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/*
* Copyright 2018 Google
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_LOCAL_LEVELDB_TRANSACTION_H_
#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_LOCAL_LEVELDB_TRANSACTION_H_
#include <cstdint>
#include <map>
#include <memory>
#include <set>
#include <string>
#include <utility>
#include "absl/strings/string_view.h"
#include "leveldb/db.h"
#if __OBJC__
#import <Protobuf/GPBProtocolBuffers.h>
#endif
namespace firebase {
namespace firestore {
namespace local {
/**
* LevelDBTransaction tracks pending changes to entries in leveldb, including
* deletions. It also provides an Iterator to traverse a merged view of pending
* changes and committed values.
*/
class LevelDbTransaction {
using Deletions = std::set<std::string>;
using Mutations = std::map<std::string, std::string>;
public:
/**
* Iterator iterates over a merged view of pending changes from the
* transaction and any unchanged values in the underlying leveldb instance.
*/
class Iterator {
public:
explicit Iterator(LevelDbTransaction* txn);
/**
* Returns true if this iterator points to an entry
*/
bool Valid();
/**
* Seeks this iterator to the first key equal to or greater than the given
* key
*/
void Seek(const std::string& key);
/**
* Advances the iterator to the next entry
*/
void Next();
/**
* Returns the key of the current entry
*/
absl::string_view key();
/**
* Returns the value of the current entry
*/
absl::string_view value();
private:
/**
* Advances to the next non-deleted key in leveldb.
*/
void AdvanceLDB();
/**
* Returns true if the given slice matches a key present in the deletions_
* set.
*/
bool IsDeleted(leveldb::Slice slice);
/**
* Syncs with the underlying transaction. If the transaction has been
* updated, the mutation iterator may need to be reset. Returns true if this
* resulted in moving to a new underlying entry (i.e. the entry represented
* by current_ was deleted).
*/
bool SyncToTransaction();
/**
* Given the current state of the internal iterators, set is_valid_,
* is_mutation_, and current_.
*/
void UpdateCurrent();
std::unique_ptr<leveldb::Iterator> db_iter_;
// The last observed version of the underlying transaction
int32_t last_version_;
// The underlying transaction.
LevelDbTransaction* txn_;
Mutations::iterator mutations_iter_;
// We save the current key and value so that once an iterator is Valid(), it
// remains so at least until the next call to Seek() or Next(), even if the
// underlying data is deleted.
std::pair<std::string, std::string> current_;
// True if current_ represents an entry in the mutations_ map, rather than
// committed data.
bool is_mutation_;
// True if the iterator pointed to a valid entry the last time Next() or
// Seek() was called.
bool is_valid_;
};
explicit LevelDbTransaction(
leveldb::DB* db,
absl::string_view label,
const leveldb::ReadOptions& read_options = DefaultReadOptions(),
const leveldb::WriteOptions& write_options = DefaultWriteOptions());
LevelDbTransaction(const LevelDbTransaction& other) = delete;
LevelDbTransaction& operator=(const LevelDbTransaction& other) = delete;
/**
* Returns a default set of ReadOptions
*/
static const leveldb::ReadOptions& DefaultReadOptions();
/**
* Returns a default set of WriteOptions
*/
static const leveldb::WriteOptions& DefaultWriteOptions();
/**
* Remove the database entry (if any) for "key". It is not an error if "key"
* did not exist in the database.
*/
void Delete(const absl::string_view& key);
#if __OBJC__
/**
* Schedules the row identified by `key` to be set to the given protocol
* buffer message when this transaction commits.
*/
void Put(const absl::string_view& key, GPBMessage* message) {
NSData* data = [message data];
std::string key_string(key);
mutations_[key_string] = std::string((const char*)data.bytes, data.length);
version_++;
}
#endif
/**
* Schedules the row identified by `key` to be set to `value` when this
* transaction commits.
*/
void Put(const absl::string_view& key, const absl::string_view& value);
/**
* Sets the contents of `value` to the latest known value for the given key,
* including any pending mutations and `Status::OK` is returned. If the key
* doesn't exist in leveldb, or it is scheduled for deletion in this
* transaction, `Status::NotFound` is returned.
*/
leveldb::Status Get(const absl::string_view& key, std::string* value);
/**
* Returns a new Iterator over the pending changes in this transaction, merged
* with the existing values already in leveldb.
*/
std::unique_ptr<Iterator> NewIterator();
/**
* Commits the transaction. All pending changes are written. The transaction
* should not be used after calling this method.
*/
void Commit();
std::string ToString();
private:
leveldb::DB* db_;
Mutations mutations_;
Deletions deletions_;
leveldb::ReadOptions read_options_;
leveldb::WriteOptions write_options_;
int32_t version_;
std::string label_;
};
} // namespace local
} // namespace firestore
} // namespace firebase
#endif // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_LOCAL_LEVELDB_TRANSACTION_H_
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