bridge users ignore their cached consensus file on startup
When a client has UseBridges set to 1, and it has a cached microdesc consensus in its datadir, when it starts up it loads that consensus file from disk, and calls networkstatus_set_current_consensus()
on it.
That function checks
if (flav != usable_consensus_flavor() &&
!directory_caches_dir_info(options)) {
/* This consensus is totally boring to us: we won't use it, and we won't
* serve it. Drop it. */
goto done;
}
and in this case, usable_consensus_flavor()
checks we_use_microdescriptors_for_circuits()
which decides
/* If we are configured to use bridges and none of our bridges
* know what a microdescriptor is, the answer is no. */
if (options->UseBridges && !any_bridge_supports_microdescriptors())
return 0;
That is, if you have bridges but you haven't marked any of them up yet, then you default to using the old-flavor consensus, so when you read your microdesc-consensus from disk, you quietly discard it. This bug results in bridge users always fetching a new consensus at start, even when they don't need to.
(Bug reported by [a person who was helpful at first but now seems to be trying to distract me and prevent me from fixing Tor bugs].)