rpc: add blockchain cumulative difficulty to getinfo call

src/rpc/core_rpc_server.cpp

@@ -142,6 +142,7 @@ namespace cryptonote
     res.white_peerlist_size = m_p2p.get_peerlist_manager().get_white_peers_count();
     res.grey_peerlist_size = m_p2p.get_peerlist_manager().get_gray_peers_count();
     res.testnet = m_testnet;
+    res.cumulative_difficulty = m_core.get_blockchain_storage().get_db().get_block_cumulative_difficulty(res.height - 1);
     res.status = CORE_RPC_STATUS_OK;
     return true;
   }
@@ -1105,6 +1106,7 @@ namespace cryptonote
     res.white_peerlist_size = m_p2p.get_peerlist_manager().get_white_peers_count();
     res.grey_peerlist_size = m_p2p.get_peerlist_manager().get_gray_peers_count();
     res.testnet = m_testnet;
+    res.cumulative_difficulty = m_core.get_blockchain_storage().get_db().get_block_cumulative_difficulty(res.height - 1);
     res.status = CORE_RPC_STATUS_OK;
     return true;
   }

src/rpc/core_rpc_server_commands_defs.h

@@ -464,6 +464,7 @@ namespace cryptonote
       uint64_t grey_peerlist_size;
       bool testnet;
       std::string top_block_hash;
+      uint64_t cumulative_difficulty;
 
       BEGIN_KV_SERIALIZE_MAP()
         KV_SERIALIZE(status)
@@ -480,6 +481,7 @@ namespace cryptonote
         KV_SERIALIZE(grey_peerlist_size)
         KV_SERIALIZE(testnet)
         KV_SERIALIZE(top_block_hash)
+        KV_SERIALIZE(cumulative_difficulty)
       END_KV_SERIALIZE_MAP()
     };
   };