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      1 /*
      2  * Copyright (C) 2016 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.system;
     18 
     19 import static android.system.OsConstants.ICMP6_ECHO_REQUEST;
     20 import static android.system.OsConstants.ICMP_ECHO;
     21 
     22 /**
     23  * Corresponds to C's {@code struct icmphdr} from linux/icmp.h and {@code struct icmp6hdr} from
     24  * linux/icmpv6.h
     25  *
     26  * @hide
     27  */
     28 public final class StructIcmpHdr {
     29     private byte[] packet;
     30 
     31     private StructIcmpHdr() {
     32         packet =  new byte[8];
     33     }
     34 
     35     /*
     36      * Echo or Echo Reply Message
     37      *
     38      * 0                   1                   2                   3
     39      * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     40      * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     41      * |     Type      |     Code      |          Checksum             |
     42      * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     43      * |           Identifier          |        Sequence Number        |
     44      * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     45      * |     Data ...
     46      * +-+-+-+-+-
     47      */
     48     public static StructIcmpHdr IcmpEchoHdr(boolean ipv4, int seq) {
     49         StructIcmpHdr hdr = new StructIcmpHdr();
     50         hdr.packet[0] = ipv4 ? (byte) ICMP_ECHO : (byte) ICMP6_ECHO_REQUEST;
     51         // packet[1]: Code is always zero.
     52         // packet[2,3]: Checksum is computed by kernel.
     53         // packet[4,5]: ID (= port) inserted by kernel.
     54         hdr.packet[6] = (byte) (seq >> 8);
     55         hdr.packet[7] = (byte) seq;
     56         return hdr;
     57     }
     58 
     59     public byte[] getBytes() {
     60         return packet.clone();
     61     }
     62 }
     63