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/*
 * Copyright 2017 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.ChannelFuture;
import io.netty.handler.codec.dns.DnsQuestion;
import io.netty.handler.codec.dns.DnsRecordType;
import io.netty.handler.codec.dns.DnsResponseCode;
import io.netty.util.internal.UnstableApi;

import java.net.InetSocketAddress;
import java.util.List;

/**
 * This interface provides visibility into individual DNS queries. The lifecycle of an objects is as follows:
 * 
    *
  1. Object creation
  2. *
  3. {@link #queryCancelled(int)}
  4. *
* OR *
    *
  1. Object creation
  2. *
  3. {@link #queryWritten(InetSocketAddress, ChannelFuture)}
  4. *
  5. {@link #queryRedirected(List)} or {@link #queryCNAMEd(DnsQuestion)} or * {@link #queryNoAnswer(DnsResponseCode)} or {@link #queryCancelled(int)} or * {@link #queryFailed(Throwable)} or {@link #querySucceed()}
  6. *
*

* This interface can be used to track metrics for individual DNS servers. Methods which may lead to another DNS query * return an object of type {@link DnsQueryLifecycleObserver}. Implementations may use this to build a query tree to * understand the "sub queries" generated by a single query. */ @UnstableApi public interface DnsQueryLifecycleObserver { /** * The query has been written. * @param dnsServerAddress The DNS server address which the query was sent to. * @param future The future which represents the status of the write operation for the DNS query. */ void queryWritten(InetSocketAddress dnsServerAddress, ChannelFuture future); /** * The query may have been written but it was cancelled at some point. * @param queriesRemaining The number of queries remaining. */ void queryCancelled(int queriesRemaining); /** * The query has been redirected to another list of DNS servers. * @param nameServers The name servers the query has been redirected to. * @return An observer for the new query which we may issue. */ DnsQueryLifecycleObserver queryRedirected(List nameServers); /** * The query returned a CNAME which we may attempt to follow with a new query. *

* Note that multiple queries may be encountering a CNAME. For example a if both {@link DnsRecordType#AAAA} and * {@link DnsRecordType#A} are supported we may query for both. * @param cnameQuestion the question we would use if we issue a new query. * @return An observer for the new query which we may issue. */ DnsQueryLifecycleObserver queryCNAMEd(DnsQuestion cnameQuestion); /** * The response to the query didn't provide the expected response code, but it didn't return * {@link DnsResponseCode#NXDOMAIN} so we may try to query again. * @param code the unexpected response code. * @return An observer for the new query which we may issue. */ DnsQueryLifecycleObserver queryNoAnswer(DnsResponseCode code); /** * The following criteria are possible: *

    *
  • IO Error
  • *
  • Server responded with an invalid DNS response
  • *
  • Server responded with a valid DNS response, but it didn't progress the resolution
  • *
* @param cause The cause which for the failure. */ void queryFailed(Throwable cause); /** * The query received the expected results. */ void querySucceed(); }




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