src/java.base/unix/classes/sun/net/PortConfig.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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package sun.net;

import jdk.internal.util.OperatingSystem;

/**
 * Determines the ephemeral port range in use on this system.
 * If this cannot be determined, then the default settings
 * of the OS are returned.
 */

public final class PortConfig {

    private static final int upper, lower;

    private PortConfig() {}

    static {
        jdk.internal.loader.BootLoader.loadLibrary("net");
        int defaultUpper;
        int defaultLower;
        switch (OperatingSystem.current()) {
            case LINUX:
                defaultLower = 32768;
                defaultUpper = 61000;
                break;
            case MACOS:
                defaultLower = 49152;
                defaultUpper = 65535;
                break;
            case AIX:
                // The ephemeral port is OS version dependent on AIX:
                // https://www.ibm.com/support/pages/node/886227
                // However, on AIX 5.3 / 6.1 / 7.1 we always see the
                // settings below by using:
                // /usr/sbin/no -a | fgrep ephemeral
                defaultLower = 32768;
                defaultUpper = 65535;
                break;
            default:
                throw new InternalError("sun.net.PortConfig: unsupported OS: " + OperatingSystem.current());
        }

        int v = getLower0();
        if (v == -1) {
            v = defaultLower;
        }
        lower = v;

        v = getUpper0();
        if (v == -1) {
            v = defaultUpper;
        }
        upper = v;
    }

    static native int getLower0();
    static native int getUpper0();

    public static int getLower() {
        return lower;
    }

    public static int getUpper() {
        return upper;
    }
}