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      1 /* libs/cutils/strdup16to8.c
      2 **
      3 ** Copyright 2006, The Android Open Source Project
      4 **
      5 ** Licensed under the Apache License, Version 2.0 (the "License");
      6 ** you may not use this file except in compliance with the License.
      7 ** You may obtain a copy of the License at
      8 **
      9 **     http://www.apache.org/licenses/LICENSE-2.0
     10 **
     11 ** Unless required by applicable law or agreed to in writing, software
     12 ** distributed under the License is distributed on an "AS IS" BASIS,
     13 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     14 ** See the License for the specific language governing permissions and
     15 ** limitations under the License.
     16 */
     17 
     18 #include <limits.h>  /* for SIZE_MAX */
     19 
     20 #include <cutils/jstring.h>
     21 #include <assert.h>
     22 #include <stdlib.h>
     23 
     24 
     25 /**
     26  * Given a UTF-16 string, compute the length of the corresponding UTF-8
     27  * string in bytes.
     28  */
     29 extern size_t strnlen16to8(const char16_t* utf16Str, size_t len)
     30 {
     31     size_t utf8Len = 0;
     32 
     33     /* A small note on integer overflow. The result can
     34      * potentially be as big as 3*len, which will overflow
     35      * for len > SIZE_MAX/3.
     36      *
     37      * Moreover, the result of a strnlen16to8 is typically used
     38      * to allocate a destination buffer to strncpy16to8 which
     39      * requires one more byte to terminate the UTF-8 copy, and
     40      * this is generally done by careless users by incrementing
     41      * the result without checking for integer overflows, e.g.:
     42      *
     43      *   dst = malloc(strnlen16to8(utf16,len)+1)
     44      *
     45      * Due to this, the following code will try to detect
     46      * overflows, and never return more than (SIZE_MAX-1)
     47      * when it detects one. A careless user will try to malloc
     48      * SIZE_MAX bytes, which will return NULL which can at least
     49      * be detected appropriately.
     50      *
     51      * As far as I know, this function is only used by strndup16(),
     52      * but better be safe than sorry.
     53      */
     54 
     55     /* Fast path for the usual case where 3*len is < SIZE_MAX-1.
     56      */
     57     if (len < (SIZE_MAX-1)/3) {
     58         while (len != 0) {
     59             len--;
     60             unsigned int uic = *utf16Str++;
     61 
     62             if (uic > 0x07ff)
     63                 utf8Len += 3;
     64             else if (uic > 0x7f || uic == 0)
     65                 utf8Len += 2;
     66             else
     67                 utf8Len++;
     68         }
     69         return utf8Len;
     70     }
     71 
     72     /* The slower but paranoid version */
     73     while (len != 0) {
     74         len--;
     75         unsigned int  uic     = *utf16Str++;
     76         size_t        utf8Cur = utf8Len;
     77 
     78         if (uic > 0x07ff)
     79             utf8Len += 3;
     80         else if (uic > 0x7f || uic == 0)
     81             utf8Len += 2;
     82         else
     83             utf8Len++;
     84 
     85         if (utf8Len < utf8Cur) /* overflow detected */
     86             return SIZE_MAX-1;
     87     }
     88 
     89     /* don't return SIZE_MAX to avoid common user bug */
     90     if (utf8Len == SIZE_MAX)
     91         utf8Len = SIZE_MAX-1;
     92 
     93     return utf8Len;
     94 }
     95 
     96 
     97 /**
     98  * Convert a Java-Style UTF-16 string + length to a JNI-Style UTF-8 string.
     99  *
    100  * This basically means: embedded \0's in the UTF-16 string are encoded
    101  * as "0xc0 0x80"
    102  *
    103  * Make sure you allocate "utf8Str" with the result of strlen16to8() + 1,
    104  * not just "len".
    105  *
    106  * Please note, a terminated \0 is always added, so your result will always
    107  * be "strlen16to8() + 1" bytes long.
    108  */
    109 extern char* strncpy16to8(char* utf8Str, const char16_t* utf16Str, size_t len)
    110 {
    111     char* utf8cur = utf8Str;
    112 
    113     /* Note on overflows: We assume the user did check the result of
    114      * strnlen16to8() properly or at a minimum checked the result of
    115      * its malloc(SIZE_MAX) in case of overflow.
    116      */
    117     while (len != 0) {
    118         len--;
    119         unsigned int uic = *utf16Str++;
    120 
    121         if (uic > 0x07ff) {
    122             *utf8cur++ = (uic >> 12) | 0xe0;
    123             *utf8cur++ = ((uic >> 6) & 0x3f) | 0x80;
    124             *utf8cur++ = (uic & 0x3f) | 0x80;
    125         } else if (uic > 0x7f || uic == 0) {
    126             *utf8cur++ = (uic >> 6) | 0xc0;
    127             *utf8cur++ = (uic & 0x3f) | 0x80;
    128         } else {
    129             *utf8cur++ = uic;
    130 
    131             if (uic == 0) {
    132                 break;
    133             }
    134         }
    135     }
    136 
    137    *utf8cur = '\0';
    138 
    139    return utf8Str;
    140 }
    141 
    142 /**
    143  * Convert a UTF-16 string to UTF-8.
    144  *
    145  */
    146 char * strndup16to8 (const char16_t* s, size_t n)
    147 {
    148     char*   ret;
    149     size_t  len;
    150 
    151     if (s == NULL) {
    152         return NULL;
    153     }
    154 
    155     len = strnlen16to8(s, n);
    156 
    157     /* We are paranoid, and we check for SIZE_MAX-1
    158      * too since it is an overflow value for our
    159      * strnlen16to8 implementation.
    160      */
    161     if (len >= SIZE_MAX-1)
    162         return NULL;
    163 
    164     ret = malloc(len + 1);
    165     if (ret == NULL)
    166         return NULL;
    167 
    168     strncpy16to8 (ret, s, n);
    169 
    170     return ret;
    171 }
    172