nix/src/libstore/sqlite.hh

#pragma once
///@file

#include <functional>
#include <string>

#include "error.hh"

struct sqlite3;
struct sqlite3_stmt;

namespace nix {

enum class SQLiteOpenMode {
    /**
     * Open the database in read-write mode.
     * If the database does not exist, it will be created.
     */
    Normal,
    /**
     * Open the database in read-write mode.
     * Fails with an error if the database does not exist.
     */
    NoCreate,
    /**
     * Open the database in immutable mode.
     * In addition to the database being read-only,
     * no wal or journal files will be created by sqlite.
     * Use this mode if the database is on a read-only filesystem.
     * Fails with an error if the database does not exist.
     */
    Immutable,
};

/**
 * RAII wrapper to close a SQLite database automatically.
 */
struct SQLite
{
    sqlite3 * db = 0;
    SQLite() { }
    SQLite(const Path & path, SQLiteOpenMode mode = SQLiteOpenMode::Normal);
    SQLite(const SQLite & from) = delete;
    SQLite& operator = (const SQLite & from) = delete;
    // NOTE: This is noexcept since we are only copying and assigning raw pointers.
    SQLite& operator = (SQLite && from) noexcept { db = from.db; from.db = 0; return *this; }
    ~SQLite();
    operator sqlite3 * () { return db; }

    /**
     * Disable synchronous mode, set truncate journal mode.
     */
    void isCache();

    void exec(const std::string & stmt);

    uint64_t getLastInsertedRowId();
};

/**
 * RAII wrapper to create and destroy SQLite prepared statements.
 */
struct SQLiteStmt
{
    sqlite3 * db = 0;
    sqlite3_stmt * stmt = 0;
    std::string sql;
    SQLiteStmt() { }
    SQLiteStmt(sqlite3 * db, const std::string & sql) { create(db, sql); }
    void create(sqlite3 * db, const std::string & s);
    ~SQLiteStmt();
    operator sqlite3_stmt * () { return stmt; }

    /**
     * Helper for binding / executing statements.
     */
    class Use
    {
        friend struct SQLiteStmt;
    private:
        SQLiteStmt & stmt;
        unsigned int curArg = 1;
        Use(SQLiteStmt & stmt);

    public:

        ~Use();

        /**
         * Bind the next parameter.
         */
        Use & operator () (std::string_view value, bool notNull = true);
        Use & operator () (const unsigned char * data, size_t len, bool notNull = true);
        Use & operator () (int64_t value, bool notNull = true);
        Use & bind(); // null

        int step();

        /**
         * Execute a statement that does not return rows.
         */
        void exec();

        /**
         * For statements that return 0 or more rows. Returns true iff
         * a row is available.
         */
        bool next();

        std::string getStr(int col);
        int64_t getInt(int col);
        bool isNull(int col);
    };

    Use use()
    {
        return Use(*this);
    }
};

/**
 * RAII helper that ensures transactions are aborted unless explicitly
 * committed.
 */
struct SQLiteTxn
{
    bool active = false;
    sqlite3 * db;

    SQLiteTxn(sqlite3 * db);

    void commit();

    ~SQLiteTxn();
};


struct SQLiteError : Error
{
    std::string path;
    std::string errMsg;
    int errNo, extendedErrNo, offset;

    template<typename... Args>
    [[noreturn]] static void throw_(sqlite3 * db, const std::string & fs, const Args & ... args) {
        throw_(db, HintFmt(fs, args...));
    }

    SQLiteError(const char *path, const char *errMsg, int errNo, int extendedErrNo, int offset, HintFmt && hf);

protected:

    template<typename... Args>
    SQLiteError(const char *path, const char *errMsg, int errNo, int extendedErrNo, int offset, const std::string & fs, const Args & ... args)
      : SQLiteError(path, errMsg, errNo, extendedErrNo, offset, HintFmt(fs, args...))
    { }

    [[noreturn]] static void throw_(sqlite3 * db, HintFmt && hf);

};

MakeError(SQLiteBusy, SQLiteError);

void handleSQLiteBusy(const SQLiteBusy & e, time_t & nextWarning);

/**
 * Convenience function for retrying a SQLite transaction when the
 * database is busy.
 */
template<typename T, typename F>
T retrySQLite(F && fun)
{
    time_t nextWarning = time(0) + 1;

    while (true) {
        try {
            return fun();
        } catch (SQLiteBusy & e) {
            handleSQLiteBusy(e, nextWarning);
        }
    }
}

}