1/* Test whether a file descriptor is a pipe.
2
3   Copyright (C) 2006, 2008-2010 Free Software Foundation, Inc.
4
5   This program is free software: you can redistribute it and/or modify
6   it under the terms of the GNU General Public License as published by
7   the Free Software Foundation; either version 3 of the License, or
8   (at your option) any later version.
9
10   This program is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13   GNU General Public License for more details.
14
15   You should have received a copy of the GNU General Public License
16   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
17
18/* Written by Paul Eggert.  */
19
20#include <config.h>
21
22#include "isapipe.h"
23
24#include <errno.h>
25
26#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
27/* Windows platforms.  */
28
29/* Get _get_osfhandle.  */
30# include <io.h>
31
32/* Get GetFileType.  */
33# include <windows.h>
34
35int
36isapipe (int fd)
37{
38  HANDLE h = (HANDLE) _get_osfhandle (fd);
39
40  if (h == INVALID_HANDLE_VALUE)
41    {
42      errno = EBADF;
43      return -1;
44    }
45
46  return (GetFileType (h) == FILE_TYPE_PIPE);
47}
48
49#else
50/* Unix platforms.  */
51
52# include <stdbool.h>
53# include <sys/types.h>
54# include <sys/stat.h>
55# include <unistd.h>
56
57/* The maximum link count for pipes; (nlink_t) -1 if not known.  */
58# ifndef PIPE_LINK_COUNT_MAX
59#  define PIPE_LINK_COUNT_MAX ((nlink_t) (-1))
60# endif
61
62/* Return 1 if FD is a pipe, 0 if not, -1 (setting errno) on error.
63
64   Test fairly strictly whether FD is a pipe.  lseek and checking for
65   ESPIPE does not suffice, since many non-pipe files cause lseek to
66   fail with errno == ESPIPE.  */
67
68int
69isapipe (int fd)
70{
71  nlink_t pipe_link_count_max = PIPE_LINK_COUNT_MAX;
72  bool check_for_fifo = (HAVE_FIFO_PIPES == 1);
73  struct stat st;
74  int fstat_result = fstat (fd, &st);
75
76  if (fstat_result != 0)
77    return fstat_result;
78
79  /* We want something that succeeds only for pipes, but on
80     POSIX-conforming hosts S_ISFIFO succeeds for both FIFOs and pipes
81     and we know of no portable, reliable way to distinguish them in
82     general.  However, in practice pipes always have a link count <=
83     PIPE_LINK_COUNT_MAX (unless someone attaches them to the file
84     system name space using fattach, in which case they're not really
85     pipes any more), so test for that as well.
86
87     On Darwin 7.7, pipes are sockets, so check for those instead.  */
88
89  if (! ((HAVE_FIFO_PIPES == 0 || HAVE_FIFO_PIPES == 1)
90         && PIPE_LINK_COUNT_MAX != (nlink_t) -1)
91      && (S_ISFIFO (st.st_mode) | S_ISSOCK (st.st_mode)))
92    {
93      int fd_pair[2];
94      int pipe_result = pipe (fd_pair);
95      if (pipe_result != 0)
96        return pipe_result;
97      else
98        {
99          struct stat pipe_st;
100          int fstat_pipe_result = fstat (fd_pair[0], &pipe_st);
101          int fstat_pipe_errno = errno;
102          close (fd_pair[0]);
103          close (fd_pair[1]);
104          if (fstat_pipe_result != 0)
105            {
106              errno = fstat_pipe_errno;
107              return fstat_pipe_result;
108            }
109          check_for_fifo = (S_ISFIFO (pipe_st.st_mode) != 0);
110          pipe_link_count_max = pipe_st.st_nlink;
111        }
112    }
113
114  return
115    (st.st_nlink <= pipe_link_count_max
116     && (check_for_fifo ? S_ISFIFO (st.st_mode) : S_ISSOCK (st.st_mode)));
117}
118
119#endif
120