io.netty.resolver.dns.DnsNameResolverContext Maven / Gradle / Ivy
/*
* Copyright 2014 The Netty Project
*
* The Netty Project 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 io.netty.resolver.dns;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufHolder;
import io.netty.channel.AddressedEnvelope;
import io.netty.channel.ChannelPromise;
import io.netty.channel.socket.InternetProtocolFamily;
import io.netty.handler.codec.CorruptedFrameException;
import io.netty.handler.codec.dns.DefaultDnsQuestion;
import io.netty.handler.codec.dns.DefaultDnsRecordDecoder;
import io.netty.handler.codec.dns.DnsQuestion;
import io.netty.handler.codec.dns.DnsRawRecord;
import io.netty.handler.codec.dns.DnsRecord;
import io.netty.handler.codec.dns.DnsRecordType;
import io.netty.handler.codec.dns.DnsResponse;
import io.netty.handler.codec.dns.DnsResponseCode;
import io.netty.handler.codec.dns.DnsSection;
import io.netty.util.ReferenceCountUtil;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.FutureListener;
import io.netty.util.concurrent.Promise;
import io.netty.util.internal.ObjectUtil;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.StringUtil;
import io.netty.util.internal.ThrowableUtil;
import java.net.IDN;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;
import static java.lang.Math.min;
import static java.util.Collections.unmodifiableList;
abstract class DnsNameResolverContext {
private static final int INADDRSZ4 = 4;
private static final int INADDRSZ6 = 16;
private static final FutureListener> RELEASE_RESPONSE =
new FutureListener>() {
@Override
public void operationComplete(Future> future) {
if (future.isSuccess()) {
future.getNow().release();
}
}
};
private static final RuntimeException NXDOMAIN_QUERY_FAILED_EXCEPTION = ThrowableUtil.unknownStackTrace(
new RuntimeException("No answer found and NXDOMAIN response code returned"),
DnsNameResolverContext.class,
"onResponse(..)");
private static final RuntimeException CNAME_NOT_FOUND_QUERY_FAILED_EXCEPTION = ThrowableUtil.unknownStackTrace(
new RuntimeException("No matching CNAME record found"),
DnsNameResolverContext.class,
"onResponseCNAME(..)");
private static final RuntimeException NO_MATCHING_RECORD_QUERY_FAILED_EXCEPTION = ThrowableUtil.unknownStackTrace(
new RuntimeException("No matching record type found"),
DnsNameResolverContext.class,
"onResponseAorAAAA(..)");
private static final RuntimeException UNRECOGNIZED_TYPE_QUERY_FAILED_EXCEPTION = ThrowableUtil.unknownStackTrace(
new RuntimeException("Response type was unrecognized"),
DnsNameResolverContext.class,
"onResponse(..)");
private static final RuntimeException NAME_SERVERS_EXHAUSTED_EXCEPTION = ThrowableUtil.unknownStackTrace(
new RuntimeException("No name servers returned an answer"),
DnsNameResolverContext.class,
"tryToFinishResolve(..)");
private final DnsNameResolver parent;
private final DnsServerAddressStream nameServerAddrs;
private final String hostname;
private final DnsCache resolveCache;
private final int maxAllowedQueries;
private final InternetProtocolFamily[] resolvedInternetProtocolFamilies;
private final DnsRecord[] additionals;
private final Set>> queriesInProgress =
Collections.newSetFromMap(
new IdentityHashMap>, Boolean>());
private List resolvedEntries;
private int allowedQueries;
private boolean triedCNAME;
DnsNameResolverContext(DnsNameResolver parent,
String hostname,
DnsRecord[] additionals,
DnsCache resolveCache,
DnsServerAddressStream nameServerAddrs) {
this.parent = parent;
this.hostname = hostname;
this.additionals = additionals;
this.resolveCache = resolveCache;
this.nameServerAddrs = ObjectUtil.checkNotNull(nameServerAddrs, "nameServerAddrs");
maxAllowedQueries = parent.maxQueriesPerResolve();
resolvedInternetProtocolFamilies = parent.resolvedInternetProtocolFamiliesUnsafe();
allowedQueries = maxAllowedQueries;
}
void resolve(final Promise promise) {
if (parent.searchDomains().length == 0 || parent.ndots() == 0 || StringUtil.endsWith(hostname, '.')) {
internalResolve(promise);
} else {
int dots = 0;
for (int idx = hostname.length() - 1; idx >= 0; idx--) {
if (hostname.charAt(idx) == '.' && ++dots >= parent.ndots()) {
internalResolve(promise);
return;
}
}
doSearchDomainQuery(0, new FutureListener() {
private int count = 1;
@Override
public void operationComplete(Future future) throws Exception {
if (future.isSuccess()) {
promise.trySuccess(future.getNow());
} else if (count < parent.searchDomains().length) {
doSearchDomainQuery(count++, this);
} else {
promise.tryFailure(new SearchDomainUnknownHostException(future.cause(), hostname));
}
}
});
}
}
private static final class SearchDomainUnknownHostException extends UnknownHostException {
private static final long serialVersionUID = -8573510133644997085L;
SearchDomainUnknownHostException(Throwable cause, String originalHostname) {
super("Search domain query failed. Original hostname: '" + originalHostname + "' " + cause.getMessage());
setStackTrace(cause.getStackTrace());
}
@Override
public Throwable fillInStackTrace() {
return this;
}
}
private void doSearchDomainQuery(int count, FutureListener listener) {
DnsNameResolverContext nextContext = newResolverContext(parent,
hostname + '.' + parent.searchDomains()[count],
additionals,
resolveCache,
nameServerAddrs);
Promise nextPromise = parent.executor().newPromise();
nextContext.internalResolve(nextPromise);
nextPromise.addListener(listener);
}
private void internalResolve(Promise promise) {
DnsServerAddressStream nameServerAddressStream = getNameServers(hostname);
DnsRecordType[] recordTypes = parent.resolveRecordTypes();
assert recordTypes.length > 0;
final int end = recordTypes.length - 1;
for (int i = 0; i < end; ++i) {
if (!query(hostname, recordTypes[i], nameServerAddressStream.duplicate(), promise)) {
return;
}
}
query(hostname, recordTypes[end], nameServerAddressStream, promise);
}
/**
* Add an authoritative nameserver to the cache if its not a root server.
*/
private void addNameServerToCache(
AuthoritativeNameServer name, InetAddress resolved, long ttl) {
if (!name.isRootServer()) {
// Cache NS record if not for a root server as we should never cache for root servers.
parent.authoritativeDnsServerCache().cache(name.domainName(),
additionals, resolved, ttl, parent.ch.eventLoop());
}
}
/**
* Returns the {@link DnsServerAddressStream} that was cached for the given hostname or {@code null} if non
* could be found.
*/
private DnsServerAddressStream getNameServersFromCache(String hostname) {
int len = hostname.length();
if (len == 0) {
// We never cache for root servers.
return null;
}
// We always store in the cache with a trailing '.'.
if (hostname.charAt(len - 1) != '.') {
hostname += ".";
}
int idx = hostname.indexOf('.');
if (idx == hostname.length() - 1) {
// We are not interested in handling '.' as we should never serve the root servers from cache.
return null;
}
// We start from the closed match and then move down.
for (;;) {
// Skip '.' as well.
hostname = hostname.substring(idx + 1);
int idx2 = hostname.indexOf('.');
if (idx2 <= 0 || idx2 == hostname.length() - 1) {
// We are not interested in handling '.TLD.' as we should never serve the root servers from cache.
return null;
}
idx = idx2;
List entries = parent.authoritativeDnsServerCache().get(hostname, additionals);
if (entries != null && !entries.isEmpty()) {
return DnsServerAddresses.sequential(new DnsCacheIterable(entries)).stream();
}
}
}
private final class DnsCacheIterable implements Iterable {
private final List entries;
DnsCacheIterable(List entries) {
this.entries = entries;
}
@Override
public Iterator iterator() {
return new Iterator() {
Iterator entryIterator = entries.iterator();
@Override
public boolean hasNext() {
return entryIterator.hasNext();
}
@Override
public InetSocketAddress next() {
InetAddress address = entryIterator.next().address();
return new InetSocketAddress(address, parent.dnsRedirectPort(address));
}
@Override
public void remove() {
entryIterator.remove();
}
};
}
}
private void query(final DnsServerAddressStream nameServerAddrStream, final int nameServerAddrStreamIndex,
final DnsQuestion question,
final Promise promise) {
query(nameServerAddrStream, nameServerAddrStreamIndex, question,
parent.dnsQueryLifecycleObserverFactory().newDnsQueryLifecycleObserver(question), promise);
}
private void query(final DnsServerAddressStream nameServerAddrStream,
final int nameServerAddrStreamIndex,
final DnsQuestion question,
final DnsQueryLifecycleObserver queryLifecycleObserver,
final Promise promise) {
if (nameServerAddrStreamIndex >= nameServerAddrStream.size() || allowedQueries == 0 || promise.isCancelled()) {
tryToFinishResolve(nameServerAddrStream, nameServerAddrStreamIndex, question, queryLifecycleObserver,
promise);
return;
}
--allowedQueries;
final InetSocketAddress nameServerAddr = nameServerAddrStream.next();
final ChannelPromise writePromise = parent.ch.newPromise();
final Future> f = parent.query0(
nameServerAddr, question, additionals, writePromise,
parent.ch.eventLoop().>newPromise());
queriesInProgress.add(f);
queryLifecycleObserver.queryWritten(nameServerAddr, writePromise);
f.addListener(new FutureListener>() {
@Override
public void operationComplete(Future> future) {
queriesInProgress.remove(future);
if (promise.isDone() || future.isCancelled()) {
queryLifecycleObserver.queryCancelled(allowedQueries);
return;
}
try {
if (future.isSuccess()) {
onResponse(nameServerAddrStream, nameServerAddrStreamIndex, question, future.getNow(),
queryLifecycleObserver, promise);
} else {
// Server did not respond or I/O error occurred; try again.
queryLifecycleObserver.queryFailed(future.cause());
query(nameServerAddrStream, nameServerAddrStreamIndex + 1, question, promise);
}
} finally {
tryToFinishResolve(nameServerAddrStream, nameServerAddrStreamIndex, question,
// queryLifecycleObserver has already been terminated at this point so we must
// not allow it to be terminated again by tryToFinishResolve.
NoopDnsQueryLifecycleObserver.INSTANCE,
promise);
}
}
});
}
void onResponse(final DnsServerAddressStream nameServerAddrStream, final int nameServerAddrStreamIndex,
final DnsQuestion question, AddressedEnvelope envelope,
final DnsQueryLifecycleObserver queryLifecycleObserver,
Promise promise) {
try {
final DnsResponse res = envelope.content();
final DnsResponseCode code = res.code();
if (code == DnsResponseCode.NOERROR) {
if (handleRedirect(question, envelope, queryLifecycleObserver, promise)) {
// Was a redirect so return here as everything else is handled in handleRedirect(...)
return;
}
final DnsRecordType type = question.type();
if (type == DnsRecordType.A || type == DnsRecordType.AAAA) {
onResponseAorAAAA(type, question, envelope, queryLifecycleObserver, promise);
} else if (type == DnsRecordType.CNAME) {
onResponseCNAME(question, envelope, queryLifecycleObserver, promise);
} else {
queryLifecycleObserver.queryFailed(UNRECOGNIZED_TYPE_QUERY_FAILED_EXCEPTION);
}
return;
}
// Retry with the next server if the server did not tell us that the domain does not exist.
if (code != DnsResponseCode.NXDOMAIN) {
query(nameServerAddrStream, nameServerAddrStreamIndex + 1, question,
queryLifecycleObserver.queryNoAnswer(code), promise);
} else {
queryLifecycleObserver.queryFailed(NXDOMAIN_QUERY_FAILED_EXCEPTION);
}
} finally {
ReferenceCountUtil.safeRelease(envelope);
}
}
/**
* Handles a redirect answer if needed and returns {@code true} if a redirect query has been made.
*/
private boolean handleRedirect(
DnsQuestion question, AddressedEnvelope envelope,
final DnsQueryLifecycleObserver queryLifecycleObserver, Promise promise) {
final DnsResponse res = envelope.content();
// Check if we have answers, if not this may be an non authority NS and so redirects must be handled.
if (res.count(DnsSection.ANSWER) == 0) {
AuthoritativeNameServerList serverNames = extractAuthoritativeNameServers(question.name(), res);
if (serverNames != null) {
List nameServers = new ArrayList(serverNames.size());
int additionalCount = res.count(DnsSection.ADDITIONAL);
for (int i = 0; i < additionalCount; i++) {
final DnsRecord r = res.recordAt(DnsSection.ADDITIONAL, i);
if (r.type() == DnsRecordType.A && !parent.supportsARecords() ||
r.type() == DnsRecordType.AAAA && !parent.supportsAAAARecords()) {
continue;
}
final String recordName = r.name();
AuthoritativeNameServer authoritativeNameServer =
serverNames.remove(recordName);
if (authoritativeNameServer == null) {
// Not a server we are interested in.
continue;
}
InetAddress resolved = parseAddress(r, recordName);
if (resolved == null) {
// Could not parse it, move to the next.
continue;
}
nameServers.add(new InetSocketAddress(resolved, parent.dnsRedirectPort(resolved)));
addNameServerToCache(authoritativeNameServer, resolved, r.timeToLive());
}
if (!nameServers.isEmpty()) {
query(parent.uncachedRedirectDnsServerStream(nameServers), 0, question,
queryLifecycleObserver.queryRedirected(unmodifiableList(nameServers)), promise);
return true;
}
}
}
return false;
}
/**
* Returns the {@code {@link AuthoritativeNameServerList} which were included in {@link DnsSection#AUTHORITY}
* or {@code null} if non are found.
*/
private static AuthoritativeNameServerList extractAuthoritativeNameServers(String questionName, DnsResponse res) {
int authorityCount = res.count(DnsSection.AUTHORITY);
if (authorityCount == 0) {
return null;
}
AuthoritativeNameServerList serverNames = new AuthoritativeNameServerList(questionName);
for (int i = 0; i < authorityCount; i++) {
serverNames.add(res.recordAt(DnsSection.AUTHORITY, i));
}
return serverNames;
}
private void onResponseAorAAAA(
DnsRecordType qType, DnsQuestion question, AddressedEnvelope envelope,
final DnsQueryLifecycleObserver queryLifecycleObserver,
Promise promise) {
// We often get a bunch of CNAMES as well when we asked for A/AAAA.
final DnsResponse response = envelope.content();
final Map cnames = buildAliasMap(response);
final int answerCount = response.count(DnsSection.ANSWER);
boolean found = false;
for (int i = 0; i < answerCount; i ++) {
final DnsRecord r = response.recordAt(DnsSection.ANSWER, i);
final DnsRecordType type = r.type();
if (type != DnsRecordType.A && type != DnsRecordType.AAAA) {
continue;
}
final String questionName = question.name().toLowerCase(Locale.US);
final String recordName = r.name().toLowerCase(Locale.US);
// Make sure the record is for the questioned domain.
if (!recordName.equals(questionName)) {
// Even if the record's name is not exactly same, it might be an alias defined in the CNAME records.
String resolved = questionName;
do {
resolved = cnames.get(resolved);
if (recordName.equals(resolved)) {
break;
}
} while (resolved != null);
if (resolved == null) {
continue;
}
}
InetAddress resolved = parseAddress(r, hostname);
if (resolved == null) {
continue;
}
if (resolvedEntries == null) {
resolvedEntries = new ArrayList(8);
}
resolvedEntries.add(
resolveCache.cache(hostname, additionals, resolved, r.timeToLive(), parent.ch.eventLoop()));
found = true;
// Note that we do not break from the loop here, so we decode/cache all A/AAAA records.
}
if (found) {
queryLifecycleObserver.querySucceed();
return;
}
if (cnames.isEmpty()) {
queryLifecycleObserver.queryFailed(NO_MATCHING_RECORD_QUERY_FAILED_EXCEPTION);
} else {
// We asked for A/AAAA but we got only CNAME.
onResponseCNAME(question, envelope, cnames, queryLifecycleObserver, promise);
}
}
private InetAddress parseAddress(DnsRecord r, String name) {
if (!(r instanceof DnsRawRecord)) {
return null;
}
final ByteBuf content = ((ByteBufHolder) r).content();
final int contentLen = content.readableBytes();
if (contentLen != INADDRSZ4 && contentLen != INADDRSZ6) {
return null;
}
final byte[] addrBytes = new byte[contentLen];
content.getBytes(content.readerIndex(), addrBytes);
try {
return InetAddress.getByAddress(
parent.isDecodeIdn() ? IDN.toUnicode(name) : name, addrBytes);
} catch (UnknownHostException e) {
// Should never reach here.
throw new Error(e);
}
}
private void onResponseCNAME(DnsQuestion question, AddressedEnvelope envelope,
final DnsQueryLifecycleObserver queryLifecycleObserver,
Promise promise) {
onResponseCNAME(question, envelope, buildAliasMap(envelope.content()), queryLifecycleObserver, promise);
}
private void onResponseCNAME(
DnsQuestion question, AddressedEnvelope response,
Map cnames, final DnsQueryLifecycleObserver queryLifecycleObserver,
Promise promise) {
// Resolve the host name in the question into the real host name.
final String name = question.name().toLowerCase(Locale.US);
String resolved = name;
boolean found = false;
while (!cnames.isEmpty()) { // Do not attempt to call Map.remove() when the Map is empty
// because it can be Collections.emptyMap()
// whose remove() throws a UnsupportedOperationException.
final String next = cnames.remove(resolved);
if (next != null) {
found = true;
resolved = next;
} else {
break;
}
}
if (found) {
followCname(resolved, queryLifecycleObserver, promise);
} else {
queryLifecycleObserver.queryFailed(CNAME_NOT_FOUND_QUERY_FAILED_EXCEPTION);
}
}
private static Map buildAliasMap(DnsResponse response) {
final int answerCount = response.count(DnsSection.ANSWER);
Map cnames = null;
for (int i = 0; i < answerCount; i ++) {
final DnsRecord r = response.recordAt(DnsSection.ANSWER, i);
final DnsRecordType type = r.type();
if (type != DnsRecordType.CNAME) {
continue;
}
if (!(r instanceof DnsRawRecord)) {
continue;
}
final ByteBuf recordContent = ((ByteBufHolder) r).content();
final String domainName = decodeDomainName(recordContent);
if (domainName == null) {
continue;
}
if (cnames == null) {
cnames = new HashMap(min(8, answerCount));
}
cnames.put(r.name().toLowerCase(Locale.US), domainName.toLowerCase(Locale.US));
}
return cnames != null? cnames : Collections.emptyMap();
}
void tryToFinishResolve(final DnsServerAddressStream nameServerAddrStream,
final int nameServerAddrStreamIndex,
final DnsQuestion question,
final DnsQueryLifecycleObserver queryLifecycleObserver,
final Promise promise) {
// There are no queries left to try.
if (!queriesInProgress.isEmpty()) {
queryLifecycleObserver.queryCancelled(allowedQueries);
// There are still some queries we did not receive responses for.
if (gotPreferredAddress()) {
// But it's OK to finish the resolution process if we got a resolved address of the preferred type.
finishResolve(promise);
}
// We did not get any resolved address of the preferred type, so we can't finish the resolution process.
return;
}
// There are no queries left to try.
if (resolvedEntries == null) {
if (nameServerAddrStreamIndex < nameServerAddrStream.size()) {
if (queryLifecycleObserver == NoopDnsQueryLifecycleObserver.INSTANCE) {
// If the queryLifecycleObserver has already been terminated we should create a new one for this
// fresh query.
query(nameServerAddrStream, nameServerAddrStreamIndex + 1, question, promise);
} else {
query(nameServerAddrStream, nameServerAddrStreamIndex + 1, question, queryLifecycleObserver,
promise);
}
return;
}
queryLifecycleObserver.queryFailed(NAME_SERVERS_EXHAUSTED_EXCEPTION);
// .. and we could not find any A/AAAA records.
if (!triedCNAME) {
// As the last resort, try to query CNAME, just in case the name server has it.
triedCNAME = true;
query(hostname, DnsRecordType.CNAME, getNameServers(hostname), promise);
return;
}
} else {
queryLifecycleObserver.queryCancelled(allowedQueries);
}
// We have at least one resolved address or tried CNAME as the last resort..
finishResolve(promise);
}
private boolean gotPreferredAddress() {
if (resolvedEntries == null) {
return false;
}
final int size = resolvedEntries.size();
final Class inetAddressType = parent.preferredAddressType().addressType();
for (int i = 0; i < size; i++) {
InetAddress address = resolvedEntries.get(i).address();
if (inetAddressType.isInstance(address)) {
return true;
}
}
return false;
}
private void finishResolve(Promise promise) {
if (!queriesInProgress.isEmpty()) {
// If there are queries in progress, we should cancel it because we already finished the resolution.
for (Iterator>> i = queriesInProgress.iterator();
i.hasNext();) {
Future> f = i.next();
i.remove();
if (!f.cancel(false)) {
f.addListener(RELEASE_RESPONSE);
}
}
}
if (resolvedEntries != null) {
// Found at least one resolved address.
for (InternetProtocolFamily f: resolvedInternetProtocolFamilies) {
if (finishResolve(f.addressType(), resolvedEntries, promise)) {
return;
}
}
}
// No resolved address found.
final int tries = maxAllowedQueries - allowedQueries;
final StringBuilder buf = new StringBuilder(64);
buf.append("failed to resolve '").append(hostname).append('\'');
if (tries > 1) {
if (tries < maxAllowedQueries) {
buf.append(" after ")
.append(tries)
.append(" queries ");
} else {
buf.append(". Exceeded max queries per resolve ")
.append(maxAllowedQueries)
.append(' ');
}
}
final UnknownHostException cause = new UnknownHostException(buf.toString());
resolveCache.cache(hostname, additionals, cause, parent.ch.eventLoop());
promise.tryFailure(cause);
}
abstract boolean finishResolve(Class addressType, List resolvedEntries,
Promise promise);
abstract DnsNameResolverContext newResolverContext(DnsNameResolver parent, String hostname,
DnsRecord[] additionals, DnsCache resolveCache,
DnsServerAddressStream nameServerAddrs);
static String decodeDomainName(ByteBuf in) {
in.markReaderIndex();
try {
return DefaultDnsRecordDecoder.decodeName(in);
} catch (CorruptedFrameException e) {
// In this case we just return null.
return null;
} finally {
in.resetReaderIndex();
}
}
private DnsServerAddressStream getNameServers(String hostname) {
DnsServerAddressStream stream = getNameServersFromCache(hostname);
return stream == null ? nameServerAddrs : stream;
}
private void followCname(String cname, final DnsQueryLifecycleObserver queryLifecycleObserver, Promise promise) {
// Use the same server for both CNAME queries
DnsServerAddressStream stream = DnsServerAddresses.singleton(getNameServers(cname).next()).stream();
DnsQuestion cnameQuestion = null;
if (parent.supportsARecords()) {
try {
if ((cnameQuestion = newQuestion(cname, DnsRecordType.A)) == null) {
return;
}
} catch (Throwable cause) {
queryLifecycleObserver.queryFailed(cause);
PlatformDependent.throwException(cause);
}
query(stream, 0, cnameQuestion, queryLifecycleObserver.queryCNAMEd(cnameQuestion), promise);
}
if (parent.supportsAAAARecords()) {
try {
if ((cnameQuestion = newQuestion(cname, DnsRecordType.AAAA)) == null) {
return;
}
} catch (Throwable cause) {
queryLifecycleObserver.queryFailed(cause);
PlatformDependent.throwException(cause);
}
query(stream, 0, cnameQuestion, queryLifecycleObserver.queryCNAMEd(cnameQuestion), promise);
}
}
private boolean query(String hostname, DnsRecordType type, DnsServerAddressStream dnsServerAddressStream,
Promise promise) {
final DnsQuestion question = newQuestion(hostname, type);
if (question == null) {
return false;
}
query(dnsServerAddressStream, 0, question, promise);
return true;
}
private static DnsQuestion newQuestion(String hostname, DnsRecordType type) {
try {
return new DefaultDnsQuestion(hostname, type);
} catch (IllegalArgumentException e) {
// java.net.IDN.toASCII(...) may throw an IllegalArgumentException if it fails to parse the hostname
return null;
}
}
/**
* Holds the closed DNS Servers for a domain.
*/
private static final class AuthoritativeNameServerList {
private final String questionName;
// We not expect the linked-list to be very long so a double-linked-list is overkill.
private AuthoritativeNameServer head;
private int count;
AuthoritativeNameServerList(String questionName) {
this.questionName = questionName.toLowerCase(Locale.US);
}
void add(DnsRecord r) {
if (r.type() != DnsRecordType.NS || !(r instanceof DnsRawRecord)) {
return;
}
// Only include servers that serve the correct domain.
if (questionName.length() < r.name().length()) {
return;
}
String recordName = r.name().toLowerCase(Locale.US);
int dots = 0;
for (int a = recordName.length() - 1, b = questionName.length() - 1; a >= 0; a--, b--) {
char c = recordName.charAt(a);
if (questionName.charAt(b) != c) {
return;
}
if (c == '.') {
dots++;
}
}
if (head != null && head.dots > dots) {
// We already have a closer match so ignore this one, no need to parse the domainName etc.
return;
}
final ByteBuf recordContent = ((ByteBufHolder) r).content();
final String domainName = decodeDomainName(recordContent);
if (domainName == null) {
// Could not be parsed, ignore.
return;
}
// We are only interested in preserving the nameservers which are the closest to our qName, so ensure
// we drop servers that have a smaller dots count.
if (head == null || head.dots < dots) {
count = 1;
head = new AuthoritativeNameServer(dots, recordName, domainName);
} else if (head.dots == dots) {
AuthoritativeNameServer serverName = head;
while (serverName.next != null) {
serverName = serverName.next;
}
serverName.next = new AuthoritativeNameServer(dots, recordName, domainName);
count++;
}
}
// Just walk the linked-list and mark the entry as removed when matched, so next lookup will need to process
// one node less.
AuthoritativeNameServer remove(String nsName) {
AuthoritativeNameServer serverName = head;
while (serverName != null) {
if (!serverName.removed && serverName.nsName.equalsIgnoreCase(nsName)) {
serverName.removed = true;
return serverName;
}
serverName = serverName.next;
}
return null;
}
int size() {
return count;
}
}
static final class AuthoritativeNameServer {
final int dots;
final String nsName;
final String domainName;
AuthoritativeNameServer next;
boolean removed;
AuthoritativeNameServer(int dots, String domainName, String nsName) {
this.dots = dots;
this.nsName = nsName;
this.domainName = domainName;
}
/**
* Returns {@code true} if its a root server.
*/
boolean isRootServer() {
return dots == 1;
}
/**
* The domain for which the {@link AuthoritativeNameServer} is responsible.
*/
String domainName() {
return domainName;
}
}
}
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