ArpPeer.java revision 21326d8b77cfd1567d87d5ebe3e327b744632e24 
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
17package android.net.arp;
18
19import android.os.SystemClock;
20import android.util.Log;
21import java.io.IOException;
22import java.net.InetAddress;
23import java.net.Inet6Address;
24import java.net.SocketException;
25import java.nio.ByteBuffer;
26import java.nio.ByteOrder;
27import java.util.Arrays;
28
29import libcore.net.RawSocket;
30
31/**
32 * This class allows simple ARP exchanges over an uninitialized network
33 * interface.
34 *
35 * @hide
36 */
37public 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        if (mac != null) {
57            for (int i = 0; i < MAC_ADDR_LENGTH; i++) {
58                mMyMac[i] = (byte) Integer.parseInt(mac.substring(
59                            i*3, (i*3) + 2), 16);
60            }
61        }
62
63        if (myAddr instanceof Inet6Address || peer instanceof Inet6Address) {
64            throw new IllegalArgumentException("IPv6 unsupported");
65        }
66
67        mPeer = peer;
68        L2_BROADCAST = new byte[MAC_ADDR_LENGTH];
69        Arrays.fill(L2_BROADCAST, (byte) 0xFF);
70
71        mSocket = new RawSocket(mInterfaceName, RawSocket.ETH_P_ARP);
72    }
73
74    /**
75     * Returns the MAC address (or null if timeout) for the requested
76     * peer.
77     */
78    public byte[] doArp(int timeoutMillis) {
79        ByteBuffer buf = ByteBuffer.allocate(MAX_LENGTH);
80        byte[] desiredIp = mPeer.getAddress();
81        long timeout = SystemClock.elapsedRealtime() + timeoutMillis;
82
83        // construct ARP request packet, using a ByteBuffer as a
84        // convenient container
85        buf.clear();
86        buf.order(ByteOrder.BIG_ENDIAN);
87
88        buf.putShort((short) ETHERNET_TYPE); // Ethernet type, 16 bits
89        buf.putShort(RawSocket.ETH_P_IP); // Protocol type IP, 16 bits
90        buf.put((byte)MAC_ADDR_LENGTH);  // MAC address length, 6 bytes
91        buf.put((byte)IPV4_LENGTH);  // IPv4 protocol size
92        buf.putShort((short) 1); // ARP opcode 1: 'request'
93        buf.put(mMyMac);        // six bytes: sender MAC
94        buf.put(mMyAddr.getAddress());  // four bytes: sender IP address
95        buf.put(new byte[MAC_ADDR_LENGTH]); // target MAC address: unknown
96        buf.put(desiredIp); // target IP address, 4 bytes
97        buf.flip();
98        mSocket.write(L2_BROADCAST, buf.array(), 0, buf.limit());
99
100        byte[] recvBuf = new byte[MAX_LENGTH];
101
102        while (SystemClock.elapsedRealtime() < timeout) {
103            long duration = (long) timeout - SystemClock.elapsedRealtime();
104            int readLen = mSocket.read(recvBuf, 0, recvBuf.length, -1,
105                (int) duration);
106
107            // Verify packet details. see RFC 826
108            if ((readLen >= ARP_LENGTH) // trailing bytes at times
109                && (recvBuf[0] == 0) && (recvBuf[1] == ETHERNET_TYPE) // type Ethernet
110                && (recvBuf[2] == 8) && (recvBuf[3] == 0) // protocol IP
111                && (recvBuf[4] == MAC_ADDR_LENGTH) // mac length
112                && (recvBuf[5] == IPV4_LENGTH) // IPv4 protocol size
113                && (recvBuf[6] == 0) && (recvBuf[7] == 2) // ARP reply
114                // verify desired IP address
115                && (recvBuf[14] == desiredIp[0]) && (recvBuf[15] == desiredIp[1])
116                && (recvBuf[16] == desiredIp[2]) && (recvBuf[17] == desiredIp[3]))
117            {
118                // looks good.  copy out the MAC
119                byte[] result = new byte[MAC_ADDR_LENGTH];
120                System.arraycopy(recvBuf, 8, result, 0, MAC_ADDR_LENGTH);
121                return result;
122            }
123        }
124
125        return null;
126    }
127
128    public void close() {
129        try {
130            mSocket.close();
131        } catch (IOException ex) {
132        }
133    }
134}
135