/*
* Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package jdk.dns.conf;
import jdk.dns.client.internal.util.ReloadTracker;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.nio.file.Paths;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedExceptionAction;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.StringTokenizer;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/*
* An implementation of DnsResolverConfiguration for Solaris
* and Linux.
*/
public class DnsResolverConfiguration {
public static String getDefaultHostsFileLocation() {
return "/etc/hosts";
}
// Lock held whilst loading configuration or checking
private static final ReadWriteLock LOCK = new ReentrantReadWriteLock();
//
private static String RESOLV_CONF_LOCATION = java.security.AccessController.doPrivileged(
(PrivilegedAction<String>) () -> System.getProperty("jdk.dns.client.resolv.conf", "/etc/resolv.conf"));
private static final ReloadTracker RESOLVE_CONF_TRACKER;
// Cache timeout (300 seconds) in nano seconds - should be converted into property
// or configured as preference in the future.
private static final long TIMEOUT = 300_000_000_000L;
// Parse /etc/resolv.conf to get the values for a particular
// keyword.
//
private List<String> resolvconf(String keyword,
int maxperkeyword,
int maxkeywords) {
LinkedList<String> ll = new LinkedList<>();
try {
BufferedReader in =
new BufferedReader(new FileReader(RESOLV_CONF_LOCATION));
String line;
while ((line = in.readLine()) != null) {
int maxvalues = maxperkeyword;
if (line.isEmpty())
continue;
if (line.charAt(0) == '#' || line.charAt(0) == ';')
continue;
if (!line.startsWith(keyword))
continue;
String value = line.substring(keyword.length());
if (value.isEmpty())
continue;
if (value.charAt(0) != ' ' && value.charAt(0) != '\t')
continue;
StringTokenizer st = new StringTokenizer(value, " \t");
while (st.hasMoreTokens()) {
String val = st.nextToken();
if (val.charAt(0) == '#' || val.charAt(0) == ';') {
break;
}
if ("nameserver".equals(keyword)) {
if (val.indexOf(':') >= 0 &&
val.indexOf('.') < 0 && // skip for IPv4 literals with port
val.indexOf('[') < 0 &&
val.indexOf(']') < 0) {
// IPv6 literal, in non-BSD-style.
val = "[" + val + "]";
}
}
ll.add(val);
if (--maxvalues == 0) {
break;
}
}
if (--maxkeywords == 0) {
break;
}
}
in.close();
} catch (IOException ioe) {
// problem reading value
}
return Collections.unmodifiableList(ll);
}
private volatile List<String> searchlist = Collections.emptyList();
private volatile List<String> nameservers = Collections.emptyList();
private volatile String domain = "";
// Load DNS configuration from OS
private void loadConfig() {
LOCK.readLock().lock();
try {
var rs = RESOLVE_CONF_TRACKER.getReloadStatus();
if (!rs.isReloadNeeded() || !rs.isFileExists()) {
return;
}
} finally {
LOCK.readLock().unlock();
}
LOCK.writeLock().lock();
try {
var rs = RESOLVE_CONF_TRACKER.getReloadStatus();
// Check if reload is needed again
if (rs.isReloadNeeded()) {
if (rs.isFileExists()) {
// get the name servers from /etc/resolv.conf
nameservers =
java.security.AccessController.doPrivileged(
(PrivilegedAction<List<String>>) () -> {
// typically MAXNS is 3 but we've picked 5 here
// to allow for additional servers if required.
return resolvconf("nameserver", 1, 5);
});
// get the search list (or domain)
searchlist = getSearchList();
// update the timestamp on the configuration
RESOLVE_CONF_TRACKER.updateTimestamps(rs);
} else {
nameservers = Collections.emptyList();
searchlist = Collections.emptyList();
}
}
} finally {
LOCK.writeLock().unlock();
}
}
// obtain search list or local domain
private List<String> getSearchList() {
List<String> sl;
// first try the search keyword in /etc/resolv.conf
/* run */
sl = java.security.AccessController.doPrivileged(
(PrivilegedAction<List<String>>) () -> {
List<String> ll;
// first try search keyword (max 6 domains)
ll = resolvconf("search", 6, 1);
if (ll.size() > 0) {
domain = ll.get(0);
return ll;
}
return null;
});
if (sl != null) {
return sl;
}
// No search keyword so use local domain
// LOCALDOMAIN has absolute priority on Solaris
String localDomain = localDomain0();
if (localDomain != null && !localDomain.isEmpty()) {
sl = new LinkedList<>();
sl.add(localDomain);
return Collections.unmodifiableList(sl);
}
// try domain keyword in /etc/resolv.conf
/* run */
sl = java.security.AccessController.doPrivileged(
(PrivilegedAction<List<String>>) () -> {
List<String> ll;
ll = resolvconf("domain", 1, 1);
if (ll.size() > 0) {
domain = ll.get(0);
return ll;
}
return null;
});
if (sl != null) {
// sl is already UnmodifiableList
return sl;
}
// no local domain so try fallback (RPC) domain or
// hostName
sl = new LinkedList<>();
String domain = fallbackDomain0();
if (domain != null && !domain.isEmpty()) {
sl.add(domain);
}
return Collections.unmodifiableList(sl);
}
// ----
public DnsResolverConfiguration() {
}
@SuppressWarnings("unchecked")
public List<String> searchlist() {
loadConfig();
// List is unmodifiable
return searchlist;
}
@SuppressWarnings("unchecked")
public List<String> nameservers() {
loadConfig();
// List is unmodifiable
return nameservers;
}
public String domain() {
loadConfig();
return domain;
}
// --- Native methods --
static native String localDomain0();
static native String fallbackDomain0();
static {
var pa = (PrivilegedAction<Void>) () -> {
System.loadLibrary("resolver");
return null;
};
if (System.getSecurityManager() == null) {
pa.run();
} else {
AccessController.doPrivileged(pa);
}
var pea = (PrivilegedExceptionAction<ReloadTracker>) () ->
ReloadTracker.newInstance(Paths.get(RESOLV_CONF_LOCATION), TIMEOUT);
// TODO: Revisit
try {
RESOLVE_CONF_TRACKER = System.getSecurityManager() == null ? pea.run()
: AccessController.doPrivileged(pea);
} catch (Exception e) {
throw new RuntimeException("Can't instantiate resolver configuration file tracker", e);
}
}
}