libassuan: Support sendfd/recvfd (possibly by new API) on Windows
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	• gniibe
	Oct 12 2022, 3:43 AM

Description

On Windows, assuan_sendfd/assuan_recvfd is not supported.

It would be good to support this feature (even if it's not that useful), so that the code base of GnuPG can be more coherent/clean (portability wise), minimizing exceptions.

Lack of UNIX domain socket's FD passing feature, we need to find two solutions for:
(1) Sharing file object (opened by sending end, used by receiving end) between different processes
(2) Multiplexing sending/receiving FD and normal message

For sharing file HANDLE, we could use DuplicateHandle (possibly by receiving end), by sending end's notifying its HANDLE (and process HANDLE) to receiving end.
We could use MSG_OOB for the notification of above, for TCP socket.

Revisions and Commits

rA Assuan
	rA17055e1c9953 w32: Fix the semantics of sending FD, it's Windows HANDLE.
	rA523e3cbfe29f w32: Fix confusion between process ID and process HANDLE.
	rAba84b780df97 w32: Have PROCESS_HANDLE in struct assuan_context_s.
	rA3297e453aa0e w32: Support fd passing through socket.
	rAa1f480468a3b w32: Support fd passing through pipe.
	rA07adf41f0f49 Show the pid of listening process in the hello line.
	rA870fdcf92e59 w32: Support sendfd/recvfd through pipe connection.
	rAce794a0a88a8 w32: Add SENDFD internal command.
	rA27acee6a04db client: Only call _assuan_waitpid when it's not socket.
	rA61f69c73f364 experiment: New SENDFD command to implement sendfd feature.
	rAfbdc77228257 experiment: Reliably send/recv fd passing, part 5/N.
	rAf0b179a0a71b experiment: Implement receving fd for Windows, part 4/N.
	rAed7fe5649648 experiment: Add fdpassing-socket test for Windows, part 3/N.
	rA29950e3387ec experiment: sendfd/recvfd on Windows, part 1/N.
	rA017d2a33d57e experiment: sendfd/recvfd on Windows, part 2/N.

Related Objects
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Status	Assigned	Task
Open	None	T6508 Port GnuPG to 64-bit Windows
Testing	• gniibe	T6599 INT2FD and npth_accept
Resolved	• gniibe	T6606 Use new API of libassuan 3
Testing	• gniibe	T4656 Windows 64-bit: functions which use pid_t
Testing	• gniibe	T4655 Windows 64-bit: gnupg_fd_t, assuan_fd_t and int for fd in the API, and casts
Resolved	• gniibe	T6236 libassuan: Support sendfd/recvfd (possibly by new API) on Windows

Event Timeline

• gniibe claimed this task.Oct 12 2022, 3:43 AM

• gniibe triaged this task as Wishlist priority.

• gniibe created this task.

• gniibe added parent tasks: T4655: Windows 64-bit: gnupg_fd_t, assuan_fd_t and int for fd in the API, and casts, T4656: Windows 64-bit: functions which use pid_t.

• gniibe added a commit: rA017d2a33d57e: experiment: sendfd/recvfd on Windows, part 2/N..Oct 12 2022, 6:08 AM

• gniibe added a commit: rA29950e3387ec: experiment: sendfd/recvfd on Windows, part 1/N..

• gniibe added a commit: rAed7fe5649648: experiment: Add fdpassing-socket test for Windows, part 3/N..Oct 12 2022, 9:44 AM

• canti59 added a commit: rG8046fcac63db: po: Update Czech translation..Oct 14 2022, 2:10 AM

• gniibe removed a commit: rG8046fcac63db: po: Update Czech translation..Oct 14 2022, 2:50 AM

• gniibe added a commit: rAf0b179a0a71b: experiment: Implement receving fd for Windows, part 4/N..Oct 14 2022, 4:46 AM

By 1/N...5/N, it works. And it shows the API needs clarification and possible modification/fixes; As written in the comment of system-w32.c, fd == POSIX fd semantics is good, which asks API/ABI break.

The implementation uses MSG_OOB to multiplex sendfd message and normal message, to emulate UNIX domain fd passing feature.
But this is not absolutely needed, because actual credential handling by system is done before sending HANDLE on Windows (the sendfd message is simple text of HANDLE).

For Windows, we could extend std_cmd_table to add, say, windows_sendfd command to receive HANDLE representation in text.
This would be better, because it also can work under pipe connection, as well as socket.

• gniibe added a commit: rAfbdc77228257: experiment: Reliably send/recv fd passing, part 5/N..Oct 14 2022, 9:15 AM

• gniibe added a commit: rA61f69c73f364: experiment: New SENDFD command to implement sendfd feature..Oct 20 2022, 8:58 AM

• gniibe added a commit: rA27acee6a04db: client: Only call _assuan_waitpid when it's not socket..Nov 4 2022, 9:05 AM

• gniibe added a commit: rAce794a0a88a8: w32: Add SENDFD internal command..Nov 4 2022, 9:58 AM

• gniibe added a commit: rA870fdcf92e59: w32: Support sendfd/recvfd through pipe connection..Nov 4 2022, 11:09 AM

Merged PIPE connection part into master.

• gniibe added a commit: rA07adf41f0f49: Show the pid of listening process in the hello line..Nov 7 2022, 2:06 AM

• gniibe added a commit: rAa1f480468a3b: w32: Support fd passing through pipe..Nov 7 2022, 3:52 AM

• gniibe added a commit: rA3297e453aa0e: w32: Support fd passing through socket..Nov 7 2022, 5:17 AM

• gniibe changed the task status from Open to Testing.Nov 7 2022, 6:11 AM

• gniibe added a commit: rAba84b780df97: w32: Have PROCESS_HANDLE in struct assuan_context_s..Nov 9 2022, 3:56 AM

• gniibe added a commit: rA523e3cbfe29f: w32: Fix confusion between process ID and process HANDLE..Nov 15 2022, 7:41 AM