/*
* dir-spec 5.1: Downloading network-status documents
*
* To avoid swarming the caches whenever a consensus expires, the clients
* download new consensuses at a randomly chosen time after the caches are
* expected to have a fresh consensus, but before their consensus will
* expire. (This time is chosen uniformly at random from the interval
* between the time 3/4 into the first interval after the consensus is no
* longer fresh, and 7/8 of the time remaining after that before the
* consensus is invalid.)
*
* [For example, if a cache has a consensus that became valid at 1:00, and
* is fresh until 2:00, and expires at 4:00, that cache will fetch a new
* consensus at a random time between 2:45 and 3:50, since 3/4 of the
* one-hour interval is 45 minutes, and 7/8 of the remaining 75 minutes is
* 65 minutes.]
*/
private Date chooseDownloadTimeForConsensus(ConsensusDocument consensus) {
final long va = getMilliseconds(consensus.getValidAfterTime());
final long fu = getMilliseconds(consensus.getFreshUntilTime());
final long vu = getMilliseconds(consensus.getValidUntilTime());
final long i1 = fu - va;
final long start = fu + ((i1 * 3) / 4);
final long i2 = ((vu - start) * 7) / 8;
final long r = random.nextLong(i2);
final long download = start + r;
return new Date(download);
}
private boolean needConsensusDownload() {
if (directory.hasPendingConsensus()) {
return false;
}
if (currentConsensus == null || !currentConsensus.isLive()) {
if (currentConsensus == null) {
logger.info("Downloading consensus because we have no consensus document");
} else {
logger.info("Downloading consensus because the document we have is not live");
}
return true;
}
return consensusDownloadTime.before(new Date());
}