/* tlv.c - Tag-Length-Value Utilities

 *  Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc.

 *

 * This file is part of GnuPG.

 *

 * This file is free software; you can redistribute it and/or modify

 * it under the terms of either

 *

 *   - 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.

 *

 * or

 *

 *   - the GNU General Public License as published by the Free

 *     Software Foundation; either version 2 of the License, or (at

 *     your option) any later version.

 *

 * or both in parallel, as here.

 *

 * This file 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; if not, see <https://www.gnu.org/licenses/>.

 */

#include <config.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <gpg-error.h>

#include "util.h"

#include "tlv.h"

static const unsigned char *

do_find_tlv (const unsigned char *buffer, size_t length,

             int tag, size_t *nbytes, int nestlevel)

{

  const unsigned char *s = buffer;

  size_t n = length;

  size_t len;

  int this_tag;

  int composite;

  for (;;)

    {

      if (n < 2)

        return NULL; /* Buffer definitely too short for tag and length. */

      if (!*s || *s == 0xff)

        { /* Skip optional filler between TLV objects. */

          s++;

          n--;

          continue;

        }

      composite = !!(*s & 0x20);

      if ((*s & 0x1f) == 0x1f)

        { /* more tag bytes to follow */

          s++;

          n--;

          if (n < 2)

            return NULL; /* buffer definitely too short for tag and length. */

          if ((*s & 0x1f) == 0x1f)

            return NULL; /* We support only up to 2 bytes. */

          this_tag = (s[-1] << 8) | (s[0] & 0x7f);

        }

      else

        this_tag = s[0];

      len = s[1];

      s += 2; n -= 2;

      if (len < 0x80)

        ;

      else if (len == 0x81)

        { /* One byte length follows. */

          if (!n)

            return NULL; /* we expected 1 more bytes with the length. */

          len = s[0];

          s++; n--;

        }

      else if (len == 0x82)

        { /* Two byte length follows. */

          if (n < 2)

            return NULL; /* We expected 2 more bytes with the length. */

          len = ((size_t)s[0] << 8) | s[1];

          s += 2; n -= 2;

        }

      else

        return NULL; /* APDU limit is 65535, thus it does not make

                        sense to assume longer length fields. */

      if (composite && nestlevel < 100)

        { /* Dive into this composite DO after checking for a too deep

             nesting. */

          const unsigned char *tmp_s;

          size_t tmp_len;

          tmp_s = do_find_tlv (s, len, tag, &tmp_len, nestlevel+1);

          if (tmp_s)

            {

              *nbytes = tmp_len;

              return tmp_s;

            }

        }

      if (this_tag == tag)

        {

          *nbytes = len;

          return s;

        }

      if (len > n)

        return NULL; /* Buffer too short to skip to the next tag. */

      s += len; n -= len;

    }

}

/* Locate a TLV encoded data object in BUFFER of LENGTH and

   return a pointer to value as well as its length in NBYTES.  Return

   NULL if it was not found or if the object does not fit into the buffer. */

const unsigned char *

find_tlv (const unsigned char *buffer, size_t length,

          int tag, size_t *nbytes)

{

  const unsigned char *p;

  p = do_find_tlv (buffer, length, tag, nbytes, 0);

  if (p && *nbytes > (length - (p-buffer)))

    p = NULL; /* Object longer than buffer. */

  return p;

}

/* Locate a TLV encoded data object in BUFFER of LENGTH and

   return a pointer to value as well as its length in NBYTES.  Return

   NULL if it was not found.  Note, that the function does not check

   whether the value fits into the provided buffer. */

const unsigned char *

find_tlv_unchecked (const unsigned char *buffer, size_t length,

                    int tag, size_t *nbytes)

{

  return do_find_tlv (buffer, length, tag, nbytes, 0);

}

/* ASN.1 BER parser: Parse BUFFER of length SIZE and return the tag

 * and the length part from the TLV triplet.  Update BUFFER and SIZE

 * on success.  Note that this function does not check that the value

 * fits into the provided buffer; this allows one to work on the TL part

 * of a TLV. */

gpg_error_t

parse_ber_header (unsigned char const **buffer, size_t *size,

                  int *r_class, int *r_tag,

                  int *r_constructed, int *r_ndef,

                  size_t *r_length, size_t *r_nhdr)

{

  int c;

  unsigned long tag;

  const unsigned char *buf = *buffer;

  size_t length = *size;

  *r_ndef = 0;

  *r_length = 0;

  *r_nhdr = 0;

  /* Get the tag. */

  if (!length)

    return gpg_err_make (default_errsource, GPG_ERR_EOF);

  c = *buf++; length--; ++*r_nhdr;

  *r_class = (c & 0xc0) >> 6;

  *r_constructed = !!(c & 0x20);

  tag = c & 0x1f;

  if (tag == 0x1f)

    {

      tag = 0;

      do

        {

          tag <<= 7;

          if (!length)

            return gpg_err_make (default_errsource, GPG_ERR_EOF);

          c = *buf++; length--; ++*r_nhdr;

          tag |= c & 0x7f;

        }

      while (c & 0x80);

    }

  *r_tag = tag;

  /* Get the length. */

  if (!length)

    return gpg_err_make (default_errsource, GPG_ERR_EOF);

  c = *buf++; length--; ++*r_nhdr;

  if ( !(c & 0x80) )

    *r_length = c;

  else if (c == 0x80)

    *r_ndef = 1;

  else if (c == 0xff)

    return gpg_err_make (default_errsource, GPG_ERR_BAD_BER);

  else

    {

      unsigned long len = 0;

      int count = (c & 0x7f);

      if (count > (sizeof(len)<sizeof(size_t)?sizeof(len):sizeof(size_t)))

        return gpg_err_make (default_errsource, GPG_ERR_BAD_BER);

      for (; count; count--)

        {

          len <<= 8;

          if (!length)

            return gpg_err_make (default_errsource, GPG_ERR_EOF);

          c = *buf++; length--; ++*r_nhdr;

          len |= c & 0xff;

        }

      *r_length = len;

    }

  if (*r_length > *r_nhdr && (*r_nhdr + *r_length) < *r_length)

    {

      return gpg_err_make (default_errsource, GPG_ERR_EOVERFLOW);

    }

  /* Without this kludge some example certs can't be parsed. */

  if (*r_class == CLASS_UNIVERSAL && !*r_tag)

    *r_length = 0;

  *buffer = buf;

  *size = length;

  return 0;

}

/* FIXME: The following function should not go into this file but for

   now it is easier to keep it here. */

/* Return the next token of an canonical encoded S-expression.  BUF

   is the pointer to the S-expression and BUFLEN is a pointer to the

   length of this S-expression (used to validate the syntax).  Both

   are updated to reflect the new position.  The token itself is

   returned as a pointer into the original buffer at TOK and TOKLEN.

   If a parentheses is the next token, TOK will be set to NULL.

   TOKLEN is checked to be within the bounds.  On error an error code

   is returned and pointers are not guaranteed to point to

   meaningful values.  DEPTH should be initialized to 0 and will

   reflect on return the actual depth of the tree. To detect the end

   of the S-expression it is advisable to check DEPTH after a

   successful return.

   depth = 0;

   while (!(err = parse_sexp (&buf, &buflen, &depth, &tok, &toklen))

          && depth)

     process_token (tok, toklen);

   if (err)

     handle_error ();

 */

gpg_error_t

parse_sexp (unsigned char const **buf, size_t *buflen,

            int *depth, unsigned char const **tok, size_t *toklen)

{

  const unsigned char *s;

  size_t n, vlen;

  s = *buf;

  n = *buflen;

  *tok = NULL;

  *toklen = 0;

  if (!n)

    return *depth ? gpg_err_make (default_errsource, GPG_ERR_INV_SEXP) : 0;

  if (*s == '(')

    {

      s++; n--;

      (*depth)++;

      *buf = s;

      *buflen = n;

      return 0;

    }

  if (*s == ')')

    {

      if (!*depth)

        return gpg_err_make (default_errsource, GPG_ERR_INV_SEXP);

      *toklen = 1;

      s++; n--;

      (*depth)--;

      *buf = s;

      *buflen = n;

      return 0;

    }

  for (vlen=0; n && *s && *s != ':' && (*s >= '0' && *s <= '9'); s++, n--)

    vlen = vlen*10 + (*s - '0');

  if (!n || *s != ':')

    return gpg_err_make (default_errsource, GPG_ERR_INV_SEXP);

  s++; n--;

  if (vlen > n)

    return gpg_err_make (default_errsource, GPG_ERR_INV_SEXP);

  *tok = s;

  *toklen = vlen;

  s += vlen;

  n -= vlen;

  *buf = s;

  *buflen = n;

  return 0;

}