Commits on Oct 28, 2021

1. win32unix: use WSADuplicateSocket in bindings of dup and dup2 …

   The WinAPI documentation of [DuplicateHandle][] gives a list of types
   of objects on which it is safe to call DuplicateHandle. In particular,
   the doc reads:
   
   > You should not use DuplicateHandle to duplicate handles to the
   > following objects:
   >
   > - Sockets. No error is returned, but the duplicate handle may not be
   >   recognized by Winsock at the target process. Also, using
   >   DuplicateHandle interferes with internal reference counting on the
   >   underlying object. To duplicate a socket handle, use the
   >   WSADuplicateSocket function.
   
   Rework the code to use DuplicateHandle for handles and
   [WSADuplicateSocket][] for sockets.
   
   WSADuplicateSocket returns an info structure that we give to WSASocket
   to create the duplicated handle. However, there seem to be no way of
   explicitely preserving the set of flags to give to WSASocket.
   Considering that as of now, OCaml uses the socket function instead of
   WSASocket, and that socket only sets WSA_FLAG_OVERLAPPED, re-set that
   flag and hope for the best (that's also the current behavior of
   libuv).
   
   It's also possible to retreive the WSA_FLAG_NO_HANDLE_INHERIT (Winsock
   mapping of HANDLE_FLAG_INHERIT) via GetHandleInformation, but that's
   not needed here since we override it with the cloexec parameter.
   
   This commit also fixes a little bug. In the error path of
   DuplicateHandle there was:
   
       win32_maperr(GetLastError());
       return -1;
   
   but the function returns a value, and from the OCaml code above it's
   better to raise an exception instead.
   
   [DuplicateHandle]: https://docs.microsoft.com/en-us/windows/win32/api/handleapi/nf-handleapi-duplicatehandle
   [WSADuplicateSocket]: https://docs.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-wsaduplicatesocketw

   

   MisterDA committed Oct 28, 2021
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2. Merge win32unix/dup2.c into win32unix/dup.c and factor code

   

   MisterDA committed Oct 28, 2021
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