.wait_for_seen() is unreliable, because sometimes Dovecot
sends only EXISTS to the IDLE connection, but not the FETCH.
Dovecot sends updates like FETCH only if some
connection has already observed the message in previous state
without the \Seen flag.
To avoid this race condition, wait until the core sets the flag,
then FETCH the message manually and check that the flag is set.
The documentation says this blocks. This should block because it also
means the error reporting is more accurate by calling set_last_error
just before returning.
Otherwise it is possible for the context that is used in the spawn to
be unreferenced. Really this should be caught by the borrow checker
that ensures we only spawn things with a 'static lifetime, but we're
handling raw pointers so it doesn't.
This replaces the mechanism by which the IoPauseGuard makes sure the
IO scheduler is resumed: it really is a drop guard now by sending a
single message on drop.
This makes it not have to hold on to anything like the context so
makes it a lot easier to use.
The trade-off is that a long-running task is spawned when the guard is
created, this task needs to receive the message from the drop guard in
order for the scheduler to resume.
This changes the JSON-RPC APIs to get a QR code from the backup
provider to block. It means once you have a (blocking) call to
provide_backup() you can call get_backup_qr() or get_backup_qr_svg()
and they will block until the QR code is available.
Calling get_backup_qr() or get_backup_qr_svg() when there is no backup
provider will immediately error.
This adds a result extension trait to explicitly set the last error,
which *should* be the default for the FFI. Currently not touching all
APIs since that's potentially disruptive and we're close to a release.
The logging story is messy, as described in the doc comment. We
should further clean this up and tidy up these APIs so it's more
obvious to people how to do the right thing.
This makes the BackupProvider automatically invoke pause-io while it
is needed.
It needed to make the guard independent from the Context lifetime to
make this work. Which is a bit sad.
