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/*
* Copyright 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 com.android.net.module.util;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.net.MacAddress;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.Objects;
import java.util.Random;
/**
* Collection of MAC address utilities.
* @hide
*/
public final class MacAddressUtils {
private static final long VALID_LONG_MASK = (1L << 48) - 1;
private static final long LOCALLY_ASSIGNED_MASK = longAddrFromByteAddr(
MacAddress.fromString("2:0:0:0:0:0").toByteArray());
private static final long MULTICAST_MASK = longAddrFromByteAddr(
MacAddress.fromString("1:0:0:0:0:0").toByteArray());
private static final long OUI_MASK = longAddrFromByteAddr(
MacAddress.fromString("ff:ff:ff:0:0:0").toByteArray());
private static final long NIC_MASK = longAddrFromByteAddr(
MacAddress.fromString("0:0:0:ff:ff:ff").toByteArray());
// Matches WifiInfo.DEFAULT_MAC_ADDRESS
private static final MacAddress DEFAULT_MAC_ADDRESS =
MacAddress.fromString("02:00:00:00:00:00");
private static final int ETHER_ADDR_LEN = 6;
/**
* @return true if this MacAddress is a multicast address.
*/
public static boolean isMulticastAddress(@NonNull MacAddress address) {
return (longAddrFromByteAddr(address.toByteArray()) & MULTICAST_MASK) != 0;
}
/**
* Returns a generated MAC address whose 46 bits, excluding the locally assigned bit and the
* unicast bit, are randomly selected.
*
* The locally assigned bit is always set to 1. The multicast bit is always set to 0.
*
* @return a random locally assigned, unicast MacAddress.
*/
public static @NonNull MacAddress createRandomUnicastAddress() {
return createRandomUnicastAddress(null, new SecureRandom());
}
/**
* Returns a randomly generated MAC address using the given Random object and the same
* OUI values as the given MacAddress.
*
* The locally assigned bit is always set to 1. The multicast bit is always set to 0.
*
* @param base a base MacAddress whose OUI is used for generating the random address.
* If base == null then the OUI will also be randomized.
* @param r a standard Java Random object used for generating the random address.
* @return a random locally assigned MacAddress.
*/
public static @NonNull MacAddress createRandomUnicastAddress(@Nullable MacAddress base,
@NonNull Random r) {
long addr;
if (base == null) {
addr = r.nextLong() & VALID_LONG_MASK;
} else {
addr = (longAddrFromByteAddr(base.toByteArray()) & OUI_MASK)
| (NIC_MASK & r.nextLong());
}
addr |= LOCALLY_ASSIGNED_MASK;
addr &= ~MULTICAST_MASK;
MacAddress mac = MacAddress.fromBytes(byteAddrFromLongAddr(addr));
if (mac.equals(DEFAULT_MAC_ADDRESS)) {
return createRandomUnicastAddress(base, r);
}
return mac;
}
/**
* Convert a byte address to long address.
*/
public static long longAddrFromByteAddr(byte[] addr) {
Objects.requireNonNull(addr);
if (!isMacAddress(addr)) {
throw new IllegalArgumentException(
Arrays.toString(addr) + " was not a valid MAC address");
}
long longAddr = 0;
for (byte b : addr) {
final int uint8Byte = b & 0xff;
longAddr = (longAddr << 8) + uint8Byte;
}
return longAddr;
}
/**
* Convert a long address to byte address.
*/
public static byte[] byteAddrFromLongAddr(long addr) {
byte[] bytes = new byte[ETHER_ADDR_LEN];
int index = ETHER_ADDR_LEN;
while (index-- > 0) {
bytes[index] = (byte) addr;
addr = addr >> 8;
}
return bytes;
}
/**
* Returns true if the given byte array is a valid MAC address.
* A valid byte array representation for a MacAddress is a non-null array of length 6.
*
* @param addr a byte array.
* @return true if the given byte array is not null and has the length of a MAC address.
*
*/
public static boolean isMacAddress(byte[] addr) {
return addr != null && addr.length == ETHER_ADDR_LEN;
}
}
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