaTupleOrig.getAlignedLength() + ctaTimeout.getAlignedLength();
+        final byte[] bytes = new byte[STRUCT_SIZE + payloadLength];
+        final ByteBuffer byteBuffer = ByteBuffer.wrap(bytes);
+        byteBuffer.order(ByteOrder.nativeOrder());
+
+        final ConntrackMessage ctmsg = new ConntrackMessage();
+        ctmsg.mHeader.nlmsg_len = bytes.length;
+        ctmsg.mHeader.nlmsg_type = (NetlinkConstants.NFNL_SUBSYS_CTNETLINK << 8)
+                | NetlinkConstants.IPCTNL_MSG_CT_NEW;
+        ctmsg.mHeader.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | NLM_F_REPLACE;
+        ctmsg.mHeader.nlmsg_seq = 1;
+        ctmsg.pack(byteBuffer);
+
+        ctaTupleOrig.pack(byteBuffer);
+        ctaTimeout.pack(byteBuffer);
+
+        return bytes;
+    }
+
+    /**
+     * Parses a netfilter conntrack message from a {@link ByteBuffer}.
+     *
+     * @param header the netlink message header.
+     * @param byteBuffer The buffer from which to parse the netfilter conntrack message.
+     * @return the parsed netfilter conntrack message, or {@code null} if the netfilter conntrack
+     *         message could not be parsed successfully (for example, if it was truncated).
+     */
+    public static ConntrackMessage parse(StructNlMsgHdr header, ByteBuffer byteBuffer) {
+        // Just build the netlink header and netfilter header for now and pretend the whole message
+        // was consumed.
+        // TODO: Parse the conntrack attributes.
+        final StructNfGenMsg nfGenMsg = StructNfGenMsg.parse(byteBuffer);
+        if (nfGenMsg == null) {
+            return null;
+        }
+
+        final int baseOffset = byteBuffer.position();
+        StructNlAttr nlAttr = findNextAttrOfType(CTA_STATUS, byteBuffer);
+        int status = 0;
+        if (nlAttr != null) {
+            status = nlAttr.getValueAsBe32(0);
+        }
+
+        byteBuffer.position(baseOffset);
+        nlAttr = findNextAttrOfType(CTA_TIMEOUT, byteBuffer);
+        int timeoutSec = 0;
+        if (nlAttr != null) {
+            timeoutSec = nlAttr.getValueAsBe32(0);
+        }
+
+        byteBuffer.position(baseOffset);
+        nlAttr = findNextAttrOfType(makeNestedType(CTA_TUPLE_ORIG), byteBuffer);
+        Tuple tupleOrig = null;
+        if (nlAttr != null) {
+            tupleOrig = parseTuple(nlAttr.getValueAsByteBuffer());
+        }
+
+        byteBuffer.position(baseOffset);
+        nlAttr = findNextAttrOfType(makeNestedType(CTA_TUPLE_REPLY), byteBuffer);
+        Tuple tupleReply = null;
+        if (nlAttr != null) {
+            tupleReply = parseTuple(nlAttr.getValueAsByteBuffer());
+        }
+
+        // Advance to the end of the message.
+        byteBuffer.position(baseOffset);
+        final int kMinConsumed = StructNlMsgHdr.STRUCT_SIZE + StructNfGenMsg.STRUCT_SIZE;
+        final int kAdditionalSpace = NetlinkConstants.alignedLengthOf(
+                header.nlmsg_len - kMinConsumed);
+        if (byteBuffer.remaining() < kAdditionalSpace) {
+            return null;
+        }
+        byteBuffer.position(baseOffset + kAdditionalSpace);
+
+        return new ConntrackMessage(header, nfGenMsg, tupleOrig, tupleReply, status, timeoutSec);
+    }
+
+    /**
+     * Parses a conntrack tuple from a {@link ByteBuffer}.
+     *
+     * The attribute parsing is interesting on:
+     * - CTA_TUPLE_IP
+     *     CTA_IP_V4_SRC
+     *     CTA_IP_V4_DST
+     * - CTA_TUPLE_PROTO
+     *     CTA_PROTO_NUM
+     *     CTA_PROTO_SRC_PORT
+     *     CTA_PROTO_DST_PORT
+     *
+     * Assume that the minimum size is the sum of CTA_TUPLE_IP (size: 20) and CTA_TUPLE_PROTO
+     * (size: 28). Here is an example for an expected CTA_TUPLE_ORIG message in raw data:
+     * +--------------------------------------------------------------------------------------+
+     * | CTA_TUPLE_ORIG                                                                       |
+     * +--------------------------+-----------------------------------------------------------+
+     * | 1400                     | nla_len = 20                                              |
+     * | 0180                     | nla_type = nested CTA_TUPLE_IP                            |
+     * |     0800 0100 C0A8500C   |     nla_type=CTA_IP_V4_SRC, ip=192.168.80.12              |
+     * |     0800 0200 8C700874   |     nla_type=CTA_IP_V4_DST, ip=140.112.8.116              |
+     * | 1C00                     | nla_len = 28                                              |
+     * | 0280                     | nla_type = nested CTA_TUPLE_PROTO                         |
+     * |     0500 0100 06 000000  |     nla_type=CTA_PROTO_NUM, proto=IPPROTO_TCP (6)         |
+     * |     0600 0200 F3F1 0000  |     nla_type=CTA_PROTO_SRC_PORT, port=62449 (big endian)  |
+     * |     0600 0300 01BB 0000  |     nla_type=CTA_PROTO_DST_PORT, port=433 (big endian)    |
+     * +--------------------------+-----------------------------------------------------------+
+     *
+     * The position of the byte buffer doesn't set to the end when the function returns. It is okay
+     * because the caller ConntrackMessage#parse has passed a copy which is used for this parser
+     * only. Moreover, the parser behavior is the same as other existing netlink struct class
+     * parser. Ex: StructInetDiagMsg#parse.
+     */
+    @Nullable
+    private static Tuple parseTuple(@Nullable ByteBuffer byteBuffer) {
+        if (byteBuffer == null) return null;
+
+        TupleIpv4 tupleIpv4 = null;
+        TupleProto tupleProto = null;
+
+        final int baseOffset = byteBuffer.position();
+        StructNlAttr nlAttr = findNextAttrOfType(makeNestedType(CTA_TUPLE_IP), byteBuffer);
+        if (nlAttr != null) {
+            tupleIpv4 = parseTupleIpv4(nlAttr.getValueAsByteBuffer());
+        }
+        if (tupleIpv4 == null) return null;
+
+        byteBuffer.position(baseOffset);
+        nlAttr = findNextAttrOfType(makeNestedType(CTA_TUPLE_PROTO), byteBuffer);
+        if (nlAttr != null) {
+            tupleProto = parseTupleProto(nlAttr.getValueAsByteBuffer());
+        }
+        if (tupleProto == null) return null;
+
+        return new Tuple(tupleIpv4, tupleProto);
+    }
+
+    @Nullable
+    private static Inet4Address castToInet4Address(@Nullable InetAddress address) {
+        if (address == null || !(address instanceof Inet4Address)) return null;
+        return (Inet4Address) address;
+    }
+
+    @Nullable
+    private static TupleIpv4 parseTupleIpv4(@Nullable ByteBuffer byteBuffer) {
+        if (byteBuffer == null) return null;
+
+        Inet4Address src = null;
+        Inet4Address dst = null;
+
+        final int baseOffset = byteBuffer.position();
+        StructNlAttr nlAttr = findNextAttrOfType(CTA_IP_V4_SRC, byteBuffer);
+        if (nlAttr != null) {
+            src = castToInet4Address(nlAttr.getValueAsInetAddress());
+        }
+        if (src == null) return null;
+
+        byteBuffer.position(baseOffset);
+        nlAttr = findNextAttrOfType(CTA_IP_V4_DST, byteBuffer);
+        if (nlAttr != null) {
+            dst = castToInet4Address(nlAttr.getValueAsInetAddress());
+        }
+        if (dst == null) return null;
+
+        return new TupleIpv4(src, dst);
+    }
+
+    @Nullable
+    private static TupleProto parseTupleProto(@Nullable ByteBuffer byteBuffer) {
+        if (byteBuffer == null) return null;
+
+        byte protoNum = 0;
+        short srcPort = 0;
+        short dstPort = 0;
+
+        final int baseOffset = byteBuffer.position();
+        StructNlAttr nlAttr = findNextAttrOfType(CTA_PROTO_NUM, byteBuffer);
+        if (nlAttr != null) {
+            protoNum = nlAttr.getValueAsByte((byte) 0);
+        }
+        if (!(protoNum == IPPROTO_TCP || protoNum == IPPROTO_UDP)) return null;
+
+        byteBuffer.position(baseOffset);
+        nlAttr = StructNlAttr.findNextAttrOfType(CTA_PROTO_SRC_PORT, byteBuffer);
+        if (nlAttr != null) {
+            srcPort = nlAttr.getValueAsBe16((short) 0);
+        }
+        if (srcPort == 0) return null;
+
+        byteBuffer.position(baseOffset);
+        nlAttr = StructNlAttr.findNextAttrOfType(CTA_PROTO_DST_PORT, byteBuffer);
+        if (nlAttr != null) {
+            dstPort = nlAttr.getValueAsBe16((short) 0);
+        }
+        if (dstPort == 0) return null;
+
+        return new TupleProto(protoNum, srcPort, dstPort);
+    }
+
+    /**
+     * Netfilter header.
+     */
+    public final StructNfGenMsg nfGenMsg;
+    /**
+     * Original direction conntrack tuple.
+     *
+     * The tuple is determined by the parsed attribute value CTA_TUPLE_ORIG, or null if the
+     * tuple could not be parsed successfully (for example, if it was truncated or absent).
+     */
+    @Nullable
+    public final Tuple tupleOrig;
+    /**
+     * Reply direction conntrack tuple.
+     *
+     * The tuple is determined by the parsed attribute value CTA_TUPLE_REPLY, or null if the
+     * tuple could not be parsed successfully (for example, if it was truncated or absent).
+     */
+    @Nullable
+    public final Tuple tupleReply;
+    /**
+     * Connection status. A bitmask of ip_conntrack_status enum flags.
+     *
+     * The status is determined by the parsed attribute value CTA_STATUS, or 0 if the status could
+     * not be parsed successfully (for example, if it was truncated or absent). For the message
+     * from kernel, the valid status is non-zero. For the message from user space, the status may
+     * be 0 (absent).
+     */
+    public final int status;
+    /**
+     * Conntrack timeout.
+     *
+     * The timeout is determined by the parsed attribute value CTA_TIMEOUT, or 0 if the timeout
+     * could not be parsed successfully (for example, if it was truncated or absent). For
+     * IPCTNL_MSG_CT_NEW event, the valid timeout is non-zero. For IPCTNL_MSG_CT_DELETE event, the
+     * timeout is 0 (absent).
+     */
+    public final int timeoutSec;
+
+    private ConntrackMessage() {
+        super(new StructNlMsgHdr());
+        nfGenMsg = new StructNfGenMsg((byte) OsConstants.AF_INET);
+
+        // This constructor is only used by #newIPv4TimeoutUpdateRequest which doesn't use these
+        // data member for packing message. Simply fill them to null or 0.
+        tupleOrig = null;
+        tupleReply = null;
+        status = 0;
+        timeoutSec = 0;
+    }
+
+    private ConntrackMessage(@NonNull StructNlMsgHdr header, @NonNull StructNfGenMsg nfGenMsg,
+            @Nullable Tuple tupleOrig, @Nullable Tuple tupleReply, int status, int timeoutSec) {
+        super(header);
+        this.nfGenMsg = nfGenMsg;
+        this.tupleOrig = tupleOrig;
+        this.tupleReply = tupleReply;
+        this.status = status;
+        this.timeoutSec = timeoutSec;
+    }
+
+    /**
+     * Write a netfilter message to {@link ByteBuffer}.
+     */
+    public void pack(ByteBuffer byteBuffer) {
+        mHeader.pack(byteBuffer);
+        nfGenMsg.pack(byteBuffer);
+    }
+
+    public short getMessageType() {
+        return (short) (getHeader().nlmsg_type & ~(NetlinkConstants.NFNL_SUBSYS_CTNETLINK << 8));
+    }
+
+    /**
+     * Convert an ip conntrack status to a string.
+     */
+    public static String stringForIpConntrackStatus(int flags) {
+        final StringBuilder sb = new StringBuilder();
+
+        if ((flags & IPS_EXPECTED) != 0) {
+            sb.append("IPS_EXPECTED");
+        }
+        if ((flags & IPS_SEEN_REPLY) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_SEEN_REPLY");
+        }
+        if ((flags & IPS_ASSURED) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_ASSURED");
+        }
+        if ((flags & IPS_CONFIRMED) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_CONFIRMED");
+        }
+        if ((flags & IPS_SRC_NAT) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_SRC_NAT");
+        }
+        if ((flags & IPS_DST_NAT) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_DST_NAT");
+        }
+        if ((flags & IPS_SEQ_ADJUST) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_SEQ_ADJUST");
+        }
+        if ((flags & IPS_SRC_NAT_DONE) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_SRC_NAT_DONE");
+        }
+        if ((flags & IPS_DST_NAT_DONE) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_DST_NAT_DONE");
+        }
+        if ((flags & IPS_DYING) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_DYING");
+        }
+        if ((flags & IPS_FIXED_TIMEOUT) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_FIXED_TIMEOUT");
+        }
+        if ((flags & IPS_TEMPLATE) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_TEMPLATE");
+        }
+        if ((flags & IPS_UNTRACKED) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_UNTRACKED");
+        }
+        if ((flags & IPS_HELPER) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_HELPER");
+        }
+        if ((flags & IPS_OFFLOAD) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_OFFLOAD");
+        }
+        if ((flags & IPS_HW_OFFLOAD) != 0) {
+            if (sb.length() > 0) sb.append("|");
+            sb.append("IPS_HW_OFFLOAD");
+        }
+        return sb.toString();
+    }
+
+    @Override
+    public String toString() {
+        return "ConntrackMessage{"
+                + "nlmsghdr{"
+                + (mHeader == null ? "" : mHeader.toString(OsConstants.NETLINK_NETFILTER))
+                + "}, "
+                + "nfgenmsg{" + nfGenMsg + "}, "
+                + "tuple_orig{" + tupleOrig + "}, "
+                + "tuple_reply{" + tupleReply + "}, "
+                + "status{" + status + "(" + stringForIpConntrackStatus(status) + ")" + "}, "
+                + "timeout_sec{" + Integer.toUnsignedLong(timeoutSec) + "}"
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/InetDiagMessage.java b/common/device/com/android/net/module/util/netlink/InetDiagMessage.java
new file mode 100644
index 00000000..7b200e75
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/InetDiagMessage.java
@@ -0,0 +1,231 @@
+/*
+ * 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 com.android.net.module.util.netlink;
+
+import static android.os.Process.INVALID_UID;
+import static android.system.OsConstants.AF_INET;
+import static android.system.OsConstants.AF_INET6;
+import static android.system.OsConstants.IPPROTO_UDP;
+import static android.system.OsConstants.NETLINK_INET_DIAG;
+
+import static com.android.net.module.util.netlink.NetlinkConstants.SOCK_DIAG_BY_FAMILY;
+import static com.android.net.module.util.netlink.NetlinkSocket.DEFAULT_RECV_BUFSIZE;
+import static com.android.net.module.util.netlink.StructNlMsgHdr.NLM_F_DUMP;
+import static com.android.net.module.util.netlink.StructNlMsgHdr.NLM_F_REQUEST;
+
+import android.net.util.SocketUtils;
+import android.system.ErrnoException;
+import android.util.Log;
+
+import androidx.annotation.Nullable;
+
+import java.io.FileDescriptor;
+import java.io.IOException;
+import java.io.InterruptedIOException;
+import java.net.Inet4Address;
+import java.net.Inet6Address;
+import java.net.InetSocketAddress;
+import java.net.SocketException;
+import java.net.UnknownHostException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+/**
+ * A NetlinkMessage subclass for netlink inet_diag messages.
+ *
+ * see also: &lt;linux_src&gt;/include/uapi/linux/inet_diag.h
+ *
+ * @hide
+ */
+public class InetDiagMessage extends NetlinkMessage {
+    public static final String TAG = "InetDiagMessage";
+    private static final int TIMEOUT_MS = 500;
+
+    /**
+     * Construct an inet_diag_req_v2 message. This method will throw {@code NullPointerException}
+     * if local and remote are not both null or both non-null.
+     */
+    public static byte[] inetDiagReqV2(int protocol, InetSocketAddress local,
+            InetSocketAddress remote, int family, short flags) {
+        return inetDiagReqV2(protocol, local, remote, family, flags, 0 /* pad */,
+                0 /* idiagExt */, StructInetDiagReqV2.INET_DIAG_REQ_V2_ALL_STATES);
+    }
+
+    /**
+     * Construct an inet_diag_req_v2 message. This method will throw {@code NullPointerException}
+     * if local and remote are not both null or both non-null.
+     *
+     * @param protocol the request protocol type. This should be set to one of IPPROTO_TCP,
+     *                 IPPROTO_UDP, or IPPROTO_UDPLITE.
+     * @param local local socket address of the target socket. This will be packed into a
+     *              {@Code StructInetDiagSockId}. Request to diagnose for all sockets if both of
+     *              local or remote address is null.
+     * @param remote remote socket address of the target socket. This will be packed into a
+     *              {@Code StructInetDiagSockId}. Request to diagnose for all sockets if both of
+     *              local or remote address is null.
+     * @param family the ip family of the request message. This should be set to either AF_INET or
+     *               AF_INET6 for IPv4 or IPv6 sockets respectively.
+     * @param flags message flags. See &lt;linux_src&gt;/include/uapi/linux/netlink.h.
+     * @param pad for raw socket protocol specification.
+     * @param idiagExt a set of flags defining what kind of extended information to report.
+     * @param state a bit mask that defines a filter of socket states.
+     *
+     * @return bytes array representation of the message
+     */
+    public static byte[] inetDiagReqV2(int protocol, @Nullable InetSocketAddress local,
+            @Nullable InetSocketAddress remote, int family, short flags, int pad, int idiagExt,
+            int state) throws NullPointerException {
+        final byte[] bytes = new byte[StructNlMsgHdr.STRUCT_SIZE + StructInetDiagReqV2.STRUCT_SIZE];
+        final ByteBuffer byteBuffer = ByteBuffer.wrap(bytes);
+        byteBuffer.order(ByteOrder.nativeOrder());
+
+        final StructNlMsgHdr nlMsgHdr = new StructNlMsgHdr();
+        nlMsgHdr.nlmsg_len = bytes.length;
+        nlMsgHdr.nlmsg_type = SOCK_DIAG_BY_FAMILY;
+        nlMsgHdr.nlmsg_flags = flags;
+        nlMsgHdr.pack(byteBuffer);
+        final StructInetDiagReqV2 inetDiagReqV2 =
+                new StructInetDiagReqV2(protocol, local, remote, family, pad, idiagExt, state);
+
+        inetDiagReqV2.pack(byteBuffer);
+        return bytes;
+    }
+
+    public StructInetDiagMsg mStructInetDiagMsg;
+
+    private InetDiagMessage(StructNlMsgHdr header) {
+        super(header);
+        mStructInetDiagMsg = new StructInetDiagMsg();
+    }
+
+    /**
+     * Parse an inet_diag_req_v2 message from buffer.
+     */
+    public static InetDiagMessage parse(StructNlMsgHdr header, ByteBuffer byteBuffer) {
+        final InetDiagMessage msg = new InetDiagMessage(header);
+        msg.mStructInetDiagMsg = StructInetDiagMsg.parse(byteBuffer);
+        return msg;
+    }
+
+    private static int lookupUidByFamily(int protocol, InetSocketAddress local,
+                                         InetSocketAddress remote, int family, short flags,
+                                         FileDescriptor fd)
+            throws ErrnoException, InterruptedIOException {
+        byte[] msg = inetDiagReqV2(protocol, local, remote, family, flags);
+        NetlinkSocket.sendMessage(fd, msg, 0, msg.length, TIMEOUT_MS);
+        ByteBuffer response = NetlinkSocket.recvMessage(fd, DEFAULT_RECV_BUFSIZE, TIMEOUT_MS);
+
+        final NetlinkMessage nlMsg = NetlinkMessage.parse(response, NETLINK_INET_DIAG);
+        final StructNlMsgHdr hdr = nlMsg.getHeader();
+        if (hdr.nlmsg_type == NetlinkConstants.NLMSG_DONE) {
+            return INVALID_UID;
+        }
+        if (nlMsg instanceof InetDiagMessage) {
+            return ((InetDiagMessage) nlMsg).mStructInetDiagMsg.idiag_uid;
+        }
+        return INVALID_UID;
+    }
+
+    private static final int[] FAMILY = {AF_INET6, AF_INET};
+
+    private static int lookupUid(int protocol, InetSocketAddress local,
+                                 InetSocketAddress remote, FileDescriptor fd)
+            throws ErrnoException, InterruptedIOException {
+        int uid;
+
+        for (int family : FAMILY) {
+            /**
+             * For exact match lookup, swap local and remote for UDP lookups due to kernel
+             * bug which will not be fixed. See aosp/755889 and
+             * https://www.mail-archive.com/netdev@vger.kernel.org/msg248638.html
+             */
+            if (protocol == IPPROTO_UDP) {
+                uid = lookupUidByFamily(protocol, remote, local, family, NLM_F_REQUEST, fd);
+            } else {
+                uid = lookupUidByFamily(protocol, local, remote, family, NLM_F_REQUEST, fd);
+            }
+            if (uid != INVALID_UID) {
+                return uid;
+            }
+        }
+
+        /**
+         * For UDP it's possible for a socket to send packets to arbitrary destinations, even if the
+         * socket is not connected (and even if the socket is connected to a different destination).
+         * If we want this API to work for such packets, then on miss we need to do a second lookup
+         * with only the local address and port filled in.
+         * Always use flags == NLM_F_REQUEST | NLM_F_DUMP for wildcard.
+         */
+        if (protocol == IPPROTO_UDP) {
+            try {
+                InetSocketAddress wildcard = new InetSocketAddress(
+                        Inet6Address.getByName("::"), 0);
+                uid = lookupUidByFamily(protocol, local, wildcard, AF_INET6,
+                        (short) (NLM_F_REQUEST | NLM_F_DUMP), fd);
+                if (uid != INVALID_UID) {
+                    return uid;
+                }
+                wildcard = new InetSocketAddress(Inet4Address.getByName("0.0.0.0"), 0);
+                uid = lookupUidByFamily(protocol, local, wildcard, AF_INET,
+                        (short) (NLM_F_REQUEST | NLM_F_DUMP), fd);
+                if (uid != INVALID_UID) {
+                    return uid;
+                }
+            } catch (UnknownHostException e) {
+                Log.e(TAG, e.toString());
+            }
+        }
+        return INVALID_UID;
+    }
+
+    /**
+     * Use an inet_diag socket to look up the UID associated with the input local and remote
+     * address/port and protocol of a connection.
+     */
+    public static int getConnectionOwnerUid(int protocol, InetSocketAddress local,
+                                            InetSocketAddress remote) {
+        int uid = INVALID_UID;
+        FileDescriptor fd = null;
+        try {
+            fd = NetlinkSocket.forProto(NETLINK_INET_DIAG);
+            NetlinkSocket.connectToKernel(fd);
+            uid = lookupUid(protocol, local, remote, fd);
+        } catch (ErrnoException | SocketException | IllegalArgumentException
+                | InterruptedIOException e) {
+            Log.e(TAG, e.toString());
+        } finally {
+            if (fd != null) {
+                try {
+                    SocketUtils.closeSocket(fd);
+                } catch (IOException e) {
+                    Log.e(TAG, e.toString());
+                }
+            }
+        }
+        return uid;
+    }
+
+    @Override
+    public String toString() {
+        return "InetDiagMessage{ "
+                + "nlmsghdr{"
+                + (mHeader == null ? "" : mHeader.toString(NETLINK_INET_DIAG)) + "}, "
+                + "inet_diag_msg{"
+                + (mStructInetDiagMsg == null ? "" : mStructInetDiagMsg.toString()) + "} "
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/NdOption.java b/common/device/com/android/net/module/util/netlink/NdOption.java
new file mode 100644
index 00000000..50a34966
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/NdOption.java
@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2020 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.net.module.util.netlink;
+
+import java.nio.ByteBuffer;
+
+/**
+ * Base class for IPv6 neighbour discovery options.
+ */
+public class NdOption {
+    public static final int STRUCT_SIZE = 2;
+
+    /** The option type. */
+    public final byte type;
+    /** The length of the option in 8-byte units. Actually an unsigned 8-bit integer */
+    public final int length;
+
+    /** Constructs a new NdOption. */
+    NdOption(byte type, int length) {
+        this.type = type;
+        this.length = length;
+    }
+
+    /**
+     * Parses a neighbour discovery option.
+     *
+     * Parses (and consumes) the option if it is of a known type. If the option is of an unknown
+     * type, advances the buffer (so the caller can continue parsing if desired) and returns
+     * {@link #UNKNOWN}. If the option claims a length of 0, returns null because parsing cannot
+     * continue.
+     *
+     * No checks are performed on the length other than ensuring it is not 0, so if a caller wants
+     * to deal with options that might overflow the structure that contains them, it must explicitly
+     * set the buffer's limit to the position at which that structure ends.
+     *
+     * @param buf the buffer to parse.
+     * @return a subclass of {@link NdOption}, or {@code null} for an unknown or malformed option.
+     */
+    public static NdOption parse(ByteBuffer buf) {
+        if (buf == null || buf.remaining() < STRUCT_SIZE) return null;
+
+        // Peek the type without advancing the buffer.
+        byte type = buf.get(buf.position());
+        int length = Byte.toUnsignedInt(buf.get(buf.position() + 1));
+        if (length == 0) return null;
+
+        switch (type) {
+            case StructNdOptPref64.TYPE:
+                return StructNdOptPref64.parse(buf);
+
+            default:
+                int newPosition = Math.min(buf.limit(), buf.position() + length * 8);
+                buf.position(newPosition);
+                return UNKNOWN;
+        }
+    }
+
+    void writeToByteBuffer(ByteBuffer buf) {
+        buf.put(type);
+        buf.put((byte) length);
+    }
+
+    @Override
+    public String toString() {
+        return String.format("NdOption(%d, %d)", Byte.toUnsignedInt(type), length);
+    }
+
+    public static final NdOption UNKNOWN = new NdOption((byte) 0, 0);
+}
diff --git a/common/device/com/android/net/module/util/netlink/NduseroptMessage.java b/common/device/com/android/net/module/util/netlink/NduseroptMessage.java
new file mode 100644
index 00000000..4e3b9f2d
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/NduseroptMessage.java
@@ -0,0 +1,141 @@
+/*
+ * Copyright (C) 2020 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.net.module.util.netlink;
+
+import static android.system.OsConstants.AF_INET6;
+
+import androidx.annotation.NonNull;
+
+import java.net.Inet6Address;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.nio.BufferUnderflowException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+/**
+ * A NetlinkMessage subclass for RTM_NEWNDUSEROPT messages.
+ */
+public class NduseroptMessage extends NetlinkMessage {
+    public static final int STRUCT_SIZE = 16;
+
+    static final int NDUSEROPT_SRCADDR = 1;
+
+    /** The address family. Presumably always AF_INET6. */
+    public final byte family;
+    /**
+     * The total length in bytes of the options that follow this structure.
+     * Actually a 16-bit unsigned integer.
+     */
+    public final int opts_len;
+    /** The interface index on which the options were received. */
+    public final int ifindex;
+    /** The ICMP type of the packet that contained the options. */
+    public final byte icmp_type;
+    /** The ICMP code of the packet that contained the options. */
+    public final byte icmp_code;
+
+    /**
+     * ND option that was in this message.
+     * Even though the length field is called "opts_len", the kernel only ever sends one option per
+     * message. It is unlikely that this will ever change as it would break existing userspace code.
+     * But if it does, we can simply update this code, since userspace is typically newer than the
+     * kernel.
+     */
+    public final NdOption option;
+
+    /** The IP address that sent the packet containing the option. */
+    public final InetAddress srcaddr;
+
+    NduseroptMessage(@NonNull StructNlMsgHdr header, @NonNull ByteBuffer buf)
+            throws UnknownHostException {
+        super(header);
+
+        // The structure itself.
+        buf.order(ByteOrder.nativeOrder());  // Restored in the finally clause inside parse().
+        final int start = buf.position();
+        family = buf.get();
+        buf.get();  // Skip 1 byte of padding.
+        opts_len = Short.toUnsignedInt(buf.getShort());
+        ifindex = buf.getInt();
+        icmp_type = buf.get();
+        icmp_code = buf.get();
+        buf.position(buf.position() + 6);  // Skip 6 bytes of padding.
+
+        // The ND option.
+        // Ensure we don't read past opts_len even if the option length is invalid.
+        // Note that this check is not really necessary since if the option length is not valid,
+        // this struct won't be very useful to the caller.
+        buf.order(ByteOrder.BIG_ENDIAN);
+        int oldLimit = buf.limit();
+        buf.limit(start + STRUCT_SIZE + opts_len);
+        try {
+            option = NdOption.parse(buf);
+        } finally {
+            buf.limit(oldLimit);
+        }
+
+        // The source address.
+        int newPosition = start + STRUCT_SIZE + opts_len;
+        if (newPosition >= buf.limit()) {
+            throw new IllegalArgumentException("ND options extend past end of buffer");
+        }
+        buf.position(newPosition);
+
+        StructNlAttr nla = StructNlAttr.parse(buf);
+        if (nla == null || nla.nla_type != NDUSEROPT_SRCADDR || nla.nla_value == null) {
+            throw new IllegalArgumentException("Invalid source address in ND useropt");
+        }
+        if (family == AF_INET6) {
+            // InetAddress.getByAddress only looks at the ifindex if the address type needs one.
+            srcaddr = Inet6Address.getByAddress(null /* hostname */, nla.nla_value, ifindex);
+        } else {
+            srcaddr = InetAddress.getByAddress(nla.nla_value);
+        }
+    }
+
+    /**
+     * Parses a StructNduseroptmsg from a {@link ByteBuffer}.
+     *
+     * @param header the netlink message header.
+     * @param buf The buffer from which to parse the option. The buffer's byte order must be
+     *            {@link java.nio.ByteOrder#BIG_ENDIAN}.
+     * @return the parsed option, or {@code null} if the option could not be parsed successfully
+     *         (for example, if it was truncated, or if the prefix length code was wrong).
+     */
+    public static NduseroptMessage parse(@NonNull StructNlMsgHdr header, @NonNull ByteBuffer buf) {
+        if (buf == null || buf.remaining() < STRUCT_SIZE) return null;
+        ByteOrder oldOrder = buf.order();
+        try {
+            return new NduseroptMessage(header, buf);
+        } catch (IllegalArgumentException | UnknownHostException | BufferUnderflowException e) {
+            // Not great, but better than throwing an exception that might crash the caller.
+            // Convention in this package is that null indicates that the option was truncated, so
+            // callers must already handle it.
+            return null;
+        } finally {
+            buf.order(oldOrder);
+        }
+    }
+
+    @Override
+    public String toString() {
+        return String.format("Nduseroptmsg(%d, %d, %d, %d, %d, %s)",
+                family, opts_len, ifindex, Byte.toUnsignedInt(icmp_type),
+                Byte.toUnsignedInt(icmp_code), srcaddr.getHostAddress());
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/NetlinkConstants.java b/common/device/com/android/net/module/util/netlink/NetlinkConstants.java
new file mode 100644
index 00000000..cf9d2c54
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/NetlinkConstants.java
@@ -0,0 +1,260 @@
+/*
+ * 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 com.android.net.module.util.netlink;
+
+import android.system.OsConstants;
+
+import androidx.annotation.NonNull;
+
+import java.nio.ByteBuffer;
+
+/**
+ * Various constants and static helper methods for netlink communications.
+ *
+ * Values taken from:
+ *
+ *     include/uapi/linux/netfilter/nfnetlink.h
+ *     include/uapi/linux/netfilter/nfnetlink_conntrack.h
+ *     include/uapi/linux/netlink.h
+ *     include/uapi/linux/rtnetlink.h
+ *
+ * @hide
+ */
+public class NetlinkConstants {
+    private NetlinkConstants() {}
+
+    public static final int NLA_ALIGNTO = 4;
+    /**
+     * Flag for dumping struct tcp_info.
+     * Corresponding to enum definition in external/strace/linux/inet_diag.h.
+     */
+    public static final int INET_DIAG_MEMINFO = 1;
+
+    public static final int SOCKDIAG_MSG_HEADER_SIZE =
+            StructNlMsgHdr.STRUCT_SIZE + StructInetDiagMsg.STRUCT_SIZE;
+
+    /**
+     * Get the aligned length based on a Short type number.
+     */
+    public static final int alignedLengthOf(short length) {
+        final int intLength = (int) length & 0xffff;
+        return alignedLengthOf(intLength);
+    }
+
+    /**
+     * Get the aligned length based on a Integer type number.
+     */
+    public static final int alignedLengthOf(int length) {
+        if (length <= 0) return 0;
+        return (((length + NLA_ALIGNTO - 1) / NLA_ALIGNTO) * NLA_ALIGNTO);
+    }
+
+    /**
+     * Convert a address family type to a string.
+     */
+    public static String stringForAddressFamily(int family) {
+        if (family == OsConstants.AF_INET) return "AF_INET";
+        if (family == OsConstants.AF_INET6) return "AF_INET6";
+        if (family == OsConstants.AF_NETLINK) return "AF_NETLINK";
+        return String.valueOf(family);
+    }
+
+    /**
+     * Convert a protocol type to a string.
+     */
+    public static String stringForProtocol(int protocol) {
+        if (protocol == OsConstants.IPPROTO_TCP) return "IPPROTO_TCP";
+        if (protocol == OsConstants.IPPROTO_UDP) return "IPPROTO_UDP";
+        return String.valueOf(protocol);
+    }
+
+    /**
+     * Convert a byte array to a hexadecimal string.
+     */
+    public static String hexify(byte[] bytes) {
+        if (bytes == null) return "(null)";
+        return toHexString(bytes, 0, bytes.length);
+    }
+
+    /**
+     * Convert a {@link ByteBuffer} to a hexadecimal string.
+     */
+    public static String hexify(ByteBuffer buffer) {
+        if (buffer == null) return "(null)";
+        return toHexString(
+                buffer.array(), buffer.position(), buffer.remaining());
+    }
+
+    // Known values for struct nlmsghdr nlm_type.
+    public static final short NLMSG_NOOP                    = 1;   // Nothing
+    public static final short NLMSG_ERROR                   = 2;   // Error
+    public static final short NLMSG_DONE                    = 3;   // End of a dump
+    public static final short NLMSG_OVERRUN                 = 4;   // Data lost
+    public static final short NLMSG_MAX_RESERVED            = 15;  // Max reserved value
+
+    public static final short RTM_NEWLINK                   = 16;
+    public static final short RTM_DELLINK                   = 17;
+    public static final short RTM_GETLINK                   = 18;
+    public static final short RTM_SETLINK                   = 19;
+    public static final short RTM_NEWADDR                   = 20;
+    public static final short RTM_DELADDR                   = 21;
+    public static final short RTM_GETADDR                   = 22;
+    public static final short RTM_NEWROUTE                  = 24;
+    public static final short RTM_DELROUTE                  = 25;
+    public static final short RTM_GETROUTE                  = 26;
+    public static final short RTM_NEWNEIGH                  = 28;
+    public static final short RTM_DELNEIGH                  = 29;
+    public static final short RTM_GETNEIGH                  = 30;
+    public static final short RTM_NEWRULE                   = 32;
+    public static final short RTM_DELRULE                   = 33;
+    public static final short RTM_GETRULE                   = 34;
+    public static final short RTM_NEWNDUSEROPT              = 68;
+
+    // Netfilter netlink message types are presented by two bytes: high byte subsystem and
+    // low byte operation. See the macro NFNL_SUBSYS_ID and NFNL_MSG_TYPE in
+    // include/uapi/linux/netfilter/nfnetlink.h
+    public static final short NFNL_SUBSYS_CTNETLINK         = 1;
+
+    public static final short IPCTNL_MSG_CT_NEW             = 0;
+    public static final short IPCTNL_MSG_CT_GET             = 1;
+    public static final short IPCTNL_MSG_CT_DELETE          = 2;
+    public static final short IPCTNL_MSG_CT_GET_CTRZERO     = 3;
+    public static final short IPCTNL_MSG_CT_GET_STATS_CPU   = 4;
+    public static final short IPCTNL_MSG_CT_GET_STATS       = 5;
+    public static final short IPCTNL_MSG_CT_GET_DYING       = 6;
+    public static final short IPCTNL_MSG_CT_GET_UNCONFIRMED = 7;
+
+    /* see include/uapi/linux/sock_diag.h */
+    public static final short SOCK_DIAG_BY_FAMILY = 20;
+
+    // Netlink groups.
+    public static final int RTNLGRP_ND_USEROPT = 20;
+    public static final int RTMGRP_ND_USEROPT = 1 << (RTNLGRP_ND_USEROPT - 1);
+
+    /**
+     * Convert a netlink message type to a string for control message.
+     */
+    @NonNull
+    private static String stringForCtlMsgType(short nlmType) {
+        switch (nlmType) {
+            case NLMSG_NOOP: return "NLMSG_NOOP";
+            case NLMSG_ERROR: return "NLMSG_ERROR";
+            case NLMSG_DONE: return "NLMSG_DONE";
+            case NLMSG_OVERRUN: return "NLMSG_OVERRUN";
+            default: return "unknown control message type: " + String.valueOf(nlmType);
+        }
+    }
+
+    /**
+     * Convert a netlink message type to a string for NETLINK_ROUTE.
+     */
+    @NonNull
+    private static String stringForRtMsgType(short nlmType) {
+        switch (nlmType) {
+            case RTM_NEWLINK: return "RTM_NEWLINK";
+            case RTM_DELLINK: return "RTM_DELLINK";
+            case RTM_GETLINK: return "RTM_GETLINK";
+            case RTM_SETLINK: return "RTM_SETLINK";
+            case RTM_NEWADDR: return "RTM_NEWADDR";
+            case RTM_DELADDR: return "RTM_DELADDR";
+            case RTM_GETADDR: return "RTM_GETADDR";
+            case RTM_NEWROUTE: return "RTM_NEWROUTE";
+            case RTM_DELROUTE: return "RTM_DELROUTE";
+            case RTM_GETROUTE: return "RTM_GETROUTE";
+            case RTM_NEWNEIGH: return "RTM_NEWNEIGH";
+            case RTM_DELNEIGH: return "RTM_DELNEIGH";
+            case RTM_GETNEIGH: return "RTM_GETNEIGH";
+            case RTM_NEWRULE: return "RTM_NEWRULE";
+            case RTM_DELRULE: return "RTM_DELRULE";
+            case RTM_GETRULE: return "RTM_GETRULE";
+            case RTM_NEWNDUSEROPT: return "RTM_NEWNDUSEROPT";
+            default: return "unknown RTM type: " + String.valueOf(nlmType);
+        }
+    }
+
+    /**
+     * Convert a netlink message type to a string for NETLINK_INET_DIAG.
+     */
+    @NonNull
+    private static String stringForInetDiagMsgType(short nlmType) {
+        switch (nlmType) {
+            case SOCK_DIAG_BY_FAMILY: return "SOCK_DIAG_BY_FAMILY";
+            default: return "unknown SOCK_DIAG type: " + String.valueOf(nlmType);
+        }
+    }
+
+    /**
+     * Convert a netlink message type to a string for NETLINK_NETFILTER.
+     */
+    @NonNull
+    private static String stringForNfMsgType(short nlmType) {
+        final byte subsysId = (byte) (nlmType >> 8);
+        final byte msgType = (byte) nlmType;
+        switch (subsysId) {
+            case NFNL_SUBSYS_CTNETLINK:
+                switch (msgType) {
+                    case IPCTNL_MSG_CT_NEW: return "IPCTNL_MSG_CT_NEW";
+                    case IPCTNL_MSG_CT_GET: return "IPCTNL_MSG_CT_GET";
+                    case IPCTNL_MSG_CT_DELETE: return "IPCTNL_MSG_CT_DELETE";
+                    case IPCTNL_MSG_CT_GET_CTRZERO: return "IPCTNL_MSG_CT_GET_CTRZERO";
+                    case IPCTNL_MSG_CT_GET_STATS_CPU: return "IPCTNL_MSG_CT_GET_STATS_CPU";
+                    case IPCTNL_MSG_CT_GET_STATS: return "IPCTNL_MSG_CT_GET_STATS";
+                    case IPCTNL_MSG_CT_GET_DYING: return "IPCTNL_MSG_CT_GET_DYING";
+                    case IPCTNL_MSG_CT_GET_UNCONFIRMED: return "IPCTNL_MSG_CT_GET_UNCONFIRMED";
+                }
+                break;
+        }
+        return "unknown NETFILTER type: " + String.valueOf(nlmType);
+    }
+
+    /**
+     * Convert a netlink message type to a string by netlink family.
+     */
+    @NonNull
+    public static String stringForNlMsgType(short nlmType, int nlFamily) {
+        // Reserved control messages. The netlink family is ignored.
+        // See NLMSG_MIN_TYPE in include/uapi/linux/netlink.h.
+        if (nlmType <= NLMSG_MAX_RESERVED) return stringForCtlMsgType(nlmType);
+
+        // Netlink family messages. The netlink family is required. Note that the reason for using
+        // if-statement is that switch-case can't be used because the OsConstants.NETLINK_* are
+        // not constant.
+        if (nlFamily == OsConstants.NETLINK_ROUTE) return stringForRtMsgType(nlmType);
+        if (nlFamily == OsConstants.NETLINK_INET_DIAG) return stringForInetDiagMsgType(nlmType);
+        if (nlFamily == OsConstants.NETLINK_NETFILTER) return stringForNfMsgType(nlmType);
+
+        return "unknown type: " + String.valueOf(nlmType);
+    }
+
+    private static final char[] HEX_DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
+            'A', 'B', 'C', 'D', 'E', 'F' };
+    /**
+     * Convert a byte array to a hexadecimal string.
+     */
+    public static String toHexString(byte[] array, int offset, int length) {
+        char[] buf = new char[length * 2];
+
+        int bufIndex = 0;
+        for (int i = offset; i < offset + length; i++) {
+            byte b = array[i];
+            buf[bufIndex++] = HEX_DIGITS[(b >>> 4) & 0x0F];
+            buf[bufIndex++] = HEX_DIGITS[b & 0x0F];
+        }
+
+        return new String(buf);
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/NetlinkErrorMessage.java b/common/device/com/android/net/module/util/netlink/NetlinkErrorMessage.java
new file mode 100644
index 00000000..d9fb09e6
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/NetlinkErrorMessage.java
@@ -0,0 +1,64 @@
+/*
+ * 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.net.module.util.netlink;
+
+import java.nio.ByteBuffer;
+
+/**
+ * A NetlinkMessage subclass for netlink error messages.
+ *
+ * @hide
+ */
+public class NetlinkErrorMessage extends NetlinkMessage {
+
+    /**
+     * Parse a netlink error message from a {@link ByteBuffer}.
+     *
+     * @param byteBuffer The buffer from which to parse the netlink error message.
+     * @return the parsed netlink error message, or {@code null} if the netlink error message
+     *         could not be parsed successfully (for example, if it was truncated).
+     */
+    public static NetlinkErrorMessage parse(StructNlMsgHdr header, ByteBuffer byteBuffer) {
+        final NetlinkErrorMessage errorMsg = new NetlinkErrorMessage(header);
+
+        errorMsg.mNlMsgErr = StructNlMsgErr.parse(byteBuffer);
+        if (errorMsg.mNlMsgErr == null) {
+            return null;
+        }
+
+        return errorMsg;
+    }
+
+    private StructNlMsgErr mNlMsgErr;
+
+    NetlinkErrorMessage(StructNlMsgHdr header) {
+        super(header);
+        mNlMsgErr = null;
+    }
+
+    public StructNlMsgErr getNlMsgError() {
+        return mNlMsgErr;
+    }
+
+    @Override
+    public String toString() {
+        return "NetlinkErrorMessage{ "
+                + "nlmsghdr{" + (mHeader == null ? "" : mHeader.toString()) + "}, "
+                + "nlmsgerr{" + (mNlMsgErr == null ? "" : mNlMsgErr.toString()) + "} "
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/NetlinkMessage.java b/common/device/com/android/net/module/util/netlink/NetlinkMessage.java
new file mode 100644
index 00000000..f425384f
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/NetlinkMessage.java
@@ -0,0 +1,153 @@
+/*
+ * 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.net.module.util.netlink;
+
+import android.system.OsConstants;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import java.nio.ByteBuffer;
+
+/**
+ * NetlinkMessage base class for other, more specific netlink message types.
+ *
+ * Classes that extend NetlinkMessage should:
+ *     - implement a public static parse(StructNlMsgHdr, ByteBuffer) method
+ *     - returning either null (parse errors) or a new object of the subclass
+ *       type (cast-able to NetlinkMessage)
+ *
+ * NetlinkMessage.parse() should be updated to know which nlmsg_type values
+ * correspond with which message subclasses.
+ *
+ * @hide
+ */
+public class NetlinkMessage {
+    private static final String TAG = "NetlinkMessage";
+
+    /**
+     * Parsing netlink messages for reserved control message or specific netlink message. The
+     * netlink family is required for parsing specific netlink message. See man-pages/netlink.
+     */
+    @Nullable
+    public static NetlinkMessage parse(@NonNull ByteBuffer byteBuffer, int nlFamily) {
+        final int startPosition = (byteBuffer != null) ? byteBuffer.position() : -1;
+        final StructNlMsgHdr nlmsghdr = StructNlMsgHdr.parse(byteBuffer);
+        if (nlmsghdr == null) {
+            return null;
+        }
+
+        int payloadLength = NetlinkConstants.alignedLengthOf(nlmsghdr.nlmsg_len);
+        payloadLength -= StructNlMsgHdr.STRUCT_SIZE;
+        if (payloadLength < 0 || payloadLength > byteBuffer.remaining()) {
+            // Malformed message or runt buffer.  Pretend the buffer was consumed.
+            byteBuffer.position(byteBuffer.limit());
+            return null;
+        }
+
+        // Reserved control messages. The netlink family is ignored.
+        // See NLMSG_MIN_TYPE in include/uapi/linux/netlink.h.
+        if (nlmsghdr.nlmsg_type <= NetlinkConstants.NLMSG_MAX_RESERVED) {
+            return parseCtlMessage(nlmsghdr, byteBuffer, payloadLength);
+        }
+
+        // Netlink family messages. The netlink family is required. Note that the reason for using
+        // if-statement is that switch-case can't be used because the OsConstants.NETLINK_* are
+        // not constant.
+        if (nlFamily == OsConstants.NETLINK_ROUTE) {
+            return parseRtMessage(nlmsghdr, byteBuffer);
+        } else if (nlFamily == OsConstants.NETLINK_INET_DIAG) {
+            return parseInetDiagMessage(nlmsghdr, byteBuffer);
+        } else if (nlFamily == OsConstants.NETLINK_NETFILTER) {
+            return parseNfMessage(nlmsghdr, byteBuffer);
+        }
+
+        return null;
+    }
+
+    protected StructNlMsgHdr mHeader;
+
+    public NetlinkMessage(StructNlMsgHdr nlmsghdr) {
+        mHeader = nlmsghdr;
+    }
+
+    public StructNlMsgHdr getHeader() {
+        return mHeader;
+    }
+
+    @Override
+    public String toString() {
+        // The netlink family is not provided to StructNlMsgHdr#toString because NetlinkMessage
+        // doesn't store the information. So the netlink message type can't be transformed into
+        // a string by StructNlMsgHdr#toString and just keep as an integer. The specific message
+        // which inherits NetlinkMessage could override NetlinkMessage#toString and provide the
+        // specific netlink family to StructNlMsgHdr#toString.
+        return "NetlinkMessage{" + (mHeader == null ? "" : mHeader.toString()) + "}";
+    }
+
+    @NonNull
+    private static NetlinkMessage parseCtlMessage(@NonNull StructNlMsgHdr nlmsghdr,
+            @NonNull ByteBuffer byteBuffer, int payloadLength) {
+        switch (nlmsghdr.nlmsg_type) {
+            case NetlinkConstants.NLMSG_ERROR:
+                return (NetlinkMessage) NetlinkErrorMessage.parse(nlmsghdr, byteBuffer);
+            default: {
+                // Other netlink control messages. Just parse the header for now,
+                // pretending the whole message was consumed.
+                byteBuffer.position(byteBuffer.position() + payloadLength);
+                return new NetlinkMessage(nlmsghdr);
+            }
+        }
+    }
+
+    @Nullable
+    private static NetlinkMessage parseRtMessage(@NonNull StructNlMsgHdr nlmsghdr,
+            @NonNull ByteBuffer byteBuffer) {
+        switch (nlmsghdr.nlmsg_type) {
+            case NetlinkConstants.RTM_NEWNEIGH:
+            case NetlinkConstants.RTM_DELNEIGH:
+            case NetlinkConstants.RTM_GETNEIGH:
+                return (NetlinkMessage) RtNetlinkNeighborMessage.parse(nlmsghdr, byteBuffer);
+            case NetlinkConstants.RTM_NEWNDUSEROPT:
+                return (NetlinkMessage) NduseroptMessage.parse(nlmsghdr, byteBuffer);
+            default: return null;
+        }
+    }
+
+    @Nullable
+    private static NetlinkMessage parseInetDiagMessage(@NonNull StructNlMsgHdr nlmsghdr,
+            @NonNull ByteBuffer byteBuffer) {
+        switch (nlmsghdr.nlmsg_type) {
+            case NetlinkConstants.SOCK_DIAG_BY_FAMILY:
+                return (NetlinkMessage) InetDiagMessage.parse(nlmsghdr, byteBuffer);
+            default: return null;
+        }
+    }
+
+    @Nullable
+    private static NetlinkMessage parseNfMessage(@NonNull StructNlMsgHdr nlmsghdr,
+            @NonNull ByteBuffer byteBuffer) {
+        switch (nlmsghdr.nlmsg_type) {
+            case NetlinkConstants.NFNL_SUBSYS_CTNETLINK << 8
+                    | NetlinkConstants.IPCTNL_MSG_CT_NEW:
+            case NetlinkConstants.NFNL_SUBSYS_CTNETLINK << 8
+                    | NetlinkConstants.IPCTNL_MSG_CT_DELETE:
+                return (NetlinkMessage) ConntrackMessage.parse(nlmsghdr, byteBuffer);
+            default: return null;
+        }
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/NetlinkSocket.java b/common/device/com/android/net/module/util/netlink/NetlinkSocket.java
new file mode 100644
index 00000000..ec326dd7
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/NetlinkSocket.java
@@ -0,0 +1,174 @@
+/*
+ * 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 com.android.net.module.util.netlink;
+
+import static android.net.util.SocketUtils.makeNetlinkSocketAddress;
+import static android.system.OsConstants.AF_NETLINK;
+import static android.system.OsConstants.EIO;
+import static android.system.OsConstants.EPROTO;
+import static android.system.OsConstants.ETIMEDOUT;
+import static android.system.OsConstants.SOCK_DGRAM;
+import static android.system.OsConstants.SOL_SOCKET;
+import static android.system.OsConstants.SO_RCVBUF;
+import static android.system.OsConstants.SO_RCVTIMEO;
+import static android.system.OsConstants.SO_SNDTIMEO;
+
+import android.net.util.SocketUtils;
+import android.system.ErrnoException;
+import android.system.Os;
+import android.system.StructTimeval;
+import android.util.Log;
+
+import java.io.FileDescriptor;
+import java.io.IOException;
+import java.io.InterruptedIOException;
+import java.net.SocketException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+
+/**
+ * NetlinkSocket
+ *
+ * A small static class to assist with AF_NETLINK socket operations.
+ *
+ * @hide
+ */
+public class NetlinkSocket {
+    private static final String TAG = "NetlinkSocket";
+    private static final long IO_TIMEOUT_MS = 300L;
+
+    public static final int DEFAULT_RECV_BUFSIZE = 8 * 1024;
+    public static final int SOCKET_RECV_BUFSIZE = 64 * 1024;
+
+    /**
+     * Send one netlink message to kernel via netlink socket.
+     *
+     * @param nlProto netlink protocol type.
+     * @param msg the raw bytes of netlink message to be sent.
+     */
+    public static void sendOneShotKernelMessage(int nlProto, byte[] msg) throws ErrnoException {
+        final String errPrefix = "Error in NetlinkSocket.sendOneShotKernelMessage";
+        final FileDescriptor fd = forProto(nlProto);
+
+        try {
+            connectToKernel(fd);
+            sendMessage(fd, msg, 0, msg.length, IO_TIMEOUT_MS);
+            final ByteBuffer bytes = recvMessage(fd, DEFAULT_RECV_BUFSIZE, IO_TIMEOUT_MS);
+            // recvMessage() guaranteed to not return null if it did not throw.
+            final NetlinkMessage response = NetlinkMessage.parse(bytes, nlProto);
+            if (response != null && response instanceof NetlinkErrorMessage
+                    && (((NetlinkErrorMessage) response).getNlMsgError() != null)) {
+                final int errno = ((NetlinkErrorMessage) response).getNlMsgError().error;
+                if (errno != 0) {
+                    // TODO: consider ignoring EINVAL (-22), which appears to be
+                    // normal when probing a neighbor for which the kernel does
+                    // not already have / no longer has a link layer address.
+                    Log.e(TAG, errPrefix + ", errmsg=" + response.toString());
+                    // Note: convert kernel errnos (negative) into userspace errnos (positive).
+                    throw new ErrnoException(response.toString(), Math.abs(errno));
+                }
+            } else {
+                final String errmsg;
+                if (response == null) {
+                    bytes.position(0);
+                    errmsg = "raw bytes: " + NetlinkConstants.hexify(bytes);
+                } else {
+                    errmsg = response.toString();
+                }
+                Log.e(TAG, errPrefix + ", errmsg=" + errmsg);
+                throw new ErrnoException(errmsg, EPROTO);
+            }
+        } catch (InterruptedIOException e) {
+            Log.e(TAG, errPrefix, e);
+            throw new ErrnoException(errPrefix, ETIMEDOUT, e);
+        } catch (SocketException e) {
+            Log.e(TAG, errPrefix, e);
+            throw new ErrnoException(errPrefix, EIO, e);
+        } finally {
+            try {
+                SocketUtils.closeSocket(fd);
+            } catch (IOException e) {
+                // Nothing we can do here
+            }
+        }
+    }
+
+    /**
+     * Create netlink socket with the given netlink protocol type.
+     *
+     * @return fd the fileDescriptor of the socket.
+     * Throw ErrnoException if the exception is thrown.
+     */
+    public static FileDescriptor forProto(int nlProto) throws ErrnoException {
+        final FileDescriptor fd = Os.socket(AF_NETLINK, SOCK_DGRAM, nlProto);
+        Os.setsockoptInt(fd, SOL_SOCKET, SO_RCVBUF, SOCKET_RECV_BUFSIZE);
+        return fd;
+    }
+
+    /**
+     * Connect to kernel via netlink socket.
+     *
+     * Throw ErrnoException, SocketException if the exception is thrown.
+     */
+    public static void connectToKernel(FileDescriptor fd) throws ErrnoException, SocketException {
+        Os.connect(fd, makeNetlinkSocketAddress(0, 0));
+    }
+
+    private static void checkTimeout(long timeoutMs) {
+        if (timeoutMs < 0) {
+            throw new IllegalArgumentException("Negative timeouts not permitted");
+        }
+    }
+
+    /**
+     * Wait up to |timeoutMs| (or until underlying socket error) for a
+     * netlink message of at most |bufsize| size.
+     *
+     * Multi-threaded calls with different timeouts will cause unexpected results.
+     */
+    public static ByteBuffer recvMessage(FileDescriptor fd, int bufsize, long timeoutMs)
+            throws ErrnoException, IllegalArgumentException, InterruptedIOException {
+        checkTimeout(timeoutMs);
+
+        Os.setsockoptTimeval(fd, SOL_SOCKET, SO_RCVTIMEO, StructTimeval.fromMillis(timeoutMs));
+
+        ByteBuffer byteBuffer = ByteBuffer.allocate(bufsize);
+        int length = Os.read(fd, byteBuffer);
+        if (length == bufsize) {
+            Log.w(TAG, "maximum read");
+        }
+        byteBuffer.position(0);
+        byteBuffer.limit(length);
+        byteBuffer.order(ByteOrder.nativeOrder());
+        return byteBuffer;
+    }
+
+    /**
+     * Send a message to a peer to which this socket has previously connected,
+     * waiting at most |timeoutMs| milliseconds for the send to complete.
+     *
+     * Multi-threaded calls with different timeouts will cause unexpected results.
+     */
+    public static int sendMessage(
+            FileDescriptor fd, byte[] bytes, int offset, int count, long timeoutMs)
+            throws ErrnoException, IllegalArgumentException, InterruptedIOException {
+        checkTimeout(timeoutMs);
+        Os.setsockoptTimeval(fd, SOL_SOCKET, SO_SNDTIMEO, StructTimeval.fromMillis(timeoutMs));
+        return Os.write(fd, bytes, offset, count);
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/RtNetlinkNeighborMessage.java b/common/device/com/android/net/module/util/netlink/RtNetlinkNeighborMessage.java
new file mode 100644
index 00000000..a75ef8dd
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/RtNetlinkNeighborMessage.java
@@ -0,0 +1,237 @@
+/*
+ * 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.net.module.util.netlink;
+
+import static com.android.net.module.util.netlink.StructNlMsgHdr.NLM_F_ACK;
+import static com.android.net.module.util.netlink.StructNlMsgHdr.NLM_F_DUMP;
+import static com.android.net.module.util.netlink.StructNlMsgHdr.NLM_F_REPLACE;
+import static com.android.net.module.util.netlink.StructNlMsgHdr.NLM_F_REQUEST;
+
+import android.system.OsConstants;
+
+import java.net.Inet6Address;
+import java.net.InetAddress;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+/**
+ * A NetlinkMessage subclass for rtnetlink neighbor messages.
+ *
+ * see also: &lt;linux_src&gt;/include/uapi/linux/neighbour.h
+ *
+ * @hide
+ */
+public class RtNetlinkNeighborMessage extends NetlinkMessage {
+    public static final short NDA_UNSPEC    = 0;
+    public static final short NDA_DST       = 1;
+    public static final short NDA_LLADDR    = 2;
+    public static final short NDA_CACHEINFO = 3;
+    public static final short NDA_PROBES    = 4;
+    public static final short NDA_VLAN      = 5;
+    public static final short NDA_PORT      = 6;
+    public static final short NDA_VNI       = 7;
+    public static final short NDA_IFINDEX   = 8;
+    public static final short NDA_MASTER    = 9;
+
+    /**
+     * Parse routing socket netlink neighbor message from ByteBuffer.
+     *
+     * @param header netlink message header.
+     * @param byteBuffer the ByteBuffer instance that wraps the raw netlink message bytes.
+     */
+    public static RtNetlinkNeighborMessage parse(StructNlMsgHdr header, ByteBuffer byteBuffer) {
+        final RtNetlinkNeighborMessage neighMsg = new RtNetlinkNeighborMessage(header);
+
+        neighMsg.mNdmsg = StructNdMsg.parse(byteBuffer);
+        if (neighMsg.mNdmsg == null) {
+            return null;
+        }
+
+        // Some of these are message-type dependent, and not always present.
+        final int baseOffset = byteBuffer.position();
+        StructNlAttr nlAttr = StructNlAttr.findNextAttrOfType(NDA_DST, byteBuffer);
+        if (nlAttr != null) {
+            neighMsg.mDestination = nlAttr.getValueAsInetAddress();
+        }
+
+        byteBuffer.position(baseOffset);
+        nlAttr = StructNlAttr.findNextAttrOfType(NDA_LLADDR, byteBuffer);
+        if (nlAttr != null) {
+            neighMsg.mLinkLayerAddr = nlAttr.nla_value;
+        }
+
+        byteBuffer.position(baseOffset);
+        nlAttr = StructNlAttr.findNextAttrOfType(NDA_PROBES, byteBuffer);
+        if (nlAttr != null) {
+            neighMsg.mNumProbes = nlAttr.getValueAsInt(0);
+        }
+
+        byteBuffer.position(baseOffset);
+        nlAttr = StructNlAttr.findNextAttrOfType(NDA_CACHEINFO, byteBuffer);
+        if (nlAttr != null) {
+            neighMsg.mCacheInfo = StructNdaCacheInfo.parse(nlAttr.getValueAsByteBuffer());
+        }
+
+        final int kMinConsumed = StructNlMsgHdr.STRUCT_SIZE + StructNdMsg.STRUCT_SIZE;
+        final int kAdditionalSpace = NetlinkConstants.alignedLengthOf(
+                neighMsg.mHeader.nlmsg_len - kMinConsumed);
+        if (byteBuffer.remaining() < kAdditionalSpace) {
+            byteBuffer.position(byteBuffer.limit());
+        } else {
+            byteBuffer.position(baseOffset + kAdditionalSpace);
+        }
+
+        return neighMsg;
+    }
+
+    /**
+     * A convenience method to create an RTM_GETNEIGH request message.
+     */
+    public static byte[] newGetNeighborsRequest(int seqNo) {
+        final int length = StructNlMsgHdr.STRUCT_SIZE + StructNdMsg.STRUCT_SIZE;
+        final byte[] bytes = new byte[length];
+        final ByteBuffer byteBuffer = ByteBuffer.wrap(bytes);
+        byteBuffer.order(ByteOrder.nativeOrder());
+
+        final StructNlMsgHdr nlmsghdr = new StructNlMsgHdr();
+        nlmsghdr.nlmsg_len = length;
+        nlmsghdr.nlmsg_type = NetlinkConstants.RTM_GETNEIGH;
+        nlmsghdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
+        nlmsghdr.nlmsg_seq = seqNo;
+        nlmsghdr.pack(byteBuffer);
+
+        final StructNdMsg ndmsg = new StructNdMsg();
+        ndmsg.pack(byteBuffer);
+
+        return bytes;
+    }
+
+    /**
+     * A convenience method to create an RTM_NEWNEIGH message, to modify
+     * the kernel's state information for a specific neighbor.
+     */
+    public static byte[] newNewNeighborMessage(
+            int seqNo, InetAddress ip, short nudState, int ifIndex, byte[] llAddr) {
+        final StructNlMsgHdr nlmsghdr = new StructNlMsgHdr();
+        nlmsghdr.nlmsg_type = NetlinkConstants.RTM_NEWNEIGH;
+        nlmsghdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | NLM_F_REPLACE;
+        nlmsghdr.nlmsg_seq = seqNo;
+
+        final RtNetlinkNeighborMessage msg = new RtNetlinkNeighborMessage(nlmsghdr);
+        msg.mNdmsg = new StructNdMsg();
+        msg.mNdmsg.ndm_family =
+                (byte) ((ip instanceof Inet6Address) ? OsConstants.AF_INET6 : OsConstants.AF_INET);
+        msg.mNdmsg.ndm_ifindex = ifIndex;
+        msg.mNdmsg.ndm_state = nudState;
+        msg.mDestination = ip;
+        msg.mLinkLayerAddr = llAddr;  // might be null
+
+        final byte[] bytes = new byte[msg.getRequiredSpace()];
+        nlmsghdr.nlmsg_len = bytes.length;
+        final ByteBuffer byteBuffer = ByteBuffer.wrap(bytes);
+        byteBuffer.order(ByteOrder.nativeOrder());
+        msg.pack(byteBuffer);
+        return bytes;
+    }
+
+    private StructNdMsg mNdmsg;
+    private InetAddress mDestination;
+    private byte[] mLinkLayerAddr;
+    private int mNumProbes;
+    private StructNdaCacheInfo mCacheInfo;
+
+    private RtNetlinkNeighborMessage(StructNlMsgHdr header) {
+        super(header);
+        mNdmsg = null;
+        mDestination = null;
+        mLinkLayerAddr = null;
+        mNumProbes = 0;
+        mCacheInfo = null;
+    }
+
+    public StructNdMsg getNdHeader() {
+        return mNdmsg;
+    }
+
+    public InetAddress getDestination() {
+        return mDestination;
+    }
+
+    public byte[] getLinkLayerAddress() {
+        return mLinkLayerAddr;
+    }
+
+    public int getProbes() {
+        return mNumProbes;
+    }
+
+    public StructNdaCacheInfo getCacheInfo() {
+        return mCacheInfo;
+    }
+
+    private int getRequiredSpace() {
+        int spaceRequired = StructNlMsgHdr.STRUCT_SIZE + StructNdMsg.STRUCT_SIZE;
+        if (mDestination != null) {
+            spaceRequired += NetlinkConstants.alignedLengthOf(
+                    StructNlAttr.NLA_HEADERLEN + mDestination.getAddress().length);
+        }
+        if (mLinkLayerAddr != null) {
+            spaceRequired += NetlinkConstants.alignedLengthOf(
+                    StructNlAttr.NLA_HEADERLEN + mLinkLayerAddr.length);
+        }
+        // Currently we don't write messages with NDA_PROBES nor NDA_CACHEINFO
+        // attributes appended.  Fix later, if necessary.
+        return spaceRequired;
+    }
+
+    private static void packNlAttr(short nlType, byte[] nlValue, ByteBuffer byteBuffer) {
+        final StructNlAttr nlAttr = new StructNlAttr();
+        nlAttr.nla_type = nlType;
+        nlAttr.nla_value = nlValue;
+        nlAttr.nla_len = (short) (StructNlAttr.NLA_HEADERLEN + nlAttr.nla_value.length);
+        nlAttr.pack(byteBuffer);
+    }
+
+    /**
+     * Write a neighbor discovery netlink message to {@link ByteBuffer}.
+     */
+    public void pack(ByteBuffer byteBuffer) {
+        getHeader().pack(byteBuffer);
+        mNdmsg.pack(byteBuffer);
+
+        if (mDestination != null) {
+            packNlAttr(NDA_DST, mDestination.getAddress(), byteBuffer);
+        }
+        if (mLinkLayerAddr != null) {
+            packNlAttr(NDA_LLADDR, mLinkLayerAddr, byteBuffer);
+        }
+    }
+
+    @Override
+    public String toString() {
+        final String ipLiteral = (mDestination == null) ? "" : mDestination.getHostAddress();
+        return "RtNetlinkNeighborMessage{ "
+                + "nlmsghdr{"
+                + (mHeader == null ? "" : mHeader.toString(OsConstants.NETLINK_ROUTE)) + "}, "
+                + "ndmsg{" + (mNdmsg == null ? "" : mNdmsg.toString()) + "}, "
+                + "destination{" + ipLiteral + "} "
+                + "linklayeraddr{" + NetlinkConstants.hexify(mLinkLayerAddr) + "} "
+                + "probes{" + mNumProbes + "} "
+                + "cacheinfo{" + (mCacheInfo == null ? "" : mCacheInfo.toString()) + "} "
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/StructInetDiagMsg.java b/common/device/com/android/net/module/util/netlink/StructInetDiagMsg.java
new file mode 100644
index 00000000..205656e3
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/StructInetDiagMsg.java
@@ -0,0 +1,62 @@
+/*
+ * 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.net.module.util.netlink;
+
+import java.nio.ByteBuffer;
+
+/**
+ * struct inet_diag_msg
+ *
+ * see &lt;linux_src&gt;/include/uapi/linux/inet_diag.h
+ *
+ * struct inet_diag_msg {
+ *      __u8    idiag_family;
+ *      __u8    idiag_state;
+ *      __u8    idiag_timer;
+ *      __u8    idiag_retrans;
+ *      struct  inet_diag_sockid id;
+ *      __u32   idiag_expires;
+ *      __u32   idiag_rqueue;
+ *      __u32   idiag_wqueue;
+ *      __u32   idiag_uid;
+ *      __u32   idiag_inode;
+ * };
+ *
+ * @hide
+ */
+public class StructInetDiagMsg {
+    public static final int STRUCT_SIZE = 4 + StructInetDiagSockId.STRUCT_SIZE + 20;
+    private static final int IDIAG_UID_OFFSET = StructNlMsgHdr.STRUCT_SIZE + 4
+            + StructInetDiagSockId.STRUCT_SIZE + 12;
+    public int idiag_uid;
+
+    /**
+     * Parse inet diag netlink message from buffer.
+     */
+    public static StructInetDiagMsg parse(ByteBuffer byteBuffer) {
+        StructInetDiagMsg struct = new StructInetDiagMsg();
+        struct.idiag_uid = byteBuffer.getInt(IDIAG_UID_OFFSET);
+        return struct;
+    }
+
+    @Override
+    public String toString() {
+        return "StructInetDiagMsg{ "
+                + "idiag_uid{" + idiag_uid + "}, "
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/StructInetDiagReqV2.java b/common/device/com/android/net/module/util/netlink/StructInetDiagReqV2.java
new file mode 100644
index 00000000..6eef8653
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/StructInetDiagReqV2.java
@@ -0,0 +1,100 @@
+/*
+ * 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.net.module.util.netlink;
+
+import androidx.annotation.Nullable;
+
+import java.net.InetSocketAddress;
+import java.nio.ByteBuffer;
+
+/**
+ * struct inet_diag_req_v2
+ *
+ * see &lt;linux_src&gt;/include/uapi/linux/inet_diag.h
+ *
+ *      struct inet_diag_req_v2 {
+ *          __u8    sdiag_family;
+ *          __u8    sdiag_protocol;
+ *          __u8    idiag_ext;
+ *          __u8    pad;
+ *          __u32   idiag_states;
+ *          struct  inet_diag_sockid id;
+ *      };
+ *
+ * @hide
+ */
+public class StructInetDiagReqV2 {
+    public static final int STRUCT_SIZE = 8 + StructInetDiagSockId.STRUCT_SIZE;
+
+    private final byte mSdiagFamily;
+    private final byte mSdiagProtocol;
+    private final byte mIdiagExt;
+    private final byte mPad;
+    private final StructInetDiagSockId mId;
+    private final int mState;
+    public static final int INET_DIAG_REQ_V2_ALL_STATES = (int) 0xffffffff;
+
+    public StructInetDiagReqV2(int protocol, InetSocketAddress local, InetSocketAddress remote,
+            int family) {
+        this(protocol, local, remote, family, 0 /* pad */, 0 /* extension */,
+                INET_DIAG_REQ_V2_ALL_STATES);
+    }
+
+    public StructInetDiagReqV2(int protocol, @Nullable InetSocketAddress local,
+            @Nullable InetSocketAddress remote, int family, int pad, int extension, int state)
+            throws NullPointerException {
+        mSdiagFamily = (byte) family;
+        mSdiagProtocol = (byte) protocol;
+        // Request for all sockets if no specific socket is requested. Specify the local and remote
+        // socket address information for target request socket.
+        if ((local == null) != (remote == null)) {
+            throw new NullPointerException("Local and remote must be both null or both non-null");
+        }
+        mId = ((local != null && remote != null) ? new StructInetDiagSockId(local, remote) : null);
+        mPad = (byte) pad;
+        mIdiagExt = (byte) extension;
+        mState = state;
+    }
+
+    /**
+     * Write the int diag request v2 message to ByteBuffer.
+     */
+    public void pack(ByteBuffer byteBuffer) {
+        // The ByteOrder must have already been set by the caller.
+        byteBuffer.put((byte) mSdiagFamily);
+        byteBuffer.put((byte) mSdiagProtocol);
+        byteBuffer.put((byte) mIdiagExt);
+        byteBuffer.put((byte) mPad);
+        byteBuffer.putInt(mState);
+        if (mId != null) mId.pack(byteBuffer);
+    }
+
+    @Override
+    public String toString() {
+        final String familyStr = NetlinkConstants.stringForAddressFamily(mSdiagFamily);
+        final String protocolStr = NetlinkConstants.stringForAddressFamily(mSdiagProtocol);
+
+        return "StructInetDiagReqV2{ "
+                + "sdiag_family{" + familyStr + "}, "
+                + "sdiag_protocol{" + protocolStr + "}, "
+                + "idiag_ext{" + mIdiagExt + ")}, "
+                + "pad{" + mPad + "}, "
+                + "idiag_states{" + Integer.toHexString(mState) + "}, "
+                + ((mId != null) ? mId.toString() : "inet_diag_sockid=null")
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/StructInetDiagSockId.java b/common/device/com/android/net/module/util/netlink/StructInetDiagSockId.java
new file mode 100644
index 00000000..95d60e53
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/StructInetDiagSockId.java
@@ -0,0 +1,90 @@
+/*
+ * 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 com.android.net.module.util.netlink;
+
+import static java.nio.ByteOrder.BIG_ENDIAN;
+
+import java.net.Inet4Address;
+import java.net.InetSocketAddress;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+/**
+ * struct inet_diag_req_v2
+ *
+ * see &lt;linux_src&gt;/include/uapi/linux/inet_diag.h
+ *
+ * struct inet_diag_sockid {
+ *        __be16    idiag_sport;
+ *        __be16    idiag_dport;
+ *        __be32    idiag_src[4];
+ *        __be32    idiag_dst[4];
+ *        __u32     idiag_if;
+ *        __u32     idiag_cookie[2];
+ * #define INET_DIAG_NOCOOKIE (~0U)
+ * };
+ *
+ * @hide
+ */
+public class StructInetDiagSockId {
+    public static final int STRUCT_SIZE = 48;
+
+    private static final byte[] INET_DIAG_NOCOOKIE = new byte[]{
+            (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff,
+            (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff};
+    private static final byte[] IPV4_PADDING = new byte[] {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+
+    private final InetSocketAddress mLocSocketAddress;
+    private final InetSocketAddress mRemSocketAddress;
+
+    public StructInetDiagSockId(InetSocketAddress loc, InetSocketAddress rem) {
+        mLocSocketAddress = loc;
+        mRemSocketAddress = rem;
+    }
+
+    /**
+     * Write inet diag socket id message to ByteBuffer in big endian.
+     */
+    public void pack(ByteBuffer byteBuffer) {
+        byteBuffer.order(BIG_ENDIAN);
+        byteBuffer.putShort((short) mLocSocketAddress.getPort());
+        byteBuffer.putShort((short) mRemSocketAddress.getPort());
+        byteBuffer.put(mLocSocketAddress.getAddress().getAddress());
+        if (mLocSocketAddress.getAddress() instanceof Inet4Address) {
+            byteBuffer.put(IPV4_PADDING);
+        }
+        byteBuffer.put(mRemSocketAddress.getAddress().getAddress());
+        if (mRemSocketAddress.getAddress() instanceof Inet4Address) {
+            byteBuffer.put(IPV4_PADDING);
+        }
+        byteBuffer.order(ByteOrder.nativeOrder());
+        byteBuffer.putInt(0);
+        byteBuffer.put(INET_DIAG_NOCOOKIE);
+    }
+
+    @Override
+    public String toString() {
+        return "StructInetDiagSockId{ "
+                + "idiag_sport{" + mLocSocketAddress.getPort() + "}, "
+                + "idiag_dport{" + mRemSocketAddress.getPort() + "}, "
+                + "idiag_src{" + mLocSocketAddress.getAddress().getHostAddress() + "}, "
+                + "idiag_dst{" + mRemSocketAddress.getAddress().getHostAddress() + "}, "
+                + "idiag_if{" + 0 + "} "
+                + "idiag_cookie{INET_DIAG_NOCOOKIE}"
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/StructNdMsg.java b/common/device/com/android/net/module/util/netlink/StructNdMsg.java
new file mode 100644
index 00000000..53ce8991
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/StructNdMsg.java
@@ -0,0 +1,198 @@
+/*
+ * 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.net.module.util.netlink;
+
+import android.system.OsConstants;
+
+import java.nio.ByteBuffer;
+
+/**
+ * struct ndmsg
+ *
+ * see: &lt;linux_src&gt;/include/uapi/linux/neighbour.h
+ *
+ * @hide
+ */
+public class StructNdMsg {
+    // Already aligned.
+    public static final int STRUCT_SIZE = 12;
+
+    // Neighbor Cache Entry States
+    public static final short NUD_NONE        = 0x00;
+    public static final short NUD_INCOMPLETE  = 0x01;
+    public static final short NUD_REACHABLE   = 0x02;
+    public static final short NUD_STALE       = 0x04;
+    public static final short NUD_DELAY       = 0x08;
+    public static final short NUD_PROBE       = 0x10;
+    public static final short NUD_FAILED      = 0x20;
+    public static final short NUD_NOARP       = 0x40;
+    public static final short NUD_PERMANENT   = 0x80;
+
+    /**
+     * Convert neighbor cache entry state integer to string.
+     */
+    public static String stringForNudState(short nudState) {
+        switch (nudState) {
+            case NUD_NONE: return "NUD_NONE";
+            case NUD_INCOMPLETE: return "NUD_INCOMPLETE";
+            case NUD_REACHABLE: return "NUD_REACHABLE";
+            case NUD_STALE: return "NUD_STALE";
+            case NUD_DELAY: return "NUD_DELAY";
+            case NUD_PROBE: return "NUD_PROBE";
+            case NUD_FAILED: return "NUD_FAILED";
+            case NUD_NOARP: return "NUD_NOARP";
+            case NUD_PERMANENT: return "NUD_PERMANENT";
+            default:
+                return "unknown NUD state: " + String.valueOf(nudState);
+        }
+    }
+
+    /**
+     * Check whether a neighbor is connected or not.
+     */
+    public static boolean isNudStateConnected(short nudState) {
+        return ((nudState & (NUD_PERMANENT | NUD_NOARP | NUD_REACHABLE)) != 0);
+    }
+
+    /**
+     * Check whether a neighbor is in the valid NUD state or not.
+     */
+    public static boolean isNudStateValid(short nudState) {
+        return (isNudStateConnected(nudState)
+                || ((nudState & (NUD_PROBE | NUD_STALE | NUD_DELAY)) != 0));
+    }
+
+    // Neighbor Cache Entry Flags
+    public static byte NTF_USE       = (byte) 0x01;
+    public static byte NTF_SELF      = (byte) 0x02;
+    public static byte NTF_MASTER    = (byte) 0x04;
+    public static byte NTF_PROXY     = (byte) 0x08;
+    public static byte NTF_ROUTER    = (byte) 0x80;
+
+    private static String stringForNudFlags(byte flags) {
+        final StringBuilder sb = new StringBuilder();
+        if ((flags & NTF_USE) != 0) {
+            sb.append("NTF_USE");
+        }
+        if ((flags & NTF_SELF) != 0) {
+            if (sb.length() > 0) {
+                sb.append("|");
+            }
+            sb.append("NTF_SELF");
+        }
+        if ((flags & NTF_MASTER) != 0) {
+            if (sb.length() > 0) {
+                sb.append("|");
+            }
+            sb.append("NTF_MASTER");
+        }
+        if ((flags & NTF_PROXY) != 0) {
+            if (sb.length() > 0) {
+                sb.append("|");
+            }
+            sb.append("NTF_PROXY");
+        }
+        if ((flags & NTF_ROUTER) != 0) {
+            if (sb.length() > 0) {
+                sb.append("|");
+            }
+            sb.append("NTF_ROUTER");
+        }
+        return sb.toString();
+    }
+
+    private static boolean hasAvailableSpace(ByteBuffer byteBuffer) {
+        return byteBuffer != null && byteBuffer.remaining() >= STRUCT_SIZE;
+    }
+
+    /**
+     * Parse a neighbor discovery netlink message header from a {@link ByteBuffer}.
+     *
+     * @param byteBuffer The buffer from which to parse the nd netlink message header.
+     * @return the parsed nd netlink message header, or {@code null} if the nd netlink message
+     *         header could not be parsed successfully (for example, if it was truncated).
+     */
+    public static StructNdMsg parse(ByteBuffer byteBuffer) {
+        if (!hasAvailableSpace(byteBuffer)) return null;
+
+        // The ByteOrder must have already been set by the caller.  In most
+        // cases ByteOrder.nativeOrder() is correct, with the possible
+        // exception of usage within unittests.
+        final StructNdMsg struct = new StructNdMsg();
+        struct.ndm_family = byteBuffer.get();
+        final byte pad1 = byteBuffer.get();
+        final short pad2 = byteBuffer.getShort();
+        struct.ndm_ifindex = byteBuffer.getInt();
+        struct.ndm_state = byteBuffer.getShort();
+        struct.ndm_flags = byteBuffer.get();
+        struct.ndm_type = byteBuffer.get();
+        return struct;
+    }
+
+    public byte ndm_family;
+    public int ndm_ifindex;
+    public short ndm_state;
+    public byte ndm_flags;
+    public byte ndm_type;
+
+    public StructNdMsg() {
+        ndm_family = (byte) OsConstants.AF_UNSPEC;
+    }
+
+    /**
+     * Write the neighbor discovery message header to {@link ByteBuffer}.
+     */
+    public void pack(ByteBuffer byteBuffer) {
+        // The ByteOrder must have already been set by the caller.  In most
+        // cases ByteOrder.nativeOrder() is correct, with the exception
+        // of usage within unittests.
+        byteBuffer.put(ndm_family);
+        byteBuffer.put((byte) 0);         // pad1
+        byteBuffer.putShort((short) 0);   // pad2
+        byteBuffer.putInt(ndm_ifindex);
+        byteBuffer.putShort(ndm_state);
+        byteBuffer.put(ndm_flags);
+        byteBuffer.put(ndm_type);
+    }
+
+    /**
+     * Check whether a neighbor is connected or not.
+     */
+    public boolean nudConnected() {
+        return isNudStateConnected(ndm_state);
+    }
+
+    /**
+     * Check whether a neighbor is in the valid NUD state or not.
+     */
+    public boolean nudValid() {
+        return isNudStateValid(ndm_state);
+    }
+
+    @Override
+    public String toString() {
+        final String stateStr = "" + ndm_state + " (" + stringForNudState(ndm_state) + ")";
+        final String flagsStr = "" + ndm_flags + " (" + stringForNudFlags(ndm_flags) + ")";
+        return "StructNdMsg{ "
+                + "family{" + NetlinkConstants.stringForAddressFamily((int) ndm_family) + "}, "
+                + "ifindex{" + ndm_ifindex + "}, "
+                + "state{" + stateStr + "}, "
+                + "flags{" + flagsStr + "}, "
+                + "type{" + ndm_type + "} "
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/StructNdOptPref64.java b/common/device/com/android/net/module/util/netlink/StructNdOptPref64.java
new file mode 100644
index 00000000..bde69831
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/StructNdOptPref64.java
@@ -0,0 +1,169 @@
+/*
+ * Copyright (C) 2020 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.net.module.util.netlink;
+
+import android.net.IpPrefix;
+import android.util.Log;
+
+import androidx.annotation.NonNull;
+
+import java.net.Inet6Address;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.nio.ByteBuffer;
+import java.util.Objects;
+
+/**
+ * The PREF64 router advertisement option. RFC 8781.
+ *
+ * 0                   1                   2                   3
+ * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |     Type      |    Length     |     Scaled Lifetime     | PLC |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |                                                               |
+ * +                                                               +
+ * |              Highest 96 bits of the Prefix                    |
+ * +                                                               +
+ * |                                                               |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ */
+public class StructNdOptPref64 extends NdOption {
+    public static final int STRUCT_SIZE = 16;
+    public static final int TYPE = 38;
+    public static final byte LENGTH = 2;
+
+    private static final String TAG = StructNdOptPref64.class.getSimpleName();
+
+    /**
+     * How many seconds the prefix is expected to remain valid.
+     * Valid values are from 0 to 65528 in multiples of 8.
+     */
+    public final int lifetime;
+    /** The NAT64 prefix. */
+    @NonNull public final IpPrefix prefix;
+
+    static int plcToPrefixLength(int plc) {
+        switch (plc) {
+            case 0: return 96;
+            case 1: return 64;
+            case 2: return 56;
+            case 3: return 48;
+            case 4: return 40;
+            case 5: return 32;
+            default:
+                throw new IllegalArgumentException("Invalid prefix length code " + plc);
+        }
+    }
+
+    static int prefixLengthToPlc(int prefixLength) {
+        switch (prefixLength) {
+            case 96: return 0;
+            case 64: return 1;
+            case 56: return 2;
+            case 48: return 3;
+            case 40: return 4;
+            case 32: return 5;
+            default:
+                throw new IllegalArgumentException("Invalid prefix length " + prefixLength);
+        }
+    }
+
+    /**
+     * Returns the 2-byte "scaled lifetime and prefix length code" field: 13-bit lifetime, 3-bit PLC
+     */
+    static short getScaledLifetimePlc(int lifetime, int prefixLengthCode) {
+        return (short) ((lifetime & 0xfff8) | (prefixLengthCode & 0x7));
+    }
+
+    public StructNdOptPref64(@NonNull IpPrefix prefix, int lifetime) {
+        super((byte) TYPE, LENGTH);
+
+        Objects.requireNonNull(prefix, "prefix must not be null");
+        if (!(prefix.getAddress() instanceof Inet6Address)) {
+            throw new IllegalArgumentException("Must be an IPv6 prefix: " + prefix);
+        }
+        prefixLengthToPlc(prefix.getPrefixLength());  // Throw if the prefix length is invalid.
+        this.prefix = prefix;
+
+        if (lifetime < 0 || lifetime > 0xfff8) {
+            throw new IllegalArgumentException("Invalid lifetime " + lifetime);
+        }
+        this.lifetime = lifetime & 0xfff8;
+    }
+
+    private StructNdOptPref64(@NonNull ByteBuffer buf) {
+        super(buf.get(), Byte.toUnsignedInt(buf.get()));
+        if (type != TYPE) throw new IllegalArgumentException("Invalid type " + type);
+        if (length != LENGTH) throw new IllegalArgumentException("Invalid length " + length);
+
+        int scaledLifetimePlc = Short.toUnsignedInt(buf.getShort());
+        lifetime = scaledLifetimePlc & 0xfff8;
+
+        byte[] addressBytes = new byte[16];
+        buf.get(addressBytes, 0, 12);
+        InetAddress addr;
+        try {
+            addr = InetAddress.getByAddress(addressBytes);
+        } catch (UnknownHostException e) {
+            throw new AssertionError("16-byte array not valid InetAddress?");
+        }
+        prefix = new IpPrefix(addr, plcToPrefixLength(scaledLifetimePlc & 7));
+    }
+
+    /**
+     * Parses an option from a {@link ByteBuffer}.
+     *
+     * @param buf The buffer from which to parse the option. The buffer's byte order must be
+     *            {@link java.nio.ByteOrder#BIG_ENDIAN}.
+     * @return the parsed option, or {@code null} if the option could not be parsed successfully
+     *         (for example, if it was truncated, or if the prefix length code was wrong).
+     */
+    public static StructNdOptPref64 parse(@NonNull ByteBuffer buf) {
+        if (buf == null || buf.remaining() < STRUCT_SIZE) return null;
+        try {
+            return new StructNdOptPref64(buf);
+        } catch (IllegalArgumentException e) {
+            // Not great, but better than throwing an exception that might crash the caller.
+            // Convention in this package is that null indicates that the option was truncated, so
+            // callers must already handle it.
+            Log.d(TAG, "Invalid PREF64 option: " + e);
+            return null;
+        }
+    }
+
+    protected void writeToByteBuffer(ByteBuffer buf) {
+        super.writeToByteBuffer(buf);
+        buf.putShort(getScaledLifetimePlc(lifetime,  prefixLengthToPlc(prefix.getPrefixLength())));
+        buf.put(prefix.getRawAddress(), 0, 12);
+    }
+
+    /** Outputs the wire format of the option to a new big-endian ByteBuffer. */
+    public ByteBuffer toByteBuffer() {
+        ByteBuffer buf = ByteBuffer.allocate(STRUCT_SIZE);
+        writeToByteBuffer(buf);
+        buf.flip();
+        return buf;
+    }
+
+    @Override
+    @NonNull
+    public String toString() {
+        return String.format("NdOptPref64(%s, %d)", prefix, lifetime);
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/StructNdaCacheInfo.java b/common/device/com/android/net/module/util/netlink/StructNdaCacheInfo.java
new file mode 100644
index 00000000..79d5ff4a
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/StructNdaCacheInfo.java
@@ -0,0 +1,133 @@
+/*
+ * 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 com.android.net.module.util.netlink;
+
+import android.system.Os;
+import android.system.OsConstants;
+
+import java.nio.ByteBuffer;
+
+/**
+ * struct nda_cacheinfo
+ *
+ * see: &lt;linux_src&gt;/include/uapi/linux/neighbour.h
+ *
+ * @hide
+ */
+public class StructNdaCacheInfo {
+    // Already aligned.
+    public static final int STRUCT_SIZE = 16;
+
+    private static boolean hasAvailableSpace(ByteBuffer byteBuffer) {
+        return byteBuffer != null && byteBuffer.remaining() >= STRUCT_SIZE;
+    }
+
+    /**
+     * Parse a nd cacheinfo netlink attribute from a {@link ByteBuffer}.
+     *
+     * @param byteBuffer The buffer from which to parse the nd cacheinfo attribute.
+     * @return the parsed nd cacheinfo attribute, or {@code null} if the nd cacheinfo attribute
+     *         could not be parsed successfully (for example, if it was truncated).
+     */
+    public static StructNdaCacheInfo parse(ByteBuffer byteBuffer) {
+        if (!hasAvailableSpace(byteBuffer)) return null;
+
+        // The ByteOrder must have already been set by the caller.  In most
+        // cases ByteOrder.nativeOrder() is correct, with the possible
+        // exception of usage within unittests.
+        final StructNdaCacheInfo struct = new StructNdaCacheInfo();
+        struct.ndm_used = byteBuffer.getInt();
+        struct.ndm_confirmed = byteBuffer.getInt();
+        struct.ndm_updated = byteBuffer.getInt();
+        struct.ndm_refcnt = byteBuffer.getInt();
+        return struct;
+    }
+
+    // TODO: investigate whether this can change during device runtime and
+    // decide what (if anything) should be done about that.
+    private static final long CLOCK_TICKS_PER_SECOND = Os.sysconf(OsConstants._SC_CLK_TCK);
+
+    private static long ticksToMilliSeconds(int intClockTicks) {
+        final long longClockTicks = (long) intClockTicks & 0xffffffff;
+        return (longClockTicks * 1000) / CLOCK_TICKS_PER_SECOND;
+    }
+
+    /**
+     * Explanatory notes, for reference.
+     *
+     * Before being returned to user space, the neighbor entry times are
+     * converted to clock_t's like so:
+     *
+     *     ndm_used      = jiffies_to_clock_t(now - neigh->used);
+     *     ndm_confirmed = jiffies_to_clock_t(now - neigh->confirmed);
+     *     ndm_updated   = jiffies_to_clock_t(now - neigh->updated);
+     *
+     * meaning that these values are expressed as "clock ticks ago".  To
+     * convert these clock ticks to seconds divide by sysconf(_SC_CLK_TCK).
+     * When _SC_CLK_TCK is 100, for example, the ndm_* times are expressed
+     * in centiseconds.
+     *
+     * These values are unsigned, but fortunately being expressed as "some
+     * clock ticks ago", these values are typically very small (and
+     * 2^31 centiseconds = 248 days).
+     *
+     * By observation, it appears that:
+     *     ndm_used: the last time ARP/ND took place for this neighbor
+     *     ndm_confirmed: the last time ARP/ND succeeded for this neighbor OR
+     *                    higher layer confirmation (TCP or MSG_CONFIRM)
+     *                    was received
+     *     ndm_updated: the time when the current NUD state was entered
+     */
+    public int ndm_used;
+    public int ndm_confirmed;
+    public int ndm_updated;
+    public int ndm_refcnt;
+
+    public StructNdaCacheInfo() {}
+
+    /**
+     * The last time ARP/ND took place for this neighbor.
+     */
+    public long lastUsed() {
+        return ticksToMilliSeconds(ndm_used);
+    }
+
+    /**
+     * The last time ARP/ND succeeded for this neighbor or higher layer confirmation (TCP or
+     * MSG_CONFIRM) was received.
+     */
+    public long lastConfirmed() {
+        return ticksToMilliSeconds(ndm_confirmed);
+    }
+
+    /**
+     * The time when the current NUD state was entered.
+     */
+    public long lastUpdated() {
+        return ticksToMilliSeconds(ndm_updated);
+    }
+
+    @Override
+    public String toString() {
+        return "NdaCacheInfo{ "
+                + "ndm_used{" + lastUsed() + "}, "
+                + "ndm_confirmed{" + lastConfirmed() + "}, "
+                + "ndm_updated{" + lastUpdated() + "}, "
+                + "ndm_refcnt{" + ndm_refcnt + "} "
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/StructNfGenMsg.java b/common/device/com/android/net/module/util/netlink/StructNfGenMsg.java
new file mode 100644
index 00000000..2de5490b
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/StructNfGenMsg.java
@@ -0,0 +1,105 @@
+/*
+ * Copyright (C) 2017 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.net.module.util.netlink;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.util.Objects;
+
+/**
+ * struct nfgenmsg
+ *
+ * see &lt;linux_src&gt;/include/uapi/linux/netfilter/nfnetlink.h
+ *
+ * @hide
+ */
+public class StructNfGenMsg {
+    public static final int STRUCT_SIZE = 2 + Short.BYTES;
+
+    public static final int NFNETLINK_V0 = 0;
+
+    public final byte nfgen_family;
+    public final byte version;
+    public final short res_id;  // N.B.: this is big endian in the kernel
+
+    /**
+     * Parse a netfilter netlink header from a {@link ByteBuffer}.
+     *
+     * @param byteBuffer The buffer from which to parse the netfilter netlink header.
+     * @return the parsed netfilter netlink header, or {@code null} if the netfilter netlink header
+     *         could not be parsed successfully (for example, if it was truncated).
+     */
+    @Nullable
+    public static StructNfGenMsg parse(@NonNull ByteBuffer byteBuffer) {
+        Objects.requireNonNull(byteBuffer);
+
+        if (!hasAvailableSpace(byteBuffer)) return null;
+
+        final byte nfgen_family = byteBuffer.get();
+        final byte version = byteBuffer.get();
+
+        final ByteOrder originalOrder = byteBuffer.order();
+        byteBuffer.order(ByteOrder.BIG_ENDIAN);
+        final short res_id = byteBuffer.getShort();
+        byteBuffer.order(originalOrder);
+
+        return new StructNfGenMsg(nfgen_family, version, res_id);
+    }
+
+    public StructNfGenMsg(byte family, byte ver, short id) {
+        nfgen_family = family;
+        version = ver;
+        res_id = id;
+    }
+
+    public StructNfGenMsg(byte family) {
+        nfgen_family = family;
+        version = (byte) NFNETLINK_V0;
+        res_id = (short) 0;
+    }
+
+    /**
+     * Write a netfilter netlink header to a {@link ByteBuffer}.
+     */
+    public void pack(ByteBuffer byteBuffer) {
+        byteBuffer.put(nfgen_family);
+        byteBuffer.put(version);
+
+        final ByteOrder originalOrder = byteBuffer.order();
+        byteBuffer.order(ByteOrder.BIG_ENDIAN);
+        byteBuffer.putShort(res_id);
+        byteBuffer.order(originalOrder);
+    }
+
+    private static boolean hasAvailableSpace(@NonNull ByteBuffer byteBuffer) {
+        return byteBuffer.remaining() >= STRUCT_SIZE;
+    }
+
+    @Override
+    public String toString() {
+        final String familyStr = NetlinkConstants.stringForAddressFamily(nfgen_family);
+
+        return "NfGenMsg{ "
+                + "nfgen_family{" + familyStr + "}, "
+                + "version{" + Byte.toUnsignedInt(version) + "}, "
+                + "res_id{" + Short.toUnsignedInt(res_id) + "} "
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/StructNlAttr.java b/common/device/com/android/net/module/util/netlink/StructNlAttr.java
new file mode 100644
index 00000000..80f00579
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/StructNlAttr.java
@@ -0,0 +1,315 @@
+/*
+ * 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.net.module.util.netlink;
+
+import androidx.annotation.Nullable;
+
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+/**
+ * struct nlattr
+ *
+ * see: &lt;linux_src&gt;/include/uapi/linux/netlink.h
+ *
+ * @hide
+ */
+public class StructNlAttr {
+    // Already aligned.
+    public static final int NLA_HEADERLEN  = 4;
+    public static final int NLA_F_NESTED   = (1 << 15);
+
+    /**
+     * Set carries nested attributes bit.
+     */
+    public static short makeNestedType(short type) {
+        return (short) (type | NLA_F_NESTED);
+    }
+
+    /**
+     * Peek and parse the netlink attribute from {@link ByteBuffer}.
+     *
+     * Return a (length, type) object only, without consuming any bytes in
+     * |byteBuffer| and without copying or interpreting any value bytes.
+     * This is used for scanning over a packed set of struct nlattr's,
+     * looking for instances of a particular type.
+     */
+    public static StructNlAttr peek(ByteBuffer byteBuffer) {
+        if (byteBuffer == null || byteBuffer.remaining() < NLA_HEADERLEN) {
+            return null;
+        }
+        final int baseOffset = byteBuffer.position();
+
+        final StructNlAttr struct = new StructNlAttr();
+        final ByteOrder originalOrder = byteBuffer.order();
+        byteBuffer.order(ByteOrder.nativeOrder());
+        try {
+            struct.nla_len = byteBuffer.getShort();
+            struct.nla_type = byteBuffer.getShort();
+        } finally {
+            byteBuffer.order(originalOrder);
+        }
+
+        byteBuffer.position(baseOffset);
+        if (struct.nla_len < NLA_HEADERLEN) {
+            // Malformed.
+            return null;
+        }
+        return struct;
+    }
+
+    /**
+     * Parse a netlink attribute from a {@link ByteBuffer}.
+     *
+     * @param byteBuffer The buffer from which to parse the netlink attriute.
+     * @return the parsed netlink attribute, or {@code null} if the netlink attribute
+     *         could not be parsed successfully (for example, if it was truncated).
+     */
+    public static StructNlAttr parse(ByteBuffer byteBuffer) {
+        final StructNlAttr struct = peek(byteBuffer);
+        if (struct == null || byteBuffer.remaining() < struct.getAlignedLength()) {
+            return null;
+        }
+
+        final int baseOffset = byteBuffer.position();
+        byteBuffer.position(baseOffset + NLA_HEADERLEN);
+
+        int valueLen = ((int) struct.nla_len) & 0xffff;
+        valueLen -= NLA_HEADERLEN;
+        if (valueLen > 0) {
+            struct.nla_value = new byte[valueLen];
+            byteBuffer.get(struct.nla_value, 0, valueLen);
+            byteBuffer.position(baseOffset + struct.getAlignedLength());
+        }
+        return struct;
+    }
+
+    /**
+     * Find next netlink attribute with a given type from {@link ByteBuffer}.
+     *
+     * @param attrType The given netlink attribute type is requested for.
+     * @param byteBuffer The buffer from which to find the netlink attribute.
+     * @return the found netlink attribute, or {@code null} if the netlink attribute could not be
+     *         found or parsed successfully (for example, if it was truncated).
+     */
+    @Nullable
+    public static StructNlAttr findNextAttrOfType(short attrType,
+            @Nullable ByteBuffer byteBuffer) {
+        while (byteBuffer != null && byteBuffer.remaining() > 0) {
+            final StructNlAttr nlAttr = StructNlAttr.peek(byteBuffer);
+            if (nlAttr == null) {
+                break;
+            }
+            if (nlAttr.nla_type == attrType) {
+                return StructNlAttr.parse(byteBuffer);
+            }
+            if (byteBuffer.remaining() < nlAttr.getAlignedLength()) {
+                break;
+            }
+            byteBuffer.position(byteBuffer.position() + nlAttr.getAlignedLength());
+        }
+        return null;
+    }
+
+    public short nla_len = (short) NLA_HEADERLEN;
+    public short nla_type;
+    public byte[] nla_value;
+
+    public StructNlAttr() {}
+
+    public StructNlAttr(short type, byte value) {
+        nla_type = type;
+        setValue(new byte[1]);
+        nla_value[0] = value;
+    }
+
+    public StructNlAttr(short type, short value) {
+        this(type, value, ByteOrder.nativeOrder());
+    }
+
+    public StructNlAttr(short type, short value, ByteOrder order) {
+        nla_type = type;
+        setValue(new byte[Short.BYTES]);
+        final ByteBuffer buf = getValueAsByteBuffer();
+        final ByteOrder originalOrder = buf.order();
+        try {
+            buf.order(order);
+            buf.putShort(value);
+        } finally {
+            buf.order(originalOrder);
+        }
+    }
+
+    public StructNlAttr(short type, int value) {
+        this(type, value, ByteOrder.nativeOrder());
+    }
+
+    public StructNlAttr(short type, int value, ByteOrder order) {
+        nla_type = type;
+        setValue(new byte[Integer.BYTES]);
+        final ByteBuffer buf = getValueAsByteBuffer();
+        final ByteOrder originalOrder = buf.order();
+        try {
+            buf.order(order);
+            buf.putInt(value);
+        } finally {
+            buf.order(originalOrder);
+        }
+    }
+
+    public StructNlAttr(short type, InetAddress ip) {
+        nla_type = type;
+        setValue(ip.getAddress());
+    }
+
+    public StructNlAttr(short type, StructNlAttr... nested) {
+        this();
+        nla_type = makeNestedType(type);
+
+        int payloadLength = 0;
+        for (StructNlAttr nla : nested) payloadLength += nla.getAlignedLength();
+        setValue(new byte[payloadLength]);
+
+        final ByteBuffer buf = getValueAsByteBuffer();
+        for (StructNlAttr nla : nested) {
+            nla.pack(buf);
+        }
+    }
+
+    /**
+     * Get aligned attribute length.
+     */
+    public int getAlignedLength() {
+        return NetlinkConstants.alignedLengthOf(nla_len);
+    }
+
+    /**
+     * Get attribute value as BE16.
+     */
+    public short getValueAsBe16(short defaultValue) {
+        final ByteBuffer byteBuffer = getValueAsByteBuffer();
+        if (byteBuffer == null || byteBuffer.remaining() != Short.BYTES) {
+            return defaultValue;
+        }
+        final ByteOrder originalOrder = byteBuffer.order();
+        try {
+            byteBuffer.order(ByteOrder.BIG_ENDIAN);
+            return byteBuffer.getShort();
+        } finally {
+            byteBuffer.order(originalOrder);
+        }
+    }
+
+    /**
+     * Get attribute value as BE32.
+     */
+    public int getValueAsBe32(int defaultValue) {
+        final ByteBuffer byteBuffer = getValueAsByteBuffer();
+        if (byteBuffer == null || byteBuffer.remaining() != Integer.BYTES) {
+            return defaultValue;
+        }
+        final ByteOrder originalOrder = byteBuffer.order();
+        try {
+            byteBuffer.order(ByteOrder.BIG_ENDIAN);
+            return byteBuffer.getInt();
+        } finally {
+            byteBuffer.order(originalOrder);
+        }
+    }
+
+    /**
+     * Get attribute value as ByteBuffer.
+     */
+    public ByteBuffer getValueAsByteBuffer() {
+        if (nla_value == null) return null;
+        final ByteBuffer byteBuffer = ByteBuffer.wrap(nla_value);
+        // By convention, all buffers in this library are in native byte order because netlink is in
+        // native byte order. It's the order that is used by NetlinkSocket.recvMessage and the only
+        // order accepted by NetlinkMessage.parse.
+        byteBuffer.order(ByteOrder.nativeOrder());
+        return byteBuffer;
+    }
+
+    /**
+     * Get attribute value as byte.
+     */
+    public byte getValueAsByte(byte defaultValue) {
+        final ByteBuffer byteBuffer = getValueAsByteBuffer();
+        if (byteBuffer == null || byteBuffer.remaining() != Byte.BYTES) {
+            return defaultValue;
+        }
+        return getValueAsByteBuffer().get();
+    }
+
+    /**
+     * Get attribute value as Integer.
+     */
+    public int getValueAsInt(int defaultValue) {
+        final ByteBuffer byteBuffer = getValueAsByteBuffer();
+        if (byteBuffer == null || byteBuffer.remaining() != Integer.BYTES) {
+            return defaultValue;
+        }
+        return getValueAsByteBuffer().getInt();
+    }
+
+    /**
+     * Get attribute value as InetAddress.
+     */
+    public InetAddress getValueAsInetAddress() {
+        if (nla_value == null) return null;
+
+        try {
+            return InetAddress.getByAddress(nla_value);
+        } catch (UnknownHostException ignored) {
+            return null;
+        }
+    }
+
+    /**
+     * Write the netlink attribute to {@link ByteBuffer}.
+     */
+    public void pack(ByteBuffer byteBuffer) {
+        final ByteOrder originalOrder = byteBuffer.order();
+        final int originalPosition = byteBuffer.position();
+
+        byteBuffer.order(ByteOrder.nativeOrder());
+        try {
+            byteBuffer.putShort(nla_len);
+            byteBuffer.putShort(nla_type);
+            if (nla_value != null) byteBuffer.put(nla_value);
+        } finally {
+            byteBuffer.order(originalOrder);
+        }
+        byteBuffer.position(originalPosition + getAlignedLength());
+    }
+
+    private void setValue(byte[] value) {
+        nla_value = value;
+        nla_len = (short) (NLA_HEADERLEN + ((nla_value != null) ? nla_value.length : 0));
+    }
+
+    @Override
+    public String toString() {
+        return "StructNlAttr{ "
+                + "nla_len{" + nla_len + "}, "
+                + "nla_type{" + nla_type + "}, "
+                + "nla_value{" + NetlinkConstants.hexify(nla_value) + "}, "
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/StructNlMsgErr.java b/common/device/com/android/net/module/util/netlink/StructNlMsgErr.java
new file mode 100644
index 00000000..b6620f3b
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/StructNlMsgErr.java
@@ -0,0 +1,77 @@
+/*
+ * 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.net.module.util.netlink;
+
+import java.nio.ByteBuffer;
+
+/**
+ * struct nlmsgerr
+ *
+ * see &lt;linux_src&gt;/include/uapi/linux/netlink.h
+ *
+ * @hide
+ */
+public class StructNlMsgErr {
+    public static final int STRUCT_SIZE = Integer.BYTES + StructNlMsgHdr.STRUCT_SIZE;
+
+    private static boolean hasAvailableSpace(ByteBuffer byteBuffer) {
+        return byteBuffer != null && byteBuffer.remaining() >= STRUCT_SIZE;
+    }
+
+    /**
+     * Parse a netlink error message payload from a {@link ByteBuffer}.
+     *
+     * @param byteBuffer The buffer from which to parse the netlink error message payload.
+     * @return the parsed netlink error message payload, or {@code null} if the netlink error
+     *         message payload could not be parsed successfully (for example, if it was truncated).
+     */
+    public static StructNlMsgErr parse(ByteBuffer byteBuffer) {
+        if (!hasAvailableSpace(byteBuffer)) return null;
+
+        // The ByteOrder must have already been set by the caller.  In most
+        // cases ByteOrder.nativeOrder() is correct, with the exception
+        // of usage within unittests.
+        final StructNlMsgErr struct = new StructNlMsgErr();
+        struct.error = byteBuffer.getInt();
+        struct.msg = StructNlMsgHdr.parse(byteBuffer);
+        return struct;
+    }
+
+    public int error;
+    public StructNlMsgHdr msg;
+
+    /**
+     * Write the netlink error message payload to {@link ByteBuffer}.
+     */
+    public void pack(ByteBuffer byteBuffer) {
+        // The ByteOrder must have already been set by the caller.  In most
+        // cases ByteOrder.nativeOrder() is correct, with the possible
+        // exception of usage within unittests.
+        byteBuffer.putInt(error);
+        if (msg != null) {
+            msg.pack(byteBuffer);
+        }
+    }
+
+    @Override
+    public String toString() {
+        return "StructNlMsgErr{ "
+                + "error{" + error + "}, "
+                + "msg{" + (msg == null ? "" : msg.toString()) + "} "
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/netlink/StructNlMsgHdr.java b/common/device/com/android/net/module/util/netlink/StructNlMsgHdr.java
new file mode 100644
index 00000000..ddf1562f
--- /dev/null
+++ b/common/device/com/android/net/module/util/netlink/StructNlMsgHdr.java
@@ -0,0 +1,173 @@
+/*
+ * 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.net.module.util.netlink;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import java.nio.ByteBuffer;
+
+/**
+ * struct nlmsghdr
+ *
+ * see &lt;linux_src&gt;/include/uapi/linux/netlink.h
+ *
+ * @hide
+ */
+public class StructNlMsgHdr {
+    // Already aligned.
+    public static final int STRUCT_SIZE = 16;
+
+    public static final short NLM_F_REQUEST = 0x0001;
+    public static final short NLM_F_MULTI   = 0x0002;
+    public static final short NLM_F_ACK     = 0x0004;
+    public static final short NLM_F_ECHO    = 0x0008;
+    // Flags for a GET request.
+    public static final short NLM_F_ROOT    = 0x0100;
+    public static final short NLM_F_MATCH   = 0x0200;
+    public static final short NLM_F_DUMP    = NLM_F_ROOT | NLM_F_MATCH;
+    // Flags for a NEW request.
+    public static final short NLM_F_REPLACE   = 0x100;
+    public static final short NLM_F_EXCL      = 0x200;
+    public static final short NLM_F_CREATE    = 0x400;
+    public static final short NLM_F_APPEND    = 0x800;
+
+    // TODO: Probably need to distinguish the flags which have the same value. For example,
+    // NLM_F_MATCH (0x200) and NLM_F_EXCL (0x200).
+    private static String stringForNlMsgFlags(short flags) {
+        final StringBuilder sb = new StringBuilder();
+        if ((flags & NLM_F_REQUEST) != 0) {
+            sb.append("NLM_F_REQUEST");
+        }
+        if ((flags & NLM_F_MULTI) != 0) {
+            if (sb.length() > 0) {
+                sb.append("|");
+            }
+            sb.append("NLM_F_MULTI");
+        }
+        if ((flags & NLM_F_ACK) != 0) {
+            if (sb.length() > 0) {
+                sb.append("|");
+            }
+            sb.append("NLM_F_ACK");
+        }
+        if ((flags & NLM_F_ECHO) != 0) {
+            if (sb.length() > 0) {
+                sb.append("|");
+            }
+            sb.append("NLM_F_ECHO");
+        }
+        if ((flags & NLM_F_ROOT) != 0) {
+            if (sb.length() > 0) {
+                sb.append("|");
+            }
+            sb.append("NLM_F_ROOT");
+        }
+        if ((flags & NLM_F_MATCH) != 0) {
+            if (sb.length() > 0) {
+                sb.append("|");
+            }
+            sb.append("NLM_F_MATCH");
+        }
+        return sb.toString();
+    }
+
+    private static boolean hasAvailableSpace(ByteBuffer byteBuffer) {
+        return byteBuffer != null && byteBuffer.remaining() >= STRUCT_SIZE;
+    }
+
+    /**
+     * Parse netlink message header from buffer.
+     */
+    public static StructNlMsgHdr parse(ByteBuffer byteBuffer) {
+        if (!hasAvailableSpace(byteBuffer)) return null;
+
+        // The ByteOrder must have already been set by the caller.  In most
+        // cases ByteOrder.nativeOrder() is correct, with the exception
+        // of usage within unittests.
+        final StructNlMsgHdr struct = new StructNlMsgHdr();
+        struct.nlmsg_len = byteBuffer.getInt();
+        struct.nlmsg_type = byteBuffer.getShort();
+        struct.nlmsg_flags = byteBuffer.getShort();
+        struct.nlmsg_seq = byteBuffer.getInt();
+        struct.nlmsg_pid = byteBuffer.getInt();
+
+        if (struct.nlmsg_len < STRUCT_SIZE) {
+            // Malformed.
+            return null;
+        }
+        return struct;
+    }
+
+    public int nlmsg_len;
+    public short nlmsg_type;
+    public short nlmsg_flags;
+    public int nlmsg_seq;
+    public int nlmsg_pid;
+
+    public StructNlMsgHdr() {
+        nlmsg_len = 0;
+        nlmsg_type = 0;
+        nlmsg_flags = 0;
+        nlmsg_seq = 0;
+        nlmsg_pid = 0;
+    }
+
+    /**
+     * Write netlink message header to ByteBuffer.
+     */
+    public void pack(ByteBuffer byteBuffer) {
+        // The ByteOrder must have already been set by the caller.  In most
+        // cases ByteOrder.nativeOrder() is correct, with the possible
+        // exception of usage within unittests.
+        byteBuffer.putInt(nlmsg_len);
+        byteBuffer.putShort(nlmsg_type);
+        byteBuffer.putShort(nlmsg_flags);
+        byteBuffer.putInt(nlmsg_seq);
+        byteBuffer.putInt(nlmsg_pid);
+    }
+
+    @Override
+    public String toString() {
+        return toString(null /* unknown netlink family */);
+    }
+
+    /**
+     * Transform a netlink header into a string. The netlink family is required for transforming
+     * a netlink type integer into a string.
+     * @param nlFamily netlink family. Using Integer will not incur autoboxing penalties because
+     *                 family values are small, and all Integer objects between -128 and 127 are
+     *                 statically cached. See Integer.IntegerCache.
+     * @return A list of header elements.
+     */
+    @NonNull
+    public String toString(@Nullable Integer nlFamily) {
+        final String typeStr = "" + nlmsg_type
+                + "(" + (nlFamily == null
+                ? "" : NetlinkConstants.stringForNlMsgType(nlmsg_type, nlFamily))
+                + ")";
+        final String flagsStr = "" + nlmsg_flags
+                + "(" + stringForNlMsgFlags(nlmsg_flags) + ")";
+        return "StructNlMsgHdr{ "
+                + "nlmsg_len{" + nlmsg_len + "}, "
+                + "nlmsg_type{" + typeStr + "}, "
+                + "nlmsg_flags{" + flagsStr + ")}, "
+                + "nlmsg_seq{" + nlmsg_seq + "}, "
+                + "nlmsg_pid{" + nlmsg_pid + "} "
+                + "}";
+    }
+}
diff --git a/common/device/com/android/net/module/util/structs/PrefixInformationOption.java b/common/device/com/android/net/module/util/structs/PrefixInformationOption.java
index 1bdee295..49d7654d 100644
--- a/common/device/com/android/net/module/util/structs/PrefixInformationOption.java
+++ b/common/device/com/android/net/module/util/structs/PrefixInformationOption.java
@@ -18,9 +18,10 @@ package com.android.net.module.util.structs;
 
 import static com.android.net.module.util.NetworkStackConstants.ICMPV6_ND_OPTION_PIO;
 
-import android.annotation.NonNull;
 import android.net.IpPrefix;
 
+import androidx.annotation.NonNull;
+
 import com.android.net.module.util.Struct;
 import com.android.net.module.util.Struct.Field;
 import com.android.net.module.util.Struct.Type;