Problems with native Unix domain sockets on Win 10/2019

[Brian Inglis]

On 2020-09-24 06:01, Michael McMahon via Cygwin wrote:
> 
> 
> On 24/09/2020 12:26, Ken Brown wrote:
>> On 9/23/2020 7:25 AM, Michael McMahon via Cygwin wrote:
>>> Hi,
>>>
>>> I searched for related issues but haven't found anything.
>>>
>>> I am having some trouble with Windows native Unix domain sockets
>>> (a recent feature in Windows 10 and 2019 server) and Cygwin.
>>> I think I possibly know the cause since I had to investigate a similar
>>> looking issue on another platform built on Windows.
>>>
>>> The problem is that cygwin commands don't seem to recognise native Unix
>>> domain sockets correctly. For example, the socket "foo.sock" should
>>> have the same ownership and similar permissions to other files
>>> in the example below:
>>>
>>> $ ls -lrt
>>> total 2181303
>>>
>>> -rw-r--r--  1 mimcmah      None             1259   Sep 23 10:22 test.c
>>> -rwxr-xr-x  1 mimcmah      None             3680   Sep 23 10:22 test.obj
>>> -rwxr-xr-x  1 mimcmah      None             121344 Sep 23 10:22 test.exe
>>> -rw-r-----  1 Unknown+User Unknown+Group         0 Sep 23 10:23 foo.sock
>>> -rw-r--r--  1 mimcmah      None             144356 Sep 23 10:27 check.ot
>>>
>>> A bigger problem is that foo.sock can't be deleted with the cygwin "rm"
>>> command.
>>>
>>> $ rm -f foo.sock
>>> rm: cannot remove 'foo.sock': Permission denied
>>>
>>> $ chmod 777 foo.sock
>>> chmod: changing permissions of 'foo.sock': Permission denied
>>>
>>> $ cmd /c del foo.sock
>>>
>>> But, native Windows commands are okay, as the third example shows.
>>>
>>> I think the problem may relate to the way native Unix domain sockets are
>>> implemented in Windows and the resulting special handling required.
>>> They are implemented as NTFS reparse points and when opening them
>>> with CreateFile, you need to specify the FILE_FLAG_OPEN_REPARSE_POINT
>>> flag. Otherwise, you get an ERROR_CANT_ACCESS_FILE. There are other
>>> complications unfortunately, which I'd be happy to discuss further.
>>>
>>> But, to reproduce it, you can compile the attached code snippet
>>> which creates foo.sock in the current directory. Obviously, this
>>> only works on recent versions of Windows 10 and 2019 server.
>>
>> Cygwin doesn't currently support native Windows AF_UNIX sockets, as you've
>> discovered.  See
>>
>>   
>> https://urldefense.com/v3/__https://cygwin.com/pipermail/cygwin/2020-June/245088.html__;!!GqivPVa7Brio!P7lIFI4rYAtWh8_DtCbRCxT-M_E4vwQ0qwzQ0p656T73BpJ0jbUkLI_bXdA6mmSL9lJcSQ$
>>
>> for the current state of AF_UNIX sockets on Cygwin, including the possibility
>> of using native Windows AF_UNIX sockets on systems that support them.
>>
>> If all you want is for Cygwin to recognize such sockets and allow you to apply
>> rm, chmod, etc., I don't think it would be hard to add that capability.  But I
>> doubt if that's all you want.
>>
>> Further discussion of this will have to wait until Corinna is available.
>>
> 
> Thanks for the info. It's mainly about recognition of sockets for
> regular commands. Since these objects can exist on Windows filesystems
> now, potentially created by any kind of Windows application,
> it would be great if Cygwin could handle them, irrespective of whether
> the Cygwin development environment does. Though that sounds like a
> good idea too.

See recent discussion:

https://cygwin.com/pipermail/cygwin/2020-June/245077.html

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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