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      1 /*
      2  * Copyright (C) 2012 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.arp;
     18 
     19 import android.os.SystemClock;
     20 import android.util.Log;
     21 import java.io.IOException;
     22 import java.net.InetAddress;
     23 import java.net.Inet6Address;
     24 import java.net.SocketException;
     25 import java.nio.ByteBuffer;
     26 import java.nio.ByteOrder;
     27 import java.util.Arrays;
     28 
     29 import libcore.net.RawSocket;
     30 
     31 /**
     32  * This class allows simple ARP exchanges over an uninitialized network
     33  * interface.
     34  *
     35  * @hide
     36  */
     37 public class ArpPeer {
     38     private String mInterfaceName;
     39     private final InetAddress mMyAddr;
     40     private final byte[] mMyMac = new byte[6];
     41     private final InetAddress mPeer;
     42     private final RawSocket mSocket;
     43     private final byte[] L2_BROADCAST;  // TODO: refactor from DhcpClient.java
     44     private static final int MAX_LENGTH = 1500; // refactor from DhcpPacket.java
     45     private static final int ETHERNET_TYPE = 1;
     46     private static final int ARP_LENGTH = 28;
     47     private static final int MAC_ADDR_LENGTH = 6;
     48     private static final int IPV4_LENGTH = 4;
     49     private static final String TAG = "ArpPeer";
     50 
     51     public ArpPeer(String interfaceName, InetAddress myAddr, String mac,
     52                    InetAddress peer) throws SocketException {
     53         mInterfaceName = interfaceName;
     54         mMyAddr = myAddr;
     55 
     56         for (int i = 0; i < MAC_ADDR_LENGTH; i++) {
     57             mMyMac[i] = (byte) Integer.parseInt(mac.substring(
     58                         i*3, (i*3) + 2), 16);
     59         }
     60 
     61         if (myAddr instanceof Inet6Address || peer instanceof Inet6Address) {
     62             throw new IllegalArgumentException("IPv6 unsupported");
     63         }
     64 
     65         mPeer = peer;
     66         L2_BROADCAST = new byte[MAC_ADDR_LENGTH];
     67         Arrays.fill(L2_BROADCAST, (byte) 0xFF);
     68 
     69         mSocket = new RawSocket(mInterfaceName, RawSocket.ETH_P_ARP);
     70     }
     71 
     72     /**
     73      * Returns the MAC address (or null if timeout) for the requested
     74      * peer.
     75      */
     76     public byte[] doArp(int timeoutMillis) {
     77         ByteBuffer buf = ByteBuffer.allocate(MAX_LENGTH);
     78         byte[] desiredIp = mPeer.getAddress();
     79         long timeout = SystemClock.elapsedRealtime() + timeoutMillis;
     80 
     81         // construct ARP request packet, using a ByteBuffer as a
     82         // convenient container
     83         buf.clear();
     84         buf.order(ByteOrder.BIG_ENDIAN);
     85 
     86         buf.putShort((short) ETHERNET_TYPE); // Ethernet type, 16 bits
     87         buf.putShort(RawSocket.ETH_P_IP); // Protocol type IP, 16 bits
     88         buf.put((byte)MAC_ADDR_LENGTH);  // MAC address length, 6 bytes
     89         buf.put((byte)IPV4_LENGTH);  // IPv4 protocol size
     90         buf.putShort((short) 1); // ARP opcode 1: 'request'
     91         buf.put(mMyMac);        // six bytes: sender MAC
     92         buf.put(mMyAddr.getAddress());  // four bytes: sender IP address
     93         buf.put(new byte[MAC_ADDR_LENGTH]); // target MAC address: unknown
     94         buf.put(desiredIp); // target IP address, 4 bytes
     95         buf.flip();
     96         mSocket.write(L2_BROADCAST, buf.array(), 0, buf.limit());
     97 
     98         byte[] recvBuf = new byte[MAX_LENGTH];
     99 
    100         while (SystemClock.elapsedRealtime() < timeout) {
    101             long duration = (long) timeout - SystemClock.elapsedRealtime();
    102             int readLen = mSocket.read(recvBuf, 0, recvBuf.length, -1,
    103                 (int) duration);
    104 
    105             // Verify packet details. see RFC 826
    106             if ((readLen >= ARP_LENGTH) // trailing bytes at times
    107                 && (recvBuf[0] == 0) && (recvBuf[1] == ETHERNET_TYPE) // type Ethernet
    108                 && (recvBuf[2] == 8) && (recvBuf[3] == 0) // protocol IP
    109                 && (recvBuf[4] == MAC_ADDR_LENGTH) // mac length
    110                 && (recvBuf[5] == IPV4_LENGTH) // IPv4 protocol size
    111                 && (recvBuf[6] == 0) && (recvBuf[7] == 2) // ARP reply
    112                 // verify desired IP address
    113                 && (recvBuf[14] == desiredIp[0]) && (recvBuf[15] == desiredIp[1])
    114                 && (recvBuf[16] == desiredIp[2]) && (recvBuf[17] == desiredIp[3]))
    115             {
    116                 // looks good.  copy out the MAC
    117                 byte[] result = new byte[MAC_ADDR_LENGTH];
    118                 System.arraycopy(recvBuf, 8, result, 0, MAC_ADDR_LENGTH);
    119                 return result;
    120             }
    121         }
    122 
    123         return null;
    124     }
    125 
    126     public void close() {
    127         try {
    128             mSocket.close();
    129         } catch (IOException ex) {
    130         }
    131     }
    132 }
    133