/*

 * Copyright (c) 1996, 2008, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.rmi.dgc;

import java.io.*;

import java.net.*;

import java.rmi.server.UID;

import java.security.*;

/**

 * A VMID is a identifier that is unique across all Java virtual

 * machines.  VMIDs are used by the distributed garbage collector

 * to identify client VMs.

 *

 * @author      Ann Wollrath

 * @author      Peter Jones

 */

public final class VMID implements java.io.Serializable {

    /** array of bytes uniquely identifying this host */

    private static byte[] localAddr = computeAddressHash();

    /**

     * @serial array of bytes uniquely identifying host created on

     */

    private byte[] addr;

    /**

     * @serial unique identifier with respect to host created on

     */

    private UID uid;

    /** indicate compatibility with JDK 1.1.x version of class */

    private static final long serialVersionUID = -538642295484486218L;

    /**

     * Create a new VMID.  Each new VMID returned from this constructor

     * is unique for all Java virtual machines under the following

     * conditions: a) the conditions for uniqueness for objects of

     * the class <code>java.rmi.server.UID</code> are satisfied, and b) an

     * address can be obtained for this host that is unique and constant

     * for the lifetime of this object.  <p>

     */

    public VMID() {

        addr = localAddr;

        uid = new UID();

    }

    /**

     * Return true if an accurate address can be determined for this

     * host.  If false, reliable VMID cannot be generated from this host

     * @return true if host address can be determined, false otherwise

     * @deprecated

     */

    @Deprecated

    public static boolean isUnique() {

        return true;

    }

    /**

     * Compute hash code for this VMID.

     */

    public int hashCode() {

        return uid.hashCode();

    }

    /**

     * Compare this VMID to another, and return true if they are the

     * same identifier.

     */

    public boolean equals(Object obj) {

        if (obj instanceof VMID) {

            VMID vmid = (VMID) obj;

            if (!uid.equals(vmid.uid))

                return false;

            if ((addr == null) ^ (vmid.addr == null))

                return false;

            if (addr != null) {

                if (addr.length != vmid.addr.length)

                    return false;

                for (int i = 0; i < addr.length; ++ i)

                    if (addr[i] != vmid.addr[i])

                        return false;

            }

            return true;

        } else {

            return false;

        }

    }

    /**

     * Return string representation of this VMID.

     */

    public String toString() {

        StringBuffer result = new StringBuffer();

        if (addr != null)

            for (int i = 0; i < addr.length; ++ i) {

                int x = (int) (addr[i] & 0xFF);

                result.append((x < 0x10 ? "0" : "") +

                              Integer.toString(x, 16));

            }

        result.append(':');

        result.append(uid.toString());

        return result.toString();

    }

    /**

     * Compute the hash an IP address.  The hash is the first 8 bytes

     * of the SHA digest of the IP address.

     */

    private static byte[] computeAddressHash() {

        /*

         * Get the local host's IP address.

         */

        byte[] addr = java.security.AccessController.doPrivileged(

            new PrivilegedAction<byte[]>() {

            public byte[] run() {

                try {

                    return InetAddress.getLocalHost().getAddress();

                } catch (Exception e) {

                }

                return new byte[] { 0, 0, 0, 0 };

            }

        });

        byte[] addrHash;

        final int ADDR_HASH_LENGTH = 8;

        try {

            /*

             * Calculate message digest of IP address using SHA.

             */

            MessageDigest md = MessageDigest.getInstance("SHA");

            ByteArrayOutputStream sink = new ByteArrayOutputStream(64);

            DataOutputStream out = new DataOutputStream(

                new DigestOutputStream(sink, md));

            out.write(addr, 0, addr.length);

            out.flush();

            byte digest[] = md.digest();

            int hashlength = Math.min(ADDR_HASH_LENGTH, digest.length);

            addrHash = new byte[hashlength];

            System.arraycopy(digest, 0, addrHash, 0, hashlength);

        } catch (IOException ignore) {

            /* can't happen, but be deterministic anyway. */

            addrHash = new byte[0];

        } catch (NoSuchAlgorithmException complain) {

        }

        return addrHash;

    }

}