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/*
* Copyright (C) 2023 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 com.android.testutils
import java.io.FileDescriptor
import java.net.InetAddress
/**
* A class that forwards packets from the external {@link TestNetworkInterface} to the internal
* {@link TestNetworkInterface} with NAT. See {@link NatPacketForwarderBase} for detail.
*/
class NatExternalPacketForwarder(
srcFd: FileDescriptor,
mtu: Int,
dstFd: FileDescriptor,
extAddr: InetAddress,
natMap: PacketBridge.NatMap
) : NatPacketForwarderBase(srcFd, mtu, dstFd, extAddr, natMap) {
/**
* Rewrite addresses, ports and fix up checksums for packets received on the external
* interface.
*
* Incoming response from external interface which is being forwarded to the internal
* interface with translated address, e.g. 1.2.3.4:80 -> 8.8.8.8:1234
* will be translated into 8.8.8.8:80 -> 192.168.1.1:5678.
*
* For packets that are not an incoming response, do not forward them to the
* internal interface.
*/
override fun preparePacketForForwarding(buf: ByteArray, len: Int, version: Int, proto: Int) {
val (addrPos, addrLen) = getAddressPositionAndLength(version)
// TODO: support one external address per ip version.
val extAddrBuf = mExtAddr.address
if (addrLen != extAddrBuf.size) throw IllegalStateException("Packet IP version mismatch")
// Get internal address by port.
val transportOffset =
if (version == 4) PacketReflector.IPV4_HEADER_LENGTH
else PacketReflector.IPV6_HEADER_LENGTH
val dstPort = getPortAt(buf, transportOffset + DESTINATION_PORT_OFFSET)
val intAddrInfo = synchronized(mNatMap) { mNatMap.fromExternalPort(dstPort) }
// No mapping, skip. This usually happens if the connection is initiated directly on
// the external interface, e.g. DNS64 resolution, network validation, etc.
if (intAddrInfo == null) return
val intAddrBuf = intAddrInfo.address.address
val intPort = intAddrInfo.port
// Copy the original destination to into the source address.
for (i in 0 until addrLen) {
buf[addrPos + i] = buf[addrPos + addrLen + i]
}
// Copy the internal address into the destination address.
for (i in 0 until addrLen) {
buf[addrPos + addrLen + i] = intAddrBuf[i]
}
// Copy the internal port into the destination port.
setPortAt(intPort, buf, transportOffset + DESTINATION_PORT_OFFSET)
// Fix IP and Transport layer checksum.
fixPacketChecksum(buf, len, version, proto.toByte())
}
}
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