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_EXPORTED_FROM_ABI size_t wcsnrtombs(
21     char* __restrict dst,
22     const wchar_t** __restrict src,
23     size_t max_source_chars,
24     size_t dst_size_bytes,
25     mbstate_t* __restrict ps) {
26   const size_t invalid_wchar = static_cast<size_t>(-1);
27 
28   size_t source_converted;
29   size_t dest_converted;
30   size_t result = 0;
31 
32   // If `dst` is null then `dst_size_bytes` should be ignored according to the
33   // standard. Setting dst_size_bytes to a large value has this effect.
34   if (dst == nullptr)
35     dst_size_bytes = static_cast<size_t>(-1);
36 
37   for (dest_converted = source_converted = 0;
38        source_converted < max_source_chars && (!dst || dest_converted < dst_size_bytes);
39        ++source_converted, dest_converted += result) {
40     wchar_t c             = (*src)[source_converted];
41     size_t dest_remaining = dst_size_bytes - dest_converted;
42 
43     if (dst == nullptr) {
44       result = wcrtomb(NULL, c, ps);
45     } else if (dest_remaining >= static_cast<size_t>(MB_CUR_MAX)) {
46       // dst has enough space to translate in-place.
47       result = wcrtomb(dst + dest_converted, c, ps);
48     } else {
49       /*
50        * dst may not have enough space, so use a temporary buffer.
51        *
52        * We need to save a copy of the conversion state
53        * here so we can restore it if the multibyte
54        * character is too long for the buffer.
55        */
56       char buff[MB_LEN_MAX];
57       mbstate_t mbstate_tmp;
58 
59       if (ps != nullptr)
60         mbstate_tmp = *ps;
61       result = wcrtomb(buff, c, ps);
62 
63       if (result > dest_remaining) {
64         // Multi-byte sequence for character won't fit.
65         if (ps != nullptr)
66           *ps = mbstate_tmp;
67         if (result != invalid_wchar)
68           break;
69       } else {
70         // The buffer was used, so we need copy the translation to dst.
71         memcpy(dst, buff, result);
72       }
73     }
74 
75     // result (char_size) contains the size of the multi-byte-sequence converted.
76     // Otherwise, result (char_size) is (size_t) -1 and wcrtomb() sets the errno.
77     if (result == invalid_wchar) {
78       if (dst)
79         *src = *src + source_converted;
80       return invalid_wchar;
81     }
82 
83     if (c == L'\0') {
84       if (dst)
85         *src = NULL;
86       return dest_converted;
87     }
88   }
89 
90   if (dst)
91     *src = *src + source_converted;
92 
93   return dest_converted;
94 }
95