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// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.net;
import java.net.*;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.stream.Collectors;
/**
* Utilities for returning localhost addresses on Linux.
* See http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4665037 on why this is necessary.
*
* @author bratseth
*/
public class LinuxInetAddress {
/**
* Returns an InetAddress representing a resolvable localhost address.
* A non-loopback address is preferred if available.
* An address that resolves to a hostname is preferred among non-loopback addresses.
* IPv4 is preferred over IPv6 among resolving addresses.
*
* @return a localhost address
*/
// Note: Checking resolvability of ipV6 addresses takes a long time on some systems (over 5 seconds
// for some addresses on my mac). This method is written to minimize the number of resolution checks done
// and to defer ip6 checks until necessary.
public static InetAddress getLocalHost() {
InetAddress fallback = InetAddress.getLoopbackAddress();
try {
fallback = InetAddress.getLocalHost();
List<InetAddress> nonLoopback =
getAllLocalFromNetwork().stream().filter(a -> ! a.isLoopbackAddress()).collect(Collectors.toList());
if (nonLoopback.isEmpty()) return fallback;
// Invariant: We got all addresses without exception
List<InetAddress> ipV4 = nonLoopback.stream().filter(a -> a instanceof Inet4Address).collect(Collectors.toList());
for (InetAddress address : ipV4)
if (doesResolve(address))
return address;
// Invariant: There are no resolving ip4 addresses
List<InetAddress> ipV6 = nonLoopback.stream().filter(a -> a instanceof Inet4Address).collect(Collectors.toList());
for (InetAddress address : ipV6)
if (doesResolve(address))
return address;
// Invariant: There are no resolving ip6 addresses either
if (! ipV4.isEmpty()) return ipV4.get(0);
return ipV6.get(0);
} catch (UnknownHostException e) {
return fallback;
}
}
/**
* Returns all local addresses of this host.
*
* @return an array of the addresses of this
* @throws UnknownHostException if we cannot access the network
*/
public static InetAddress[] getAllLocal() throws UnknownHostException {
InetAddress[] localInetAddresses = InetAddress.getAllByName("127.0.0.1");
if ( ! localInetAddresses[0].isLoopbackAddress()) return localInetAddresses;
return getAllLocalFromNetwork().toArray(new InetAddress[0]);
}
/**
* Returns all local addresses of this host.
*
* @return a list of the addresses of this
* @throws UnknownHostException if we cannot access the network
*/
private static List<InetAddress> getAllLocalFromNetwork() throws UnknownHostException {
try {
List<InetAddress> addresses = new ArrayList<>();
for (NetworkInterface networkInterface : Collections.list(NetworkInterface.getNetworkInterfaces()))
addresses.addAll(Collections.list(networkInterface.getInetAddresses()));
return addresses;
}
catch (SocketException ex) {
throw new UnknownHostException("127.0.0.1");
}
}
private static boolean doesResolve(InetAddress address) {
// The latter returns a name if resolvable to one and the host address otherwise
return ! address.getHostAddress().equals(address.getCanonicalHostName());
}
}
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