1 /*
2  * Copyright (C) 2017 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.netlink;
18 
19 import android.annotation.NonNull;
20 import android.annotation.Nullable;
21 
22 import java.nio.ByteBuffer;
23 import java.nio.ByteOrder;
24 import java.util.Objects;
25 
26 
27 /**
28  * struct nfgenmsg
29  *
30  * see <linux_src>/include/uapi/linux/netfilter/nfnetlink.h
31  *
32  * @hide
33  */
34 public class StructNfGenMsg {
35     public static final int STRUCT_SIZE = 2 + Short.BYTES;
36 
37     public static final int NFNETLINK_V0 = 0;
38 
39     final public byte nfgen_family;
40     final public byte version;
41     final public short res_id;  // N.B.: this is big endian in the kernel
42 
43     /**
44      * Parses a netfilter netlink header from a {@link ByteBuffer}.
45      *
46      * @param byteBuffer The buffer from which to parse the netfilter netlink header.
47      * @return the parsed netfilter netlink header, or {@code null} if the netfilter netlink header
48      *         could not be parsed successfully (for example, if it was truncated).
49      */
50     @Nullable
parse(@onNull ByteBuffer byteBuffer)51     public static StructNfGenMsg parse(@NonNull ByteBuffer byteBuffer) {
52         Objects.requireNonNull(byteBuffer);
53 
54         if (!hasAvailableSpace(byteBuffer)) return null;
55 
56         final byte nfgen_family = byteBuffer.get();
57         final byte version = byteBuffer.get();
58 
59         final ByteOrder originalOrder = byteBuffer.order();
60         byteBuffer.order(ByteOrder.BIG_ENDIAN);
61         final short res_id = byteBuffer.getShort();
62         byteBuffer.order(originalOrder);
63 
64         return new StructNfGenMsg(nfgen_family, version, res_id);
65     }
66 
StructNfGenMsg(byte family, byte ver, short id)67     public StructNfGenMsg(byte family, byte ver, short id) {
68         nfgen_family = family;
69         version = ver;
70         res_id = id;
71     }
72 
StructNfGenMsg(byte family)73     public StructNfGenMsg(byte family) {
74         nfgen_family = family;
75         version = (byte) NFNETLINK_V0;
76         res_id = (short) 0;
77     }
78 
pack(ByteBuffer byteBuffer)79     public void pack(ByteBuffer byteBuffer) {
80         byteBuffer.put(nfgen_family);
81         byteBuffer.put(version);
82 
83         final ByteOrder originalOrder = byteBuffer.order();
84         byteBuffer.order(ByteOrder.BIG_ENDIAN);
85         byteBuffer.putShort(res_id);
86         byteBuffer.order(originalOrder);
87     }
88 
hasAvailableSpace(@onNull ByteBuffer byteBuffer)89     private static boolean hasAvailableSpace(@NonNull ByteBuffer byteBuffer) {
90         return byteBuffer.remaining() >= STRUCT_SIZE;
91     }
92 
93     @Override
toString()94     public String toString() {
95         final String familyStr = NetlinkConstants.stringForAddressFamily(nfgen_family);
96 
97         return "NfGenMsg{ "
98                 + "nfgen_family{" + familyStr + "}, "
99                 + "version{" + Byte.toUnsignedInt(version) + "}, "
100                 + "res_id{" + Short.toUnsignedInt(res_id) + "} "
101                 + "}";
102     }
103 }
104