p2p: avoid sending the same peer list over and over

Nodes remember which connections have been sent which peer addresses
and won't send it again. This causes more addresses to be sent as
the connection lifetime grows, since there is no duplication anymore,
which increases the diffusion speed of peer addresses. The whole
white list is now considered for sending, not just the most recent
seen peers. This further hardens against topology discovery, though
it will more readily send peers that have been last seen earlier
than it otherwise would. While this does save a fair amount of net
bandwidth, it makes heavy use of std::set lookups, which does bring
network_address::less up the profile, though not too aggressively.

1 files changed, 13 insertions, 1 deletions

diff --git a/src/p2p/net_node.inl b/src/p2p/net_node.inl
index 7a2feddc8..13da53b1d 100644
--- a/src/p2p/net_node.inl
+++ b/src/p2p/net_node.inl
@@ -2294,7 +2294,17 @@ namespace nodetool
     const epee::net_utils::zone zone_type = context.m_remote_address.get_zone();
     network_zone& zone = m_network_zones.at(zone_type);
 
-    zone.m_peerlist.get_peerlist_head(rsp.local_peerlist_new, true);
+    std::vector<peerlist_entry> local_peerlist_new;
+    zone.m_peerlist.get_peerlist_head(local_peerlist_new, true, P2P_DEFAULT_PEERS_IN_HANDSHAKE);
+
+    //only include out peers we did not already send
+    rsp.local_peerlist_new.reserve(local_peerlist_new.size());
+    for (auto &pe: local_peerlist_new)
+    {
+      if (!context.sent_addresses.insert(pe.adr).second)
+        continue;
+      rsp.local_peerlist_new.push_back(std::move(pe));
+    }
     m_payload_handler.get_payload_sync_data(rsp.payload_data);
 
     /* Tor/I2P nodes receiving connections via forwarding (from tor/i2p daemon)
@@ -2416,6 +2426,8 @@ namespace nodetool
 
     //fill response
     zone.m_peerlist.get_peerlist_head(rsp.local_peerlist_new, true);
+    for (const auto &e: rsp.local_peerlist_new)
+      context.sent_addresses.insert(e.adr);
     get_local_node_data(rsp.node_data, zone);
     m_payload_handler.get_payload_sync_data(rsp.payload_data);
     LOG_DEBUG_CC(context, "COMMAND_HANDSHAKE");