[tor-dev] Dealing with frequent suspends on Android

[Nick Mathewson]

On Wed, Nov 21, 2018 at 5:10 PM Michael Rogers <michael at briarproject.org> wrote:
>
> On 20/11/2018 19:28, Nick Mathewson wrote:
> > Hi!  I don't know if this will be useful or not, but I'm wondering if
> > you've seen this ticket:
> >   https://trac.torproject.org/projects/tor/ticket/28335
> >
> > The goal of this branch is to create a "dormant mode" where Tor does
> > not run any but the most delay- and rescheduling-tolerant of its
> > periodic events.  Tor enters this mode if a controller tells it to, or
> > if (as a client) it passes long enough without user activity.  When in
> > dormant mode, it doesn't disconnect from the network, and it will wake
> > up again if the controller tells it to, or it receives a new client
> > connection.
> >
> > Would this be at all helpful for any of this?
>
> This looks really useful for mobile clients, thank you!

Glad to hear it -- it's now merged into Tor's master branch.

> The comments on the pull request
> (https://github.com/torproject/tor/pull/502) suggest that Tor won't
> enter dormant mode if it's running a hidden service. Are there any plans
> to support that in future?

I want to support this for hidden services.  Here's the ticket to
track that: https://trac.torproject.org/projects/tor/ticket/28424

This is going to be harder than the other cases, though, so we decided
to defer it for now and see if we have time later.

> One of the comments mentions a break-even point for consensus diffs,
> where it costs less bandwidth to fetch a fresh consensus than all the
> diffs from the last consensus you know about. Are diffs likely to remain
> available up to the break-even point, or are there times when it would
> be cheaper to use diffs, but you have to fetch a fresh consensus because
> some of the diffs have expired?

This shouldn't be a problem: directory caches will (by default) keep
diffs slightly beyond the break-even point.

(I think. I haven't measured this in a while.)

> Essentially I'm wondering whether we'd
> want to wake Tor from dormant mode occasionally to fetch diffs before
> they expire, so we can avoid fetching a fresh consensus later.