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Easy Redis Java client and Real-Time Data Platform. Valkey compatible. Sync/Async/RxJava3/Reactive API. Client side caching. Over 50 Redis based Java objects and services: JCache API, Apache Tomcat, Hibernate, Spring, Set, Multimap, SortedSet, Map, List, Queue, Deque, Semaphore, Lock, AtomicLong, Map Reduce, Bloom filter, Scheduler, RPC

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/*
 * Copyright 2015 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:
 *
 *   https://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;

import io.netty.util.CharsetUtil;
import io.netty.util.internal.PlatformDependent;

import java.net.InetAddress;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
import java.util.Map;

/**
 * Default {@link HostsFileEntriesResolver} that resolves hosts file entries only once.
 */
public final class DefaultHostsFileEntriesResolver implements HostsFileEntriesResolver {

    private final Map> inet4Entries;
    private final Map> inet6Entries;

    public DefaultHostsFileEntriesResolver() {
        this(parseEntries());
    }

    // for testing purpose only
    DefaultHostsFileEntriesResolver(HostsFileEntriesProvider entries) {
        inet4Entries = entries.ipv4Entries();
        inet6Entries = entries.ipv6Entries();
    }

    @Override
    public InetAddress address(String inetHost, ResolvedAddressTypes resolvedAddressTypes) {
        String normalized = normalize(inetHost);
        switch (resolvedAddressTypes) {
            case IPV4_ONLY:
                return firstAddress(inet4Entries.get(normalized));
            case IPV6_ONLY:
                return firstAddress(inet6Entries.get(normalized));
            case IPV4_PREFERRED:
                InetAddress inet4Address = firstAddress(inet4Entries.get(normalized));
                return inet4Address != null ? inet4Address : firstAddress(inet6Entries.get(normalized));
            case IPV6_PREFERRED:
                InetAddress inet6Address = firstAddress(inet6Entries.get(normalized));
                return inet6Address != null ? inet6Address : firstAddress(inet4Entries.get(normalized));
            default:
                throw new IllegalArgumentException("Unknown ResolvedAddressTypes " + resolvedAddressTypes);
        }
    }

    /**
     * Resolves all addresses of a hostname against the entries in a hosts file, depending on the specified
     * {@link ResolvedAddressTypes}.
     *
     * @param inetHost the hostname to resolve
     * @param resolvedAddressTypes the address types to resolve
     * @return all matching addresses or {@code null} in case the hostname cannot be resolved
     */
    public List addresses(String inetHost, ResolvedAddressTypes resolvedAddressTypes) {
        String normalized = normalize(inetHost);
        switch (resolvedAddressTypes) {
            case IPV4_ONLY:
                return inet4Entries.get(normalized);
            case IPV6_ONLY:
                return inet6Entries.get(normalized);
            case IPV4_PREFERRED:
                List allInet4Addresses = inet4Entries.get(normalized);
                return allInet4Addresses != null ? allAddresses(allInet4Addresses, inet6Entries.get(normalized)) :
                        inet6Entries.get(normalized);
            case IPV6_PREFERRED:
                List allInet6Addresses = inet6Entries.get(normalized);
                return allInet6Addresses != null ? allAddresses(allInet6Addresses, inet4Entries.get(normalized)) :
                        inet4Entries.get(normalized);
            default:
                throw new IllegalArgumentException("Unknown ResolvedAddressTypes " + resolvedAddressTypes);
        }
    }

    // package-private for testing purposes
    String normalize(String inetHost) {
        return inetHost.toLowerCase(Locale.ENGLISH);
    }

    private static List allAddresses(List a, List b) {
        List result = new ArrayList(a.size() + (b == null ? 0 : b.size()));
        result.addAll(a);
        if (b != null) {
            result.addAll(b);
        }
        return result;
    }

    private static InetAddress firstAddress(List addresses) {
        return addresses != null && !addresses.isEmpty() ? addresses.get(0) : null;
    }

    private static HostsFileEntriesProvider parseEntries() {
        if (PlatformDependent.isWindows()) {
            // Ony windows there seems to be no standard for the encoding used for the hosts file, so let us
            // try multiple until we either were able to parse it or there is none left and so we return an
            // empty instance.
            return HostsFileEntriesProvider.parser()
                    .parseSilently(Charset.defaultCharset(), CharsetUtil.UTF_16, CharsetUtil.UTF_8);
        }
        return HostsFileEntriesProvider.parser().parseSilently();
    }
}