1 /*
2  * Copyright (C) 2015 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.util;
18 
19 import java.net.Inet6Address;
20 import java.net.InetAddress;
21 import java.nio.BufferOverflowException;
22 import java.nio.BufferUnderflowException;
23 import java.nio.ByteBuffer;
24 import java.nio.ShortBuffer;
25 
26 import static android.system.OsConstants.IPPROTO_TCP;
27 import static android.system.OsConstants.IPPROTO_UDP;
28 
29 /**
30  * @hide
31  */
32 public class IpUtils {
33     /**
34      * Converts a signed short value to an unsigned int value.  Needed
35      * because Java does not have unsigned types.
36      */
intAbs(short v)37     private static int intAbs(short v) {
38         return v & 0xFFFF;
39     }
40 
41     /**
42      * Performs an IP checksum (used in IP header and across UDP
43      * payload) on the specified portion of a ByteBuffer.  The seed
44      * allows the checksum to commence with a specified value.
45      */
checksum(ByteBuffer buf, int seed, int start, int end)46     private static int checksum(ByteBuffer buf, int seed, int start, int end) {
47         int sum = seed;
48         final int bufPosition = buf.position();
49 
50         // set position of original ByteBuffer, so that the ShortBuffer
51         // will be correctly initialized
52         buf.position(start);
53         ShortBuffer shortBuf = buf.asShortBuffer();
54 
55         // re-set ByteBuffer position
56         buf.position(bufPosition);
57 
58         final int numShorts = (end - start) / 2;
59         for (int i = 0; i < numShorts; i++) {
60             sum += intAbs(shortBuf.get(i));
61         }
62         start += numShorts * 2;
63 
64         // see if a singleton byte remains
65         if (end != start) {
66             short b = buf.get(start);
67 
68             // make it unsigned
69             if (b < 0) {
70                 b += 256;
71             }
72 
73             sum += b * 256;
74         }
75 
76         sum = ((sum >> 16) & 0xFFFF) + (sum & 0xFFFF);
77         sum = ((sum + ((sum >> 16) & 0xFFFF)) & 0xFFFF);
78         int negated = ~sum;
79         return intAbs((short) negated);
80     }
81 
pseudoChecksumIPv4( ByteBuffer buf, int headerOffset, int protocol, int transportLen)82     private static int pseudoChecksumIPv4(
83             ByteBuffer buf, int headerOffset, int protocol, int transportLen) {
84         int partial = protocol + transportLen;
85         partial += intAbs(buf.getShort(headerOffset + 12));
86         partial += intAbs(buf.getShort(headerOffset + 14));
87         partial += intAbs(buf.getShort(headerOffset + 16));
88         partial += intAbs(buf.getShort(headerOffset + 18));
89         return partial;
90     }
91 
pseudoChecksumIPv6( ByteBuffer buf, int headerOffset, int protocol, int transportLen)92     private static int pseudoChecksumIPv6(
93             ByteBuffer buf, int headerOffset, int protocol, int transportLen) {
94         int partial = protocol + transportLen;
95         for (int offset = 8; offset < 40; offset += 2) {
96             partial += intAbs(buf.getShort(headerOffset + offset));
97         }
98         return partial;
99     }
100 
ipversion(ByteBuffer buf, int headerOffset)101     private static byte ipversion(ByteBuffer buf, int headerOffset) {
102         return (byte) ((buf.get(headerOffset) & (byte) 0xf0) >> 4);
103    }
104 
ipChecksum(ByteBuffer buf, int headerOffset)105     public static short ipChecksum(ByteBuffer buf, int headerOffset) {
106         byte ihl = (byte) (buf.get(headerOffset) & 0x0f);
107         return (short) checksum(buf, 0, headerOffset, headerOffset + ihl * 4);
108     }
109 
transportChecksum(ByteBuffer buf, int protocol, int ipOffset, int transportOffset, int transportLen)110     private static short transportChecksum(ByteBuffer buf, int protocol,
111             int ipOffset, int transportOffset, int transportLen) {
112         if (transportLen < 0) {
113             throw new IllegalArgumentException("Transport length < 0: " + transportLen);
114         }
115         int sum;
116         byte ver = ipversion(buf, ipOffset);
117         if (ver == 4) {
118             sum = pseudoChecksumIPv4(buf, ipOffset, protocol, transportLen);
119         } else if (ver == 6) {
120             sum = pseudoChecksumIPv6(buf, ipOffset, protocol, transportLen);
121         } else {
122             throw new UnsupportedOperationException("Checksum must be IPv4 or IPv6");
123         }
124 
125         sum = checksum(buf, sum, transportOffset, transportOffset + transportLen);
126         if (protocol == IPPROTO_UDP && sum == 0) {
127             sum = (short) 0xffff;
128         }
129         return (short) sum;
130     }
131 
udpChecksum(ByteBuffer buf, int ipOffset, int transportOffset)132     public static short udpChecksum(ByteBuffer buf, int ipOffset, int transportOffset) {
133         int transportLen = intAbs(buf.getShort(transportOffset + 4));
134         return transportChecksum(buf, IPPROTO_UDP, ipOffset, transportOffset, transportLen);
135     }
136 
tcpChecksum(ByteBuffer buf, int ipOffset, int transportOffset, int transportLen)137     public static short tcpChecksum(ByteBuffer buf, int ipOffset, int transportOffset,
138             int transportLen) {
139         return transportChecksum(buf, IPPROTO_TCP, ipOffset, transportOffset, transportLen);
140     }
141 
addressAndPortToString(InetAddress address, int port)142     public static String addressAndPortToString(InetAddress address, int port) {
143         return String.format(
144                 (address instanceof Inet6Address) ? "[%s]:%d" : "%s:%d",
145                 address.getHostAddress(), port);
146     }
147 
isValidUdpOrTcpPort(int port)148     public static boolean isValidUdpOrTcpPort(int port) {
149         return port > 0 && port < 65536;
150     }
151 }
152