/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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.
 */
package org.apache.coyote.ajp;

import java.nio.ByteBuffer;

import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import org.apache.tomcat.util.buf.ByteChunk;
import org.apache.tomcat.util.buf.HexUtils;
import org.apache.tomcat.util.buf.MessageBytes;
import org.apache.tomcat.util.res.StringManager;

/**
 * A single packet for communication between the web server and the container. Designed to be reused many times with no
 * creation of garbage. Understands the format of data types for these packets. Can be used (somewhat confusingly) for
 * both incoming and outgoing packets.
 *
 * @author Henri Gomez
 * @author Dan Milstein
 * @author Keith Wannamaker
 * @author Kevin Seguin
 * @author Costin Manolache
 */
public class AjpMessage {


    private static final Log log = LogFactory.getLog(AjpMessage.class);

    /**
     * The string manager for this package.
     */
    protected static final StringManager sm = StringManager.getManager(AjpMessage.class);


    // ------------------------------------------------------------ Constructor


    public AjpMessage(int packetSize) {
        buf = new byte[packetSize];
    }


    // ----------------------------------------------------- Instance Variables


    /**
     * Fixed size buffer.
     */
    protected final byte[] buf;


    /**
     * The current read or write position in the buffer.
     */
    protected int pos;


    /**
     * This actually means different things depending on whether the packet is read or write. For read, it's the length
     * of the payload (excluding the header). For write, it's the length of the packet as a whole (counting the header).
     * Oh, well.
     */
    protected int len;


    // --------------------------------------------------------- Public Methods


    /**
     * Prepare this packet for accumulating a message from the container to the web server. Set the write position to
     * just after the header (but leave the length unwritten, because it is as yet unknown).
     */
    public void reset() {
        len = 4;
        pos = 4;
    }


    /**
     * For a packet to be sent to the web server, finish the process of accumulating data and write the length of the
     * data payload into the header.
     */
    public void end() {
        len = pos;
        int dLen = len - 4;

        buf[0] = (byte) 0x41;
        buf[1] = (byte) 0x42;
        buf[2] = (byte) ((dLen >>> 8) & 0xFF);
        buf[3] = (byte) (dLen & 0xFF);
    }


    /**
     * Return the underlying byte buffer.
     *
     * @return The buffer
     */
    public byte[] getBuffer() {
        return buf;
    }


    /**
     * Return the current message length.
     *
     * @return For read, it's the length of the payload (excluding the header). For write, it's the length of the packet
     *             as a whole (counting the header).
     */
    public int getLen() {
        return len;
    }


    /**
     * Add a short integer (2 bytes) to the message.
     *
     * @param val The integer to append
     */
    public void appendInt(int val) {
        buf[pos++] = (byte) ((val >>> 8) & 0xFF);
        buf[pos++] = (byte) (val & 0xFF);
    }


    /**
     * Append a byte (1 byte) to the message.
     *
     * @param val The byte value to append
     */
    public void appendByte(int val) {
        buf[pos++] = (byte) val;
    }


    /**
     * Write a MessageBytes out at the current write position. A null MessageBytes is encoded as a string with length 0.
     *
     * @param mb The data to write
     */
    public void appendBytes(MessageBytes mb) {
        if (mb == null) {
            log.error(sm.getString("ajpmessage.null"), new NullPointerException());
            appendInt(0);
            appendByte(0);
            return;
        }
        if (mb.getType() != MessageBytes.T_BYTES) {
            mb.toBytes();
            ByteChunk bc = mb.getByteChunk();
            // Need to filter out CTLs excluding TAB. ISO-8859-1 and UTF-8
            // values will be OK. Strings using other encodings may be
            // corrupted.
            byte[] buffer = bc.getBuffer();
            for (int i = bc.getStart(); i < bc.getLength(); i++) {
                // byte values are signed i.e. -128 to 127
                // The values are used unsigned. 0 to 31 are CTLs so they are
                // filtered (apart from TAB which is 9). 127 is a control (DEL).
                // The values 128 to 255 are all OK. Converting those to signed
                // gives -128 to -1.
                if ((buffer[i] > -1 && buffer[i] <= 31 && buffer[i] != 9) || buffer[i] == 127) {
                    buffer[i] = ' ';
                }
            }
        }
        appendByteChunk(mb.getByteChunk());
    }


    /**
     * Write a ByteChunk out at the current write position. A null ByteChunk is encoded as a string with length 0.
     *
     * @param bc The data to write
     */
    public void appendByteChunk(ByteChunk bc) {
        if (bc == null) {
            log.error(sm.getString("ajpmessage.null"), new NullPointerException());
            appendInt(0);
            appendByte(0);
            return;
        }
        appendBytes(bc.getBytes(), bc.getStart(), bc.getLength());
    }


    /**
     * Copy a chunk of bytes into the packet, starting at the current write position. The chunk of bytes is encoded with
     * the length in two bytes first, then the data itself, and finally a terminating \0 (which is <B>not</B> included
     * in the encoded length).
     *
     * @param b        The array from which to copy bytes.
     * @param off      The offset into the array at which to start copying
     * @param numBytes The number of bytes to copy.
     */
    public void appendBytes(byte[] b, int off, int numBytes) {
        if (checkOverflow(numBytes)) {
            return;
        }
        appendInt(numBytes);
        System.arraycopy(b, off, buf, pos, numBytes);
        pos += numBytes;
        appendByte(0);
    }


    /**
     * Copy a chunk of bytes into the packet, starting at the current write position. The chunk of bytes is encoded with
     * the length in two bytes first, then the data itself, and finally a terminating \0 (which is <B>not</B> included
     * in the encoded length).
     *
     * @param b The ByteBuffer from which to copy bytes.
     */
    public void appendBytes(ByteBuffer b) {
        int numBytes = b.remaining();
        if (checkOverflow(numBytes)) {
            return;
        }
        appendInt(numBytes);
        b.get(buf, pos, numBytes);
        pos += numBytes;
        appendByte(0);
    }


    private boolean checkOverflow(int numBytes) {
        if (pos + numBytes + 3 > buf.length) {
            log.error(sm.getString("ajpmessage.overflow", "" + numBytes, "" + pos),
                    new ArrayIndexOutOfBoundsException());
            if (log.isDebugEnabled()) {
                dump("Overflow/coBytes");
            }
            return true;
        }
        return false;
    }


    /**
     * Read an integer from packet, and advance the read position past it. Integers are encoded as two unsigned bytes
     * with the high-order byte first, and, as far as I can tell, in little-endian order within each byte.
     *
     * @return The integer value read from the message
     */
    public int getInt() {
        int b1 = buf[pos++] & 0xFF;
        int b2 = buf[pos++] & 0xFF;
        validatePos(pos);
        return (b1 << 8) + b2;
    }


    public int peekInt() {
        validatePos(pos + 2);
        int b1 = buf[pos] & 0xFF;
        int b2 = buf[pos + 1] & 0xFF;
        return (b1 << 8) + b2;
    }


    public byte getByte() {
        byte res = buf[pos++];
        validatePos(pos);
        return res;
    }


    public void getBytes(MessageBytes mb) {
        doGetBytes(mb, true);
    }

    public void getBodyBytes(MessageBytes mb) {
        doGetBytes(mb, false);
    }

    private void doGetBytes(MessageBytes mb, boolean terminated) {
        int length = getInt();
        if (length == 0xFFFF || length == -1) {
            mb.recycle();
            return;
        }
        if (terminated) {
            validatePos(pos + length + 1);
        } else {
            validatePos(pos + length);
        }
        mb.setBytes(buf, pos, length);
        mb.getCharChunk().recycle(); // not valid anymore
        pos += length;
        if (terminated) {
            pos++; // Skip the terminating \0
        }
    }


    /**
     * Read a 32 bits integer from packet, and advance the read position past it. Integers are encoded as four unsigned
     * bytes with the high-order byte first, and, as far as I can tell, in little-endian order within each byte.
     *
     * @return The long value read from the message
     */
    public int getLongInt() {
        int b1 = buf[pos++] & 0xFF; // No swap, Java order
        b1 <<= 8;
        b1 |= (buf[pos++] & 0xFF);
        b1 <<= 8;
        b1 |= (buf[pos++] & 0xFF);
        b1 <<= 8;
        b1 |= (buf[pos++] & 0xFF);
        validatePos(pos);
        return b1;
    }


    public int processHeader(boolean toContainer) {
        pos = 0;
        int mark = getInt();
        len = getInt();
        // Verify message signature
        if ((toContainer && mark != 0x1234) || (!toContainer && mark != 0x4142)) {
            log.error(sm.getString("ajpmessage.invalid", "" + mark));
            if (log.isTraceEnabled()) {
                dump("In");
            }
            return -1;
        }
        if (log.isTraceEnabled()) {
            log.trace("Received " + len + " " + buf[0]);
        }
        return len;
    }


    private void dump(String prefix) {
        if (log.isTraceEnabled()) {
            log.trace(prefix + ": " + HexUtils.toHexString(buf) + " " + pos + "/" + (len + 4));
        }
        int max = pos;
        if (len + 4 > pos) {
            max = len + 4;
        }
        if (max > 1000) {
            max = 1000;
        }
        if (log.isTraceEnabled()) {
            for (int j = 0; j < max; j += 16) {
                log.trace(hexLine(buf, j, len));
            }
        }
    }


    private void validatePos(int posToTest) {
        if (posToTest > len + 4) {
            // Trying to read data beyond the end of the AJP message
            throw new ArrayIndexOutOfBoundsException(sm.getString("ajpMessage.invalidPos", Integer.valueOf(posToTest)));
        }
    }
    // ------------------------------------------------------ Protected Methods


    protected static String hexLine(byte[] buf, int start, int len) {
        StringBuilder sb = new StringBuilder();
        for (int i = start; i < start + 16; i++) {
            if (i < len + 4) {
                sb.append(hex(buf[i])).append(' ');
            } else {
                sb.append("   ");
            }
        }
        sb.append(" | ");
        for (int i = start; i < start + 16 && i < len + 4; i++) {
            if (!Character.isISOControl((char) buf[i])) {
                sb.append(Character.valueOf((char) buf[i]));
            } else {
                sb.append('.');
            }
        }
        return sb.toString();
    }


    protected static String hex(int x) {
        String h = Integer.toHexString(x);
        if (h.length() == 1) {
            h = "0" + h;
        }
        return h.substring(h.length() - 2);
    }


}