We had no function to infallibly convert BoundedInt32<{0 or 1},H>
into a u32, even though we could have. Because of that, we were
treating weight_scale as an i32 when logically it's a u32 or a
NonZeroU32.
Moreover, it turns out we were using an incorrect minimum for the
bwweightscale param, which would in theory have allowed the
authorities to make us divide by zero.
This patch introduces the necessary From<> implementation and uses
it. It corrects the binimum bwweightscale, and prevents a
division-by-zero issue in case weight_scale is zero.
Because of arti#257, compatibility with earlier versions of rust are
broken: we hope this is temporary, but fixing it will probably
require a new version of rusqlite.
We don't want MutCfg to be automatially coneable, or we'll wind up with
surprises like the one that this patch fixes in TorClient.
(The "surprise" is that reconfigure() would only apply its
client-specific options to one client instance.)
If we allow overlapping reconfiguration requests, we introduce all
kinds of "fun" bugs. For example, we could wind up with a configuration
made up of parts of one reconfiguration attempt, and parts of another.
We can't change the authorities while in-flight: that would be pretty
miserable to implement.
Similarly we can't change the cache while in-flight.
Everything else should be fair game, though there are a couple of tricky
bits. I've tried to document those.
This required re-centralizing the configuration object for preemptive
circuits, since previously the settings from it were a bit spread out
over the crate.
And now the complexity begins: when the user changes the path_rules,
they not only want new circuits to obey those rules: they want
_all new requests_ to be put onto circuits that obey those rules.
That means that when the path rules become more restrictive, we need
to retire all the circuits, and make sure that currently pending
circuits aren't used for any requests.
If it's any comfort, doing this was even more complicated in C tor. ;)
It's useful to keep configuration objects inside a RwLock<Arc<>>, so we
can have slightly-stale pointers to the existing configuration structure
without holding locks too long.
This code adds a MutCfg type with basic support for this pattern,
and functions to make it a bit more ergonomic.
This patch doesn't actually make anything reconfigurable, but it
does create an API that will tell you "you can't change the value of
that!" If the API looks reasonable, I can start making it possible
to change the values of individual items.
eta
Neel Chauhan
Daniel Eades
Trinity Pointard
Nick Mathewson