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.
4 Copyright (C) 2001, 2003-2007, 2009 Free Software Foundation, Inc.
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.
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.
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/>. */
19 /* Written by Jim Meyering <jim@meyering.net>
20 and Bruno Haible <bruno@clisp.org>. */
25 #include "areadlink.h"
35 # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
38 /* The initial buffer size for the link value. A power of 2
39 detects arithmetic overflow earlier, but is not required. */
41 INITIAL_BUF_SIZE = 1024
44 /* Call readlink to get the symbolic link value of FILENAME.
45 Return a pointer to that NUL-terminated string in malloc'd storage.
46 If readlink fails, return NULL and set errno.
47 If realloc fails, or if the link value is longer than SIZE_MAX :-),
48 return NULL and set errno to ENOMEM. */
51 areadlink (char const *filename)
53 /* Allocate the initial buffer on the stack. This way, in the common
54 case of a symlink of small size, we get away with a single small malloc()
55 instead of a big malloc() followed by a shrinking realloc(). */
56 char initial_buf[INITIAL_BUF_SIZE];
58 char *buffer = initial_buf;
59 size_t buf_size = sizeof initial_buf;
63 /* Attempt to read the link into the current buffer. */
64 ssize_t link_length = readlink (filename, buffer, buf_size);
66 /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
67 with errno == ERANGE if the buffer is too small. */
68 if (link_length < 0 && errno != ERANGE)
70 if (buffer != initial_buf)
72 int saved_errno = errno;
79 if ((size_t) link_length < buf_size)
81 buffer[link_length++] = '\0';
83 /* Return it in a chunk of memory as small as possible. */
84 if (buffer == initial_buf)
86 buffer = (char *) malloc (link_length);
88 /* errno is ENOMEM. */
90 memcpy (buffer, initial_buf, link_length);
94 /* Shrink buffer before returning it. */
95 if ((size_t) link_length < buf_size)
97 char *smaller_buffer = (char *) realloc (buffer, link_length);
99 if (smaller_buffer != NULL)
100 buffer = smaller_buffer;
106 if (buffer != initial_buf)
109 if (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0))
114 buffer = (char *) malloc (buf_size);
116 /* errno is ENOMEM. */