Verify callback is run in either side.

[gnutls.git] / lib / gnutls_record.c

/*
 * Copyright (C) 2000-2012 Free Software Foundation, Inc.
 *
 * Author: Nikos Mavrogiannopoulos
 *
 * This file is part of GnuTLS.
 *
 * The GnuTLS is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 3 of
 * the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 *
 */

/* Functions that are record layer specific, are included in this file.
 */

/* allocate this many bytes more when encrypting or decrypting, to
 * compensate for broken backends such as cryptodev.
 */
#define CIPHER_SLACK_SIZE 32

#include "gnutls_int.h"
#include "gnutls_errors.h"
#include "debug.h"
#include "gnutls_compress.h"
#include "gnutls_cipher.h"
#include "gnutls_buffers.h"
#include "gnutls_mbuffers.h"
#include "gnutls_handshake.h"
#include "gnutls_hash_int.h"
#include "gnutls_cipher_int.h"
#include "algorithms.h"
#include "gnutls_db.h"
#include "gnutls_auth.h"
#include "gnutls_num.h"
#include "gnutls_record.h"
#include "gnutls_datum.h"
#include "gnutls_constate.h"
#include "ext/max_record.h"
#include <ext/heartbeat.h>
#include <gnutls_state.h>
#include <gnutls_dtls.h>
#include <gnutls_dh.h>
#include <random.h>

struct tls_record_st {
  uint16_t header_size;
  uint8_t version[2];
  uint64 sequence; /* DTLS */
  uint16_t length;
  uint16_t packet_size; /* header_size + length */
  content_type_t type;
  uint16_t epoch; /* valid in DTLS only */
  int v2:1; /* whether an SSLv2 client hello */
  /* the data */
};

/**
 * gnutls_record_disable_padding:
 * @session: is a #gnutls_session_t structure.
 *
 * Used to disabled padding in TLS 1.0 and above.  Normally you do not
 * need to use this function, but there are buggy clients that
 * complain if a server pads the encrypted data.  This of course will
 * disable protection against statistical attacks on the data.
 *
 * Normally only servers that require maximum compatibility with everything
 * out there, need to call this function.
 **/
void
gnutls_record_disable_padding (gnutls_session_t session)
{
  session->internals.priorities.no_padding = 1;
}

/**
 * gnutls_transport_set_ptr:
 * @session: is a #gnutls_session_t structure.
 * @ptr: is the value.
 *
 * Used to set the first argument of the transport function (for push
 * and pull callbacks). In berkeley style sockets this function will set the
 * connection descriptor.
 **/
void
gnutls_transport_set_ptr (gnutls_session_t session,
                          gnutls_transport_ptr_t ptr)
{
  session->internals.transport_recv_ptr = ptr;
  session->internals.transport_send_ptr = ptr;
}

/**
 * gnutls_transport_set_ptr2:
 * @session: is a #gnutls_session_t structure.
 * @recv_ptr: is the value for the pull function
 * @send_ptr: is the value for the push function
 *
 * Used to set the first argument of the transport function (for push
 * and pull callbacks). In berkeley style sockets this function will set the
 * connection descriptor.  With this function you can use two different
 * pointers for receiving and sending.
 **/
void
gnutls_transport_set_ptr2 (gnutls_session_t session,
                           gnutls_transport_ptr_t recv_ptr,
                           gnutls_transport_ptr_t send_ptr)
{
  session->internals.transport_send_ptr = send_ptr;
  session->internals.transport_recv_ptr = recv_ptr;
}

/**
 * gnutls_transport_get_ptr:
 * @session: is a #gnutls_session_t structure.
 *
 * Used to get the first argument of the transport function (like
 * PUSH and PULL).  This must have been set using
 * gnutls_transport_set_ptr().
 *
 * Returns: The first argument of the transport function.
 **/
gnutls_transport_ptr_t
gnutls_transport_get_ptr (gnutls_session_t session)
{
  return session->internals.transport_recv_ptr;
}

/**
 * gnutls_transport_get_ptr2:
 * @session: is a #gnutls_session_t structure.
 * @recv_ptr: will hold the value for the pull function
 * @send_ptr: will hold the value for the push function
 *
 * Used to get the arguments of the transport functions (like PUSH
 * and PULL).  These should have been set using
 * gnutls_transport_set_ptr2().
 **/
void
gnutls_transport_get_ptr2 (gnutls_session_t session,
                           gnutls_transport_ptr_t * recv_ptr,
                           gnutls_transport_ptr_t * send_ptr)
{

  *recv_ptr = session->internals.transport_recv_ptr;
  *send_ptr = session->internals.transport_send_ptr;
}

/**
 * gnutls_bye:
 * @session: is a #gnutls_session_t structure.
 * @how: is an integer
 *
 * Terminates the current TLS/SSL connection. The connection should
 * have been initiated using gnutls_handshake().  @how should be one
 * of %GNUTLS_SHUT_RDWR, %GNUTLS_SHUT_WR.
 *
 * In case of %GNUTLS_SHUT_RDWR the TLS session gets
 * terminated and further receives and sends will be disallowed.  If
 * the return value is zero you may continue using the underlying
 * transport layer. %GNUTLS_SHUT_RDWR sends an alert containing a close
 * request and waits for the peer to reply with the same message.
 *
 * In case of %GNUTLS_SHUT_WR the TLS session gets terminated
 * and further sends will be disallowed. In order to reuse the
 * connection you should wait for an EOF from the peer.
 * %GNUTLS_SHUT_WR sends an alert containing a close request.
 *
 * Note that not all implementations will properly terminate a TLS
 * connection.  Some of them, usually for performance reasons, will
 * terminate only the underlying transport layer, and thus not
 * distinguishing between a malicious party prematurely terminating 
 * the connection and normal termination. 
 *
 * This function may also return %GNUTLS_E_AGAIN or
 * %GNUTLS_E_INTERRUPTED; cf.  gnutls_record_get_direction().
 *
 * Returns: %GNUTLS_E_SUCCESS on success, or an error code, see
 *   function documentation for entire semantics.
 **/
int
gnutls_bye (gnutls_session_t session, gnutls_close_request_t how)
{
  int ret = 0;

  switch (STATE)
    {
    case STATE0:
    case STATE60:
      ret = _gnutls_io_write_flush (session);
      STATE = STATE60;
      if (ret < 0)
        {
          gnutls_assert ();
          return ret;
        }

    case STATE61:
      ret =
        gnutls_alert_send (session, GNUTLS_AL_WARNING, GNUTLS_A_CLOSE_NOTIFY);
      STATE = STATE61;
      if (ret < 0)
        {
          gnutls_assert ();
          return ret;
        }

    case STATE62:
      STATE = STATE62;
      if (how == GNUTLS_SHUT_RDWR)
        {
          do
            {
              ret = _gnutls_recv_int (session, GNUTLS_ALERT, -1, NULL, 0, NULL, 0);
            }
          while (ret == GNUTLS_E_GOT_APPLICATION_DATA);

          if (ret >= 0)
            session->internals.may_not_read = 1;

          if (ret < 0)
            {
              gnutls_assert ();
              return ret;
            }
        }
      STATE = STATE62;

      break;
    default:
      gnutls_assert ();
      return GNUTLS_E_INTERNAL_ERROR;
    }

  STATE = STATE0;

  session->internals.may_not_write = 1;
  return 0;
}

inline static void
session_invalidate (gnutls_session_t session)
{
  session->internals.invalid_connection = 1;
}


inline static void
session_unresumable (gnutls_session_t session)
{
  session->internals.resumable = RESUME_FALSE;
}

/* returns 0 if session is valid
 */
inline static int
session_is_valid (gnutls_session_t session)
{
  if (session->internals.invalid_connection != 0)
    return GNUTLS_E_INVALID_SESSION;

  return 0;
}

/* Copies the record version into the headers. The 
 * version must have 2 bytes at least.
 */
inline static void
copy_record_version (gnutls_session_t session,
                     gnutls_handshake_description_t htype, uint8_t version[2])
{
  gnutls_protocol_t lver;

  if (session->internals.initial_negotiation_completed || htype != GNUTLS_HANDSHAKE_CLIENT_HELLO
      || session->internals.default_record_version[0] == 0)
    {
      lver = gnutls_protocol_get_version (session);

      version[0] = _gnutls_version_get_major (lver);
      version[1] = _gnutls_version_get_minor (lver);
    }
  else
    {
      version[0] = session->internals.default_record_version[0];
      version[1] = session->internals.default_record_version[1];
    }
}

/* Increments the sequence value
 */
inline static int
sequence_increment (gnutls_session_t session,
                    uint64 * value)
{
  if (IS_DTLS(session))
    {
      return _gnutls_uint48pp(value);
    }
  else
    {
      return _gnutls_uint64pp(value);
    }
}

/* This function behaves exactly like write(). The only difference is
 * that it accepts, the gnutls_session_t and the content_type_t of data to
 * send (if called by the user the Content is specific)
 * It is intended to transfer data, under the current session.    
 *
 * Oct 30 2001: Removed capability to send data more than MAX_RECORD_SIZE.
 * This makes the function much easier to read, and more error resistant
 * (there were cases were the old function could mess everything up).
 * --nmav
 *
 * This function may accept a NULL pointer for data, and 0 for size, if
 * and only if the previous send was interrupted for some reason.
 *
 */
ssize_t
_gnutls_send_int (gnutls_session_t session, content_type_t type,
                  gnutls_handshake_description_t htype,
                  unsigned int epoch_rel, const void *_data,
                  size_t data_size, unsigned int mflags)
{
  mbuffer_st *bufel;
  ssize_t cipher_size;
  int retval, ret;
  int send_data_size;
  uint8_t headers[MAX_RECORD_HEADER_SIZE];
  int header_size;
  const uint8_t *data = _data;
  record_parameters_st *record_params;
  record_state_st *record_state;

  ret = _gnutls_epoch_get (session, epoch_rel, &record_params);
  if (ret < 0)
    return gnutls_assert_val(ret);

  /* Safeguard against processing data with an incomplete cipher state. */
  if (!record_params->initialized)
    return gnutls_assert_val(GNUTLS_E_INVALID_REQUEST);

  record_state = &record_params->write;

  /* Do not allow null pointer if the send buffer is empty.
   * If the previous send was interrupted then a null pointer is
   * ok, and means to resume.
   */
  if (session->internals.record_send_buffer.byte_length == 0 &&
      (data_size == 0 && _data == NULL))
    {
      gnutls_assert ();
      return GNUTLS_E_INVALID_REQUEST;
    }

  if (type != GNUTLS_ALERT)     /* alert messages are sent anyway */
    if (session_is_valid (session) || session->internals.may_not_write != 0)
      {
        gnutls_assert ();
        return GNUTLS_E_INVALID_SESSION;
      }

  headers[0] = type;

  /* Use the default record version, if it is
   * set.
   */
  copy_record_version (session, htype, &headers[1]);

  header_size = RECORD_HEADER_SIZE(session);
  /* Adjust header length and add sequence for DTLS */
  if (IS_DTLS(session))
    memcpy(&headers[3], &record_state->sequence_number.i, 8);

  _gnutls_record_log
    ("REC[%p]: Preparing Packet %s(%d) with length: %d\n", session,
     _gnutls_packet2str (type), type, (int) data_size);

  if (data_size > MAX_RECORD_SEND_SIZE(session))
    {
      if (IS_DTLS(session))
        {
          gnutls_assert ();
          return GNUTLS_E_LARGE_PACKET;
        }
      send_data_size = MAX_RECORD_SEND_SIZE(session);
    }
  else
    send_data_size = data_size;

  /* Only encrypt if we don't have data to send 
   * from the previous run. - probably interrupted.
   */
  if (mflags != 0 && session->internals.record_send_buffer.byte_length > 0)
    {
      ret = _gnutls_io_write_flush (session);
      if (ret > 0)
        cipher_size = ret;
      else
        cipher_size = 0;

      retval = session->internals.record_send_buffer_user_size;
    }
  else
    {
      /* now proceed to packet encryption
       */
      cipher_size = send_data_size + MAX_RECORD_OVERHEAD + CIPHER_SLACK_SIZE;
      bufel = _mbuffer_alloc (cipher_size, cipher_size);
      if (bufel == NULL)
        return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);

      ret =
        _gnutls_encrypt (session, headers, header_size, data,
                         send_data_size, _mbuffer_get_udata_ptr (bufel),
                         cipher_size, type, record_params);
      if (ret <= 0)
        {
          gnutls_assert ();
          if (ret == 0)
            ret = GNUTLS_E_ENCRYPTION_FAILED;
          gnutls_free (bufel);
          return ret;   /* error */
        }

      cipher_size = ret;
      retval = send_data_size;
      session->internals.record_send_buffer_user_size = send_data_size;

      /* increase sequence number
       */
      if (sequence_increment (session, &record_state->sequence_number) != 0)
        {
          session_invalidate (session);
          gnutls_free (bufel);
          return gnutls_assert_val(GNUTLS_E_RECORD_LIMIT_REACHED);
        }

      _mbuffer_set_udata_size (bufel, cipher_size);
      ret = _gnutls_io_write_buffered (session, bufel, mflags);
    }

  if (ret != cipher_size)
    {
      /* If we have sent any data then just return
       * the error value. Do not invalidate the session.
       */
      if (ret < 0 && gnutls_error_is_fatal (ret) == 0)
        return gnutls_assert_val(ret);

      if (ret > 0)
        ret = gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

      session_unresumable (session);
      session->internals.may_not_write = 1;
      return gnutls_assert_val(ret);
    }

  session->internals.record_send_buffer_user_size = 0;

  _gnutls_record_log ("REC[%p]: Sent Packet[%d] %s(%d) in epoch %d and length: %d\n",
                      session,
                      (unsigned int)
                      _gnutls_uint64touint32
                      (&record_state->sequence_number),
                      _gnutls_packet2str (type), type, 
                      (int) record_params->epoch,
                      (int) cipher_size);

  return retval;
}

inline static int
check_recv_type (gnutls_session_t session, content_type_t recv_type)
{
  switch (recv_type)
    {
    case GNUTLS_CHANGE_CIPHER_SPEC:
    case GNUTLS_ALERT:
    case GNUTLS_HANDSHAKE:
    case GNUTLS_HEARTBEAT:
    case GNUTLS_APPLICATION_DATA:
      return 0;
    default:
      gnutls_assert ();
      _gnutls_audit_log(session, "Received record packet of unknown type %u\n", (unsigned int)recv_type);
      return GNUTLS_E_UNEXPECTED_PACKET;
    }

}


/* Checks if there are pending data in the record buffers. If there are
 * then it copies the data.
 */
static int
check_buffers (gnutls_session_t session, content_type_t type,
               uint8_t * data, int data_size, void* seq)
{
  if ((type == GNUTLS_APPLICATION_DATA ||
       type == GNUTLS_HANDSHAKE ||
       type == GNUTLS_CHANGE_CIPHER_SPEC)
      && _gnutls_record_buffer_get_size (session) > 0)
    {
      int ret;
      ret = _gnutls_record_buffer_get (type, session, data, data_size, seq);
      if (ret < 0)
        {
          if (IS_DTLS(session))
            {
              if (ret == GNUTLS_E_UNEXPECTED_PACKET)
                {
                  ret = GNUTLS_E_AGAIN;
                }
            }
          gnutls_assert ();
          return ret;
        }

      return ret;
    }

  return 0;
}



/* Here we check if the advertized version is the one we
 * negotiated in the handshake.
 */
inline static int
record_check_version (gnutls_session_t session,
                      gnutls_handshake_description_t htype, uint8_t version[2])
{
  if (htype == GNUTLS_HANDSHAKE_CLIENT_HELLO)
    {
      /* Reject hello packets with major version higher than 3.
       */
      if (!(IS_DTLS(session)) && version[0] > 3)
        {
          gnutls_assert ();
          _gnutls_record_log
            ("REC[%p]: INVALID VERSION PACKET: (%d) %d.%d\n", session,
             htype, version[0], version[1]);
          return GNUTLS_E_UNSUPPORTED_VERSION_PACKET;
        }
    }
  else if (htype != GNUTLS_HANDSHAKE_SERVER_HELLO &&
           gnutls_protocol_get_version (session) !=
           _gnutls_version_get (version[0], version[1]))
    {
      /* Reject record packets that have a different version than the
       * one negotiated. Note that this version is not protected by any
       * mac. I don't really think that this check serves any purpose.
       */
      gnutls_assert ();
      _gnutls_record_log ("REC[%p]: INVALID VERSION PACKET: (%d) %d.%d\n",
                          session, htype, version[0], version[1]);

      return GNUTLS_E_UNSUPPORTED_VERSION_PACKET;
    }

  return 0;
}

/* This function will check if the received record type is
 * the one we actually expect and adds it to the proper
 * buffer. The bufel will be deinitialized after calling
 * this function, even if it fails.
 */
static int
record_add_to_buffers (gnutls_session_t session,
                   struct tls_record_st *recv, content_type_t type,
                   gnutls_handshake_description_t htype, 
                   uint64* seq,
                   mbuffer_st* bufel)
{

  int ret;

  if ((recv->type == type)
      && (type == GNUTLS_APPLICATION_DATA ||
          type == GNUTLS_CHANGE_CIPHER_SPEC ||
          type == GNUTLS_HANDSHAKE))
    {
      _gnutls_record_buffer_put (session, type, seq, bufel);
      
      /* if we received application data as expected then we
       * deactivate the async timer */
      _dtls_async_timer_delete(session);
    }
  else
    {
      /* if the expected type is different than the received 
       */
      switch (recv->type)
        {
        case GNUTLS_ALERT:
          if (bufel->msg.size < 2)
            {
              ret = gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
              goto unexpected_packet;
            }

          _gnutls_record_log
            ("REC[%p]: Alert[%d|%d] - %s - was received\n", session,
             bufel->msg.data[0], bufel->msg.data[1], gnutls_alert_get_name ((int) bufel->msg.data[1]));

          session->internals.last_alert = bufel->msg.data[1];

          /* if close notify is received and
           * the alert is not fatal
           */
          if (bufel->msg.data[1] == GNUTLS_A_CLOSE_NOTIFY && bufel->msg.data[0] != GNUTLS_AL_FATAL)
            {
              /* If we have been expecting for an alert do 
               */
              session->internals.read_eof = 1;
              ret = GNUTLS_E_SESSION_EOF;
              goto cleanup;
            }
          else
            {
              /* if the alert is FATAL or WARNING
               * return the apropriate message
               */

              gnutls_assert ();
              ret = GNUTLS_E_WARNING_ALERT_RECEIVED;
              if (bufel->msg.data[0] == GNUTLS_AL_FATAL)
                {
                  session_unresumable (session);
                  session_invalidate (session);
                  ret = gnutls_assert_val(GNUTLS_E_FATAL_ALERT_RECEIVED);
                }
              goto cleanup;
            }
          break;

        case GNUTLS_CHANGE_CIPHER_SPEC:
          if (!(IS_DTLS(session)))
            return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET);
            
          _gnutls_record_buffer_put (session, recv->type, seq, bufel);

          break;

        case GNUTLS_HEARTBEAT:
            ret = _gnutls_heartbeat_handle (session, bufel);
            goto cleanup;

        case GNUTLS_APPLICATION_DATA:
          if (session->internals.initial_negotiation_completed == 0)
            {
              ret = gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET);
              goto unexpected_packet;
            }


          /* the got_application data is only returned
           * if expecting client hello (for rehandshake
           * reasons). Otherwise it is an unexpected packet
           */
          if (type == GNUTLS_ALERT || (htype == GNUTLS_HANDSHAKE_CLIENT_HELLO
                                       && type == GNUTLS_HANDSHAKE))
            {
              /* even if data is unexpected put it into the buffer */
              if ((ret =
                   _gnutls_record_buffer_put (session, recv->type, seq,
                                              bufel)) < 0)
                {
                  gnutls_assert ();
                  goto cleanup;
                }

              return gnutls_assert_val(GNUTLS_E_GOT_APPLICATION_DATA);
            }
          else
            {
              ret = gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET);
              goto unexpected_packet;
            }

          break;

        case GNUTLS_HANDSHAKE:
          /* In DTLS we might receive a handshake replay from the peer to indicate
           * the our last TLS handshake messages were not received.
           */
          if (IS_DTLS(session))
            {
              if (type == GNUTLS_CHANGE_CIPHER_SPEC)
                {
                  ret = gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET);
                  goto unexpected_packet;
                }

              if (_dtls_is_async(session) && _dtls_async_timer_active(session))
                {
                  if (session->security_parameters.entity == GNUTLS_SERVER &&
                      bufel->htype == GNUTLS_HANDSHAKE_CLIENT_HELLO)
                    {
                      /* client requested rehandshake. Delete the timer */
                      _dtls_async_timer_delete(session);
                    }
                  else
                    {
                      session->internals.recv_state = RECV_STATE_DTLS_RETRANSMIT;
                      ret = _dtls_retransmit(session);
                      if (ret == 0) 
                        {
                          session->internals.recv_state = RECV_STATE_0;
                          ret = gnutls_assert_val(GNUTLS_E_AGAIN);
                          goto unexpected_packet;
                        }
                      goto cleanup;
                    }
                }
            }

          /* This is legal if HELLO_REQUEST is received - and we are a client.
           * If we are a server, a client may initiate a renegotiation at any time.
           */
          if (session->security_parameters.entity == GNUTLS_SERVER &&
              bufel->htype == GNUTLS_HANDSHAKE_CLIENT_HELLO)
            {
              gnutls_assert ();
              ret =
                _gnutls_record_buffer_put (session, recv->type, seq, bufel);
              if (ret < 0)
                {
                  gnutls_assert ();
                  goto cleanup;
                }
              return GNUTLS_E_REHANDSHAKE;
            }

          /* If we are already in a handshake then a Hello
           * Request is illegal. But here we don't really care
           * since this message will never make it up here.
           */

          /* So we accept it, if it is a Hello. If not, this will
           * fail and trigger flight retransmissions after some time. */
          ret = _gnutls_recv_hello_request (session, bufel->msg.data, bufel->msg.size);
          goto unexpected_packet;

          break;
        default:

          _gnutls_record_log
            ("REC[%p]: Received unexpected packet %d (%s) expecting %d (%s)\n",
             session, recv->type, _gnutls_packet2str(recv->type), type, _gnutls_packet2str(type));

          gnutls_assert ();
          ret = GNUTLS_E_UNEXPECTED_PACKET;
          goto unexpected_packet;
        }
    }

  return 0;

unexpected_packet:
  if (IS_DTLS(session) && ret != GNUTLS_E_REHANDSHAKE)
    {
      _mbuffer_xfree(&bufel);
      RETURN_DTLS_EAGAIN_OR_TIMEOUT(session, ret);
    }

cleanup:
  _mbuffer_xfree(&bufel);
  return ret;

}

int _gnutls_get_max_decrypted_data(gnutls_session_t session)
{
int ret;

  if (gnutls_compression_get (session) != GNUTLS_COMP_NULL ||
      session->internals.priorities.allow_large_records != 0)
    ret = MAX_RECORD_RECV_SIZE(session) + EXTRA_COMP_SIZE;
  else
    ret = MAX_RECORD_RECV_SIZE(session);

  return ret;
}

/* Checks the record headers and returns the length, version and
 * content type.
 */
static void
record_read_headers (gnutls_session_t session,
                      uint8_t headers[MAX_RECORD_HEADER_SIZE],
                      content_type_t type,
                      gnutls_handshake_description_t htype,
                      struct tls_record_st* record)
{

  /* Read the first two bytes to determine if this is a 
   * version 2 message 
   */

  if (htype == GNUTLS_HANDSHAKE_CLIENT_HELLO && type == GNUTLS_HANDSHAKE
      && headers[0] > 127 && !(IS_DTLS(session)))
    {

      /* if msb set and expecting handshake message
       * it should be SSL 2 hello 
       */
      record->version[0] = 3;           /* assume SSL 3.0 */
      record->version[1] = 0;

      record->length = (((headers[0] & 0x7f) << 8)) | headers[1];

      /* SSL 2.0 headers */
      record->header_size = record->packet_size = 2;
      record->type = GNUTLS_HANDSHAKE;    /* we accept only v2 client hello
                                         */

      /* in order to assist the handshake protocol.
       * V2 compatibility is a mess.
       */
      record->v2 = 1;
      record->epoch = 0;

      _gnutls_record_log ("REC[%p]: SSL 2.0 %s packet received. Length: %d\n",
                          session, 
                          _gnutls_packet2str (record->type),
                          record->length);

    }
  else 
    {
      /* dtls version 1.0 and TLS version 1.x */
      record->v2 = 0;

      record->type = headers[0];
      record->version[0] = headers[1];
      record->version[1] = headers[2];
      
      if(IS_DTLS(session))
        {
          memcpy(record->sequence.i, &headers[3], 8);
          record->length = _gnutls_read_uint16 (&headers[11]);
          record->epoch = _gnutls_read_uint16(record->sequence.i);
        }
      else
        {
          record->length = _gnutls_read_uint16 (&headers[3]);
          record->epoch = 0;
        }

      _gnutls_record_log ("REC[%p]: SSL %d.%d %s packet received. Epoch %d, length: %d\n",
                          session, (int)record->version[0], (int)record->version[1], 
                          _gnutls_packet2str (record->type),
                          (int)record->epoch, record->length);

    }

  record->packet_size += record->length;
}


static int recv_headers( gnutls_session_t session, content_type_t type, 
                         gnutls_handshake_description_t htype, 
                         struct tls_record_st* record,
                         unsigned int *ms)
{
int ret;
gnutls_datum_t raw; /* raw headers */
  /* Read the headers.
   */
  record->header_size = record->packet_size = RECORD_HEADER_SIZE(session);

  if ((ret =
       _gnutls_io_read_buffered (session, record->header_size, -1, ms)) != record->header_size)
    {
      if (ret < 0 && gnutls_error_is_fatal (ret) == 0)
        return ret;
      
      if (ret > 0)
        ret = GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
      else if (ret == 0)
        ret = GNUTLS_E_PREMATURE_TERMINATION;

      return gnutls_assert_val(ret);
    }

  ret = _mbuffer_linearize (&session->internals.record_recv_buffer);
  if (ret < 0)
    return gnutls_assert_val(ret);

  _mbuffer_head_get_first (&session->internals.record_recv_buffer, &raw);
  if (raw.size < RECORD_HEADER_SIZE(session))
    return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

  record_read_headers (session, raw.data, type, htype, record);

  /* Check if the DTLS epoch is valid */
  if (IS_DTLS(session)) 
    {
      if (_gnutls_epoch_is_valid(session, record->epoch) == 0)
        {
          _gnutls_audit_log(session, "Discarded message[%u] with invalid epoch %u.\n",
            (unsigned int)_gnutls_uint64touint32 (&record->sequence), 
            (unsigned int)record->sequence.i[0]*256+(unsigned int)record->sequence.i[1]);
          gnutls_assert();
          /* doesn't matter, just a fatal error */
          return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
        }
    }

  /* Here we check if the Type of the received packet is
   * ok. 
   */
  if ((ret = check_recv_type (session, record->type)) < 0)
    return gnutls_assert_val(ret);

  /* Here we check if the advertized version is the one we
   * negotiated in the handshake.
   */
  if ((ret = record_check_version (session, htype, record->version)) < 0)
    return gnutls_assert_val(ret);

  if (record->length > MAX_RECV_SIZE(session))
    {
      _gnutls_audit_log
        (session, "Received packet with illegal length: %u\n", (unsigned int)record->length);
      return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
    }

  _gnutls_record_log
    ("REC[%p]: Expected Packet %s(%d)\n", session,
     _gnutls_packet2str (type), type);
  _gnutls_record_log ("REC[%p]: Received Packet %s(%d) with length: %d\n",
                      session,
                      _gnutls_packet2str (record->type), record->type, record->length);

  
  return 0;
}

#define MAX_EMPTY_PACKETS_SEQUENCE 4

/* @ms: is the number of milliseconds to wait for data. Use zero for indefinite.
 *
 * This will receive record layer packets and add them to 
 * application_data_buffer and handshake_data_buffer.
 *
 * If the htype is not -1 then handshake timeouts
 * will be enforced.
 */
ssize_t
_gnutls_recv_in_buffers (gnutls_session_t session, content_type_t type,
                         gnutls_handshake_description_t htype, unsigned int ms)
{
  uint64 *packet_sequence;
  uint8_t *ciphertext;
  mbuffer_st* bufel = NULL, *decrypted = NULL;
  int ret;
  int empty_packet = 0;
  record_parameters_st *record_params;
  record_state_st *record_state;
  struct tls_record_st record;

begin:

  if (empty_packet > MAX_EMPTY_PACKETS_SEQUENCE)
    {
      gnutls_assert ();
      return GNUTLS_E_TOO_MANY_EMPTY_PACKETS;
    }

  memset(&record, 0, sizeof(record));

  if (session->internals.read_eof != 0)
    {
      /* if we have already read an EOF
       */
      return 0;
    }
  else if (session_is_valid (session) != 0
           || session->internals.may_not_read != 0)
    return gnutls_assert_val(GNUTLS_E_INVALID_SESSION);

  /* get the record state parameters */
  ret = _gnutls_epoch_get (session, EPOCH_READ_CURRENT, &record_params);
  if (ret < 0)
    return gnutls_assert_val (ret);

  /* Safeguard against processing data with an incomplete cipher state. */
  if (!record_params->initialized)
    return gnutls_assert_val (GNUTLS_E_INTERNAL_ERROR);

  record_state = &record_params->read;

  /* receive headers */
  ret = recv_headers(session, type, htype, &record, &ms);
  if (ret < 0)
    {
      ret = gnutls_assert_val_fatal(ret);
      goto recv_error;
    }

  if (IS_DTLS(session)) 
    packet_sequence = &record.sequence;
  else
    packet_sequence = &record_state->sequence_number;

  /* Read the packet data and insert it to record_recv_buffer.
   */
  ret =
       _gnutls_io_read_buffered (session, record.packet_size,
                                 record.type, &ms);
  if (ret != record.packet_size)
    {
      gnutls_assert();
      goto recv_error;
    }

  /* ok now we are sure that we have read all the data - so
   * move on !
   */
  ret = _mbuffer_linearize (&session->internals.record_recv_buffer);
  if (ret < 0)
    return gnutls_assert_val(ret);

  bufel = _mbuffer_head_get_first (&session->internals.record_recv_buffer, NULL);
  if (bufel == NULL)
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  /* We allocate the maximum possible to allow few compressed bytes to expand to a
   * full record.
   */
  decrypted = _mbuffer_alloc(MAX_RECORD_RECV_SIZE(session), 
                             MAX_RECORD_RECV_SIZE(session));
  if (decrypted == NULL)
    return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);

  ciphertext = (uint8_t*)_mbuffer_get_udata_ptr(bufel) + record.header_size;

  /* decrypt the data we got. 
   */
  ret =
    _gnutls_decrypt (session, ciphertext, record.length, 
        _mbuffer_get_udata_ptr(decrypted), _mbuffer_get_udata_size(decrypted),
                     record.type, record_params, packet_sequence);
  if (ret >= 0) _mbuffer_set_udata_size(decrypted, ret);

  _mbuffer_head_remove_bytes (&session->internals.record_recv_buffer,
                              record.header_size + record.length);
  if (ret < 0)
    {
      gnutls_assert();
      _gnutls_audit_log(session, "Discarded message[%u] due to invalid decryption\n", 
            (unsigned int)_gnutls_uint64touint32 (packet_sequence));
      goto sanity_check_error;
    }

  /* check for duplicates. We check after the message
   * is processed and authenticated to avoid someone
   * messing with our windows.
   */
  if (IS_DTLS(session)) 
    {
      ret = _dtls_record_check(record_params, packet_sequence);
      if (ret < 0)
        {
          _gnutls_audit_log(session, "Discarded duplicate message[%u]: %s\n",
            (unsigned int) _gnutls_uint64touint32 (packet_sequence), _gnutls_packet2str (record.type));
          goto sanity_check_error;
        }
      _gnutls_record_log
        ("REC[%p]: Decrypted Packet[%u.%u] %s(%d) with length: %d\n", session,
        (unsigned int)record.sequence.i[0]*256 +(unsigned int)record.sequence.i[1],
        (unsigned int) _gnutls_uint64touint32 (packet_sequence),
        _gnutls_packet2str (record.type), record.type, (int)_mbuffer_get_udata_size(decrypted));
    }
  else
    {
      _gnutls_record_log
        ("REC[%p]: Decrypted Packet[%u] %s(%d) with length: %d\n", session,
        (unsigned int) _gnutls_uint64touint32 (packet_sequence),
        _gnutls_packet2str (record.type), record.type, (int)_mbuffer_get_udata_size(decrypted));
    }

  /* increase sequence number 
   */
  if (!IS_DTLS(session) && sequence_increment (session, &record_state->sequence_number) != 0)
    {
      session_invalidate (session);
      gnutls_assert ();
      ret = GNUTLS_E_RECORD_LIMIT_REACHED;
      goto sanity_check_error;
    }

/* (originally for) TLS 1.0 CBC protection. 
 * Actually this code is called if we just received
 * an empty packet. An empty TLS packet is usually
 * sent to protect some vulnerabilities in the CBC mode.
 * In that case we go to the beginning and start reading
 * the next packet.
 */
  if (_mbuffer_get_udata_size(decrypted) == 0)
    {
      _mbuffer_xfree(&decrypted);
      empty_packet++;
      goto begin;
    }

  if (record.v2)
    decrypted->htype = GNUTLS_HANDSHAKE_CLIENT_HELLO_V2;
  else
    {
      uint8_t * p = _mbuffer_get_udata_ptr(decrypted);
      decrypted->htype = p[0];
    }

  ret =
    record_add_to_buffers (session, &record, type, htype, 
                           packet_sequence, decrypted);

  /* bufel is now either deinitialized or buffered somewhere else */

  if (ret < 0)
    return gnutls_assert_val(ret);

  return ret;

discard:
  session->internals.dtls.packets_dropped++;

  /* discard the whole received fragment. */
  bufel = _mbuffer_head_pop_first(&session->internals.record_recv_buffer);
  _mbuffer_xfree(&bufel);
  return gnutls_assert_val(GNUTLS_E_AGAIN);

sanity_check_error:
  if (IS_DTLS(session))
    {
      session->internals.dtls.packets_dropped++;
      ret = gnutls_assert_val(GNUTLS_E_AGAIN);
      goto cleanup;
    }

  session_unresumable (session);
  session_invalidate (session);

cleanup:
  _mbuffer_xfree(&decrypted);
  return ret;

recv_error:
  if (ret < 0 && (gnutls_error_is_fatal (ret) == 0 || ret == GNUTLS_E_TIMEDOUT))
    return ret;

  if (IS_DTLS(session))
    {
      goto discard;
    }

  session_invalidate (session);
  if (type == GNUTLS_ALERT) /* we were expecting close notify */
    {
      gnutls_assert ();
      return 0;             
    }
  session_unresumable (session);

  if (ret == 0)
    return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
  else
    return ret;
}

/* This function behaves exactly like read(). The only difference is
 * that it accepts the gnutls_session_t and the content_type_t of data to
 * receive (if called by the user the Content is Userdata only)
 * It is intended to receive data, under the current session.
 *
 * The gnutls_handshake_description_t was introduced to support SSL V2.0 client hellos.
 */
ssize_t
_gnutls_recv_int (gnutls_session_t session, content_type_t type,
                  gnutls_handshake_description_t htype,
                  uint8_t * data, size_t data_size, void* seq,
                  unsigned int ms)
{
  int ret;

  if ((type != GNUTLS_ALERT && type != GNUTLS_HEARTBEAT) && (data_size == 0 || data == NULL))
    return gnutls_assert_val(GNUTLS_E_INVALID_REQUEST);

  if (session->internals.read_eof != 0)
    {
      /* if we have already read an EOF
       */
      return 0;
    }
  else if (session_is_valid (session) != 0
           || session->internals.may_not_read != 0)
    {
      gnutls_assert ();
      return GNUTLS_E_INVALID_SESSION;
    }
    
  switch(session->internals.recv_state)
    {
      case RECV_STATE_DTLS_RETRANSMIT:
        ret = _dtls_retransmit(session);
        if (ret < 0)
          return gnutls_assert_val(ret);
        
        session->internals.recv_state = RECV_STATE_0;
      case RECV_STATE_0:

        _dtls_async_timer_check(session);
        /* If we have enough data in the cache do not bother receiving
         * a new packet. (in order to flush the cache)
         */ 
        ret = check_buffers (session, type, data, data_size, seq);
        if (ret != 0)
          return ret;

        ret = _gnutls_recv_in_buffers(session, type, htype, ms);
        if (ret < 0 && ret != GNUTLS_E_SESSION_EOF)
          return gnutls_assert_val(ret);

        return check_buffers (session, type, data, data_size, seq);
      default:
        return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
    }
}

/**
 * gnutls_record_send:
 * @session: is a #gnutls_session_t structure.
 * @data: contains the data to send
 * @data_size: is the length of the data
 *
 * This function has the similar semantics with send().  The only
 * difference is that it accepts a GnuTLS session, and uses different
 * error codes.
 * Note that if the send buffer is full, send() will block this
 * function.  See the send() documentation for full information.  You
 * can replace the default push function by using
 * gnutls_transport_set_ptr2() with a call to send() with a
 * MSG_DONTWAIT flag if blocking is a problem.
 * If the EINTR is returned by the internal push function (the
 * default is send()) then %GNUTLS_E_INTERRUPTED will be returned. If
 * %GNUTLS_E_INTERRUPTED or %GNUTLS_E_AGAIN is returned, you must
 * call this function again, with the same parameters; alternatively
 * you could provide a %NULL pointer for data, and 0 for
 * size. cf. gnutls_record_get_direction(). The errno value EMSGSIZE
 * maps to %GNUTLS_E_LARGE_PACKET.
 *
 * Returns: The number of bytes sent, or a negative error code.  The
 *   number of bytes sent might be less than @data_size.  The maximum
 *   number of bytes this function can send in a single call depends
 *   on the negotiated maximum record size.
 **/
ssize_t
gnutls_record_send (gnutls_session_t session, const void *data,
                    size_t data_size)
{
  return _gnutls_send_int (session, GNUTLS_APPLICATION_DATA, -1,
                           EPOCH_WRITE_CURRENT, data, data_size,
                           MBUFFER_FLUSH);
}

/**
 * gnutls_record_recv:
 * @session: is a #gnutls_session_t structure.
 * @data: the buffer that the data will be read into
 * @data_size: the number of requested bytes
 *
 * This function has the similar semantics with recv().  The only
 * difference is that it accepts a GnuTLS session, and uses different
 * error codes.
 * In the special case that a server requests a renegotiation, the
 * client may receive an error code of %GNUTLS_E_REHANDSHAKE.  This
 * message may be simply ignored, replied with an alert
 * %GNUTLS_A_NO_RENEGOTIATION, or replied with a new handshake,
 * depending on the client's will.
 * If %EINTR is returned by the internal push function (the default
 * is recv()) then %GNUTLS_E_INTERRUPTED will be returned.  If
 * %GNUTLS_E_INTERRUPTED or %GNUTLS_E_AGAIN is returned, you must
 * call this function again to get the data.  See also
 * gnutls_record_get_direction().
 * A server may also receive %GNUTLS_E_REHANDSHAKE when a client has
 * initiated a handshake. In that case the server can only initiate a
 * handshake or terminate the connection.
 *
 * Returns: The number of bytes received and zero on EOF (for stream
 * connections).  A negative error code is returned in case of an error.  
 * The number of bytes received might be less than the requested @data_size.
 **/
ssize_t
gnutls_record_recv (gnutls_session_t session, void *data, size_t data_size) 
{
    return _gnutls_recv_int (session, GNUTLS_APPLICATION_DATA, -1, data, data_size, NULL, 0);
}

/**
 * gnutls_record_recv_seq:
 * @session: is a #gnutls_session_t structure.
 * @data: the buffer that the data will be read into
 * @data_size: the number of requested bytes
 * @seq: is the packet's 64-bit sequence number. Should have space for 8 bytes.
 *
 * This function is the same as gnutls_record_recv(), except that
 * it returns in addition to data, the sequence number of the data.
 * This is useful in DTLS where record packets might be received
 * out-of-order. The returned 8-byte sequence number is an
 * integer in big-endian format and should be
 * treated as a unique message identification. 
 *
 * Returns: The number of bytes received and zero on EOF.  A negative
 *   error code is returned in case of an error.  The number of bytes
 *   received might be less than @data_size.
 *
 * Since: 3.0
 **/
ssize_t
gnutls_record_recv_seq (gnutls_session_t session, void *data, size_t data_size,
  unsigned char *seq)
{
  return _gnutls_recv_int (session, GNUTLS_APPLICATION_DATA, -1, data,
                           data_size, seq, 0);
}