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1 /* Append a null-terminated string to another string, with length checking.
2 * Copyright (C) 2016 Free Software Foundation, Inc.
3 * This file is part of the GNU C Library.
4 *
5 * The GNU C Library is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU Lesser General Public
7 * License as published by the Free Software Foundation; either
8 * version 2.1 of the License, or (at your option) any later version.
9 *
10 * The GNU C Library is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * Lesser General Public License for more details.
14 *
15 * You should have received a copy of the GNU Lesser General Public
16 * License along with the GNU C Library; if not, see
17 * <http://www.gnu.org/licenses/>.
18 */
19
20 /* adapted for Quagga from glibc patch submission originally from
21 * Florian Weimer <fweimer@redhat.com>, 2016-05-18 */
22
23 #ifdef HAVE_CONFIG_H
24 #include "config.h"
25 #endif
26
27 #include <stdint.h>
28 #include <string.h>
29
30 #ifndef HAVE_STRLCAT
31 #undef strlcat
32
33 size_t strlcat(char *__restrict dest,
34 const char *__restrict src, size_t destsize);
35
36 size_t strlcat(char *__restrict dest,
37 const char *__restrict src, size_t destsize)
38 {
39 size_t src_length = strlen(src);
40
41 /* Our implementation strlcat supports dest == NULL if size == 0
42 (for consistency with snprintf and strlcpy), but strnlen does
43 not, so we have to cover this case explicitly. */
44 if (destsize == 0)
45 return src_length;
46
47 size_t dest_length = strnlen(dest, destsize);
48 if (dest_length != destsize) {
49 /* Copy at most the remaining number of characters in the
50 destination buffer. Leave for the NUL terminator. */
51 size_t to_copy = destsize - dest_length - 1;
52 /* But not more than what is available in the source string. */
53 if (to_copy > src_length)
54 to_copy = src_length;
55
56 char *target = dest + dest_length;
57 memcpy(target, src, to_copy);
58 target[to_copy] = '\0';
59 }
60
61 /* If the sum wraps around, we have more than SIZE_MAX + 2 bytes in
62 the two input strings (including both null terminators). If each
63 byte in the address space can be assigned a unique size_t value
64 (which the static_assert checks), then by the pigeonhole
65 principle, the two input strings must overlap, which is
66 undefined. */
67 _Static_assert(sizeof(uintptr_t) == sizeof(size_t),
68 "theoretical maximum object size covers address space");
69 return dest_length + src_length;
70 }
71 #endif /* HAVE_STRLCAT */