key_stream.h

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// Copyright (c) 2018-2022, The Monero Project
 
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#pragma once
 
#include <boost/range/iterator_range.hpp>
#include <cstdint>
#include <cstring>
#include <iterator>
#include <lmdb.h>
#include <utility>
 
#include "lmdb/value_stream.h"
#include "span.h"
 
namespace lmdb
{

    template<typename K, typename V>
    class key_iterator
    {
        MDB_cursor* cur;
        epee::span<const std::uint8_t> key;
        
        void increment()
        {
            // MDB_NEXT_MULTIPLE doesn't work if only one value is stored :/
            if (cur)
                key = lmdb::stream::get(*cur, MDB_NEXT_NODUP, sizeof(K), sizeof(V)).first;
        }
 
    public:
        using value_type = std::pair<K, boost::iterator_range<value_iterator<V>>>;
        using reference = value_type;
        using pointer = void;
        using difference_type = std::size_t;
        using iterator_category = std::input_iterator_tag;

        key_iterator() noexcept
          : cur(nullptr), key()
        {}

        key_iterator(MDB_cursor* cur)
          : cur(cur), key()
        {
            if (cur)
                key = lmdb::stream::get(*cur, MDB_GET_CURRENT, sizeof(K), sizeof(V)).first;
        }

        bool is_end() const noexcept { return key.empty(); }

        bool equal(key_iterator const& rhs) const noexcept
        {
            return
                (key.empty() && rhs.key.empty()) ||
                key.data() == rhs.key.data();
        }

        key_iterator& operator++()
        {
            increment();
            return *this;
        }

        key_iterator operator++(int)
        {
            key_iterator out{*this};
            increment();
            return out;
        }

        value_type operator*() const
        {
            return {get_key(), make_value_range()};
        }

        K get_key() const noexcept
        {
            static_assert(std::is_trivially_copyable<K>(), "key is not memcpy safe");
            assert(!is_end());
            K out;
            std::memcpy(std::addressof(out), key.data(), sizeof(out));
            return out;
        }

        template<typename T = V, typename F = T, std::size_t offset = 0>
        value_iterator<T, F, offset> make_value_iterator() const
        {
            static_assert(std::is_same<T, V>(), "bad MONERO_FIELD usage?");
            return {cur};
        }

        template<typename T = V, typename F = T, std::size_t offset = 0>
        boost::iterator_range<value_iterator<T, F, offset>> make_value_range() const
        {
            return {make_value_iterator<T, F, offset>(), value_iterator<T, F, offset>{}};
        }
    };

    template<typename K, typename V, typename D>
    class key_stream
    {
        std::unique_ptr<MDB_cursor, D> cur;
    public:

        explicit key_stream(std::unique_ptr<MDB_cursor, D> cur)
          : cur(std::move(cur))
        {}
 
        key_stream(key_stream&&) = default;
        key_stream(key_stream const&) = delete;
        ~key_stream() = default;
        key_stream& operator=(key_stream&&) = default;
        key_stream& operator=(key_stream const&) = delete;

        std::unique_ptr<MDB_cursor, D> give_cursor() noexcept
        {
            return {std::move(cur)};
        }

        void reset()
        {
            if (cur)
                lmdb::stream::get(*cur, MDB_FIRST, 0, 0);
        }

        key_iterator<K, V> make_iterator() const
        {
            return {cur.get()};
        }

        boost::iterator_range<key_iterator<K, V>> make_range() const
        {
            return {make_iterator(), key_iterator<K, V>{}};
        }
    };
 
    template<typename K, typename V>
    inline
    bool operator==(key_iterator<K, V> const& lhs, key_iterator<K, V> const& rhs) noexcept
    {
        return lhs.equal(rhs);
    }
 
    template<typename K, typename V>
    inline
    bool operator!=(key_iterator<K, V> const& lhs, key_iterator<K, V> const& rhs) noexcept
    {
        return !lhs.equal(rhs);
    }
} // lmdb