| 1 | /* Append a null-terminated string to another string, with length checking. |
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| 2 | Copyright (C) 2023-2024 Free Software Foundation, Inc. |
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| 3 | This file is part of the GNU C Library. |
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| 4 | |
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| 5 | The GNU C Library is free software; you can redistribute it and/or |
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| 6 | modify it under the terms of the GNU Lesser General Public |
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| 7 | License as published by the Free Software Foundation; either |
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| 8 | version 2.1 of the License, or (at your option) any later version. |
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| 9 | |
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| 10 | The GNU C Library is distributed in the hope that it will be useful, |
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 13 | Lesser General Public License for more details. |
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| 14 | |
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| 15 | You should have received a copy of the GNU Lesser General Public |
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| 16 | License along with the GNU C Library; if not, see |
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| 17 | <https://www.gnu.org/licenses/>. */ |
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| 18 | |
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| 19 | #include <stdint.h> |
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| 20 | #include <string.h> |
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| 21 | |
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| 22 | size_t |
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| 23 | __strlcat (char *__restrict dest, const char *__restrict src, size_t size) |
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| 24 | { |
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| 25 | size_t src_length = strlen (src); |
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| 26 | |
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| 27 | /* Our implementation strlcat supports dest == NULL if size == 0 |
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| 28 | (for consistency with snprintf and strlcpy), but strnlen does |
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| 29 | not, so we have to cover this case explicitly. */ |
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| 30 | if (size == 0) |
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| 31 | return src_length; |
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| 32 | |
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| 33 | size_t dest_length = __strnlen (dest, size); |
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| 34 | if (dest_length != size) |
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| 35 | { |
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| 36 | /* Copy at most the remaining number of characters in the |
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| 37 | destination buffer. Leave for the NUL terminator. */ |
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| 38 | size_t to_copy = size - dest_length - 1; |
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| 39 | /* But not more than what is available in the source string. */ |
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| 40 | if (to_copy > src_length) |
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| 41 | to_copy = src_length; |
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| 42 | |
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| 43 | char *target = dest + dest_length; |
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| 44 | memcpy (target, src, to_copy); |
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| 45 | target[to_copy] = '\0'; |
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| 46 | } |
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| 47 | |
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| 48 | /* If the sum wraps around, we have more than SIZE_MAX + 2 bytes in |
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| 49 | the two input strings (including both null terminators). If each |
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| 50 | byte in the address space can be assigned a unique size_t value |
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| 51 | (which the static_assert checks), then by the pigeonhole |
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| 52 | principle, the two input strings must overlap, which is |
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| 53 | undefined. */ |
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| 54 | _Static_assert (sizeof (uintptr_t) == sizeof (size_t), |
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| 55 | "theoretical maximum object size covers address space" ); |
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| 56 | return dest_length + src_length; |
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| 57 | } |
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| 58 | libc_hidden_def (__strlcat) |
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| 59 | weak_alias (__strlcat, strlcat) |
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| 60 | |
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