Line data    Source code

       1             : /* readlink wrapper to return the link name in malloc'd storage.
       2             :    Unlike xreadlink and xreadlink_with_size, don't ever call exit.
       3             : 
       4             :    Copyright (C) 2001, 2003-2007 Free Software Foundation, Inc.
       5             : 
       6             :    This program is free software: you can redistribute it and/or modify
       7             :    it under the terms of the GNU General Public License as published by
       8             :    the Free Software Foundation; either version 3 of the License, or
       9             :    (at your option) any later version.
      10             : 
      11             :    This program is distributed in the hope that it will be useful,
      12             :    but WITHOUT ANY WARRANTY; without even the implied warranty of
      13             :    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      14             :    GNU General Public License for more details.
      15             : 
      16             :    You should have received a copy of the GNU General Public License
      17             :    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
      18             : 
      19             : /* Written by Jim Meyering <jim@meyering.net>  */
      20             : 
      21             : #include <config.h>
      22             : 
      23             : #include "areadlink.h"
      24             : 
      25             : #include <stdio.h>
      26             : #include <errno.h>
      27             : #include <limits.h>
      28             : #include <sys/types.h>
      29             : #include <stdlib.h>
      30             : #include <unistd.h>
      31             : 
      32             : #ifndef SIZE_MAX
      33             : # define SIZE_MAX ((size_t) -1)
      34             : #endif
      35             : #ifndef SSIZE_MAX
      36             : # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
      37             : #endif
      38             : 
      39             : /* SYMLINK_MAX is used only for an initial memory-allocation sanity
      40             :    check, so it's OK to guess too small on hosts where there is no
      41             :    arbitrary limit to symbolic link length.  */
      42             : #ifndef SYMLINK_MAX
      43             : # define SYMLINK_MAX 1024
      44             : #endif
      45             : 
      46             : #define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
      47             : 
      48             : /* Call readlink to get the symbolic link value of FILE.
      49             :    SIZE is a hint as to how long the link is expected to be;
      50             :    typically it is taken from st_size.  It need not be correct.
      51             :    Return a pointer to that NUL-terminated string in malloc'd storage.
      52             :    If readlink fails, malloc fails, or if the link value is longer
      53             :    than SSIZE_MAX, return NULL (caller may use errno to diagnose).  */
      54             : 
      55             : char *
      56          26 : areadlink_with_size (char const *file, size_t size)
      57             : {
      58             :   /* Some buggy file systems report garbage in st_size.  Defend
      59             :      against them by ignoring outlandish st_size values in the initial
      60             :      memory allocation.  */
      61          26 :   size_t symlink_max = SYMLINK_MAX;
      62          26 :   size_t INITIAL_LIMIT_BOUND = 8 * 1024;
      63          26 :   size_t initial_limit = (symlink_max < INITIAL_LIMIT_BOUND
      64             :                           ? symlink_max + 1
      65          26 :                           : INITIAL_LIMIT_BOUND);
      66             : 
      67             :   /* The initial buffer size for the link value.  */
      68          26 :   size_t buf_size = size < initial_limit ? size + 1 : initial_limit;
      69             : 
      70             :   while (1)
      71           0 :     {
      72             :       ssize_t r;
      73             :       size_t link_length;
      74          26 :       char *buffer = malloc (buf_size);
      75             : 
      76          26 :       if (buffer == NULL)
      77           0 :         return NULL;
      78          26 :       r = readlink (file, buffer, buf_size);
      79          26 :       link_length = r;
      80             : 
      81             :       /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
      82             :          with errno == ERANGE if the buffer is too small.  */
      83          26 :       if (r < 0 && errno != ERANGE)
      84             :         {
      85           5 :           int saved_errno = errno;
      86           5 :           free (buffer);
      87           5 :           errno = saved_errno;
      88           5 :           return NULL;
      89             :         }
      90             : 
      91          21 :       if (link_length < buf_size)
      92             :         {
      93          21 :           buffer[link_length] = 0;
      94          21 :           return buffer;
      95             :         }
      96             : 
      97           0 :       free (buffer);
      98           0 :       if (buf_size <= MAXSIZE / 2)
      99           0 :         buf_size *= 2;
     100           0 :       else if (buf_size < MAXSIZE)
     101           0 :         buf_size = MAXSIZE;
     102             :       else
     103             :         {
     104           0 :           errno = ENOMEM;
     105           0 :           return NULL;
     106             :         }
     107             :     }
     108             : }