1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include <cwchar>  // mbstate_t
10 #include <limits.h> // MB_LEN_MAX
11 #include <stdlib.h> // MB_CUR_MAX, size_t
12 #include <string.h> // memcpy
13 
14 // Converts `max_source_chars` from the wide character buffer pointer to by *`src`,
15 // into the multi byte character sequence buffer stored at `dst`, which must be
16 // `dst_size_bytes` bytes in size. Returns the number of bytes in the sequence
17 // converted from *src, excluding the null terminator.
18 // Returns (size_t) -1 if an error occurs and sets errno.
19 // If `dst` is NULL, `dst_size_bytes` is ignored and no bytes are copied to `dst`.
20 _LIBCPP_FUNC_VIS
21 size_t wcsnrtombs(char *__restrict dst, const wchar_t **__restrict src,
22                    size_t max_source_chars, size_t dst_size_bytes,
23                    mbstate_t *__restrict ps) {
24 
25   const size_t invalid_wchar = static_cast<size_t>(-1);
26 
27   size_t source_converted;
28   size_t dest_converted;
29   size_t result = 0;
30 
31   // If `dst` is null then `dst_size_bytes` should be ignored according to the
32   // standard. Setting dst_size_bytes to a large value has this effect.
33   if (dst == nullptr)
34     dst_size_bytes = static_cast<size_t>(-1);
35 
36   for (dest_converted = source_converted = 0;
37        source_converted < max_source_chars && (!dst || dest_converted < dst_size_bytes);
38        ++source_converted, dest_converted += result) {
39     wchar_t c = (*src)[source_converted];
40     size_t dest_remaining = dst_size_bytes - dest_converted;
41 
42     if (dst == nullptr) {
43       result = wcrtomb(NULL, c, ps);
44     } else if (dest_remaining >= static_cast<size_t>(MB_CUR_MAX)) {
45       // dst has enough space to translate in-place.
46       result = wcrtomb(dst + dest_converted, c, ps);
47     } else {
48       /*
49       * dst may not have enough space, so use a temporary buffer.
50       *
51       * We need to save a copy of the conversion state
52       * here so we can restore it if the multibyte
53       * character is too long for the buffer.
54       */
55       char buff[MB_LEN_MAX];
56       mbstate_t mbstate_tmp;
57 
58       if (ps != nullptr)
59         mbstate_tmp = *ps;
60       result = wcrtomb(buff, c, ps);
61 
62       if (result > dest_remaining) {
63         // Multi-byte sequence for character won't fit.
64         if (ps != nullptr)
65           *ps = mbstate_tmp;
66         if (result != invalid_wchar)
67           break;
68       } else {
69         // The buffer was used, so we need copy the translation to dst.
70         memcpy(dst, buff, result);
71       }
72     }
73 
74     // result (char_size) contains the size of the multi-byte-sequence converted.
75     // Otherwise, result (char_size) is (size_t) -1 and wcrtomb() sets the errno.
76     if (result == invalid_wchar) {
77       if (dst)
78         *src = *src + source_converted;
79       return invalid_wchar;
80     }
81 
82     if (c == L'\0') {
83       if (dst)
84         *src = NULL;
85       return dest_converted;
86     }
87   }
88 
89   if (dst)
90     *src = *src + source_converted;
91 
92   return dest_converted;
93 }
94