WindowsConsoleIO fileno() passes wrong flags to _open_osfhandle

[eryksun]

BPO	28163
Nosy	@pfmoore, @tjguk, @zware, @eryksun, @zooba
PRs	[Do Not Merge] Convert Misc/NEWS so that it is managed by towncrier #552

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/zooba'
closed_at = <Date 2016-09-17.20:53:13.149>
created_at = <Date 2016-09-15.03:26:21.248>
labels = ['3.7', 'type-bug', 'library', 'expert-IO', 'OS-windows']
title = 'WindowsConsoleIO fileno() passes wrong flags to _open_osfhandle'
updated_at = <Date 2017-03-31.16:36:12.311>
user = 'https://github.com/eryksun'

bugs.python.org fields:

activity = <Date 2017-03-31.16:36:12.311>
actor = 'dstufft'
assignee = 'steve.dower'
closed = True
closed_date = <Date 2016-09-17.20:53:13.149>
closer = 'steve.dower'
components = ['Library (Lib)', 'Windows', 'IO']
creation = <Date 2016-09-15.03:26:21.248>
creator = 'eryksun'
dependencies = []
files = []
hgrepos = []
issue_num = 28163
keywords = []
message_count = 3.0
messages = ['276509', '276840', '276846']
nosy_count = 6.0
nosy_names = ['paul.moore', 'tim.golden', 'python-dev', 'zach.ware', 'eryksun', 'steve.dower']
pr_nums = ['552']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue28163'
versions = ['Python 3.6', 'Python 3.7']

[eryksun]

WindowsConsoleIO fileno() gets a file descriptor on demand by calling _open_osfhandle. As a low I/O function this expects _open flags, but currently the code is passing 'rb' (int 0x7262) and 'wb' (int 0x7762). It should use _O_RDONLY | _O_BINARY and _O_WRONLY | _O_BINARY.

Actually, _open_osfhandle isn't actually opening the file, so it only cares about a few flags. Specifically, in lowio\osfinfo.cpp I see that it looks for _O_APPEND, _O_TEXT, and _O_NOINHERIT. So in this case passing 0 for the flags would also be ok.

[zooba]

I'll pass the "correct" flags, since the docs don't specify that they aren't used, which means one day they might become relevant.

[python-dev]

New changeset d0bab9fda568 by Steve Dower in branch '3.6':
Issue bpo-28161: Opening CON for write access fails
https://hg.python.org/cpython/rev/d0bab9fda568

New changeset 187a114b9ef4 by Steve Dower in branch 'default':
Issue bpo-28161: Opening CON for write access fails
https://hg.python.org/cpython/rev/187a114b9ef4