Packet.java

/*
 * Copyright (c) 1998, 2017, 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 com.sun.tools.jdi;

import java.io.IOException;

public class Packet extends Object {
    public final static short NoFlags = 0x0;
    public final static short Reply = 0x80;
    public final static short ReplyNoError = 0x0;

    static int uID = 1;
    final static byte[] nullData = new byte[0];

    // Note! flags, cmdSet, and cmd are all byte values.
    // We represent them as shorts to make them easier
    // to work with.
    int id;
    short flags;
    short cmdSet;
    short cmd;
    short errorCode;
    byte[] data;
    volatile boolean replied = false;

    /**
     * Return byte representation of the packet
     */
    public byte[] toByteArray() {
        int len = data.length + 11;
        byte b[] = new byte[len];
        b[0] = (byte)((len >>> 24) & 0xff);
        b[1] = (byte)((len >>> 16) & 0xff);
        b[2] = (byte)((len >>>  8) & 0xff);
        b[3] = (byte)((len >>>  0) & 0xff);
        b[4] = (byte)((id >>> 24) & 0xff);
        b[5] = (byte)((id >>> 16) & 0xff);
        b[6] = (byte)((id >>>  8) & 0xff);
        b[7] = (byte)((id >>>  0) & 0xff);
        b[8] = (byte)flags;
        if ((flags & Packet.Reply) == 0) {
            b[9] = (byte)cmdSet;
            b[10] = (byte)cmd;
        } else {
            b[9] = (byte)((errorCode >>>  8) & 0xff);
            b[10] = (byte)((errorCode >>>  0) & 0xff);
        }
        if (data.length > 0) {
            System.arraycopy(data, 0, b, 11, data.length);
        }
        return b;
    }

    /**
     * Create a packet from its byte array representation
     */
    public static Packet fromByteArray(byte b[]) throws IOException {
        if (b.length < 11) {
            throw new IOException("packet is insufficient size");
        }

        int b0 = b[0] & 0xff;
        int b1 = b[1] & 0xff;
        int b2 = b[2] & 0xff;
        int b3 = b[3] & 0xff;
        int len = ((b0 << 24) | (b1 << 16) | (b2 << 8) | (b3 << 0));
        if (len != b.length) {
            throw new IOException("length size mis-match");
        }

        int b4 = b[4] & 0xff;
        int b5 = b[5] & 0xff;
        int b6 = b[6] & 0xff;
        int b7 = b[7] & 0xff;

        Packet p = new Packet();
        p.id = ((b4 << 24) | (b5 << 16) | (b6 << 8) | (b7 << 0));

        p.flags = (short)(b[8] & 0xff);

        if ((p.flags & Packet.Reply) == 0) {
            p.cmdSet = (short)(b[9] & 0xff);
            p.cmd = (short)(b[10] & 0xff);
        } else {
            short b9 = (short)(b[9] & 0xff);
            short b10 = (short)(b[10] & 0xff);
            p.errorCode = (short)((b9 << 8) + (b10 << 0));
        }

        p.data = new byte[b.length - 11];
        System.arraycopy(b, 11, p.data, 0, p.data.length);
        return p;
    }

    Packet() {
        id = uniqID();
        flags = NoFlags;
        data = nullData;
    }

    static synchronized private int uniqID() {
        /*
         * JDWP spec does not require this id to be sequential and
         * increasing, but our implementation does. See
         * VirtualMachine.notifySuspend, for example.
         */
        return uID++;
    }
}