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Diffstat (limited to 'lib/xreadlink.c')
| -rw-r--r-- | lib/xreadlink.c | 131 |
1 files changed, 131 insertions, 0 deletions
diff --git a/lib/xreadlink.c b/lib/xreadlink.c new file mode 100644 index 0000000..2aba265 --- /dev/null +++ b/lib/xreadlink.c @@ -0,0 +1,131 @@ +/* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage + + Copyright (C) 2001, 2003-2007 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 2, 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; see the file COPYING. + If not, write to the Free Software Foundation, + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ + +/* Written by Jim Meyering <jim@meyering.net> + and Bruno Haible <bruno@clisp.org>. */ + +#include <config.h> + +/* Specification. */ +#include "xreadlink.h" + +#include <stdio.h> +#include <string.h> +#include <errno.h> +#include <limits.h> +#include <sys/types.h> +#include <stdlib.h> +#include <unistd.h> + +#ifndef SIZE_MAX +# define SIZE_MAX ((size_t) -1) +#endif +#ifndef SSIZE_MAX +# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2)) +#endif + +#ifdef NO_XMALLOC +# define xmalloc malloc +#else +# include "xalloc.h" +#endif + +/* Call readlink to get the symbolic link value of FILENAME. + Return a pointer to that NUL-terminated string in malloc'd storage. + If readlink fails, return NULL (caller may use errno to diagnose). + If realloc fails, or if the link value is longer than SIZE_MAX :-), + give a diagnostic and exit. */ + +char * +xreadlink (char const *filename) +{ + /* The initial buffer size for the link value. A power of 2 + detects arithmetic overflow earlier, but is not required. */ +#define INITIAL_BUF_SIZE 1024 + + /* Allocate the initial buffer on the stack. This way, in the common + case of a symlink of small size, we get away with a single small malloc() + instead of a big malloc() followed by a shrinking realloc(). */ + char initial_buf[INITIAL_BUF_SIZE]; + + char *buffer = initial_buf; + size_t buf_size = sizeof (initial_buf); + + while (1) + { + /* Attempt to read the link into the current buffer. */ + ssize_t link_length = readlink (filename, buffer, buf_size); + + /* 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 (link_length < 0 && errno != ERANGE) + { + if (buffer != initial_buf) + { + int saved_errno = errno; + free (buffer); + errno = saved_errno; + } + return NULL; + } + + if ((size_t) link_length < buf_size) + { + buffer[link_length++] = '\0'; + + /* Return it in a chunk of memory as small as possible. */ + if (buffer == initial_buf) + { + buffer = (char *) xmalloc (link_length); +#ifdef NO_XMALLOC + if (buffer == NULL) + return NULL; +#endif + memcpy (buffer, initial_buf, link_length); + } + else + { + /* Shrink buffer before returning it. */ + if ((size_t) link_length < buf_size) + { + char *smaller_buffer = (char *) realloc (buffer, link_length); + + if (smaller_buffer != NULL) + buffer = smaller_buffer; + } + } + return buffer; + } + + if (buffer != initial_buf) + free (buffer); + buf_size *= 2; + if (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0)) +#ifdef NO_XMALLOC + return NULL; +#else + xalloc_die (); +#endif + buffer = (char *) xmalloc (buf_size); +#ifdef NO_XMALLOC + if (buffer == NULL) + return NULL; +#endif + } +} |