package gnu.crypto.sasl;

// ----------------------------------------------------------------------------
// $Id: InputBuffer.java,v 1.5 2005/10/06 04:24:18 rsdio Exp $
//
// Copyright (C) 2003 Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2, or (at your option)
// any later version.
//
// GNU Crypto 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 for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; see the file COPYING.  If not, write to the
//
//    Free Software Foundation Inc.,
//    51 Franklin Street, Fifth Floor,
//    Boston, MA 02110-1301
//    USA
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
//
// As a special exception, the copyright holders of this library give
// you permission to link this library with independent modules to
// produce an executable, regardless of the license terms of these
// independent modules, and to copy and distribute the resulting
// executable under terms of your choice, provided that you also meet,
// for each linked independent module, the terms and conditions of the
// license of that module.  An independent module is a module which is
// not derived from or based on this library.  If you modify this
// library, you may extend this exception to your version of the
// library, but you are not obligated to do so.  If you do not wish to
// do so, delete this exception statement from your version.
// ----------------------------------------------------------------------------

import gnu.crypto.Registry;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.math.BigInteger;

/**
 * <p>The implementation of an incoming SASL buffer.</p>
 *
 * <p>The data elements this class caters for are described in [1].</p>
 *
 * <p>References:</p>
 * <ol>
 *    <li><a href="http://www.ietf.org/internet-drafts/draft-burdis-cat-srp-sasl-09.txt">
 *    Secure Remote Password Authentication Mechanism</a>;<br/>
 *    draft-burdis-cat-srp-sasl-09,<br/>
 *    <a href="mailto:keith@rucus.ru.ac.za">Keith Burdis</a> and
 *    <a href="mailto:raif@forge.com.au">Ra&iuml;f S. Naffah</a>.</li>
 * </ol>
 *
 * @version $Revision: 1.5 $
 */
public class InputBuffer {

   // Constants and variables
   // -------------------------------------------------------------------------

   /** The internal buffer stream containing the buffer's contents. */
   protected ByteArrayInputStream in;

   /** The length of the buffer, according to its header. */
   protected int length;

   // Constructor(s)
   // -------------------------------------------------------------------------

   /**
    * <p>Constructs a SASL buffer given the buffer's encoded form, including its
    * header bytes.</p>
    *
    * @param frame the encoded form, including the header bytes, of a SASL buffer.
    * @throws SaslEncodingException if the buffer is malformed.
    */
   public InputBuffer(byte[] frame) throws SaslEncodingException {
      this();

      if (frame.length < 4) {
         throw new SaslEncodingException("SASL buffer header too short");
      }

      length = (frame[0] & 0xFF) << 24 |
               (frame[1] & 0xFF) << 16 |
               (frame[2] & 0xFF) <<  8 |
               (frame[3] & 0xFF);
      if (length > Registry.SASL_BUFFER_MAX_LIMIT || length < 0) {
         throw new SaslEncodingException("SASL buffer size limit exceeded");
      }

      in = new ByteArrayInputStream(frame, 4, length);
   }

   /** Trivial private constructor for use by the class method. */
   private InputBuffer() {
      super();
   }

   // Class methods
   // -------------------------------------------------------------------------

   /**
    * <p>Returns an instance of a SASL buffer given the buffer's encoded contents,
    * excluding the buffer's header bytes.</p>
    *
    * <p>Calls the method with the same name and three arguments as:
    * <code>getInstance(raw, 0, raw.length)</code>.
    *
    * @param raw the encoded form, excluding the header bytes, of a SASL buffer.
    * @return a new instance of {@link InputBuffer}.
    */
   public static InputBuffer getInstance(byte[] raw) {
      return getInstance(raw, 0, raw.length);
   }

   /**
    * <p>Returns an instance of a SASL buffer given the buffer's encoded
    * contents, excluding the buffer's header bytes.</p>
    *
    * @param raw the encoded form, excluding the header bytes, of a SASL buffer.
    * @param offset offset where to start using raw bytes from.
    * @param len number of bytes to use.
    * @return a new instance of {@link InputBuffer}.
    */
   public static InputBuffer getInstance(byte[] raw, int offset, int len) {
      InputBuffer result = new InputBuffer();
      result.in = new ByteArrayInputStream(raw, offset, len);
      return result;
   }

   /**
    * <p>Converts four octets into the number that they represent.</p>
    *
    * @param b the four octets.
    * @return the length.
    */
//   public static int fourBytesToLength(byte[] b) throws SaslEncodingException {
//      int result = b[0] << 24 | (b[1] & 0xFF) << 16 | (b[2] & 0xFF) << 8 | (b[3] & 0xFF);
//      if (result > Registry.SASL_FOUR_BYTE_MAX_LIMIT || result < 0) {
//         throw new SaslEncodingException("SASL EOS size limit exceeded");
//      }
//      return result;
//   }

   /**
    * <p>Converts two octets into the number that they represent.</p>
    *
    * @param b the two octets.
    * @return the length.
    */
   public static int twoBytesToLength(byte[] b) throws SaslEncodingException {
      final int result = (b[0] & 0xFF) << 8 | (b[1] & 0xFF);
      if (result > Registry.SASL_TWO_BYTE_MAX_LIMIT) {
         throw new SaslEncodingException("SASL MPI/Text size limit exceeded");
      }
      return result;
   }

   // Instance methods
   // -------------------------------------------------------------------------

   public boolean hasMoreElements() {
      return (in.available() > 0);
   }

   /**
    * <p>Decodes a SASL scalar quantity, <code>count</code>-octet long, from the
    * current buffer.</p>
    *
    * @param count the number of octets of this scalar quantity.
    * @return a native representation of a SASL scalar (unsigned integer) quantity.
    * @throws SaslEncodingException if an encoding exception occurs during the
    * operation.
    * @throws IOException if any other I/O exception occurs during the operation.
    */
   public long getScalar(int count) throws IOException {
      if (count < 0 || count > 4) {
         throw new SaslEncodingException("Invalid SASL scalar octet count: "
            +String.valueOf(count));
      }
      if (!hasMoreElements()) {
         throw new SaslEncodingException("Not enough bytes for a scalar in buffer");
      }
      if (in.available() < count) {
         throw new SaslEncodingException("Illegal SASL scalar encoding");
      }
      byte[] element = new byte[count];
      in.read(element);

      long result = 0L;
      for (int i = 0; i < count; i++) {
         result <<= 8;
         result |= element[i] & 0xFFL;
      }
      return result;
   }

   /**
    * <p>Decodes a SASL OS from the current buffer.</p>
    *
    * @return a native representation of a SASL OS.
    * @throws SaslEncodingException if an encoding exception occurs during the
    * operation.
    * @throws IOException if any other I/O exception occurs during the operation.
    */
   public byte[] getOS() throws IOException {
      if (!hasMoreElements()) {
         throw new SaslEncodingException("Not enough bytes for an octet-sequence in buffer");
      }
      final int elementLength = in.read();
      if (elementLength > Registry.SASL_ONE_BYTE_MAX_LIMIT) {
         throw new SaslEncodingException("SASL octet-sequence size limit exceeded");
      }

      if (in.available() < elementLength) {
         throw new SaslEncodingException("Illegal SASL octet-sequence encoding");
      }

      byte[] result = new byte[elementLength];
      in.read(result);

      return result;
   }

   /**
    * <p>Decodes a SASL EOS from the current buffer.</p>
    *
    * @return a native representation of a SASL EOS.
    * @throws SaslEncodingException if an encoding exception occurs during the
    * operation.
    * @throws IOException if any other I/O exception occurs during the operation.
    */
   public byte[] getEOS() throws IOException {
      if (in.available() < 2) {
         throw new SaslEncodingException(
               "Not enough bytes for an extended octet-sequence in buffer");
      }

      byte[] elementLengthBytes = new byte[2];
      in.read(elementLengthBytes);
      final int elementLength = twoBytesToLength(elementLengthBytes);
      if (in.available() < elementLength) {
         throw new SaslEncodingException("Illegal SASL extended octet-sequence encoding");
      }

      byte[] result = new byte[elementLength];
      in.read(result);

      return result;
   }

   /**
    * <p>Decodes a SASL MPI from the current buffer.</p>
    *
    * @return a native representation of a SASL MPI.
    * @throws SaslEncodingException if an encoding exception occurs during the
    * operation.
    * @throws IOException if any other I/O exception occurs during the operation.
    */
   public BigInteger getMPI() throws IOException {
      if (in.available() < 2) {
         throw new SaslEncodingException("Not enough bytes for an MPI in buffer");
      }
      byte[] elementLengthBytes = new byte[2];
      in.read(elementLengthBytes);
      final int elementLength = twoBytesToLength(elementLengthBytes);
      if (in.available() < elementLength) {
         throw new SaslEncodingException("Illegal SASL multi-precision integer encoding");
      }

      byte[] element = new byte[elementLength];
      in.read(element);

      return new BigInteger(1, element);
   }

   /**
    * <p>Decodes a SASL Text from the current buffer.</p>
    *
    * @return a native representation of a SASL Text.
    * @throws SaslEncodingException if an encoding exception occurs during the
    * operation.
    * @throws SaslEncodingException if the UTF-8 character encoding is not
    * supported on this platform.
    * @throws IOException if any other I/O exception occurs during the operation.
    */
   public String getText() throws IOException {
      if (in.available() < 2) {
         throw new SaslEncodingException("Not enough bytes for a text in buffer");
      }
      byte[] elementLengthBytes = new byte[2];
      in.read(elementLengthBytes);
      final int elementLength = twoBytesToLength(elementLengthBytes);
      if (in.available() < elementLength) {
         throw new SaslEncodingException("Illegal SASL text encoding");
      }

      byte[] element = new byte[elementLength];
      in.read(element);

      return new String(element, "UTF8");
   }
}
