Always attempt to resync when receiving a block less than LIB.

plugins/net_plugin/net_plugin.cpp

@@ -249,6 +249,7 @@ namespace eosio {
       uint32_t                              max_nodes_per_host = 1;
       bool                                  p2p_accept_transactions = true;
       bool                                  p2p_reject_incomplete_blocks = true;
+      bool                                  p2p_always_resync = false;
 
       /// Peer clock may be no more than 1 second skewed from our clock, including network latency.
       const std::chrono::system_clock::duration peer_authentication_interval{std::chrono::seconds{1}};
@@ -2918,9 +2919,18 @@ namespace eosio {
             std::unique_lock<std::mutex> g( conn_mtx );
             const auto last_sent_lib = last_handshake_sent.last_irreversible_block_num;
             g.unlock();
+
             if( blk_num < last_sent_lib ) {
                fc_ilog( logger, "received block ${n} less than sent lib ${lib}", ("n", blk_num)("lib", last_sent_lib) );
-               close();
+               if(my_impl->p2p_always_resync) {
+                  fc_ilog( logger, "attempting to resync with peer that is sending blocks less than sent lib ${lib}", ("lib", last_sent_lib) );
+                  enqueue( (sync_request_message) {0, 0} );
+                  send_handshake();
+                  cancel_wait();
+               }
+               else {
+                  close();
+               }
             } else {
                fc_ilog( logger, "received block ${n} less than lib ${lib}", ("n", blk_num)("lib", lib) );
                enqueue( (sync_request_message) {0, 0} );
@@ -3971,6 +3981,7 @@ namespace eosio {
            "   _port  \tremote port number of peer\n\n"
            "   _lip   \tlocal IP address connected to peer\n\n"
            "   _lport \tlocal port number connected to peer\n\n")
+         ( "p2p-always-resync", bpo::value<bool>()->default_value(false), "Always attempt to resync even when peer sends blocks earlier than this node's last irreversible block")
          ( "p2p-keepalive-interval-ms", bpo::value<int>()->default_value(def_keepalive_interval), "peer heartbeat keepalive message interval in milliseconds")
          ( "p2p-tls-security-group-ca-file", bpo::value<bfs::path>(), "Certificate Authority's certificate file used for verifying peers TLS connection when security groups feature enabled" )
          ( "p2p-tls-own-certificate-file", bpo::value<bfs::path>(), "Certificate file that will be used to authenticate running node if TLS is enabled")
@@ -3998,6 +4009,7 @@ namespace eosio {
          my->max_nodes_per_host = options.at( "p2p-max-nodes-per-host" ).as<int>();
          my->p2p_accept_transactions = options.at( "p2p-accept-transactions" ).as<bool>();
          my->p2p_reject_incomplete_blocks = options.at("p2p-reject-incomplete-blocks").as<bool>();
+         my->p2p_always_resync = options.at( "p2p-always-resync" ).as<bool>();
 
          my->use_socket_read_watermark = options.at( "use-socket-read-watermark" ).as<bool>();
          my->keepalive_interval = std::chrono::milliseconds( options.at( "p2p-keepalive-interval-ms" ).as<int>() );