Add basic netlink library code.

Add netlink socket helpers and parsing code for basic netlink messages.
Additionally, support from some neighbor discovery -specific messages
is included.

Bug: 18581716
Change-Id: Ib2aa924222b63cdbebf09a8bf8ff35ee24269fc5

10 files changed, 1252 insertions, 0 deletions

diff --git a/core/java/android/net/netlink/NetlinkConstants.java b/core/java/android/net/netlink/NetlinkConstants.java
new file mode 100644
index 0000000..e331701
--- /dev/null
+++ b/core/java/android/net/netlink/NetlinkConstants.java
@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.netlink;
+
+import android.system.OsConstants;
+import com.android.internal.util.HexDump;
+
+import java.nio.ByteBuffer;
+
+
+/**
+ * Various constants and static helper methods for netlink communications.
+ *
+ * Values taken from:
+ *
+ *     <linux_src>/include/uapi/linux/netlink.h
+ *     <linux_src>/include/uapi/linux/rtnetlink.h
+ *
+ * @hide
+ */
+public class NetlinkConstants {
+    private NetlinkConstants() {}
+
+    public static final int NLA_ALIGNTO = 4;
+
+    public static final int alignedLengthOf(short length) {
+        final int intLength = (int) length & 0xffff;
+        return alignedLengthOf(intLength);
+    }
+
+    public static final int alignedLengthOf(int length) {
+        if (length <= 0) { return 0; }
+        return (((length + NLA_ALIGNTO - 1) / NLA_ALIGNTO) * NLA_ALIGNTO);
+    }
+
+    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);
+    }
+
+    public static String hexify(byte[] bytes) {
+        if (bytes == null) { return "(null)"; }
+        return HexDump.toHexString(bytes);
+    }
+
+    public static String hexify(ByteBuffer buffer) {
+        if (buffer == null) { return "(null)"; }
+        return HexDump.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;
+
+    public static String stringForNlMsgType(short nlm_type) {
+        switch (nlm_type) {
+            case NLMSG_NOOP: return "NLMSG_NOOP";
+            case NLMSG_ERROR: return "NLMSG_ERROR";
+            case NLMSG_DONE: return "NLMSG_DONE";
+            case NLMSG_OVERRUN: return "NLMSG_OVERRUN";
+            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(nlm_type);
+        }
+    }
+}
diff --git a/core/java/android/net/netlink/NetlinkErrorMessage.java b/core/java/android/net/netlink/NetlinkErrorMessage.java
new file mode 100644
index 0000000..dbc10d6
--- /dev/null
+++ b/core/java/android/net/netlink/NetlinkErrorMessage.java
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.netlink;
+
+import android.net.netlink.StructNlMsgHdr;
+import android.net.netlink.NetlinkMessage;
+import android.util.Log;
+
+import java.nio.ByteBuffer;
+
+
+/**
+ * A NetlinkMessage subclass for netlink error messages.
+ *
+ * @hide
+ */
+public class NetlinkErrorMessage extends NetlinkMessage {
+
+    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/core/java/android/net/netlink/NetlinkMessage.java b/core/java/android/net/netlink/NetlinkMessage.java
new file mode 100644
index 0000000..bc04a16
--- /dev/null
+++ b/core/java/android/net/netlink/NetlinkMessage.java
@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.netlink;
+
+import android.net.netlink.NetlinkConstants;
+import android.net.netlink.NetlinkErrorMessage;
+import android.net.netlink.RtNetlinkNeighborMessage;
+import android.net.netlink.StructNlAttr;
+import android.net.netlink.StructNlMsgHdr;
+import android.util.Log;
+
+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 final static String TAG = "NetlinkMessage";
+
+    public static NetlinkMessage parse(ByteBuffer byteBuffer) {
+        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;
+        }
+
+        switch (nlmsghdr.nlmsg_type) {
+            //case NetlinkConstants.NLMSG_NOOP:
+            case NetlinkConstants.NLMSG_ERROR:
+                return (NetlinkMessage) NetlinkErrorMessage.parse(byteBuffer);
+            case NetlinkConstants.NLMSG_DONE:
+                byteBuffer.position(byteBuffer.position() + payloadLength);
+                return new NetlinkMessage(nlmsghdr);
+            //case NetlinkConstants.NLMSG_OVERRUN:
+            case NetlinkConstants.RTM_NEWNEIGH:
+            case NetlinkConstants.RTM_DELNEIGH:
+            case NetlinkConstants.RTM_GETNEIGH:
+                return (NetlinkMessage) RtNetlinkNeighborMessage.parse(nlmsghdr, byteBuffer);
+            default:
+                if (nlmsghdr.nlmsg_type <= NetlinkConstants.NLMSG_MAX_RESERVED) {
+                    // Netlink control message.  Just parse the header for now,
+                    // pretending the whole message was consumed.
+                    byteBuffer.position(byteBuffer.position() + payloadLength);
+                    return new NetlinkMessage(nlmsghdr);
+                }
+                return null;
+        }
+    }
+
+    protected StructNlMsgHdr mHeader;
+
+    public NetlinkMessage(StructNlMsgHdr nlmsghdr) {
+        mHeader = nlmsghdr;
+    }
+
+    public StructNlMsgHdr getHeader() {
+        return mHeader;
+    }
+
+    @Override
+    public String toString() {
+        return "NetlinkMessage{" + (mHeader == null ? "" : mHeader.toString()) + "}";
+    }
+}
diff --git a/core/java/android/net/netlink/NetlinkSocket.java b/core/java/android/net/netlink/NetlinkSocket.java
new file mode 100644
index 0000000..657d48c
--- /dev/null
+++ b/core/java/android/net/netlink/NetlinkSocket.java
@@ -0,0 +1,169 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.netlink;
+
+import android.system.ErrnoException;
+import android.system.NetlinkSocketAddress;
+import android.system.Os;
+import android.system.OsConstants;
+import android.system.StructTimeval;
+import android.util.Log;
+import libcore.io.IoUtils;
+import libcore.io.Libcore;
+
+import java.io.Closeable;
+import java.io.FileDescriptor;
+import java.io.InterruptedIOException;
+import java.net.SocketAddress;
+import java.net.SocketException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+
+/**
+ * NetlinkSocket
+ *
+ * A small wrapper class to assist with AF_NETLINK socket operations.
+ *
+ * @hide
+ */
+public class NetlinkSocket implements Closeable {
+    private static final String TAG = "NetlinkSocket";
+    private static final int SOCKET_RECV_BUFSIZE = 64 * 1024;
+    private static final int DEFAULT_RECV_BUFSIZE = 8 * 1024;
+
+    final private FileDescriptor mDescriptor;
+    private NetlinkSocketAddress mAddr;
+    private long mLastRecvTimeoutMs;
+    private long mLastSendTimeoutMs;
+
+    public NetlinkSocket(int nlProto) throws ErrnoException {
+        mDescriptor = Os.socket(
+                OsConstants.AF_NETLINK, OsConstants.SOCK_DGRAM, nlProto);
+
+        Libcore.os.setsockoptInt(
+                mDescriptor, OsConstants.SOL_SOCKET,
+                OsConstants.SO_RCVBUF, SOCKET_RECV_BUFSIZE);
+    }
+
+    public NetlinkSocketAddress getLocalAddress() throws ErrnoException {
+        return (NetlinkSocketAddress) Os.getsockname(mDescriptor);
+    }
+
+    public void bind(NetlinkSocketAddress localAddr) throws ErrnoException, SocketException {
+        Os.bind(mDescriptor, (SocketAddress)localAddr);
+    }
+
+    public void connectTo(NetlinkSocketAddress peerAddr)
+            throws ErrnoException, SocketException {
+        Os.connect(mDescriptor, (SocketAddress) peerAddr);
+    }
+
+    public void connectToKernel() throws ErrnoException, SocketException {
+        connectTo(new NetlinkSocketAddress(0, 0));
+    }
+
+    /**
+     * Wait indefinitely (or until underlying socket error) for a
+     * netlink message of at most DEFAULT_RECV_BUFSIZE size.
+     */
+    public ByteBuffer recvMessage()
+            throws ErrnoException, InterruptedIOException {
+        return recvMessage(DEFAULT_RECV_BUFSIZE, 0);
+    }
+
+    /**
+     * Wait up to |timeoutMs| (or until underlying socket error) for a
+     * netlink message of at most DEFAULT_RECV_BUFSIZE size.
+     */
+    public ByteBuffer recvMessage(long timeoutMs) throws ErrnoException, InterruptedIOException {
+        return recvMessage(DEFAULT_RECV_BUFSIZE, timeoutMs);
+    }
+
+    private 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 ByteBuffer recvMessage(int bufsize, long timeoutMs)
+            throws ErrnoException, IllegalArgumentException, InterruptedIOException {
+        checkTimeout(timeoutMs);
+
+        synchronized (mDescriptor) {
+            if (mLastRecvTimeoutMs != timeoutMs) {
+                Os.setsockoptTimeval(mDescriptor,
+                        OsConstants.SOL_SOCKET, OsConstants.SO_RCVTIMEO,
+                        StructTimeval.fromMillis(timeoutMs));
+                mLastRecvTimeoutMs = timeoutMs;
+            }
+        }
+
+        ByteBuffer byteBuffer = ByteBuffer.allocate(bufsize);
+        int length = Os.read(mDescriptor, 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.
+     *
+     * This blocks until completion or an error occurs.
+     */
+    public boolean sendMessage(byte[] bytes, int offset, int count)
+            throws ErrnoException, InterruptedIOException {
+        return sendMessage(bytes, offset, count, 0);
+    }
+
+    /**
+     * 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 boolean sendMessage(byte[] bytes, int offset, int count, long timeoutMs)
+            throws ErrnoException, IllegalArgumentException, InterruptedIOException {
+        checkTimeout(timeoutMs);
+
+        synchronized (mDescriptor) {
+            if (mLastSendTimeoutMs != timeoutMs) {
+                Os.setsockoptTimeval(mDescriptor,
+                        OsConstants.SOL_SOCKET, OsConstants.SO_SNDTIMEO,
+                        StructTimeval.fromMillis(timeoutMs));
+                mLastSendTimeoutMs = timeoutMs;
+            }
+        }
+
+        return (count == Os.write(mDescriptor, bytes, offset, count));
+    }
+
+    @Override
+    public void close() {
+        IoUtils.closeQuietly(mDescriptor);
+    }
+}
diff --git a/core/java/android/net/netlink/RtNetlinkNeighborMessage.java b/core/java/android/net/netlink/RtNetlinkNeighborMessage.java
new file mode 100644
index 0000000..d4b572c
--- /dev/null
+++ b/core/java/android/net/netlink/RtNetlinkNeighborMessage.java
@@ -0,0 +1,181 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.netlink;
+
+import android.net.netlink.StructNdaCacheInfo;
+import android.net.netlink.StructNdMsg;
+import android.net.netlink.StructNlAttr;
+import android.net.netlink.StructNlMsgHdr;
+import android.net.netlink.NetlinkMessage;
+import android.util.Log;
+
+import java.net.InetAddress;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+
+/**
+ * A NetlinkMessage subclass for netlink error 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;
+
+    private static StructNlAttr findNextAttrOfType(short attrType, 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 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 = findNextAttrOfType(NDA_DST, byteBuffer);
+        if (nlAttr != null) {
+            neighMsg.mDestination = nlAttr.getValueAsInetAddress();
+        }
+
+        byteBuffer.position(baseOffset);
+        nlAttr = findNextAttrOfType(NDA_LLADDR, byteBuffer);
+        if (nlAttr != null) {
+            neighMsg.mLinkLayerAddr = nlAttr.nla_value;
+        }
+
+        byteBuffer.position(baseOffset);
+        nlAttr = findNextAttrOfType(NDA_PROBES, byteBuffer);
+        if (nlAttr != null) {
+            neighMsg.mNumProbes = nlAttr.getValueAsInt(0);
+        }
+
+        byteBuffer.position(baseOffset);
+        nlAttr = 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 = StructNlMsgHdr.NLM_F_REQUEST|StructNlMsgHdr.NLM_F_DUMP;
+        nlmsghdr.nlmsg_seq = seqNo;
+        nlmsghdr.pack(byteBuffer);
+
+        final StructNdMsg ndmsg = new StructNdMsg();
+        ndmsg.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;
+    }
+
+    @Override
+    public String toString() {
+        final String ipLiteral = (mDestination == null) ? "" : mDestination.getHostAddress();
+        return "RtNetlinkNeighborMessage{ "
+                + "nlmsghdr{" + (mHeader == null ? "" : mHeader.toString()) + "}, "
+                + "ndmsg{" + (mNdmsg == null ? "" : mNdmsg.toString()) + "}, "
+                + "destination{" + ipLiteral + "} "
+                + "linklayeraddr{" + NetlinkConstants.hexify(mLinkLayerAddr) + "} "
+                + "probes{" + mNumProbes + "} "
+                + "cacheinfo{" + (mCacheInfo == null ? "" : mCacheInfo.toString()) + "} "
+                + "}";
+    }
+}
diff --git a/core/java/android/net/netlink/StructNdMsg.java b/core/java/android/net/netlink/StructNdMsg.java
new file mode 100644
index 0000000..e66d45d
--- /dev/null
+++ b/core/java/android/net/netlink/StructNdMsg.java
@@ -0,0 +1,162 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.netlink;
+
+import android.net.netlink.NetlinkConstants;
+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_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;
+
+    public static String stringForNudState(short nudState) {
+        switch (nudState) {
+            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);
+        }
+    }
+
+    public static boolean isNudStateConnected(short nudState) {
+        return ((nudState & (NUD_PERMANENT|NUD_NOARP|NUD_REACHABLE)) != 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;
+
+    public 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;
+    }
+
+    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;
+    }
+
+    public boolean pack(ByteBuffer byteBuffer) {
+        if (!hasAvailableSpace(byteBuffer)) { return false; }
+
+        // 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);
+        return true;
+    }
+
+    public boolean nudConnected() {
+        return isNudStateConnected(ndm_state);
+    }
+
+    public boolean nudValid() {
+        return (nudConnected() || ((ndm_state & (NUD_PROBE|NUD_STALE|NUD_DELAY)) != 0));
+    }
+
+    @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/core/java/android/net/netlink/StructNdaCacheInfo.java b/core/java/android/net/netlink/StructNdaCacheInfo.java
new file mode 100644
index 0000000..16cf563
--- /dev/null
+++ b/core/java/android/net/netlink/StructNdaCacheInfo.java
@@ -0,0 +1,117 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.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;
+    }
+
+    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() {}
+
+    public long lastUsed() {
+        return ticksToMilliSeconds(ndm_used);
+    }
+
+    public long lastConfirmed() {
+        return ticksToMilliSeconds(ndm_confirmed);
+    }
+
+    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/core/java/android/net/netlink/StructNlAttr.java b/core/java/android/net/netlink/StructNlAttr.java
new file mode 100644
index 0000000..9aef4c7
--- /dev/null
+++ b/core/java/android/net/netlink/StructNlAttr.java
@@ -0,0 +1,127 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.netlink;
+
+import android.net.netlink.NetlinkConstants;
+import libcore.io.SizeOf;
+
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.nio.ByteOrder;
+import java.nio.ByteBuffer;
+
+
+/**
+ * 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;
+
+    // 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();
+        struct.nla_len = byteBuffer.getShort();
+        struct.nla_type = byteBuffer.getShort();
+        struct.mByteOrder = byteBuffer.order();
+
+        byteBuffer.position(baseOffset);
+        if (struct.nla_len < NLA_HEADERLEN) {
+            // Malformed.
+            return null;
+        }
+        return struct;
+    }
+
+    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;
+    }
+
+    public short nla_len;
+    public short nla_type;
+    public byte[] nla_value;
+    public ByteOrder mByteOrder;
+
+    public StructNlAttr() {
+        mByteOrder = ByteOrder.nativeOrder();
+    }
+
+    public int getAlignedLength() {
+        return NetlinkConstants.alignedLengthOf(nla_len);
+    }
+
+    public ByteBuffer getValueAsByteBuffer() {
+        if (nla_value == null) { return null; }
+        final ByteBuffer byteBuffer = ByteBuffer.wrap(nla_value);
+        byteBuffer.order(mByteOrder);
+        return byteBuffer;
+    }
+
+    public int getValueAsInt(int defaultValue) {
+        final ByteBuffer byteBuffer = getValueAsByteBuffer();
+        if (byteBuffer == null || byteBuffer.remaining() != SizeOf.INT) {
+            return defaultValue;
+        }
+        return getValueAsByteBuffer().getInt();
+    }
+
+    public InetAddress getValueAsInetAddress() {
+        if (nla_value == null) { return null; }
+
+        try {
+            return InetAddress.getByAddress(nla_value);
+        } catch (UnknownHostException ignored) {
+            return null;
+        }
+    }
+
+    @Override
+    public String toString() {
+        return "StructNlAttr{ "
+                + "nla_len{" + nla_len + "}, "
+                + "nla_type{" + nla_type + "}, "
+                + "nla_value{" + NetlinkConstants.hexify(nla_value) + "}, "
+                + "}";
+    }
+}
diff --git a/core/java/android/net/netlink/StructNlMsgErr.java b/core/java/android/net/netlink/StructNlMsgErr.java
new file mode 100644
index 0000000..5da19a2
--- /dev/null
+++ b/core/java/android/net/netlink/StructNlMsgErr.java
@@ -0,0 +1,80 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.netlink;
+
+import android.net.netlink.NetlinkConstants;
+import android.net.netlink.StructNlMsgHdr;
+import libcore.io.SizeOf;
+
+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 = SizeOf.INT + StructNlMsgHdr.STRUCT_SIZE;
+
+    public static boolean hasAvailableSpace(ByteBuffer byteBuffer) {
+        return byteBuffer != null && byteBuffer.remaining() >= STRUCT_SIZE;
+    }
+
+    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;
+
+    public StructNlMsgErr() {
+        error = 0;
+        msg = null;
+    }
+
+    public boolean pack(ByteBuffer byteBuffer) {
+        if (!hasAvailableSpace(byteBuffer)) { return false; }
+
+        // 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);
+        }
+        return true;
+    }
+
+    @Override
+    public String toString() {
+        return "StructNlMsgErr{ "
+                + "error{" + error + "}, "
+                + "msg{" + (msg == null ? "" : msg.toString()) + "} "
+                + "}";
+    }
+}
diff --git a/core/java/android/net/netlink/StructNlMsgHdr.java b/core/java/android/net/netlink/StructNlMsgHdr.java
new file mode 100644
index 0000000..67925ac
--- /dev/null
+++ b/core/java/android/net/netlink/StructNlMsgHdr.java
@@ -0,0 +1,137 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.netlink;
+
+import android.net.netlink.NetlinkConstants;
+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;
+
+    public 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();
+    }
+
+    public static boolean hasAvailableSpace(ByteBuffer byteBuffer) {
+        return byteBuffer != null && byteBuffer.remaining() >= STRUCT_SIZE;
+    }
+
+    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;
+    }
+
+    public boolean pack(ByteBuffer byteBuffer) {
+        if (!hasAvailableSpace(byteBuffer)) { return false; }
+
+        // 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);
+        return true;
+    }
+
+    @Override
+    public String toString() {
+        final String typeStr = "" + nlmsg_type
+                + "(" + NetlinkConstants.stringForNlMsgType(nlmsg_type) + ")";
+        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 + "} "
+                + "}";
+    }
+}