Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you 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 org.apache.hadoop.net; import com.google.common.net.InetAddresses; import com.sun.istack.Nullable; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import java.net.InetAddress; import java.net.NetworkInterface; import java.net.SocketException; import java.net.UnknownHostException; import java.util.Arrays; import java.util.Collections; import java.util.Enumeration; import java.util.LinkedHashSet; import java.util.List; import java.util.Vector; import javax.naming.NamingException; import javax.naming.directory.Attributes; import javax.naming.directory.DirContext; import javax.naming.directory.InitialDirContext; /** * * A class that provides direct and reverse lookup functionalities, allowing * the querying of specific network interfaces or nameservers. * * */ @InterfaceAudience.LimitedPrivate({ "HDFS", "MapReduce" }) @InterfaceStability.Unstable public class DNS { private static final Logger LOG = LoggerFactory.getLogger(DNS.class); /** * The cached hostname -initially null. */ private static final String cachedHostname = resolveLocalHostname(); private static final String cachedHostAddress = resolveLocalHostIPAddress(); private static final String LOCALHOST = "localhost"; /** * Returns the hostname associated with the specified IP address by the * provided nameserver. * * Loopback addresses * @param hostIp The address to reverse lookup * @param ns The host name of a reachable DNS server * @return The host name associated with the provided IP * @throws NamingException If a NamingException is encountered */ public static String reverseDns(InetAddress hostIp, @Nullable String ns) throws NamingException { // // Builds the reverse IP lookup form // This is formed by reversing the IP numbers and appending in-addr.arpa // String[] parts = hostIp.getHostAddress().split("\\."); String reverseIP = parts[3] + "." + parts[2] + "." + parts[1] + "." + parts[0] + ".in-addr.arpa"; DirContext ictx = new InitialDirContext(); Attributes attribute; try { attribute = ictx.getAttributes("dns://" // Use "dns:///" if the default + ((ns == null) ? "" : ns) + // nameserver is to be used "/" + reverseIP, new String[] { "PTR" }); } finally { ictx.close(); } String hostname = attribute.get("PTR").get().toString(); int hostnameLength = hostname.length(); if (hostname.charAt(hostnameLength - 1) == '.') { hostname = hostname.substring(0, hostnameLength - 1); } return hostname; } /** * @return NetworkInterface for the given subinterface name (eg eth0:0) * or null if no interface with the given name can be found */ private static NetworkInterface getSubinterface(String strInterface) throws SocketException { Enumeration<NetworkInterface> nifs = NetworkInterface.getNetworkInterfaces(); while (nifs.hasMoreElements()) { Enumeration<NetworkInterface> subNifs = nifs.nextElement().getSubInterfaces(); while (subNifs.hasMoreElements()) { NetworkInterface nif = subNifs.nextElement(); if (nif.getName().equals(strInterface)) { return nif; } } } return null; } /** * @param nif network interface to get addresses for * @return set containing addresses for each subinterface of nif, * see below for the rationale for using an ordered set */ private static LinkedHashSet<InetAddress> getSubinterfaceInetAddrs(NetworkInterface nif) { LinkedHashSet<InetAddress> addrs = new LinkedHashSet<InetAddress>(); Enumeration<NetworkInterface> subNifs = nif.getSubInterfaces(); while (subNifs.hasMoreElements()) { NetworkInterface subNif = subNifs.nextElement(); addrs.addAll(Collections.list(subNif.getInetAddresses())); } return addrs; } /** * Like {@link DNS#getIPs(String, boolean), but returns all * IPs associated with the given interface and its subinterfaces. */ public static String[] getIPs(String strInterface) throws UnknownHostException { return getIPs(strInterface, true); } /** * Returns all the IPs associated with the provided interface, if any, in * textual form. * * @param strInterface * The name of the network interface or sub-interface to query * (eg eth0 or eth0:0) or the string "default" * @param returnSubinterfaces * Whether to return IPs associated with subinterfaces of * the given interface * @return A string vector of all the IPs associated with the provided * interface. The local host IP is returned if the interface * name "default" is specified or there is an I/O error looking * for the given interface. * @throws UnknownHostException * If the given interface is invalid * */ public static String[] getIPs(String strInterface, boolean returnSubinterfaces) throws UnknownHostException { if ("default".equals(strInterface)) { return new String[] { cachedHostAddress }; } NetworkInterface netIf; try { netIf = NetworkInterface.getByName(strInterface); if (netIf == null) { netIf = getSubinterface(strInterface); } } catch (SocketException e) { LOG.warn("I/O error finding interface {}", strInterface, e); return new String[] { cachedHostAddress }; } if (netIf == null) { throw new UnknownHostException("No such interface " + strInterface); } // NB: Using a LinkedHashSet to preserve the order for callers // that depend on a particular element being 1st in the array. // For example, getDefaultIP always returns the first element. LinkedHashSet<InetAddress> allAddrs = new LinkedHashSet<InetAddress>(); allAddrs.addAll(Collections.list(netIf.getInetAddresses())); if (!returnSubinterfaces) { allAddrs.removeAll(getSubinterfaceInetAddrs(netIf)); } String ips[] = new String[allAddrs.size()]; int i = 0; for (InetAddress addr : allAddrs) { ips[i++] = addr.getHostAddress(); } return ips; } /** * Returns the first available IP address associated with the provided * network interface or the local host IP if "default" is given. * * @param strInterface * The name of the network interface or subinterface to query * (e.g. eth0 or eth0:0) or the string "default" * @return The IP address in text form, the local host IP is returned * if the interface name "default" is specified * @throws UnknownHostException * If the given interface is invalid */ public static String getDefaultIP(String strInterface) throws UnknownHostException { String[] ips = getIPs(strInterface); return ips[0]; } /** * Returns all the host names associated by the provided nameserver with the * address bound to the specified network interface * * @param strInterface * The name of the network interface or subinterface to query * (e.g. eth0 or eth0:0) * @param nameserver * The DNS host name * @param tryfallbackResolution * if true and if reverse DNS resolution fails then attempt to * resolve the hostname with * {@link InetAddress#getCanonicalHostName()} which includes * hosts file resolution. * @return A string vector of all host names associated with the IPs tied to * the specified interface * @throws UnknownHostException if the given interface is invalid */ public static String[] getHosts(String strInterface, @Nullable String nameserver, boolean tryfallbackResolution) throws UnknownHostException { final List<String> hosts = new Vector<String>(); final List<InetAddress> addresses = getIPsAsInetAddressList(strInterface, true); for (InetAddress address : addresses) { try { hosts.add(reverseDns(address, nameserver)); } catch (NamingException ignored) { } } if (hosts.isEmpty() && tryfallbackResolution) { for (InetAddress address : addresses) { final String canonicalHostName = address.getCanonicalHostName(); // Don't use the result if it looks like an IP address. if (!InetAddresses.isInetAddress(canonicalHostName)) { hosts.add(canonicalHostName); } } } if (hosts.isEmpty()) { LOG.warn("Unable to determine hostname for interface {}", strInterface); hosts.add(cachedHostname); } return hosts.toArray(new String[hosts.size()]); } /** * Determine the local hostname; retrieving it from cache if it is known * If we cannot determine our host name, return "localhost" * @return the local hostname or "localhost" */ private static String resolveLocalHostname() { String localhost; try { localhost = InetAddress.getLocalHost().getCanonicalHostName(); } catch (UnknownHostException e) { LOG.warn("Unable to determine local hostname -falling back to '{}'", LOCALHOST, e); localhost = LOCALHOST; } return localhost; } /** * Get the IPAddress of the local host as a string. * This will be a loop back value if the local host address cannot be * determined. * If the loopback address of "localhost" does not resolve, then the system's * network is in such a state that nothing is going to work. A message is * logged at the error level and a null pointer returned, a pointer * which will trigger failures later on the application * @return the IPAddress of the local host or null for a serious problem. */ private static String resolveLocalHostIPAddress() { String address; try { address = InetAddress.getLocalHost().getHostAddress(); } catch (UnknownHostException e) { LOG.warn("Unable to determine address of the host " + "-falling back to '{}' address", LOCALHOST, e); try { address = InetAddress.getByName(LOCALHOST).getHostAddress(); } catch (UnknownHostException noLocalHostAddressException) { //at this point, deep trouble LOG.error("Unable to determine local loopback address of '{}' " + "-this system's network configuration is unsupported", LOCALHOST, e); address = null; } } return address; } /** * Returns all the host names associated by the default nameserver with the * address bound to the specified network interface * * @param strInterface * The name of the network interface to query (e.g. eth0) * @return The list of host names associated with IPs bound to the network * interface * @throws UnknownHostException * If one is encountered while querying the default interface * */ public static String[] getHosts(String strInterface) throws UnknownHostException { return getHosts(strInterface, null, false); } /** * Returns the default (first) host name associated by the provided * nameserver with the address bound to the specified network interface * * @param strInterface * The name of the network interface to query (e.g. eth0) * @param nameserver * The DNS host name * @return The default host names associated with IPs bound to the network * interface * @throws UnknownHostException * If one is encountered while querying the default interface */ public static String getDefaultHost(@Nullable String strInterface, @Nullable String nameserver, boolean tryfallbackResolution) throws UnknownHostException { if (strInterface == null || "default".equals(strInterface)) { return cachedHostname; } if (nameserver != null && "default".equals(nameserver)) { nameserver = null; } String[] hosts = getHosts(strInterface, nameserver, tryfallbackResolution); return hosts[0]; } /** * Returns the default (first) host name associated by the default * nameserver with the address bound to the specified network interface * * @param strInterface * The name of the network interface to query (e.g. eth0). * Must not be null. * @return The default host name associated with IPs bound to the network * interface * @throws UnknownHostException * If one is encountered while querying the default interface */ public static String getDefaultHost(@Nullable String strInterface) throws UnknownHostException { return getDefaultHost(strInterface, null, false); } /** * Returns the default (first) host name associated by the provided * nameserver with the address bound to the specified network interface. * * @param strInterface * The name of the network interface to query (e.g. eth0) * @param nameserver * The DNS host name * @throws UnknownHostException * If one is encountered while querying the default interface */ public static String getDefaultHost(@Nullable String strInterface, @Nullable String nameserver) throws UnknownHostException { return getDefaultHost(strInterface, nameserver, false); } /** * Returns all the IPs associated with the provided interface, if any, as * a list of InetAddress objects. * * @param strInterface * The name of the network interface or sub-interface to query * (eg eth0 or eth0:0) or the string "default" * @param returnSubinterfaces * Whether to return IPs associated with subinterfaces of * the given interface * @return A list of all the IPs associated with the provided * interface. The local host IP is returned if the interface * name "default" is specified or there is an I/O error looking * for the given interface. * @throws UnknownHostException * If the given interface is invalid * */ public static List<InetAddress> getIPsAsInetAddressList(String strInterface, boolean returnSubinterfaces) throws UnknownHostException { if ("default".equals(strInterface)) { return Arrays.asList(InetAddress.getByName(cachedHostAddress)); } NetworkInterface netIf; try { netIf = NetworkInterface.getByName(strInterface); if (netIf == null) { netIf = getSubinterface(strInterface); } } catch (SocketException e) { LOG.warn("I/O error finding interface {}: {}", strInterface, e.getMessage()); return Arrays.asList(InetAddress.getByName(cachedHostAddress)); } if (netIf == null) { throw new UnknownHostException("No such interface " + strInterface); } // NB: Using a LinkedHashSet to preserve the order for callers // that depend on a particular element being 1st in the array. // For example, getDefaultIP always returns the first element. LinkedHashSet<InetAddress> allAddrs = new LinkedHashSet<InetAddress>(); allAddrs.addAll(Collections.list(netIf.getInetAddresses())); if (!returnSubinterfaces) { allAddrs.removeAll(getSubinterfaceInetAddrs(netIf)); } return new Vector<InetAddress>(allAddrs); } }