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Annotation of embedaddon/libiconv/srclib/areadlink.c, revision 1.1.1.1

1.1       misho       1: /* areadlink.c -- 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:    and Bruno Haible <bruno@clisp.org>.  */
                     21: 
                     22: #include <config.h>
                     23: 
                     24: /* Specification.  */
                     25: #include "areadlink.h"
                     26: 
                     27: #include <string.h>
                     28: #include <errno.h>
                     29: #include <limits.h>
                     30: #include <sys/types.h>
                     31: #include <stdlib.h>
                     32: #include <unistd.h>
                     33: 
                     34: #ifndef SIZE_MAX
                     35: # define SIZE_MAX ((size_t) -1)
                     36: #endif
                     37: #ifndef SSIZE_MAX
                     38: # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
                     39: #endif
                     40: 
                     41: /* Call readlink to get the symbolic link value of FILENAME.
                     42:    Return a pointer to that NUL-terminated string in malloc'd storage.
                     43:    If readlink fails, return NULL and set errno.
                     44:    If realloc fails, or if the link value is longer than SIZE_MAX :-),
                     45:    return NULL and set errno to ENOMEM.  */
                     46: 
                     47: char *
                     48: areadlink (char const *filename)
                     49: {
                     50:   /* The initial buffer size for the link value.  A power of 2
                     51:      detects arithmetic overflow earlier, but is not required.  */
                     52: #define INITIAL_BUF_SIZE 1024
                     53: 
                     54:   /* Allocate the initial buffer on the stack.  This way, in the common
                     55:      case of a symlink of small size, we get away with a single small malloc()
                     56:      instead of a big malloc() followed by a shrinking realloc().  */
                     57:   char initial_buf[INITIAL_BUF_SIZE];
                     58: 
                     59:   char *buffer = initial_buf;
                     60:   size_t buf_size = sizeof (initial_buf);
                     61: 
                     62:   while (1)
                     63:     {
                     64:       /* Attempt to read the link into the current buffer.  */
                     65:       ssize_t link_length = readlink (filename, buffer, buf_size);
                     66: 
                     67:       /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
                     68:         with errno == ERANGE if the buffer is too small.  */
                     69:       if (link_length < 0 && errno != ERANGE)
                     70:        {
                     71:          if (buffer != initial_buf)
                     72:            {
                     73:              int saved_errno = errno;
                     74:              free (buffer);
                     75:              errno = saved_errno;
                     76:            }
                     77:          return NULL;
                     78:        }
                     79: 
                     80:       if ((size_t) link_length < buf_size)
                     81:        {
                     82:          buffer[link_length++] = '\0';
                     83: 
                     84:          /* Return it in a chunk of memory as small as possible.  */
                     85:          if (buffer == initial_buf)
                     86:            {
                     87:              buffer = (char *) malloc (link_length);
                     88:              if (buffer == NULL)
                     89:                /* errno is ENOMEM.  */
                     90:                return NULL;
                     91:              memcpy (buffer, initial_buf, link_length);
                     92:            }
                     93:          else
                     94:            {
                     95:              /* Shrink buffer before returning it.  */
                     96:              if ((size_t) link_length < buf_size)
                     97:                {
                     98:                  char *smaller_buffer = (char *) realloc (buffer, link_length);
                     99: 
                    100:                  if (smaller_buffer != NULL)
                    101:                    buffer = smaller_buffer;
                    102:                }
                    103:            }
                    104:          return buffer;
                    105:        }
                    106: 
                    107:       if (buffer != initial_buf)
                    108:        free (buffer);
                    109:       buf_size *= 2;
                    110:       if (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0))
                    111:        {
                    112:          errno = ENOMEM;
                    113:          return NULL;
                    114:        }
                    115:       buffer = (char *) malloc (buf_size);
                    116:       if (buffer == NULL)
                    117:        /* errno is ENOMEM.  */
                    118:        return NULL;
                    119:     }
                    120: }