Revert "GH-1092 Remove unneeded extra checks for duplicate connections"

This reverts commit 77198f2.

Author: heifner

plugins/net_plugin/net_plugin.cpp

@@ -3413,6 +3413,7 @@ namespace eosio {
       peer_fork_db_head_block_num = msg.fork_db_head_num;
       fc::unique_lock g_conn( conn_mtx );
       last_handshake_recv = msg;
+      auto c_time = last_handshake_sent.time;
       g_conn.unlock();
 
       set_state(connection_state::connected);
@@ -3456,7 +3457,35 @@ namespace eosio {
                fc::unique_lock g_check_conn( check->conn_mtx );
                fc_dlog( logger, "dup check: connected ${c}, ${l} =? ${r}",
                         ("c", check->connected())("l", check->last_handshake_recv.node_id)("r", msg.node_id) );
-               return check->connected() && check->last_handshake_recv.node_id == msg.node_id;
+               if(check->connected() && check->last_handshake_recv.node_id == msg.node_id) {
+                  if (net_version < proto_dup_goaway_resolution || msg.network_version < proto_dup_goaway_resolution) {
+                     // It's possible that both peers could arrive here at relatively the same time, so
+                     // we need to avoid the case where they would both tell a different connection to go away.
+                     // Using the sum of the initial handshake times of the two connections, we will
+                     // arbitrarily (but consistently between the two peers) keep one of them.
+
+                     auto check_time = check->last_handshake_sent.time + check->last_handshake_recv.time;
+                     g_check_conn.unlock();
+                     if (msg.time + c_time <= check_time)
+                        return false;
+                  } else if (net_version < proto_dup_node_id_goaway || msg.network_version < proto_dup_node_id_goaway) {
+                     if (listen_address < msg.p2p_address) {
+                        fc_dlog( logger, "listen_address '${lhs}' < msg.p2p_address '${rhs}'",
+                                 ("lhs", listen_address)( "rhs", msg.p2p_address ) );
+                        // only the connection from lower p2p_address to higher p2p_address will be considered as a duplicate,
+                        // so there is no chance for both connections to be closed
+                        return false;
+                     }
+                  } else if (my_impl->node_id < msg.node_id) {
+                     fc_dlog( logger, "not duplicate, my_impl->node_id '${lhs}' < msg.node_id '${rhs}'",
+                              ("lhs", my_impl->node_id)("rhs", msg.node_id) );
+                     // only the connection from lower node_id to higher node_id will be considered as a duplicate,
+                     // so there is no chance for both connections to be closed
+                     return false;
+                  }
+                  return true;
+               }
+               return false;
             };
             if (my_impl->connections.any_of_connections(std::move(is_duplicate))) {
                peer_dlog( this, "sending go_away duplicate, msg.p2p_address: ${add}", ("add", msg.p2p_address) );