Fixes #759 Add sanity check on restore height

src/wallet/wallet2.cpp

@@ -2413,26 +2413,7 @@ crypto::secret_key wallet2::generate(const std::string& wallet_, const std::stri
 
   // try asking the daemon first
   if(m_refresh_from_block_height == 0 && !recover){
-    std::string err;
-    uint64_t height = 0;
-
-    // we get the max of approximated height and known height
-    // approximated height is the least of daemon target height
-    // (the max of what the other daemons are claiming is their
-    // height) and the theoretical height based on the local
-    // clock. This will be wrong only if both the local clock
-    // is bad *and* a peer daemon claims a highest height than
-    // the real chain.
-    // known height is the height the local daemon is currently
-    // synced to, it will be lower than the real chain height if
-    // the daemon is currently syncing.
-    height = get_approximate_blockchain_height();
-    uint64_t target_height = get_daemon_blockchain_target_height(err);
-    if (err.empty() && target_height < height)
-      height = target_height;
-    uint64_t local_height = get_daemon_blockchain_height(err);
-    if (err.empty() && local_height > height)
-      height = local_height;
+    uint64_t height = estimate_blockchain_height();
     m_refresh_from_block_height = height >= blocks_per_month ? height - blocks_per_month : 0;
   }
 
@@ -2451,6 +2432,38 @@ crypto::secret_key wallet2::generate(const std::string& wallet_, const std::stri
   return retval;
 }
 
+ uint64_t wallet2::estimate_blockchain_height()
+ {
+   // -1 month for fluctuations in block time and machine date/time setup.
+   // avg seconds per block
+   const int seconds_per_block = DIFFICULTY_TARGET_V2;
+   // ~num blocks per month
+   const uint64_t blocks_per_month = 60*60*24*30/seconds_per_block;
+
+   // try asking the daemon first
+   std::string err;
+   uint64_t height = 0;
+
+   // we get the max of approximated height and known height
+   // approximated height is the least of daemon target height
+   // (the max of what the other daemons are claiming is their
+   // height) and the theoretical height based on the local
+   // clock. This will be wrong only if both the local clock
+   // is bad *and* a peer daemon claims a highest height than
+   // the real chain.
+   // known height is the height the local daemon is currently
+   // synced to, it will be lower than the real chain height if
+   // the daemon is currently syncing.
+   height = get_approximate_blockchain_height();
+   uint64_t target_height = get_daemon_blockchain_target_height(err);
+   if (err.empty() && target_height < height)
+     height = target_height;
+   uint64_t local_height = get_daemon_blockchain_height(err);
+   if (err.empty() && local_height > height)
+     height = local_height;
+   return height;
+ }
+
 /*!
 * \brief Creates a watch only wallet from a public address and a view secret key.
 * \param  wallet_        Name of wallet file

src/wallet/wallet2.h

@@ -709,6 +709,7 @@ namespace tools
     * \brief Calculates the approximate blockchain height from current date/time.
     */
     uint64_t get_approximate_blockchain_height() const;
+    uint64_t estimate_blockchain_height();
     std::vector<size_t> select_available_outputs_from_histogram(uint64_t count, bool atleast, bool unlocked, bool allow_rct, bool trusted_daemon);
     std::vector<size_t> select_available_outputs(const std::function<bool(const transfer_details &td)> &f);
     std::vector<size_t> select_available_unmixable_outputs(bool trusted_daemon);