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