wallet: generate keys ahead of use so a backup outlives the next block (#85)

The wallet made a key per address and per block mined, so a backup only ever
contained the keys that existed the moment it was taken -- mine one block and
the coin lands on a key the backup has never heard of. The README warned about
it, which is an admission rather than a fix.

Keys are now generated a hundred at a time and handed out one at a time, each
written to wallet.dat before it can be pointed at. A backup covers the next
hundred addresses. Deterministic derivation (#47) stays open; this buys back the
distance between a backup and the next mistake.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/db.h b/src/db.h
index 22efc77..f51047e 100644
--- a/src/db.h
+++ b/src/db.h
@@ -386,6 +386,19 @@ public:
         return Write(string("defaultkey"), vchPubKey);
     }
 
+    // Keys generated ahead of time and not yet handed out. The private key of
+    // each is already stored under its own "key" record by AddKey; a "pool"
+    // record only says that this one is still unspoken for.
+    bool WritePool(int64 nIndex, const vector<unsigned char>& vchPubKey)
+    {
+        return Write(make_pair(string("pool"), nIndex), vchPubKey);
+    }
+
+    bool ErasePool(int64 nIndex)
+    {
+        return Erase(make_pair(string("pool"), nIndex));
+    }
+
     template<typename T>
     bool ReadSetting(const string& strKey, T& value)
     {