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 */
strnlen16to8(const char16_t * utf16Str,size_t len)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 */
strncpy16to8(char * utf8Str,const char16_t * utf16Str,size_t len)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 */
strndup16to8(const char16_t * s,size_t n)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