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Use jndi-dns to obtain default name servers

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Motivation:

Using reflection to obtain the default name servers may fail in Java9 and also in previous Java versions if a SecurityManager is present.

Modifications:

Try using jndi-dns to obtain default name servers and only try using reflection if this fails.

Result:

Be able to detect default name servers in all cases. Fixes [#6347].
This commit is contained in:
Norman Maurer 2017-03-31 08:05:46 +02:00
parent e482d933f7
commit a0fcb72e5d
1 changed files with 46 additions and 13 deletions
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59
resolver-dns/src/main/java/io/netty/resolver/dns/DefaultDnsServerAddressStreamProvider.java
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@ -20,10 +20,17 @@ import io.netty.util.internal.UnstableApi;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
import javax.naming.Context;
import javax.naming.NamingException;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;
import java.lang.reflect.Method;
import java.net.InetSocketAddress;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Hashtable;
import java.util.List;
import static io.netty.resolver.dns.DnsServerAddresses.sequential;
@ -47,22 +54,48 @@ public final class DefaultDnsServerAddressStreamProvider implements DnsServerAdd
static {
final List<InetSocketAddress> defaultNameServers = new ArrayList<InetSocketAddress>(2);
try {
Class<?> configClass = Class.forName("sun.net.dns.ResolverConfiguration");
Method open = configClass.getMethod("open");
Method nameservers = configClass.getMethod("nameservers");
Object instance = open.invoke(null);
@SuppressWarnings("unchecked")
final List<String> list = (List<String>) nameservers.invoke(instance);
for (String a: list) {
if (a != null) {
defaultNameServers.add(new InetSocketAddress(SocketUtils.addressByName(a), DNS_PORT));
// Using jndi-dns to obtain the default name servers.
//
// See:
// - http://docs.oracle.com/javase/8/docs/technotes/guides/jndi/jndi-dns.html
// - http://mail.openjdk.java.net/pipermail/net-dev/2017-March/010695.html
Hashtable<String, String> env = new Hashtable<String, String>();
env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");
env.put("java.naming.provider.url", "dns://");
try {
DirContext ctx = new InitialDirContext(env);
String dnsUrls = (String) ctx.getEnvironment().get("java.naming.provider.url");
String[] servers = dnsUrls.split(" ");
for (String server : servers) {
try {
defaultNameServers.add(SocketUtils.socketAddress(new URI(server).getHost(), DNS_PORT));
} catch (URISyntaxException e) {
logger.debug("Skipping a malformed nameserver URI: {}", server, e);
}
}
} catch (Exception ignore) {
// Failed to get the system name server list.
// Will add the default name servers afterwards.
} catch (NamingException ignore) {
// Will try reflection if this fails.
}
if (defaultNameServers.isEmpty()) {
try {
Class<?> configClass = Class.forName("sun.net.dns.ResolverConfiguration");
Method open = configClass.getMethod("open");
Method nameservers = configClass.getMethod("nameservers");
Object instance = open.invoke(null);
@SuppressWarnings("unchecked")
final List<String> list = (List<String>) nameservers.invoke(instance);
for (String a: list) {
if (a != null) {
defaultNameServers.add(new InetSocketAddress(SocketUtils.addressByName(a), DNS_PORT));
}
}
} catch (Exception ignore) {
// Failed to get the system name server list via reflection.
// Will add the default name servers afterwards.
}
}
if (!defaultNameServers.isEmpty()) {