/*

 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")

 *

 * SPDX-License-Identifier: MPL-2.0

 *

 * This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, you can obtain one at https://mozilla.org/MPL/2.0/.

 *

 * See the COPYRIGHT file distributed with this work for additional

 * information regarding copyright ownership.

 */

#include <string.h>

#include <isc/utf8.h>

#include <isc/util.h>

/*

 * UTF-8 is defined in "The Unicode Standard -- Version 4.0"

 * Also see RFC 3629.

 *

 * Char. number range  |        UTF-8 octet sequence

 *    (hexadecimal)    |              (binary)

 *  --------------------+---------------------------------------------

 * 0000 0000-0000 007F | 0xxxxxxx

 * 0000 0080-0000 07FF | 110xxxxx 10xxxxxx

 * 0000 0800-0000 FFFF | 1110xxxx 10xxxxxx 10xxxxxx

 * 0001 0000-0010 FFFF | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

 */

bool

isc_utf8_valid(const unsigned char *buf, size_t len) {

  REQUIRE(buf != NULL);

  for (size_t i = 0; i < len; i++) {

    /*

     * ASCII character range (first row).

     */

    if (buf[i] <= 0x7f) {

      continue;

    }

    /*

     * 0x80 -> 1000 0000

     * 0xC0 -> 1100 0000

     * 0xE0 -> 1110 0000

     *

     * Is unicode character is encoded using 2 bytes (second row).

     */

    if ((i + 1) < len && (buf[i] & 0xe0) == 0xc0 &&

        (buf[i + 1] & 0xc0) == 0x80)

    {

      unsigned int w;

      w = (buf[i] & 0x1f) << 6;

      w |= (buf[++i] & 0x3f);

      if (w < 0x80) {

        return false;

      }

      continue;

    }

    /*

     * 0x80 -> 1000 0000

     * 0xC0 -> 1100 0000

     * 0xE0 -> 1110 0000

     * 0xF0 -> 1111 0000

     *

     * Is unicode character is encoded within 3 bytes (third row).

     */

    if ((i + 2) < len && (buf[i] & 0xf0) == 0xe0 &&

        (buf[i + 1] & 0xc0) == 0x80 && (buf[i + 2] & 0xc0) == 0x80)

    {

      unsigned int w;

      w = (buf[i] & 0x0f) << 12;

      w |= (buf[++i] & 0x3f) << 6;

      w |= (buf[++i] & 0x3f);

      if (w < 0x0800) {

        return false;

      }

      /*

       * Unicode range 0xD800..0xDFFF is reserved (UTF16

       * surrogates)

       */

      if (w >= 0xD800 && w <= 0xDFFF) {

        return false;

      }

      continue;

    }

    /*

     * 0x80 -> 1000 0000

     * 0xC0 -> 1100 0000

     * 0xE0 -> 1110 0000

     * 0xF0 -> 1111 0000

     * 0xF8 -> 1111 1000

     *

     * Is unicode character is encoded within 4 bytes (fourth row).

     */

    if ((i + 3) < len && (buf[i] & 0xf8) == 0xf0 &&

        (buf[i + 1] & 0xc0) == 0x80 &&

        (buf[i + 2] & 0xc0) == 0x80 && (buf[i + 3] & 0xc0) == 0x80)

    {

      unsigned int w;

      w = (buf[i] & 0x07) << 18;

      w |= (buf[++i] & 0x3f) << 12;

      w |= (buf[++i] & 0x3f) << 6;

      w |= (buf[++i] & 0x3f);

      if (w < 0x10000 || w > 0x10FFFF) {

        return false;

      }

      continue;

    }

    return false;

  }

  return true;

}

bool

isc_utf8_bom(const unsigned char *buf, size_t len) {

  REQUIRE(buf != NULL);

  if (len >= 3U && !memcmp(buf, "\xef\xbb\xbf", 3)) {

    return true;

  }

  return false;

}