Windows 10 [received support](https://devblogs.microsoft.com/commandline/af_unix-comes-to-window… for AF_UNIX sockets in Insider Build 17063. This merge request adds basic support for AF_UNIX sockets to ws2_32 and wineserver.
Of particular note is the difficulty in handling `sun_path`. Most of the functions that allow for translating Windows paths to Unix paths are not accessible from ws2_32. I considered the following options:
* Pass the Windows path to wineserver and do the conversion there.
* This is, as far as I can tell, not possible without major rearchitecting. wineserver does not have functions to translate Windows paths to Unix paths, for obvious reasons.
* Obtain the current working directory of the requesting process and temporarily change directories to there.
* This only handles relative paths and fails for absolute paths, UNC paths, etc.
* Conditionally change directories based on whether the path is relative or not.
* This is error-prone and wineserver does not have the requisite functions to do this cleanly.
I ultimately decided to pass the translated Unix path to wineserver, which changes directories to `dirname(path)`. It then provides `bind` and `connect` with `basename(path)`. This is not threadsafe, but wineserver is not (currently) multithreaded.
Abstract sockets are not fully supported by this patch, matching the behavior of Windows.
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v67: ws2_32/tests: Add test for AF_UNIX sockets.
server: Fix getsockname() and accept() on AF_UNIX sockets.
server: Introduce error when attempting to create a SOCK_DGRAM AF_UNIX socket.
server: Allow for deletion of socket files.
ws2_32: Add support for AF_UNIX sockets.
ws2_32: Add afunix.h header.
https://gitlab.winehq.org/wine/wine/-/merge_requests/2786