txdb: Add Cursor() method to CCoinsView to iterate over UTXO set

Add a method Cursor() to CCoinsView that returns a cursor which can be
used to iterate over the whole UTXO set.

- rpc: Change gettxoutsetinfo to use new Cursor method

- txdb: Remove GetStats method - Now that GetStats is implemented in
  terms of Cursor, remove it.

1 files changed, 40 insertions, 38 deletions

diff --git a/src/txdb.cpp b/src/txdb.cpp
index f99e11f26e..be86cceeb3 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -94,50 +94,52 @@ bool CBlockTreeDB::ReadLastBlockFile(int &nFile) {
     return Read(DB_LAST_BLOCK, nFile);
 }
 
-bool CCoinsViewDB::GetStats(CCoinsStats &stats) const {
+CCoinsViewCursor *CCoinsViewDB::Cursor() const
+{
+    CCoinsViewDBCursor *i = new CCoinsViewDBCursor(const_cast<CDBWrapper*>(&db)->NewIterator(), GetBestBlock());
     /* It seems that there are no "const iterators" for LevelDB.  Since we
        only need read operations on it, use a const-cast to get around
        that restriction.  */
-    boost::scoped_ptr<CDBIterator> pcursor(const_cast<CDBWrapper*>(&db)->NewIterator());
-    pcursor->Seek(DB_COINS);
+    i->pcursor->Seek(DB_COINS);
+    // Cache key of first record
+    i->pcursor->GetKey(i->keyTmp);
+    return i;
+}
 
-    CHashWriter ss(SER_GETHASH, PROTOCOL_VERSION);
-    stats.hashBlock = GetBestBlock();
-    ss << stats.hashBlock;
-    CAmount nTotalAmount = 0;
-    while (pcursor->Valid()) {
-        boost::this_thread::interruption_point();
-        std::pair<char, uint256> key;
-        CCoins coins;
-        if (pcursor->GetKey(key) && key.first == DB_COINS) {
-            if (pcursor->GetValue(coins)) {
-                stats.nTransactions++;
-                for (unsigned int i=0; i<coins.vout.size(); i++) {
-                    const CTxOut &out = coins.vout[i];
-                    if (!out.IsNull()) {
-                        stats.nTransactionOutputs++;
-                        ss << VARINT(i+1);
-                        ss << out;
-                        nTotalAmount += out.nValue;
-                    }
-                }
-                stats.nSerializedSize += 32 + pcursor->GetValueSize();
-                ss << VARINT(0);
-            } else {
-                return error("CCoinsViewDB::GetStats() : unable to read value");
-            }
-        } else {
-            break;
-        }
-        pcursor->Next();
+bool CCoinsViewDBCursor::GetKey(uint256 &key) const
+{
+    // Return cached key
+    if (keyTmp.first == DB_COINS) {
+        key = keyTmp.second;
+        return true;
     }
-    {
-        LOCK(cs_main);
-        stats.nHeight = mapBlockIndex.find(stats.hashBlock)->second->nHeight;
+    return false;
+}
+
+bool CCoinsViewDBCursor::GetValue(CCoins &coins) const
+{
+    return pcursor->GetValue(coins);
+}
+
+unsigned int CCoinsViewDBCursor::GetValueSize() const
+{
+    return pcursor->GetValueSize();
+}
+
+bool CCoinsViewDBCursor::Valid() const
+{
+    return keyTmp.first == DB_COINS;
+}
+
+void CCoinsViewDBCursor::Next()
+{
+    pcursor->Next();
+    if (pcursor->Valid()) {
+        bool ok = pcursor->GetKey(keyTmp);
+        assert(ok); // If GetKey fails here something must be wrong with underlying database, we cannot handle that here
+    } else {
+        keyTmp.first = 0; // Invalidate cached key after last record so that Valid() and GetKey() return false
     }
-    stats.hashSerialized = ss.GetHash();
-    stats.nTotalAmount = nTotalAmount;
-    return true;
 }
 
 bool CBlockTreeDB::WriteBatchSync(const std::vector<std::pair<int, const CBlockFileInfo*> >& fileInfo, int nLastFile, const std::vector<const CBlockIndex*>& blockinfo) {