[issue34187] Issues with lazy fd support in _WindowsConsoleIO fileno() and close()

[Eryk Sun]

Eryk Sun  added the comment:

The issues brought up here are addressed in a more direct, comprehensive, and 
productive way in PR 1927 for bpo-30555.

--
resolution:  -> duplicate
stage: patch review -> resolved
status: open -> closed
superseder:  -> _io._WindowsConsoleIO breaks in the face of fd redirection

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[issue34187] Issues with lazy fd support in _WindowsConsoleIO fileno() and close()

[Tal Einat]

Change by Tal Einat :


--
nosy: +taleinat

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[issue34187] Issues with lazy fd support in _WindowsConsoleIO fileno() and close()

[Gus Goulart]

Change by Gus Goulart :


--
keywords: +patch
pull_requests: +9275
stage: needs patch -> patch review

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[issue34187] Issues with lazy fd support in _WindowsConsoleIO fileno() and close()

[Gus Goulart]

Gus Goulart  added the comment:

Hi everyone, I would like to let you know that I'm starting working on this 
one. Thanks!

--
nosy: +Gus

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[issue34187] Issues with lazy fd support in _WindowsConsoleIO fileno() and close()

[Eryk Sun]

New submission from Eryk Sun :

The _WindowsConsoleIO implementation of fileno should raise a ValueError if the 
internal handle value is INVALID_HANDLE_VALUE. Currently it raises 
io.UnsupportedOperation, and only if closefd=True. 

>>> f = open('conin$', 'r')
>>> f.close()
>>> f.fileno()
Traceback (most recent call last):
  File "", line 1, in 
io.UnsupportedOperation: Console buffer does not support fileno

>>> f = open(0, 'r', closefd=False)
>>> f.close()
>>> f.fileno()
0

Also, if lazily opening an fd fails when opening by name (con, conin$, 
conout$), it should also close the file handle to maintain a consistent state. 

This can be fixed as follows: error out immediately and call err_closed instead 
of err_mode; and close the handle if _open_osfhandle fails (i.e. fd == -1) and 
closehandle is set:

static PyObject *
_io__WindowsConsoleIO_fileno_impl(winconsoleio *self)
{
if (self->handle == INVALID_HANDLE_VALUE) {
return err_closed();
}

if (self->fd < 0) {
_Py_BEGIN_SUPPRESS_IPH
if (self->writable) {
self->fd = _open_osfhandle((intptr_t)self->handle,
_O_WRONLY | _O_BINARY);
} else {
self->fd = _open_osfhandle((intptr_t)self->handle,
_O_RDONLY | _O_BINARY);
}
_Py_END_SUPPRESS_IPH
}

if (self->fd < 0) {
if (self->closehandle) {
CloseHandle(self->handle);
}
self->handle = INVALID_HANDLE_VALUE;
return err_closed();
}

return PyLong_FromLong(self->fd);
}

On a related note, there's a bug in internal_close that could potentially be a 
race condition that closes a handle to an unrelated object. If an fd has been 
opened, the CRT takes control of the handle. Calling close() will also close 
the underlying handle. In this case CloseHandle should not be called. This just 
needs a minor fix to add an `else` clause:

static int
internal_close(winconsoleio *self)
{
if (self->handle != INVALID_HANDLE_VALUE) {
if (self->closehandle) {
if (self->fd >= 0) {
_Py_BEGIN_SUPPRESS_IPH
close(self->fd);
_Py_END_SUPPRESS_IPH
} else {
CloseHandle(self->handle);
}
}
self->handle = INVALID_HANDLE_VALUE;
self->fd = -1;
}
return 0;
}

--
components: IO, Windows
keywords: easy (C)
messages: 322138
nosy: eryksun, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
stage: needs patch
status: open
title: Issues with lazy fd support in _WindowsConsoleIO fileno() and close()
type: behavior
versions: Python 3.6, Python 3.7, Python 3.8

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