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/*
* Copyright (C) 2019 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.net;
import static android.net.SocketKeepalive.ERROR_INVALID_IP_ADDRESS;
import static android.net.SocketKeepalive.ERROR_INVALID_PORT;
import android.net.SocketKeepalive.InvalidPacketException;
import android.net.util.IpUtils;
import android.system.OsConstants;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
/** @hide */
public final class NattKeepalivePacketData extends KeepalivePacketData {
// This should only be constructed via static factory methods, such as
// nattKeepalivePacket
private NattKeepalivePacketData(InetAddress srcAddress, int srcPort,
InetAddress dstAddress, int dstPort, byte[] data) throws
InvalidPacketException {
super(srcAddress, srcPort, dstAddress, dstPort, data);
}
/**
* Factory method to create Nat-T keepalive packet structure.
*/
public static NattKeepalivePacketData nattKeepalivePacket(
InetAddress srcAddress, int srcPort, InetAddress dstAddress, int dstPort)
throws InvalidPacketException {
if (!(srcAddress instanceof Inet4Address) || !(dstAddress instanceof Inet4Address)) {
throw new InvalidPacketException(ERROR_INVALID_IP_ADDRESS);
}
if (dstPort != NattSocketKeepalive.NATT_PORT) {
throw new InvalidPacketException(ERROR_INVALID_PORT);
}
int length = IPV4_HEADER_LENGTH + UDP_HEADER_LENGTH + 1;
ByteBuffer buf = ByteBuffer.allocate(length);
buf.order(ByteOrder.BIG_ENDIAN);
buf.putShort((short) 0x4500); // IP version and TOS
buf.putShort((short) length);
buf.putInt(0); // ID, flags, offset
buf.put((byte) 64); // TTL
buf.put((byte) OsConstants.IPPROTO_UDP);
int ipChecksumOffset = buf.position();
buf.putShort((short) 0); // IP checksum
buf.put(srcAddress.getAddress());
buf.put(dstAddress.getAddress());
buf.putShort((short) srcPort);
buf.putShort((short) dstPort);
buf.putShort((short) (length - 20)); // UDP length
int udpChecksumOffset = buf.position();
buf.putShort((short) 0); // UDP checksum
buf.put((byte) 0xff); // NAT-T keepalive
buf.putShort(ipChecksumOffset, IpUtils.ipChecksum(buf, 0));
buf.putShort(udpChecksumOffset, IpUtils.udpChecksum(buf, 0, IPV4_HEADER_LENGTH));
return new NattKeepalivePacketData(srcAddress, srcPort, dstAddress, dstPort, buf.array());
}
}
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