/* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage Copyright (C) 2001, 2003, 2004, 2005 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> */ #ifdef HAVE_CONFIG_H # include <config.h> #endif #include "xreadlink.h" #include <stdio.h> #include <errno.h> #include <limits.h> #include <sys/types.h> #include <stdlib.h> #if HAVE_UNISTD_H # include <unistd.h> #endif #ifndef SIZE_MAX # define SIZE_MAX ((size_t) -1) #endif #ifndef SSIZE_MAX # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2)) #endif #define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX) #include "xalloc.h" /* 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, return NULL (caller may use errno to diagnose). If malloc fails, or if the link value is longer than SSIZE_MAX :-), give a diagnostic and exit. */ char * xreadlink (char const *file, size_t size) { /* The initial buffer size for the link value. A power of 2 detects arithmetic overflow earlier, but is not required. */ size_t buf_size = size < MAXSIZE ? size + 1 : MAXSIZE; while (1) { char *buffer = xmalloc (buf_size); ssize_t r = readlink (file, buffer, buf_size); size_t 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 xalloc_die (); } }