dbwrapper.h
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dbwrapper.h
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	// Copyright (c) 2012-2016 The Bitcoin Core developers
	// Distributed under the MIT software license, see the accompanying
	// file COPYING or http://www.opensource.org/licenses/mit-license.php.

	#ifndef BITCOIN_DBWRAPPER_H
	#define BITCOIN_DBWRAPPER_H

	#include <clientversion.h>
	#include <fs.h>
	#include <serialize.h>
	#include <streams.h>
	#include <util/strencodings.h>
	#include <util/system.h>

	#include <leveldb/db.h>
	#include <leveldb/write_batch.h>

	static const size_t DBWRAPPER_PREALLOC_KEY_SIZE = 64;
	static const size_t DBWRAPPER_PREALLOC_VALUE_SIZE = 1024;

	class dbwrapper_error : public std::runtime_error {
	public:
	explicit dbwrapper_error(const std::string &msg)
	: std::runtime_error(msg) {}
	};

	class CDBWrapper;

	/**
	* These should be considered an implementation detail of the specific database.
	*/
	namespace dbwrapper_private {

	/**
	* Handle database error by throwing dbwrapper_error exception.
	*/
	void HandleError(const leveldb::Status &status);

	/**
	* Work around circular dependency, as well as for testing in dbwrapper_tests.
	* Database obfuscation should be considered an implementation detail of the
	* specific database.
	*/
	const std::vector<uint8_t> &GetObfuscateKey(const CDBWrapper &w);
	}; // namespace dbwrapper_private

	/** Batch of changes queued to be written to a CDBWrapper */
	class CDBBatch {
	friend class CDBWrapper;

	private:
	const CDBWrapper &parent;
	leveldb::WriteBatch batch;

	CDataStream ssKey;
	CDataStream ssValue;

	size_t size_estimate;

	public:
	/**
	* @param[in] _parent CDBWrapper that this batch is to be submitted to
	*/
	explicit CDBBatch(const CDBWrapper &_parent)
	: parent(_parent), ssKey(SER_DISK, CLIENT_VERSION),
	ssValue(SER_DISK, CLIENT_VERSION), size_estimate(0){};

	void Clear() {
	batch.Clear();
	size_estimate = 0;
	}

	template <typename K, typename V> void Write(const K &key, const V &value) {
	ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
	ssKey << key;
	leveldb::Slice slKey(ssKey.data(), ssKey.size());

	ssValue.reserve(DBWRAPPER_PREALLOC_VALUE_SIZE);
	ssValue << value;
	ssValue.Xor(dbwrapper_private::GetObfuscateKey(parent));
	leveldb::Slice slValue(ssValue.data(), ssValue.size());

	batch.Put(slKey, slValue);
	// LevelDB serializes writes as:
	// - byte: header
	// - varint: key length (1 byte up to 127B, 2 bytes up to 16383B, ...)
	// - byte[]: key
	// - varint: value length
	// - byte[]: value
	// The formula below assumes the key and value are both less than 16k.
	size_estimate += 3 + (slKey.size() > 127) + slKey.size() +
	(slValue.size() > 127) + slValue.size();
	ssKey.clear();
	ssValue.clear();
	}

	template <typename K> void Erase(const K &key) {
	ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
	ssKey << key;
	leveldb::Slice slKey(ssKey.data(), ssKey.size());

	batch.Delete(slKey);
	// LevelDB serializes erases as:
	// - byte: header
	// - varint: key length
	// - byte[]: key
	// The formula below assumes the key is less than 16kB.
	size_estimate += 2 + (slKey.size() > 127) + slKey.size();
	ssKey.clear();
	}

	size_t SizeEstimate() const { return size_estimate; }
	};

	class CDBIterator {
	private:
	const CDBWrapper &parent;
	leveldb::Iterator *piter;

	public:
	/**
	* @param[in] _parent Parent CDBWrapper instance.
	* @param[in] _piter The original leveldb iterator.
	*/
	CDBIterator(const CDBWrapper &_parent, leveldb::Iterator *_piter)
	: parent(_parent), piter(_piter){};
	~CDBIterator();

	bool Valid() const;

	void SeekToFirst();

	template <typename K> void Seek(const K &key) {
	CDataStream ssKey(SER_DISK, CLIENT_VERSION);
	ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
	ssKey << key;
	leveldb::Slice slKey(ssKey.data(), ssKey.size());
	piter->Seek(slKey);
	}

	void Next();

	template <typename K> bool GetKey(K &key) {
	leveldb::Slice slKey = piter->key();
	try {
	CDataStream ssKey(slKey.data(), slKey.data() + slKey.size(),
	SER_DISK, CLIENT_VERSION);
	ssKey >> key;
	} catch (const std::exception &) {
	return false;
	}
	return true;
	}

	template <typename V> bool GetValue(V &value) {
	leveldb::Slice slValue = piter->value();
	try {
	CDataStream ssValue(slValue.data(), slValue.data() + slValue.size(),
	SER_DISK, CLIENT_VERSION);
	ssValue.Xor(dbwrapper_private::GetObfuscateKey(parent));
	ssValue >> value;
	} catch (const std::exception &) {
	return false;
	}
	return true;
	}

	unsigned int GetValueSize() { return piter->value().size(); }
	};

	class CDBWrapper {
	friend const std::vector<uint8_t> &
	dbwrapper_private::GetObfuscateKey(const CDBWrapper &w);

	private:
	//! custom environment this database is using (may be nullptr in case of
	//! default environment)
	leveldb::Env *penv;

	//! database options used
	leveldb::Options options;

	//! options used when reading from the database
	leveldb::ReadOptions readoptions;

	//! options used when iterating over values of the database
	leveldb::ReadOptions iteroptions;

	//! options used when writing to the database
	leveldb::WriteOptions writeoptions;

	//! options used when sync writing to the database
	leveldb::WriteOptions syncoptions;

	//! the database itself
	leveldb::DB *pdb;

	//! the name of this database
	std::string m_name;

	//! a key used for optional XOR-obfuscation of the database
	std::vector<uint8_t> obfuscate_key;

	//! the key under which the obfuscation key is stored
	static const std::string OBFUSCATE_KEY_KEY;

	//! the length of the obfuscate key in number of bytes
	static const unsigned int OBFUSCATE_KEY_NUM_BYTES;

	std::vector<uint8_t> CreateObfuscateKey() const;

	public:
	/**
	* @param[in] path Location in the filesystem where leveldb data will
	* be stored.
	* @param[in] nCacheSize Configures various leveldb cache settings.
	* @param[in] fMemory If true, use leveldb's memory environment.
	* @param[in] fWipe If true, remove all existing data.
	* @param[in] obfuscate If true, store data obfuscated via simple XOR. If
	* false, XOR
	* with a zero'd byte array.
	*/
	CDBWrapper(const fs::path &path, size_t nCacheSize, bool fMemory = false,
	bool fWipe = false, bool obfuscate = false);
	~CDBWrapper();

	CDBWrapper(const CDBWrapper &) = delete;
	CDBWrapper &operator=(const CDBWrapper &) = delete;

	template <typename K, typename V> bool Read(const K &key, V &value) const {
	CDataStream ssKey(SER_DISK, CLIENT_VERSION);
	ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
	ssKey << key;
	leveldb::Slice slKey(ssKey.data(), ssKey.size());

	std::string strValue;
	leveldb::Status status = pdb->Get(readoptions, slKey, &strValue);
	if (!status.ok()) {
	if (status.IsNotFound()) return false;
	LogPrintf("LevelDB read failure: %s\n", status.ToString());
	dbwrapper_private::HandleError(status);
	}
	try {
	CDataStream ssValue(strValue.data(),
	strValue.data() + strValue.size(), SER_DISK,
	CLIENT_VERSION);
	ssValue.Xor(obfuscate_key);
	ssValue >> value;
	} catch (const std::exception &) {
	return false;
	}
	return true;
	}

	template <typename K, typename V>
	bool Write(const K &key, const V &value, bool fSync = false) {
	CDBBatch batch(*this);
	batch.Write(key, value);
	return WriteBatch(batch, fSync);
	}

	template <typename K> bool Exists(const K &key) const {
	CDataStream ssKey(SER_DISK, CLIENT_VERSION);
	ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
	ssKey << key;
	leveldb::Slice slKey(ssKey.data(), ssKey.size());

	std::string strValue;
	leveldb::Status status = pdb->Get(readoptions, slKey, &strValue);
	if (!status.ok()) {
	if (status.IsNotFound()) return false;
	LogPrintf("LevelDB read failure: %s\n", status.ToString());
	dbwrapper_private::HandleError(status);
	}
	return true;
	}

	template <typename K> bool Erase(const K &key, bool fSync = false) {
	CDBBatch batch(*this);
	batch.Erase(key);
	return WriteBatch(batch, fSync);
	}

	bool WriteBatch(CDBBatch &batch, bool fSync = false);

	// Get an estimate of LevelDB memory usage (in bytes).
	size_t DynamicMemoryUsage() const;

	// not available for LevelDB; provide for compatibility with BDB
	bool Flush() { return true; }

	bool Sync() {
	CDBBatch batch(*this);
	return WriteBatch(batch, true);
	}

	CDBIterator *NewIterator() {
	return new CDBIterator(*this, pdb->NewIterator(iteroptions));
	}

	/**
	* Return true if the database managed by this class contains no entries.
	*/
	bool IsEmpty();

	template <typename K>
	size_t EstimateSize(const K &key_begin, const K &key_end) const {
	CDataStream ssKey1(SER_DISK, CLIENT_VERSION),
	ssKey2(SER_DISK, CLIENT_VERSION);
	ssKey1.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
	ssKey2.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
	ssKey1 << key_begin;
	ssKey2 << key_end;
	leveldb::Slice slKey1(ssKey1.data(), ssKey1.size());
	leveldb::Slice slKey2(ssKey2.data(), ssKey2.size());
	uint64_t size = 0;
	leveldb::Range range(slKey1, slKey2);
	pdb->GetApproximateSizes(&range, 1, &size);
	return size;
	}

	/**
	* Compact a certain range of keys in the database.
	*/
	template <typename K>
	void CompactRange(const K &key_begin, const K &key_end) const {
	CDataStream ssKey1(SER_DISK, CLIENT_VERSION),
	ssKey2(SER_DISK, CLIENT_VERSION);
	ssKey1.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
	ssKey2.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
	ssKey1 << key_begin;
	ssKey2 << key_end;
	leveldb::Slice slKey1(ssKey1.data(), ssKey1.size());
	leveldb::Slice slKey2(ssKey2.data(), ssKey2.size());
	pdb->CompactRange(&slKey1, &slKey2);
	}
	};

	#endif // BITCOIN_DBWRAPPER_H

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