rpc: add blockchain disk size to getinfo

This should help new nodes predict how much disk space will be
needed for a full sync

src/blockchain_db/lmdb/db_lmdb.cpp

@@ -35,6 +35,7 @@
 #include <random>
 
 #include "string_tools.h"
+#include "file_io_utils.h"
 #include "common/util.h"
 #include "cryptonote_basic/cryptonote_format_utils.h"
 #include "crypto/crypto.h"
@@ -3422,6 +3423,16 @@ bool BlockchainLMDB::is_read_only() const
   return false;
 }
 
+uint64_t BlockchainLMDB::get_database_size() const
+{
+  uint64_t size = 0;
+  boost::filesystem::path datafile(m_folder);
+  datafile /= CRYPTONOTE_BLOCKCHAINDATA_FILENAME;
+  if (!epee::file_io_utils::get_file_size(datafile.string(), size))
+    size = 0;
+  return size;
+}
+
 void BlockchainLMDB::fixup()
 {
   LOG_PRINT_L3("BlockchainLMDB::" << __func__);

src/blockchain_db/lmdb/db_lmdb.h

@@ -375,6 +375,8 @@ private:
 
   virtual bool is_read_only() const;
 
+  virtual uint64_t get_database_size() const;
+
   // fix up anything that may be wrong due to past bugs
   virtual void fixup();