lib/strlcat.c

   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 #include <stdint.h>
  24 #include <string.h>
  25
  26 #include "config.h"
  27
  28 #ifndef HAVE_STRLCAT
  29 #undef strlcat
  30
  31 size_t strlcat(char *__restrict dest, const char *__restrict src, size_t size);
  32
  33 size_t strlcat(char *__restrict dest, const char *__restrict src, size_t size)
  34 {
  35         size_t src_length = strlen(src);
  36
  37         /* Our implementation strlcat supports dest == NULL if size == 0
  38            (for consistency with snprintf and strlcpy), but strnlen does
  39            not, so we have to cover this case explicitly.  */
  40         if (size == 0)
  41                 return src_length;
  42
  43         size_t dest_length = strnlen(dest, size);
  44         if (dest_length != size) {
  45                 /* Copy at most the remaining number of characters in the
  46                    destination buffer.  Leave for the NUL terminator.  */
  47                 size_t to_copy = size - dest_length - 1;
  48                 /* But not more than what is available in the source string.  */
  49                 if (to_copy > src_length)
  50                         to_copy = src_length;
  51
  52                 char *target = dest + dest_length;
  53                 memcpy(target, src, to_copy);
  54                 target[to_copy] = '\0';
  55         }
  56
  57 /* If the sum wraps around, we have more than SIZE_MAX + 2 bytes in
  58    the two input strings (including both null terminators).  If each
  59    byte in the address space can be assigned a unique size_t value
  60    (which the static_assert checks), then by the pigeonhole
  61    principle, the two input strings must overlap, which is
  62    undefined.  */
  63 #if __STDC_VERSION__ >= 201112L
  64         _Static_assert(sizeof(uintptr_t) == sizeof(size_t),
  65                        "theoretical maximum object size covers address space");
  66 #endif
  67         return dest_length + src_length;
  68 }
  69 #endif /* HAVE_STRLCAT */