sqlite.h

// Copyright (c) 2020-2021 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_WALLET_SQLITE_H
#define BITCOIN_WALLET_SQLITE_H

#include <sync.h>
#include <wallet/db.h>

struct bilingual_str;

struct sqlite3_stmt;
struct sqlite3;

namespace wallet {
class SQLiteDatabase;

/** RAII class that provides a database cursor */
class SQLiteCursor : public DatabaseCursor
{
public:
    sqlite3_stmt* m_cursor_stmt{nullptr};
    // Copies of the prefix things for the prefix cursor.
    // Prevents SQLite from accessing temp variables for the prefix things.
    std::vector<std::byte> m_prefix_range_start;
    std::vector<std::byte> m_prefix_range_end;

    explicit SQLiteCursor() {}
    explicit SQLiteCursor(std::vector<std::byte> start_range, std::vector<std::byte> end_range)
        : m_prefix_range_start(std::move(start_range)),
        m_prefix_range_end(std::move(end_range))
    {}
    ~SQLiteCursor() override;

    Status Next(DataStream& key, DataStream& value) override;
};

/** Class responsible for executing SQL statements in SQLite databases.
 *  Methods are virtual so they can be overridden by unit tests testing unusual database conditions. */
class SQliteExecHandler
{
public:
    virtual ~SQliteExecHandler() {}
    virtual int Exec(SQLiteDatabase& database, const std::string& statement);
};

/** RAII class that provides access to a WalletDatabase */
class SQLiteBatch : public DatabaseBatch
{
private:
    SQLiteDatabase& m_database;
    std::unique_ptr<SQliteExecHandler> m_exec_handler{std::make_unique<SQliteExecHandler>()};

    sqlite3_stmt* m_read_stmt{nullptr};
    sqlite3_stmt* m_insert_stmt{nullptr};
    sqlite3_stmt* m_overwrite_stmt{nullptr};
    sqlite3_stmt* m_delete_stmt{nullptr};
    sqlite3_stmt* m_delete_prefix_stmt{nullptr};

    /** Whether this batch has started a database transaction and whether it owns SQLiteDatabase::m_write_semaphore.
     * If the batch starts a db tx, it acquires the semaphore and sets this to true, keeping the semaphore
     * until the transaction ends to prevent other batch objects from writing to the database.
     *
     * If this batch did not start a transaction, the semaphore is acquired transiently when writing and m_txn
     * is not set.
     *
     * m_txn is different from HasActiveTxn() as it is only true when this batch has started the transaction,
     * not just when any batch has started a transaction.
     */
    bool m_txn{false};

    void SetupSQLStatements();
    bool ExecStatement(sqlite3_stmt* stmt, Span<const std::byte> blob);

    bool ReadKey(DataStream&& key, DataStream& value) override;
    bool WriteKey(DataStream&& key, DataStream&& value, bool overwrite = true) override;
    bool EraseKey(DataStream&& key) override;
    bool HasKey(DataStream&& key) override;
    bool ErasePrefix(Span<const std::byte> prefix) override;

public:
    explicit SQLiteBatch(SQLiteDatabase& database);
    ~SQLiteBatch() override { Close(); }

    void SetExecHandler(std::unique_ptr<SQliteExecHandler>&& handler) { m_exec_handler = std::move(handler); }

    /* No-op. See comment on SQLiteDatabase::Flush */
    void Flush() override {}

    void Close() override;

    std::unique_ptr<DatabaseCursor> GetNewCursor() override;
    std::unique_ptr<DatabaseCursor> GetNewPrefixCursor(Span<const std::byte> prefix) override;
    bool TxnBegin() override;
    bool TxnCommit() override;
    bool TxnAbort() override;
};

/** An instance of this class represents one SQLite3 database.
 **/
class SQLiteDatabase : public WalletDatabase
{
private:
    const bool m_mock{false};

    const std::string m_dir_path;

    const std::string m_file_path;

    /**
     * This mutex protects SQLite initialization and shutdown.
     * sqlite3_config() and sqlite3_shutdown() are not thread-safe (sqlite3_initialize() is).
     * Concurrent threads that execute SQLiteDatabase::SQLiteDatabase() should have just one
     * of them do the init and the rest wait for it to complete before all can proceed.
     */
    static Mutex g_sqlite_mutex;
    static int g_sqlite_count GUARDED_BY(g_sqlite_mutex);

    void Cleanup() noexcept EXCLUSIVE_LOCKS_REQUIRED(!g_sqlite_mutex);

public:
    SQLiteDatabase() = delete;

    /** Create DB handle to real database */
    SQLiteDatabase(const fs::path& dir_path, const fs::path& file_path, const DatabaseOptions& options, bool mock = false);

    ~SQLiteDatabase();

    // Batches must acquire this semaphore on writing, and release when done writing.
    // This ensures that only one batch is modifying the database at a time.
    CSemaphore m_write_semaphore;

    bool Verify(bilingual_str& error);

    /** Open the database if it is not already opened */
    void Open() override;

    /** Close the database */
    void Close() override;

    /* These functions are unused */
    void AddRef() override { assert(false); }
    void RemoveRef() override { assert(false); }

    /** Rewrite the entire database on disk */
    bool Rewrite(const char* skip = nullptr) override;

    /** Back up the entire database to a file.
     */
    bool Backup(const std::string& dest) const override;

    /** No-ops
     *
     * SQLite always flushes everything to the database file after each transaction
     * (each Read/Write/Erase that we do is its own transaction unless we called
     * TxnBegin) so there is no need to have Flush or Periodic Flush.
     *
     * There is no DB env to reload, so ReloadDbEnv has nothing to do
     */
    void Flush() override {}
    bool PeriodicFlush() override { return false; }
    void ReloadDbEnv() override {}

    void IncrementUpdateCounter() override { ++nUpdateCounter; }

    std::string Filename() override { return m_file_path; }
    std::string Format() override { return "sqlite"; }

    /** Make a SQLiteBatch connected to this database */
    std::unique_ptr<DatabaseBatch> MakeBatch(bool flush_on_close = true) override;

    /** Return true if there is an on-going txn in this connection */
    bool HasActiveTxn();

    sqlite3* m_db{nullptr};
    bool m_use_unsafe_sync;
};

std::unique_ptr<SQLiteDatabase> MakeSQLiteDatabase(const fs::path& path, const DatabaseOptions& options, DatabaseStatus& status, bilingual_str& error);

std::string SQLiteDatabaseVersion();
} // namespace wallet

#endif // BITCOIN_WALLET_SQLITE_H