1 /* Read the contents of a symbolic link. 2 Copyright (C) 2003-2007, 2009-2021 Free Software Foundation, Inc. 3 4 This file is free software: you can redistribute it and/or modify 5 it under the terms of the GNU Lesser General Public License as 6 published by the Free Software Foundation; either version 2.1 of the 7 License, or (at your option) any later version. 8 9 This file is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 GNU Lesser General Public License for more details. 13 14 You should have received a copy of the GNU Lesser General Public License 15 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 16 17 #include <config.h> 18 19 /* Specification. */ 20 #include <unistd.h> 21 22 #include <errno.h> 23 #include <string.h> 24 #include <sys/stat.h> 25 26 #if !HAVE_READLINK 27 28 /* readlink() substitute for systems that don't have a readlink() function, 29 such as DJGPP 2.03 and mingw32. */ 30 31 ssize_t 32 readlink (char const *file, _GL_UNUSED char *buf, /* */ 33 _GL_UNUSED size_t bufsize) 34 { 35 struct stat statbuf; 36 37 /* In general we should use lstat() here, not stat(). But on platforms 38 without symbolic links, lstat() - if it exists - would be equivalent to 39 stat(), therefore we can use stat(). This saves us a configure check. */ 40 if (stat (file, &statbuf) >= 0) 41 errno = EINVAL; 42 return -1; 43 } 44 45 #else /* HAVE_READLINK */ 46 47 # undef readlink 48 49 /* readlink() wrapper that uses correct types, for systems like cygwin 50 1.5.x where readlink returns int, and which rejects trailing slash, 51 for Solaris 9. */ 52 53 ssize_t 54 rpl_readlink (char const *file, char *buf, size_t bufsize) /* */ 55 { 56 # if READLINK_TRAILING_SLASH_BUG 57 size_t file_len = strlen (file); 58 if (file_len && file[file_len - 1] == '/') 59 { 60 /* Even if FILE without the slash is a symlink to a directory, 61 both lstat() and stat() must resolve the trailing slash to 62 the directory rather than the symlink. We can therefore 63 safely use stat() to distinguish between EINVAL and 64 ENOTDIR/ENOENT, avoiding extra overhead of rpl_lstat(). */ 65 struct stat st; 66 if (stat (file, &st) == 0 || errno == EOVERFLOW) 67 errno = EINVAL; 68 return -1; 69 } 70 # endif /* READLINK_TRAILING_SLASH_BUG */ 71 72 ssize_t r = readlink (file, buf, bufsize); 73 74 # if READLINK_TRUNCATE_BUG 75 if (r < 0 && errno == ERANGE) 76 { 77 /* Try again with a bigger buffer. This is just for test cases; 78 real code invariably discards short reads. */ 79 char stackbuf[4032]; 80 r = readlink (file, stackbuf, sizeof stackbuf); 81 if (r < 0) 82 { 83 if (errno == ERANGE) 84 { 85 /* Clear the buffer, which is good enough for real code. 86 Thankfully, no test cases try short reads of enormous 87 symlinks and what would be the point anyway? */ 88 r = bufsize; 89 memset (buf, 0, r); 90 } 91 } 92 else 93 { 94 if (bufsize < r) 95 r = bufsize; 96 memcpy (buf, stackbuf, r); 97 } 98 } 99 # endif 100 101 return r; 102 } 103 104 #endif /* HAVE_READLINK */