On Nov 26 10:08, Konstantin Kouptsov wrote:
> On Windows, if I compile it using a Microsoft compiler:
>
> C: > cl /out:checktty.exe checktty.c
>
> the program behaves correctly when I run it from a DOS prompt or from a
> Cywin's bash prompt. However, if I connect to the Windows computer running
> Cygwin's sshd service from another Linux or Windows computer, it always gives
> the same result:
>
> $ ./checktty.exe
> not a tty
>
> $ ./checktty.exe < checktty.c
> not a tty
>
> (When I compile with Cygwin's gcc, everything is fine)
>
> What happens here?
Cygwin pseudo ttys are implemented as pipes, and the msvcrt runtime
has no idea about that. It sees a pipe and that's no tty from its
POV.
> Given that I must compile the program using Microsoft's compiler on Windows,
> how this can be worked around?
The workaround is to implement your own isatty function which recognizes
Cygwin pseudo ttys as well. I had a customer asking this question, too,
at one point and I sent them example code. I attached it to this mail.
HTH,
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Project Co-Leader cygwin AT cygwin DOT com
Red Hat
#include <stdio.h>
#include <io.h>
#include <errno.h>
#include <wchar.h>
#include <windows.h>
#include <winternl.h>
#ifndef __MINGW64_VERSION_MAJOR
/* MS winternl.h defines FILE_INFORMATION_CLASS, but with only a
different single member. */
enum FILE_INFORMATION_CLASSX
{
FileNameInformation = 9
};
typedef struct _FILE_NAME_INFORMATION
{
ULONG FileNameLength;
WCHAR FileName[1];
} FILE_NAME_INFORMATION, *PFILE_NAME_INFORMATION;
NTSTATUS (NTAPI *pNtQueryInformationFile) (HANDLE, PIO_STATUS_BLOCK, PVOID,
ULONG, FILE_INFORMATION_CLASSX);
#else
NTSTATUS (NTAPI *pNtQueryInformationFile) (HANDLE, PIO_STATUS_BLOCK, PVOID,
ULONG, FILE_INFORMATION_CLASS);
#endif
int
isatty (int fd)
{
HANDLE fh;
NTSTATUS status;
IO_STATUS_BLOCK io;
long buf[66]; /* NAME_MAX + 1 + sizeof ULONG */
PFILE_NAME_INFORMATION pfni = (PFILE_NAME_INFORMATION) buf;
PWCHAR cp;
/* First check using _isatty.
Note that this returns the wrong result for NUL, for instance!
Workaround is not to use _isatty at all, but rather GetFileType
plus object name checking. */
if (_isatty (fd))
return 1;
/* Now fetch the underlying HANDLE. */
fh = (HANDLE) _get_osfhandle (fd);
if (!fh || fh == INVALID_HANDLE_VALUE)
{
errno = EBADF;
return 0;
}
/* Must be a pipe. */
if (GetFileType (fh) != FILE_TYPE_PIPE)
goto no_tty;
/* Calling the native NT function NtQueryInformationFile is required to
support pre-Vista systems. If that's of no concern, Vista introduced
the GetFileInformationByHandleEx call with the FileNameInfo info class,
which can be used instead. */
if (!pNtQueryInformationFile)
{
pNtQueryInformationFile = (NTSTATUS (NTAPI *)(HANDLE, PIO_STATUS_BLOCK,
PVOID, ULONG, FILE_INFORMATION_CLASS))
GetProcAddress (GetModuleHandle ("ntdll.dll"),
"NtQueryInformationFile");
if (!pNtQueryInformationFile)
goto no_tty;
}
if (!NT_SUCCESS (pNtQueryInformationFile (fh, &io, pfni, sizeof buf,
FileNameInformation)))
goto no_tty;
/* The filename is not guaranteed to be NUL-terminated. */
pfni->FileName[pfni->FileNameLength / sizeof (WCHAR)] = L'\0';
/* Now check the name pattern. The filename of a Cygwin pseudo tty pipe
looks like this:
\cygwin-%16llx-pty%d-{to,from}-master
%16llx is the hash of the Cygwin installation, (to support multiple
parallel installations), %d id the pseudo tty number, "to" or "from"
differs the pipe direction. "from" is a stdin, "to" a stdout-like
pipe. */
cp = pfni->FileName;
if (!wcsncmp (cp, L"\\cygwin-", 8)
&& !wcsncmp (cp + 24, L"-pty", 4))
{
cp = wcschr (cp + 28, '-');
if (!cp)
goto no_tty;
if (!wcscmp (cp, L"-from-master") || !wcscmp (cp, L"-to-master"))
return 1;
}
no_tty:
errno = EINVAL;
return 0;
}
int
main ()
{
if (isatty(0))
printf("tty\n");
else
printf("not a tty\n");
return 0;
}
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