fix peer picking algorithm

The old code was always picking the first to_pick peers from the set.
This commit is contained in:
Steven Siloti 2016-09-21 20:04:40 -07:00
parent c75b243490
commit 23e11af899
2 changed files with 49 additions and 23 deletions

View File

@ -214,18 +214,15 @@ namespace
else
{
tcp const protocol = requester.is_v4() ? tcp::v4() : tcp::v6();
int max = m_settings.max_peers_reply;
int to_pick = m_settings.max_peers_reply;
// if these are IPv6 peers their addresses are 4x the size of IPv4
// so reduce the max peers 4 fold to compensate
// max_peers_reply should probably be specified in bytes
if (!v.peers.empty() && protocol == tcp::v6())
max /= 4;
// we're picking "to_pick" from a list of "num" at random.
int const to_pick = std::min(int(v.peers.size()), max);
std::set<peer_entry>::const_iterator iter = v.peers.begin();
to_pick /= 4;
entry::list_type& pe = peers["values"].list();
for (int t = 0, m = 0; m < to_pick && iter != v.peers.end(); ++iter)
for (auto iter = v.peers.begin(); to_pick > 0 && iter != v.peers.end(); ++iter)
{
// if the node asking for peers is a seed, skip seeds from the
// peer list
@ -235,26 +232,20 @@ namespace
if (iter->addr.protocol() != protocol)
continue;
++t;
std::string* str;
if (t <= to_pick)
{
pe.push_back(entry());
str = &pe.back().string();
}
else
{
// maybe replace an item we've already picked
if (random(t - 1) >= to_pick) continue;
str = &pe[random(to_pick - 1)].string();
}
// pick this peer with probability
// <peers left to pick> / <peers left in the set>
if (random(uint32_t(std::distance(iter, v.peers.end()))) > to_pick)
continue;
str->resize(18);
std::string::iterator out = str->begin();
pe.push_back(entry());
std::string& str = pe.back().string();
str.resize(18);
std::string::iterator out = str.begin();
detail::write_endpoint(iter->addr, out);
str->resize(out - str->begin());
str.resize(out - str.begin());
++m;
--to_pick;
}
}

View File

@ -339,6 +339,41 @@ TORRENT_TEST(mutable_item_limit)
TEST_EQUAL(cnt.mutable_data, 42);
}
TORRENT_TEST(get_peers_dist)
{
// test that get_peers returns reasonably disjoint sets of peers with each call
// take two samples of 100 peers from 1000 and make sure there aren't too many
// peers found in both lists
dht_settings sett = test_settings();
sett.max_peers = 1000;
sett.max_peers_reply = 100;
std::unique_ptr<dht_storage_interface> s(create_default_dht_storage(sett));
address addr = rand_v4();
for (int i = 0; i < 1000; ++i)
{
s->announce_peer(n1, tcp::endpoint(addr, uint16_t(i))
, "torrent_name", false);
}
std::set<int> peer_set;
int duplicates = 0;
for (int i = 0; i < 2; ++i)
{
entry peers;
s->get_peers(n1, false, false, address(), peers);
TEST_EQUAL(peers["values"].list().size(), 100);
for (auto const& p : peers["values"].list())
{
int port = detail::read_v4_endpoint<tcp::endpoint>(p.string().begin()).port();
if (!peer_set.insert(port).second)
++duplicates;
}
}
std::printf("duplicate peers found: %d\n", duplicates);
TEST_CHECK(duplicates < 20);
}
TORRENT_TEST(update_node_ids)
{
dht_settings sett = test_settings();