/*
* Copyright 2016 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.channel.EventLoop;
import io.netty.handler.codec.dns.DnsRecord;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.UnstableApi;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.TimeUnit;
import static io.netty.util.internal.ObjectUtil.checkNotNull;
import static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
/**
* Default implementation of {@link DnsCache}, backed by a {@link ConcurrentMap}.
* If any additional {@link DnsRecord} is used, no caching takes place.
*/
@UnstableApi
public class DefaultDnsCache implements DnsCache {
private final ConcurrentMap<String, List<DnsCacheEntry>> resolveCache = PlatformDependent.newConcurrentHashMap();
private final int minTtl;
private final int maxTtl;
private final int negativeTtl;
/**
* Create a cache that respects the TTL returned by the DNS server
* and doesn't cache negative responses.
*/
public DefaultDnsCache() {
this(0, Integer.MAX_VALUE, 0);
}
/**
* Create a cache.
* @param minTtl the minimum TTL
* @param maxTtl the maximum TTL
* @param negativeTtl the TTL for failed queries
*/
public DefaultDnsCache(int minTtl, int maxTtl, int negativeTtl) {
this.minTtl = checkPositiveOrZero(minTtl, "minTtl");
this.maxTtl = checkPositiveOrZero(maxTtl, "maxTtl");
if (minTtl > maxTtl) {
throw new IllegalArgumentException(
"minTtl: " + minTtl + ", maxTtl: " + maxTtl + " (expected: 0 <= minTtl <= maxTtl)");
}
this.negativeTtl = checkPositiveOrZero(negativeTtl, "negativeTtl");
}
/**
* Returns the minimum TTL of the cached DNS resource records (in seconds).
*
* @see #maxTtl()
*/
public int minTtl() {
return minTtl;
}
/**
* Returns the maximum TTL of the cached DNS resource records (in seconds).
*
* @see #minTtl()
*/
public int maxTtl() {
return maxTtl;
}
/**
* Returns the TTL of the cache for the failed DNS queries (in seconds). The default value is {@code 0}, which
* disables the cache for negative results.
*/
public int negativeTtl() {
return negativeTtl;
}
@Override
public void clear() {
for (Iterator<Map.Entry<String, List<DnsCacheEntry>>> i = resolveCache.entrySet().iterator(); i.hasNext();) {
final Map.Entry<String, List<DnsCacheEntry>> e = i.next();
i.remove();
cancelExpiration(e.getValue());
}
}
@Override
public boolean clear(String hostname) {
checkNotNull(hostname, "hostname");
boolean removed = false;
for (Iterator<Map.Entry<String, List<DnsCacheEntry>>> i = resolveCache.entrySet().iterator(); i.hasNext();) {
final Map.Entry<String, List<DnsCacheEntry>> e = i.next();
if (e.getKey().equals(hostname)) {
i.remove();
cancelExpiration(e.getValue());
removed = true;
}
}
return removed;
}
private static boolean emptyAdditionals(DnsRecord[] additionals) {
return additionals == null || additionals.length == 0;
}
@Override
public List<DnsCacheEntry> get(String hostname, DnsRecord[] additionals) {
checkNotNull(hostname, "hostname");
if (!emptyAdditionals(additionals)) {
return null;
}
return resolveCache.get(hostname);
}
private List<DnsCacheEntry> cachedEntries(String hostname) {
List<DnsCacheEntry> oldEntries = resolveCache.get(hostname);
final List<DnsCacheEntry> entries;
if (oldEntries == null) {
List<DnsCacheEntry> newEntries = new ArrayList<DnsCacheEntry>(8);
oldEntries = resolveCache.putIfAbsent(hostname, newEntries);
entries = oldEntries != null? oldEntries : newEntries;
} else {
entries = oldEntries;
}
return entries;
}
@Override
public void cache(String hostname, DnsRecord[] additionals,
InetAddress address, long originalTtl, EventLoop loop) {
checkNotNull(hostname, "hostname");
checkNotNull(address, "address");
checkNotNull(loop, "loop");
if (maxTtl == 0 || !emptyAdditionals(additionals)) {
return;
}
final int ttl = Math.max(minTtl, (int) Math.min(maxTtl, originalTtl));
final List<DnsCacheEntry> entries = cachedEntries(hostname);
final DnsCacheEntry e = new DnsCacheEntry(hostname, address);
synchronized (entries) {
if (!entries.isEmpty()) {
final DnsCacheEntry firstEntry = entries.get(0);
if (firstEntry.cause() != null) {
assert entries.size() == 1;
firstEntry.cancelExpiration();
entries.clear();
}
}
entries.add(e);
}
scheduleCacheExpiration(entries, e, ttl, loop);
}
@Override
public void cache(String hostname, DnsRecord[] additionals, Throwable cause, EventLoop loop) {
checkNotNull(hostname, "hostname");
checkNotNull(cause, "cause");
checkNotNull(loop, "loop");
if (negativeTtl == 0 || !emptyAdditionals(additionals)) {
return;
}
final List<DnsCacheEntry> entries = cachedEntries(hostname);
final DnsCacheEntry e = new DnsCacheEntry(hostname, cause);
synchronized (entries) {
final int numEntries = entries.size();
for (int i = 0; i < numEntries; i ++) {
entries.get(i).cancelExpiration();
}
entries.clear();
entries.add(e);
}
scheduleCacheExpiration(entries, e, negativeTtl, loop);
}
private static void cancelExpiration(List<DnsCacheEntry> entries) {
final int numEntries = entries.size();
for (int i = 0; i < numEntries; i++) {
entries.get(i).cancelExpiration();
}
}
private void scheduleCacheExpiration(final List<DnsCacheEntry> entries,
final DnsCacheEntry e,
int ttl,
EventLoop loop) {
e.scheduleExpiration(loop, new Runnable() {
@Override
public void run() {
synchronized (entries) {
entries.remove(e);
if (entries.isEmpty()) {
resolveCache.remove(e.hostname());
}
}
}
}, ttl, TimeUnit.SECONDS);
}
@Override
public String toString() {
return new StringBuilder()
.append("DefaultDnsCache(minTtl=")
.append(minTtl).append(", maxTtl=")
.append(maxTtl).append(", negativeTtl=")
.append(negativeTtl).append(", cached resolved hostname=")
.append(resolveCache.size()).append(")")
.toString();
}
}