lib/strlcat.c

   1 // SPDX-License-Identifier: LGPL-2.1-or-later
   2 /* Append a null-terminated string to another string, with length checking.
   3  * Copyright (C) 2016 Free Software Foundation, Inc.
   4  * This file is part of the GNU C Library.
   5  */
   6
   7 /* adapted for Quagga from glibc patch submission originally from
   8  * Florian Weimer <fweimer@redhat.com>, 2016-05-18 */
   9
  10 #ifdef HAVE_CONFIG_H
  11 #include "config.h"
  12 #endif
  13
  14 #include <stdint.h>
  15 #include <string.h>
  16
  17 #ifndef HAVE_STRLCAT
  18 #undef strlcat
  19
  20 size_t strlcat(char *__restrict dest,
  21                const char *__restrict src, size_t destsize);
  22
  23 size_t strlcat(char *__restrict dest,
  24                const char *__restrict src, size_t destsize)
  25 {
  26         size_t src_length = strlen(src);
  27
  28         /* Our implementation strlcat supports dest == NULL if size == 0
  29            (for consistency with snprintf and strlcpy), but strnlen does
  30            not, so we have to cover this case explicitly.  */
  31         if (destsize == 0)
  32                 return src_length;
  33
  34         size_t dest_length = strnlen(dest, destsize);
  35         if (dest_length != destsize) {
  36                 /* Copy at most the remaining number of characters in the
  37                    destination buffer.  Leave for the NUL terminator.  */
  38                 size_t to_copy = destsize - dest_length - 1;
  39                 /* But not more than what is available in the source string.  */
  40                 if (to_copy > src_length)
  41                         to_copy = src_length;
  42
  43                 char *target = dest + dest_length;
  44                 memcpy(target, src, to_copy);
  45                 target[to_copy] = '\0';
  46         }
  47
  48 /* If the sum wraps around, we have more than SIZE_MAX + 2 bytes in
  49    the two input strings (including both null terminators).  If each
  50    byte in the address space can be assigned a unique size_t value
  51    (which the static_assert checks), then by the pigeonhole
  52    principle, the two input strings must overlap, which is
  53    undefined.  */
  54         _Static_assert(sizeof(uintptr_t) == sizeof(size_t),
  55                        "theoretical maximum object size covers address space");
  56         return dest_length + src_length;
  57 }
  58 #endif /* HAVE_STRLCAT */