text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2016 The Bitcoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include "txdb.h"
  
  #include "chainparams.h"
  #include "hash.h"
  #include "pow.h"
  #include "uint256.h"
  
  #include <cstdint>
  
  #include <boost/thread.hpp>
  
  static const char DB_COINS = 'c';
  static const char DB_BLOCK_FILES = 'f';
  static const char DB_TXINDEX = 't';
  static const char DB_BLOCK_INDEX = 'b';
  
  static const char DB_BEST_BLOCK = 'B';
  static const char DB_FLAG = 'F';
  static const char DB_REINDEX_FLAG = 'R';
  static const char DB_LAST_BLOCK = 'l';
  
  CCoinsViewDB::CCoinsViewDB(size_t nCacheSize, bool fMemory, bool fWipe)
      : db(GetDataDir() / "chainstate", nCacheSize, fMemory, fWipe, true) {}
  
  bool CCoinsViewDB::GetCoins(const uint256 &txid, CCoins &coins) const {
      return db.Read(std::make_pair(DB_COINS, txid), coins);
  }
  
  bool CCoinsViewDB::HaveCoins(const uint256 &txid) const {
      return db.Exists(std::make_pair(DB_COINS, txid));
  }
  
  uint256 CCoinsViewDB::GetBestBlock() const {
      uint256 hashBestChain;
      if (!db.Read(DB_BEST_BLOCK, hashBestChain)) return uint256();
      return hashBestChain;
  }
  
  bool CCoinsViewDB::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) {
      CDBBatch batch(db);
      size_t count = 0;
      size_t changed = 0;
      for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end();) {
          if (it->second.flags & CCoinsCacheEntry::DIRTY) {
              if (it->second.coins.IsPruned())
                  batch.Erase(std::make_pair(DB_COINS, it->first));
              else
                  batch.Write(std::make_pair(DB_COINS, it->first),
                              it->second.coins);
              changed++;
          }
          count++;
          CCoinsMap::iterator itOld = it++;
          mapCoins.erase(itOld);
      }
      if (!hashBlock.IsNull()) batch.Write(DB_BEST_BLOCK, hashBlock);
  
      LogPrint(
          "coindb",
          "Committing %u changed transactions (out of %u) to coin database...\n",
          (unsigned int)changed, (unsigned int)count);
      return db.WriteBatch(batch);
  }
  
  CBlockTreeDB::CBlockTreeDB(size_t nCacheSize, bool fMemory, bool fWipe)
      : CDBWrapper(GetDataDir() / "blocks" / "index", nCacheSize, fMemory,
                   fWipe) {}
  
  bool CBlockTreeDB::ReadBlockFileInfo(int nFile, CBlockFileInfo &info) {
      return Read(std::make_pair(DB_BLOCK_FILES, nFile), info);
  }
  
  bool CBlockTreeDB::WriteReindexing(bool fReindexing) {
      if (fReindexing)
          return Write(DB_REINDEX_FLAG, '1');
      else
          return Erase(DB_REINDEX_FLAG);
  }
  
  bool CBlockTreeDB::ReadReindexing(bool &fReindexing) {
      fReindexing = Exists(DB_REINDEX_FLAG);
      return true;
  }
  
  bool CBlockTreeDB::ReadLastBlockFile(int &nFile) {
      return Read(DB_LAST_BLOCK, nFile);
  }
  
  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.
       */
      i->pcursor->Seek(DB_COINS);
      // Cache key of first record
      i->pcursor->GetKey(i->keyTmp);
      return i;
  }
  
  bool CCoinsViewDBCursor::GetKey(uint256 &key) const {
      // Return cached key
      if (keyTmp.first == DB_COINS) {
          key = keyTmp.second;
          return true;
      }
      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() || !pcursor->GetKey(keyTmp))
          // Invalidate cached key after last record so that Valid() and GetKey()
          // return false
          keyTmp.first = 0;
  }
  
  bool CBlockTreeDB::WriteBatchSync(
      const std::vector<std::pair<int, const CBlockFileInfo *>> &fileInfo,
      int nLastFile, const std::vector<const CBlockIndex *> &blockinfo) {
      CDBBatch batch(*this);
      for (std::vector<std::pair<int, const CBlockFileInfo *>>::const_iterator
               it = fileInfo.begin();
           it != fileInfo.end(); it++) {
          batch.Write(std::make_pair(DB_BLOCK_FILES, it->first), *it->second);
      }
      batch.Write(DB_LAST_BLOCK, nLastFile);
      for (std::vector<const CBlockIndex *>::const_iterator it =
               blockinfo.begin();
           it != blockinfo.end(); it++) {
          batch.Write(std::make_pair(DB_BLOCK_INDEX, (*it)->GetBlockHash()),
                      CDiskBlockIndex(*it));
      }
      return WriteBatch(batch, true);
  }
  
  bool CBlockTreeDB::ReadTxIndex(const uint256 &txid, CDiskTxPos &pos) {
      return Read(std::make_pair(DB_TXINDEX, txid), pos);
  }
  
  bool CBlockTreeDB::WriteTxIndex(
      const std::vector<std::pair<uint256, CDiskTxPos>> &vect) {
      CDBBatch batch(*this);
      for (std::vector<std::pair<uint256, CDiskTxPos>>::const_iterator it =
               vect.begin();
           it != vect.end(); it++)
          batch.Write(std::make_pair(DB_TXINDEX, it->first), it->second);
      return WriteBatch(batch);
  }
  
  bool CBlockTreeDB::WriteFlag(const std::string &name, bool fValue) {
      return Write(std::make_pair(DB_FLAG, name), fValue ? '1' : '0');
  }
  
  bool CBlockTreeDB::ReadFlag(const std::string &name, bool &fValue) {
      char ch;
      if (!Read(std::make_pair(DB_FLAG, name), ch)) return false;
      fValue = ch == '1';
      return true;
  }
  
  bool CBlockTreeDB::LoadBlockIndexGuts(
      boost::function<CBlockIndex *(const uint256 &)> insertBlockIndex) {
      std::unique_ptr<CDBIterator> pcursor(NewIterator());
  
      pcursor->Seek(std::make_pair(DB_BLOCK_INDEX, uint256()));
  
      // Load mapBlockIndex
      while (pcursor->Valid()) {
          boost::this_thread::interruption_point();
          std::pair<char, uint256> key;
          if (!pcursor->GetKey(key) || key.first != DB_BLOCK_INDEX) {
              break;
          }
  
          CDiskBlockIndex diskindex;
          if (!pcursor->GetValue(diskindex)) {
              return error("LoadBlockIndex() : failed to read value");
          }
  
          // Construct block index object
          CBlockIndex *pindexNew = insertBlockIndex(diskindex.GetBlockHash());
          pindexNew->pprev = insertBlockIndex(diskindex.hashPrev);
          pindexNew->nHeight = diskindex.nHeight;
          pindexNew->nFile = diskindex.nFile;
          pindexNew->nDataPos = diskindex.nDataPos;
          pindexNew->nUndoPos = diskindex.nUndoPos;
          pindexNew->nVersion = diskindex.nVersion;
          pindexNew->hashMerkleRoot = diskindex.hashMerkleRoot;
          pindexNew->nTime = diskindex.nTime;
          pindexNew->nBits = diskindex.nBits;
          pindexNew->nNonce = diskindex.nNonce;
          pindexNew->nStatus = diskindex.nStatus;
          pindexNew->nTx = diskindex.nTx;
  
          if (!CheckProofOfWork(pindexNew->GetBlockHash(), pindexNew->nBits,
                                Params().GetConsensus()))
              return error("LoadBlockIndex(): CheckProofOfWork failed: %s",
                           pindexNew->ToString());
  
          pcursor->Next();
      }
  
      return true;
  }
  