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Improved version of the DBus-Java library provided by freedesktop.org (https://dbus.freedesktop.org/doc/dbus-java/). This is the OSGi compliant bundle of all required libraries in one bundle.
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package org.freedesktop.dbus.utils;

import org.freedesktop.dbus.config.DBusSysProps;
import org.freedesktop.dbus.connections.BusAddress;
import org.freedesktop.dbus.exceptions.AddressResolvingException;
import org.slf4j.LoggerFactory;

import java.io.File;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.*;

public final class AddressBuilder {

    private AddressBuilder() {}

    /**
     * Determine the address of the DBus system connection.
     *
     * @return String
     */
    public static BusAddress getSystemConnection() {
        String bus = System.getenv(DBusSysProps.DBUS_SYSTEM_BUS_ADDRESS);
        if (bus == null) {
            bus = DBusSysProps.DEFAULT_SYSTEM_BUS_ADDRESS;
        }
        return BusAddress.of(bus);
    }

    /**
     * Retrieves the connection address to connect to the DBus session-bus.

     * Will return TCP connection when no unix transport found and TCP is available.
     *
     * @param _dbusMachineIdFile alternative location of dbus machine id file, use null if not needed
     *
     * @return address
     *
     * @throws AddressResolvingException when no suitable address can be found for any available transport
     */
    public static BusAddress getSessionConnection(String _dbusMachineIdFile) {

        // try to read session address from running process instance properties first
        String s = System.getProperty(DBusSysProps.DBUS_SESSION_BUS_ADDRESS);

        // no session address in process properties, try to get it from environment
        if (s == null) {
            // MacOS support: e.g DBUS_LAUNCHD_SESSION_BUS_SOCKET=/private/tmp/com.apple.launchd.4ojrKe6laI/unix_domain_listener
            if (Util.isMacOs()) {
                s = "unix:path=" + System.getenv(DBusSysProps.DBUS_SESSION_BUS_ADDRESS_MACOS);
            } else { // all others (linux)
                s = System.getenv(DBusSysProps.DBUS_SESSION_BUS_ADDRESS);
            }
        }

        // no address found in instance properties and environment, try to get the address from session properties file
        if (s == null) {
            // address gets stashed in $HOME/.dbus/session-bus/`dbus-uuidgen --get`-`sed 's/:\(.\)\..*/\1/' <<<
            // $DISPLAY`
            String display = System.getenv("DISPLAY");
            if (display == null) {
                throw new AddressResolvingException("Cannot Resolve Session Bus Address: DISPLAY variable not set");
            }
            if (display.charAt(0) != ':' && display.contains(":")) { // display seems to be a remote display
                                                                     // (e.g. X forward through SSH)
                display = display.substring(display.indexOf(':'));
            }

            String uuid = getDbusMachineId(_dbusMachineIdFile);
            String homedir = System.getProperty("user.home");
            File addressfile = new File(homedir + "/.dbus/session-bus",
                    uuid + "-" + display.replaceAll(":([0-9]*)\\..*", "$1"));

            if (!addressfile.exists()) {
                throw new AddressResolvingException("Cannot Resolve Session Bus Address: " + addressfile + " not found");
            }

            Properties readProperties = Util.readProperties(addressfile);
            if (readProperties == null) {
                throw new AddressResolvingException("Cannot Resolve Session Bus Address: Unable to read " + addressfile);
            }
            String sessionAddress = readProperties.getProperty(DBusSysProps.DBUS_SESSION_BUS_ADDRESS);

            if (Util.isEmpty(sessionAddress)) {
                throw new AddressResolvingException("Cannot Resolve Session Bus Address: No session information found in " + addressfile);
            }

            // sometimes (e.g. Ubuntu 18.04) the returned address is wrapped in single quotes ('), we have to remove them
            if (sessionAddress.matches("^'[^']+'$")) {
                sessionAddress = sessionAddress.replaceFirst("^'([^']+)'$", "$1");
            }

            return BusAddress.of(sessionAddress);
        }

        return BusAddress.of(s);
    }

    /**
     * Extracts the machine-id usually found on Linux in various system directories, or
     * generate a fake id for non-Linux platforms.
     *
     * @param _dbusMachineIdFile alternative location of dbus machine id file, null if not needed
     * @return machine-id string, never null
     */
    public static String getDbusMachineId(String _dbusMachineIdFile) {
        File uuidfile = determineMachineIdFile(_dbusMachineIdFile);
        if (uuidfile != null) {
            String uuid = Util.readFileToString(uuidfile);
            if (uuid.length() > 0) {
                return uuid;
            } else {
                throw new AddressResolvingException("Cannot Resolve Session Bus Address: MachineId file is empty.");
            }
        }
        if (Util.isWindows() || Util.isMacOs()) {
            /* Linux *should* have a machine-id */
            return getFakeDbusMachineId();
        }
        throw new AddressResolvingException("Cannot Resolve Session Bus Address: MachineId file can not be found");
    }

    /**
     * Tries to find the DBus machine-id file in different locations.
     *
     * @param _dbusMachineIdFile alternative location of dbus machine id file
     *
     * @return File with machine-id
     */
    private static File determineMachineIdFile(String _dbusMachineIdFile) {
        List locationPriorityList = Arrays.asList(System.getenv(DBusSysProps.DBUS_MACHINE_ID_SYS_VAR), _dbusMachineIdFile,
                "/var/lib/dbus/machine-id", "/usr/local/var/lib/dbus/machine-id", "/etc/machine-id");
        return locationPriorityList.stream()
                .filter(Objects::nonNull)
                .map(File::new)
                .filter(f -> f.exists() && f.length() > 0)
                .findFirst()
                .orElse(null);
    }

    /**
     * Generates a fake machine-id when DBus is running on Windows.
     * @return String
     */
    private static String getFakeDbusMachineId() {
        // we create a fake id on windows
        return String.format("%s@%s", Util.getCurrentUser(), Util.getHostName());
    }

    /**
     * Creates a machine identifier by using the MD5 sum of the hostname.
     * If hostname could not be determined, a random string will be used.
     *
     * @return String
     */
    public static String createMachineId() {
        String ascii;

        try {
            ascii = Hexdump.toAscii(MessageDigest.getInstance("MD5").digest(InetAddress.getLocalHost().getHostName().getBytes()));
            return ascii;
        } catch (NoSuchAlgorithmException _ex) {
            LoggerFactory.getLogger(AddressBuilder.class).trace("MD5 algorithm not present", _ex);
        } catch (UnknownHostException _ex) {
            LoggerFactory.getLogger(AddressBuilder.class).trace("Unable to determine this machines hostname", _ex);
        }

        return Util.randomString(32);
    }
}