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      1 /*
      2  * Copyright (C) 2019 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.net;
     18 
     19 import static android.net.SocketKeepalive.ERROR_INVALID_IP_ADDRESS;
     20 import static android.net.SocketKeepalive.ERROR_INVALID_PORT;
     21 
     22 import android.net.SocketKeepalive.InvalidPacketException;
     23 import android.net.util.IpUtils;
     24 import android.os.Parcel;
     25 import android.os.Parcelable;
     26 import android.system.OsConstants;
     27 
     28 import java.net.Inet4Address;
     29 import java.net.InetAddress;
     30 import java.nio.ByteBuffer;
     31 import java.nio.ByteOrder;
     32 
     33 /** @hide */
     34 public final class NattKeepalivePacketData extends KeepalivePacketData implements Parcelable {
     35     // This should only be constructed via static factory methods, such as
     36     // nattKeepalivePacket
     37     private NattKeepalivePacketData(InetAddress srcAddress, int srcPort,
     38             InetAddress dstAddress, int dstPort, byte[] data) throws
     39             InvalidPacketException {
     40         super(srcAddress, srcPort, dstAddress, dstPort, data);
     41     }
     42 
     43     /**
     44      * Factory method to create Nat-T keepalive packet structure.
     45      */
     46     public static NattKeepalivePacketData nattKeepalivePacket(
     47             InetAddress srcAddress, int srcPort, InetAddress dstAddress, int dstPort)
     48             throws InvalidPacketException {
     49 
     50         if (!(srcAddress instanceof Inet4Address) || !(dstAddress instanceof Inet4Address)) {
     51             throw new InvalidPacketException(ERROR_INVALID_IP_ADDRESS);
     52         }
     53 
     54         if (dstPort != NattSocketKeepalive.NATT_PORT) {
     55             throw new InvalidPacketException(ERROR_INVALID_PORT);
     56         }
     57 
     58         int length = IPV4_HEADER_LENGTH + UDP_HEADER_LENGTH + 1;
     59         ByteBuffer buf = ByteBuffer.allocate(length);
     60         buf.order(ByteOrder.BIG_ENDIAN);
     61         buf.putShort((short) 0x4500);             // IP version and TOS
     62         buf.putShort((short) length);
     63         buf.putInt(0);                            // ID, flags, offset
     64         buf.put((byte) 64);                       // TTL
     65         buf.put((byte) OsConstants.IPPROTO_UDP);
     66         int ipChecksumOffset = buf.position();
     67         buf.putShort((short) 0);                  // IP checksum
     68         buf.put(srcAddress.getAddress());
     69         buf.put(dstAddress.getAddress());
     70         buf.putShort((short) srcPort);
     71         buf.putShort((short) dstPort);
     72         buf.putShort((short) (length - 20));      // UDP length
     73         int udpChecksumOffset = buf.position();
     74         buf.putShort((short) 0);                  // UDP checksum
     75         buf.put((byte) 0xff);                     // NAT-T keepalive
     76         buf.putShort(ipChecksumOffset, IpUtils.ipChecksum(buf, 0));
     77         buf.putShort(udpChecksumOffset, IpUtils.udpChecksum(buf, 0, IPV4_HEADER_LENGTH));
     78 
     79         return new NattKeepalivePacketData(srcAddress, srcPort, dstAddress, dstPort, buf.array());
     80     }
     81 
     82     /** Parcelable Implementation */
     83     public int describeContents() {
     84         return 0;
     85     }
     86 
     87     /** Write to parcel */
     88     public void writeToParcel(Parcel out, int flags) {
     89         out.writeString(srcAddress.getHostAddress());
     90         out.writeString(dstAddress.getHostAddress());
     91         out.writeInt(srcPort);
     92         out.writeInt(dstPort);
     93     }
     94 
     95     /** Parcelable Creator */
     96     public static final Parcelable.Creator<NattKeepalivePacketData> CREATOR =
     97             new Parcelable.Creator<NattKeepalivePacketData>() {
     98                 public NattKeepalivePacketData createFromParcel(Parcel in) {
     99                     final InetAddress srcAddress =
    100                             InetAddresses.parseNumericAddress(in.readString());
    101                     final InetAddress dstAddress =
    102                             InetAddresses.parseNumericAddress(in.readString());
    103                     final int srcPort = in.readInt();
    104                     final int dstPort = in.readInt();
    105                     try {
    106                         return NattKeepalivePacketData.nattKeepalivePacket(srcAddress, srcPort,
    107                                     dstAddress, dstPort);
    108                     } catch (InvalidPacketException e) {
    109                         throw new IllegalArgumentException(
    110                                 "Invalid NAT-T keepalive data: " + e.error);
    111                     }
    112                 }
    113 
    114                 public NattKeepalivePacketData[] newArray(int size) {
    115                     return new NattKeepalivePacketData[size];
    116                 }
    117             };
    118 }
    119