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The Async Http Client (AHC) classes.
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/*
 *    Copyright (c) 2015-2023 AsyncHttpClient Project. All rights reserved.
 *
 *    Licensed 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 org.asynchttpclient.resolver;

import io.netty.resolver.NameResolver;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.ImmediateEventExecutor;
import io.netty.util.concurrent.Promise;
import org.asynchttpclient.AsyncHandler;
import org.asynchttpclient.netty.SimpleFutureListener;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

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

public enum RequestHostnameResolver {

    INSTANCE;

    private static final Logger LOGGER = LoggerFactory.getLogger(RequestHostnameResolver.class);

    public Future> resolve(NameResolver nameResolver, InetSocketAddress unresolvedAddress, AsyncHandler asyncHandler) {
        final String hostname = unresolvedAddress.getHostString();
        final int port = unresolvedAddress.getPort();
        final Promise> promise = ImmediateEventExecutor.INSTANCE.newPromise();

        try {
            asyncHandler.onHostnameResolutionAttempt(hostname);
        } catch (Exception e) {
            LOGGER.error("onHostnameResolutionAttempt crashed", e);
            promise.tryFailure(e);
            return promise;
        }

        final Future> whenResolved = nameResolver.resolveAll(hostname);

        whenResolved.addListener(new SimpleFutureListener>() {

            @Override
            protected void onSuccess(List value) {
                ArrayList socketAddresses = new ArrayList<>(value.size());
                for (InetAddress a : value) {
                    socketAddresses.add(new InetSocketAddress(a, port));
                }
                try {
                    asyncHandler.onHostnameResolutionSuccess(hostname, socketAddresses);
                } catch (Exception e) {
                    LOGGER.error("onHostnameResolutionSuccess crashed", e);
                    promise.tryFailure(e);
                    return;
                }
                promise.trySuccess(socketAddresses);
            }

            @Override
            protected void onFailure(Throwable t) {
                try {
                    asyncHandler.onHostnameResolutionFailure(hostname, t);
                } catch (Exception e) {
                    LOGGER.error("onHostnameResolutionFailure crashed", e);
                    promise.tryFailure(e);
                    return;
                }
                promise.tryFailure(t);
            }
        });

        return promise;
    }
}