Mercurial > gnulib
view lib/areadlink-with-size.c @ 40196:e63f5d3edab5
relocatable-prog: Update documentation.
* doc/relocatable-maint.texi (Supporting Relocation): Update to match
the recent changes.
author | Bruno Haible <bruno@clisp.org> |
---|---|
date | Sun, 24 Feb 2019 01:49:15 +0100 |
parents | b06060465f09 |
children |
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/* readlink wrapper to return the link name in malloc'd storage. Unlike xreadlink and xreadlink_with_size, don't ever call exit. Copyright (C) 2001, 2003-2007, 2009-2019 Free Software Foundation, Inc. This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. */ /* Written by Jim Meyering <jim@meyering.net> */ #include <config.h> #include "areadlink.h" #include <errno.h> #include <limits.h> #include <stdint.h> #include <stdlib.h> #include <unistd.h> #ifndef SSIZE_MAX # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2)) #endif /* SYMLINK_MAX is used only for an initial memory-allocation sanity check, so it's OK to guess too small on hosts where there is no arbitrary limit to symbolic link length. */ #ifndef SYMLINK_MAX # define SYMLINK_MAX 1024 #endif #define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX) /* Call readlink to get the symbolic link value of FILE. SIZE is a hint as to how long the link is expected to be; typically it is taken from st_size. It need not be correct. Return a pointer to that NUL-terminated string in malloc'd storage. If readlink fails, malloc fails, or if the link value is longer than SSIZE_MAX, return NULL (caller may use errno to diagnose). */ char * areadlink_with_size (char const *file, size_t size) { /* Some buggy file systems report garbage in st_size. Defend against them by ignoring outlandish st_size values in the initial memory allocation. */ size_t symlink_max = SYMLINK_MAX; size_t INITIAL_LIMIT_BOUND = 8 * 1024; size_t initial_limit = (symlink_max < INITIAL_LIMIT_BOUND ? symlink_max + 1 : INITIAL_LIMIT_BOUND); /* The initial buffer size for the link value. */ size_t buf_size = size < initial_limit ? size + 1 : initial_limit; while (1) { ssize_t r; size_t link_length; char *buffer = malloc (buf_size); if (buffer == NULL) return NULL; r = readlink (file, buffer, buf_size); link_length = r; /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1 with errno == ERANGE if the buffer is too small. */ if (r < 0 && errno != ERANGE) { int saved_errno = errno; free (buffer); errno = saved_errno; return NULL; } if (link_length < buf_size) { buffer[link_length] = 0; return buffer; } free (buffer); if (buf_size <= MAXSIZE / 2) buf_size *= 2; else if (buf_size < MAXSIZE) buf_size = MAXSIZE; else { errno = ENOMEM; return NULL; } } }