package gnu.crypto.key;

// ----------------------------------------------------------------------------
// $Id: IncomingMessage.java,v 1.2 2005/10/06 04:24:16 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.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.PrivateKey;
import java.security.PublicKey;

/**
 * <p>An implementation of an incoming message for use with key agreement
 * protocols.</p>
 *
 * @version $Revision: 1.2 $
 */
public class IncomingMessage {

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

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

   /** The length of the message contents, according to its 4-byte header. */
   protected int length;

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

   /**
    * <p>Constructs an incoming message given the message's encoded form,
    * including its header bytes.</p>
    *
    * @param b the encoded form, including the header bytes, of an incoming
    * message.
    * @throws KeyAgreementException if the buffer is malformed.
    */
   public IncomingMessage(byte[] b) throws KeyAgreementException {
      this();

      if (b.length < 4) {
         throw new KeyAgreementException("message header too short");
      }
      length = b[0] << 24 | (b[1] & 0xFF) << 16 | (b[2] & 0xFF) << 8 | (b[3] & 0xFF);
      if (length > Registry.SASL_BUFFER_MAX_LIMIT || length < 0) {
         throw new KeyAgreementException("message size limit exceeded");
      }
      in = new ByteArrayInputStream(b, 4, length);
   }

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

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

   /**
    * <p>Returns an instance of a message given its encoded contents, excluding
    * the message'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.
    * @return a new instance of <code>IncomingMessage</code>.
    */
   public static IncomingMessage getInstance(byte[] raw) {
      return getInstance(raw, 0, raw.length);
   }

   /**
    * <p>Returns an instance of a message given its encoded contents, excluding
    * the message's header bytes.</p>
    *
    * @param raw the encoded form, excluding the header bytes.
    * @param offset offset where to start using raw bytes from.
    * @param len number of bytes to use.
    * @return a new instance of <code>IncomingMessage</code>.
    */
   public static IncomingMessage getInstance(byte[] raw, int offset, int len) {
      IncomingMessage result = new IncomingMessage();
      result.in = new ByteArrayInputStream(raw, offset, len);
      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 KeyAgreementException {
      int result = (b[0] & 0xFF) << 8 | (b[1] & 0xFF);
      if (result > Registry.SASL_TWO_BYTE_MAX_LIMIT) {
         throw new KeyAgreementException("encoded MPI size limit exceeded");
      }
      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 KeyAgreementException {
      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 KeyAgreementException("encoded entity size limit exceeded");
      }
      return result;
   }

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

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

   public PublicKey readPublicKey() throws KeyAgreementException {
      if (in.available() < 4) {
         throw new KeyAgreementException("not enough bytes for a public key in message");
      }

      byte[] elementLengthBytes = new byte[4];
      in.read(elementLengthBytes, 0, 4);
      int elementLength = fourBytesToLength(elementLengthBytes);
      if (in.available() < elementLength) {
         throw new KeyAgreementException("illegal public key encoding");
      }

      byte[] kb = new byte[elementLength];
      in.read(kb, 0, elementLength);

      // instantiate the right codec and decode
      IKeyPairCodec kpc = KeyPairCodecFactory.getInstance(kb);
      if (kpc == null) {
         throw new KeyAgreementException(
               "invalid public key, or encoded with an unknown codec");
      }

      return kpc.decodePublicKey(kb);
   }

   public PrivateKey readPrivateKey() throws KeyAgreementException {
      if (in.available() < 4) {
         throw new KeyAgreementException("not enough bytes for a private key in message");
      }

      byte[] elementLengthBytes = new byte[4];
      in.read(elementLengthBytes, 0, 4);
      int elementLength = fourBytesToLength(elementLengthBytes);
      if (in.available() < elementLength) {
         throw new KeyAgreementException("illegal private key encoding");
      }

      byte[] kb = new byte[elementLength];
      in.read(kb, 0, elementLength);

      // instantiate the right codec and decode
      IKeyPairCodec kpc = KeyPairCodecFactory.getInstance(kb);
      if (kpc == null) {
         throw new KeyAgreementException(
               "invalid private key, or encoded with an unknown codec");
      }

      return kpc.decodePrivateKey(kb);
   }

   /**
    * <p>Decodes an MPI from the current message's contents.</p>
    *
    * @return a native representation of an MPI.
    * @throws KeyAgreementException if an encoding exception occurs during the
    * operation.
    */
   public BigInteger readMPI() throws KeyAgreementException {
      if (in.available() < 2) {
         throw new KeyAgreementException("not enough bytes for an MPI in message");
      }
      byte[] elementLengthBytes = new byte[2];
      in.read(elementLengthBytes, 0, 2);
      int elementLength = twoBytesToLength(elementLengthBytes);
      if (in.available() < elementLength) {
         throw new KeyAgreementException("illegal MPI encoding");
      }

      byte[] element = new byte[elementLength];
      in.read(element, 0, element.length);

      return new BigInteger(1, element);
   }

   public String readString() throws KeyAgreementException {
      if (in.available() < 2) {
         throw new KeyAgreementException("not enough bytes for a text in message");
      }
      byte[] elementLengthBytes = new byte[2];
      in.read(elementLengthBytes, 0, 2);
      int elementLength = twoBytesToLength(elementLengthBytes);
      if (in.available() < elementLength) {
         throw new KeyAgreementException("illegal text encoding");
      }

      byte[] element = new byte[elementLength];
      in.read(element, 0, element.length);
      String result = null;
      try {
         result = new String(element, "UTF8");
      } catch (UnsupportedEncodingException x) {
         throw new KeyAgreementException("unxupported UTF8 encoding", x);
      }

      return result;
   }
}
