/*

 * Copyright (c) 1999, 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.jndi.ldap;

import java.io.UnsupportedEncodingException;

/**

  * A BER decoder. Contains methods to parse a BER buffer.

  *

  * @author Jagane Sundar

  * @author Vincent Ryan

  */

public final class BerDecoder extends Ber {

    private int origOffset;  // The start point in buf to decode

    /**

     * Creates a BER decoder that reads bytes from the specified buffer.

     */

    public BerDecoder(byte buf[], int offset, int bufsize) {

        this.bufsize = bufsize;

        this.origOffset = offset;

        reset();

    }

    /**

     * Resets this decode to start parsing from the initial offset

     * (ie., same state as after calling the constructor).

     */

    public void reset() {

        offset = origOffset;

    }

    /**

      * Returns the current parse position.

      * It points to the byte that will be parsed next.

      * Useful for parsing sequences.

      */

    public int getParsePosition() {

        return offset;

    }

    /**

      * Parses a possibly variable length field.

      */

    public int parseLength() throws DecodeException {

        int lengthbyte = parseByte();

        if ((lengthbyte & 0x80) == 0x80) {

            lengthbyte &= 0x7f;

            if (lengthbyte == 0) {

                throw new DecodeException(

                    "Indefinite length not supported");

            }

            if (lengthbyte > 4) {

                throw new DecodeException("encoding too long");

            }

            if (bufsize - offset < lengthbyte) {

                throw new DecodeException("Insufficient data");

            }

            int retval = 0;

            for( int i = 0; i < lengthbyte; i++) {

                retval = (retval << 8) + (buf[offset++] & 0xff);

            }

            return retval;

        } else {

            return lengthbyte;

        }

    }

    /**

     * Parses the next sequence in this BER buffer.

     * @param rlen An array for returning size of the sequence in bytes. If null,

     *          the size is not returned.

     * @return The sequence's tag.

     */

    public int parseSeq(int rlen[]) throws DecodeException {

        int seq = parseByte();

        int len = parseLength();

        if (rlen != null) {

            rlen[0] = len;

        }

        return seq;

    }

    /**

     * Used to skip bytes. Usually used when trying to recover from parse error.

     * Don't need to be public right now?

     * @param i The number of bytes to skip

     */

    void seek(int i) throws DecodeException {

        if (offset + i > bufsize || offset + i < 0) {

            throw new DecodeException("array index out of bounds");

        }

        offset += i;

    }

    /**

     * Parses the next byte in this BER buffer.

     * @return The byte parsed.

     */

    public int parseByte() throws DecodeException {

        if (bufsize - offset < 1) {

            throw new DecodeException("Insufficient data");

        }

        return buf[offset++] & 0xff;

    }

    /**

     * Returns the next byte in this BER buffer without consuming it.

     * @return The next byte.

     */

    public int peekByte() throws DecodeException {

        if (bufsize - offset < 1) {

            throw new DecodeException("Insufficient data");

        }

        return buf[offset] & 0xff;

    }

    /**

     * Parses an ASN_BOOLEAN tagged integer from this BER buffer.

     * @return true if the tagged integer is 0; false otherwise.

     */

    public boolean parseBoolean() throws DecodeException {

        return ((parseIntWithTag(ASN_BOOLEAN) == 0x00) ? false : true);

    }

    /**

     * Parses an ASN_ENUMERATED tagged integer from this BER buffer.

     * @return The tag of enumeration.

     */

    public int parseEnumeration() throws DecodeException {

        return parseIntWithTag(ASN_ENUMERATED);

    }

    /**

     * Parses an ASN_INTEGER tagged integer from this BER buffer.

     * @return The value of the integer.

     */

    public int parseInt() throws DecodeException {

        return parseIntWithTag(ASN_INTEGER);

    }

    /**

      * Parses an integer that's preceded by a tag.

      *<blockquote><pre>

      * BER integer ::= tag length byte {byte}*

      *</pre></blockquote>

      */

    private int parseIntWithTag(int tag) throws DecodeException {

        if (parseByte() != tag) {

            throw new DecodeException("Encountered ASN.1 tag " +

                Integer.toString(buf[offset - 1] & 0xff) +

                " (expected tag " + Integer.toString(tag) + ")");

        }

        int len = parseLength();

        if (len > 4) {

            throw new DecodeException("INTEGER too long");

        } else if (len > bufsize - offset) {

            throw new DecodeException("Insufficient data");

        }

        byte fb = buf[offset++];

        int value = 0;

        value = fb & 0x7F;

        for( int i = 1 /* first byte already read */ ; i < len; i++) {

            value <<= 8;

            value |= (buf[offset++] & 0xff);

        }

        if ((fb & 0x80) == 0x80) {

            value = -value;

        }

        return value;

    }

    /**

      * Parses a string.

      */

    public String parseString(boolean decodeUTF8) throws DecodeException {

        return parseStringWithTag(ASN_SIMPLE_STRING, decodeUTF8, null);

    }

    /**

      * Parses a string of a given tag from this BER buffer.

      *<blockquote><pre>

      *BER simple string ::= tag length {byte}*

      *</pre></blockquote>

      * @param rlen An array for holding the relative parsed offset; if null

      *  offset not set.

      * @param decodeUTF8 If true, use UTF-8 when decoding the string; otherwise

      * use ISO-Latin-1 (8859_1). Use true for LDAPv3; false for LDAPv2.

      * @param tag The tag that precedes the string.

      * @return The non-null parsed string.

      */

    public String parseStringWithTag(int tag, boolean decodeUTF8, int rlen[])

        throws DecodeException {

        int st;

        int origOffset = offset;

        if ((st = parseByte()) != tag) {

            throw new DecodeException("Encountered ASN.1 tag " +

                Integer.toString((byte)st) + " (expected tag " + tag + ")");

        }

        int len = parseLength();

        if (len > bufsize - offset) {

            throw new DecodeException("Insufficient data");

        }

        String retstr;

        if (len == 0) {

            retstr = "";

        } else {

            byte[] buf2 = new byte[len];

            System.arraycopy(buf, offset, buf2, 0, len);

            if (decodeUTF8) {

                try {

                    retstr = new String(buf2, "UTF8");

                } catch (UnsupportedEncodingException e) {

                    throw new DecodeException("UTF8 not available on platform");

                }

            } else {

                try {

                    retstr = new String(buf2, "8859_1");

                } catch (UnsupportedEncodingException e) {

                    throw new DecodeException("8859_1 not available on platform");

                }

            }

            offset += len;

        }

        if (rlen != null) {

            rlen[0] = offset - origOffset;

        }

        return retstr;

    }

    /**

     * Parses an octet string of a given type(tag) from this BER buffer.

     * <blockquote><pre>

     * BER Binary Data of type "tag" ::= tag length {byte}*

     *</pre></blockquote>

     *

     * @param tag The tag to look for.

     * @param rlen An array for returning the relative parsed position. If null,

     *          the relative parsed position is not returned.

     * @return A non-null array containing the octet string.

     * @throws DecodeException If the next byte in the BER buffer is not

     * <tt>tag</tt>, or if length specified in the BER buffer exceeds the

     * number of bytes left in the buffer.

     */

    public byte[] parseOctetString(int tag, int rlen[]) throws DecodeException {

        int origOffset = offset;

        int st;

        if ((st = parseByte()) != tag) {

            throw new DecodeException("Encountered ASN.1 tag " +

                Integer.toString(st) +

                " (expected tag " + Integer.toString(tag) + ")");

        }

        int len = parseLength();

        if (len > bufsize - offset) {

            throw new DecodeException("Insufficient data");

        }

        byte retarr[] = new byte[len];

        if (len > 0) {

            System.arraycopy(buf, offset, retarr, 0, len);

            offset += len;

        }

        if (rlen != null) {

            rlen[0] = offset - origOffset;

        }

        return retarr;

    }

    /**

     * Returns the number of unparsed bytes in this BER buffer.

     */

    public int bytesLeft() {

        return bufsize - offset;

    }

}