2 * Copyright (C) 2012 The Android Open Source Project
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
17 package android.net.arp;
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;
29 import libcore.net.RawSocket;
32 * This class allows simple ARP exchanges over an uninitialized network
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";
51 public ArpPeer(String interfaceName, InetAddress myAddr, String mac,
52 InetAddress peer) throws SocketException {
53 mInterfaceName = interfaceName;
57 for (int i = 0; i < MAC_ADDR_LENGTH; i++) {
58 mMyMac[i] = (byte) Integer.parseInt(mac.substring(
63 if (myAddr instanceof Inet6Address || peer instanceof Inet6Address) {
64 throw new IllegalArgumentException("IPv6 unsupported");
68 L2_BROADCAST = new byte[MAC_ADDR_LENGTH];
69 Arrays.fill(L2_BROADCAST, (byte) 0xFF);
71 mSocket = new RawSocket(mInterfaceName, RawSocket.ETH_P_ARP);
75 * Returns the MAC address (or null if timeout) for the requested
78 public byte[] doArp(int timeoutMillis) {
79 ByteBuffer buf = ByteBuffer.allocate(MAX_LENGTH);
80 byte[] desiredIp = mPeer.getAddress();
81 long timeout = SystemClock.elapsedRealtime() + timeoutMillis;
83 // construct ARP request packet, using a ByteBuffer as a
84 // convenient container
86 buf.order(ByteOrder.BIG_ENDIAN);
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
98 mSocket.write(L2_BROADCAST, buf.array(), 0, buf.limit());
100 byte[] recvBuf = new byte[MAX_LENGTH];
102 while (SystemClock.elapsedRealtime() < timeout) {
103 long duration = (long) timeout - SystemClock.elapsedRealtime();
104 int readLen = mSocket.read(recvBuf, 0, recvBuf.length, -1,
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]))
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);
128 public void close() {
131 } catch (IOException ex) {