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RESTHeart Commons - Common classes for core components and plugins.
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/*-
 * ========================LICENSE_START=================================
 * restheart-commons
 * %%
 * Copyright (C) 2019 - 2024 SoftInstigate
 * %%
 * 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.
 * =========================LICENSE_END==================================
 */
package org.restheart.utils;

import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.UnknownHostException;
import java.util.Enumeration;

/**
 * this duplicates si-lka Utils class
 */
public class NetUtils {
    /**
     * Returns an InetAddress object encapsulating what is most
     * likely the machine's LAN IP address.
     * {@literal }
     * This method is intended for use as a replacement of JDK method
     * InetAddress.getLocalHost, because that method is ambiguous
     * on Linux systems. Linux systems enumerate the loopback network interface
     * the same way as regular LAN network interfaces, but the JDK
     * InetAddress.getLocalHost method does not specify the
     * algorithm used to select the address returned under such circumstances,
     * and will often return the loopback address, which is not valid for
     * network communication. Details
     * here.
     * {@literal 
}
     * This method will scan all IP addresses on all network interfaces on the
     * host machine to determine the IP address most likely to be the machine's
     * LAN address. If the machine has multiple IP addresses, this method will
     * prefer a site-local IP address (e.g. 192.168.x.x or 10.10.x.x, usually
     * IPv4) if the machine has one (and will return the first site-local
     * address if the machine has more than one), but if the machine does not
     * hold a site-local address, this method will return simply the first
     * non-loopback address found (IPv4 or IPv6).
     * {@literal 
}
     * If this method cannot find a non-loopback address using this selection
     * algorithm, it will fall back to calling and returning the result of JDK
     * method InetAddress.getLocalHost.
     * {@literal }
     *
     * @throws UnknownHostException If the LAN address of the machine cannot be
     * found.
     */
    @SuppressWarnings("rawtypes")
    public static InetAddress getLocalHostLANAddress() throws UnknownHostException {
        try {
            InetAddress candidateAddress = null;
            // Iterate all NICs (network interface cards)...
            for (Enumeration ifaces = NetworkInterface.getNetworkInterfaces(); ifaces.hasMoreElements();) {
                NetworkInterface iface = (NetworkInterface) ifaces.nextElement();
                // Iterate all IP addresses assigned to each card...
                for (Enumeration inetAddrs = iface.getInetAddresses(); inetAddrs.hasMoreElements();) {
                    InetAddress inetAddr = (InetAddress) inetAddrs.nextElement();
                    if (!inetAddr.isLoopbackAddress()) {
                        if (inetAddr.isSiteLocalAddress()) {
                            // Found non-loopback site-local address. Return it immediately...
                            return inetAddr;
                        } else if (candidateAddress == null) {
                            // Found non-loopback address, but not necessarily site-local.
                            // Store it as a candidate to be returned if site-local address is not subsequently found...
                            candidateAddress = inetAddr;
                            // Note that we don't repeatedly assign non-loopback non-site-local addresses as candidates,
                            // only the first. For subsequent iterations, candidate will be non-null.
                        }
                    }
                }
            }
            if (candidateAddress != null) {
                // We did not find a site-local address, but we found some other non-loopback address.
                // Server might have a non-site-local address assigned to its NIC (or it might be running
                // IPv6 which deprecates the "site-local" concept).
                // Return this non-loopback candidate address...
                return candidateAddress;
            }
            // At this point, we did not find a non-loopback address.
            // Fall back to returning whatever InetAddress.getLocalHost() returns...
            InetAddress jdkSuppliedAddress = InetAddress.getLocalHost();
            if (jdkSuppliedAddress == null) {
                throw new UnknownHostException("The JDK InetAddress.getLocalHost() method unexpectedly returned null.");
            }
            return jdkSuppliedAddress;
        } catch (Exception e) {
            UnknownHostException unknownHostException = new UnknownHostException("Failed to determine LAN address: " + e);
            unknownHostException.initCause(e);
            throw unknownHostException;
        }
    }
}