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-rw-r--r--gl/lseek.c89
1 files changed, 89 insertions, 0 deletions
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1/* An lseek() function that detects pipes.
2 Copyright (C) 2007, 2009-2023 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#if defined _WIN32 && ! defined __CYGWIN__
23/* Windows platforms. */
24/* Get GetFileType. */
25# include <windows.h>
26/* Get _get_osfhandle. */
27# if GNULIB_MSVC_NOTHROW
28# include "msvc-nothrow.h"
29# else
30# include <io.h>
31# endif
32#else
33# include <sys/stat.h>
34#endif
35#include <errno.h>
36
37#undef lseek
38
39off_t
40rpl_lseek (int fd, off_t offset, int whence)
41{
42#if defined _WIN32 && ! defined __CYGWIN__
43 /* mingw lseek mistakenly succeeds on pipes, sockets, and terminals. */
44 HANDLE h = (HANDLE) _get_osfhandle (fd);
45 if (h == INVALID_HANDLE_VALUE)
46 {
47 errno = EBADF;
48 return -1;
49 }
50 if (GetFileType (h) != FILE_TYPE_DISK)
51 {
52 errno = ESPIPE;
53 return -1;
54 }
55#elif defined __APPLE__ && defined __MACH__ && defined SEEK_DATA
56 if (whence == SEEK_DATA)
57 {
58 /* If OFFSET points to data, macOS lseek+SEEK_DATA returns the
59 start S of the first data region that begins *after* OFFSET,
60 where the region from OFFSET to S consists of possibly-empty
61 data followed by a possibly-empty hole. To work around this
62 portability glitch, check whether OFFSET is within data by
63 using lseek+SEEK_HOLE, and if so return to OFFSET by using
64 lseek+SEEK_SET. Also, contrary to the macOS documentation,
65 lseek+SEEK_HOLE can fail with ENXIO if there are no holes on
66 or after OFFSET. What a mess! */
67 off_t next_hole = lseek (fd, offset, SEEK_HOLE);
68 if (next_hole < 0)
69 return errno == ENXIO ? offset : next_hole;
70 if (next_hole != offset)
71 whence = SEEK_SET;
72 }
73#else
74 /* BeOS lseek mistakenly succeeds on pipes... */
75 struct stat statbuf;
76 if (fstat (fd, &statbuf) < 0)
77 return -1;
78 if (!S_ISREG (statbuf.st_mode))
79 {
80 errno = ESPIPE;
81 return -1;
82 }
83#endif
84#if _GL_WINDOWS_64_BIT_OFF_T || (defined __MINGW32__ && defined _FILE_OFFSET_BITS && (_FILE_OFFSET_BITS == 64))
85 return _lseeki64 (fd, offset, whence);
86#else
87 return lseek (fd, offset, whence);
88#endif
89}