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| -rw-r--r-- | src/lmdb/key_stream.h | 264 |
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diff --git a/src/lmdb/key_stream.h b/src/lmdb/key_stream.h new file mode 100644 index 000000000..40434d3a1 --- /dev/null +++ b/src/lmdb/key_stream.h @@ -0,0 +1,264 @@ +// Copyright (c) 2018, The Monero Project +// All rights reserved. +// +// Redistribution and use in source and binary forms, with or without modification, are +// permitted provided that the following conditions are met: +// +// 1. Redistributions of source code must retain the above copyright notice, this list of +// conditions and the following disclaimer. +// +// 2. Redistributions in binary form must reproduce the above copyright notice, this list +// of conditions and the following disclaimer in the documentation and/or other +// materials provided with the distribution. +// +// 3. Neither the name of the copyright holder nor the names of its contributors may be +// used to endorse or promote products derived from this software without specific +// prior written permission. +// +// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY +// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF +// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL +// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, +// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS +// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, +// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF +// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. +#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 +{ + + /*! + An InputIterator for a fixed-sized LMDB key and value. `operator++` + iterates over keys. + + \tparam K Key type in database records. + \tparam V Value type in database records. + + \note This meets requirements for an InputIterator only. The iterator + can only be incremented and dereferenced. All copies of an iterator + share the same LMDB cursor, and therefore incrementing any copy will + change the cursor state for all (incrementing an iterator will + invalidate all prior copies of the iterator). Usage is identical + to `std::istream_iterator`. + */ + 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; + + //! Construct an "end" iterator. + key_iterator() noexcept + : cur(nullptr), key() + {} + + /*! + \param cur Iterate over keys starting at this cursor position. + \throw std::system_error if unexpected LMDB error. This can happen + if `cur` is invalid. + */ + key_iterator(MDB_cursor* cur) + : cur(cur), key() + { + if (cur) + key = lmdb::stream::get(*cur, MDB_GET_CURRENT, sizeof(K), sizeof(V)).first; + } + + //! \return True if `this` is one-past the last key. + bool is_end() const noexcept { return key.empty(); } + + //! \return True iff `rhs` is referencing `this` key. + bool equal(key_iterator const& rhs) const noexcept + { + return + (key.empty() && rhs.key.empty()) || + key.data() == rhs.key.data(); + } + + /*! + Moves iterator to next key or end. Invalidates all prior copies of + the iterator. + */ + key_iterator& operator++() + { + increment(); + return *this; + } + + /*! + Moves iterator to next key or end. + + \return A copy that is already invalidated, ignore + */ + key_iterator operator++(int) + { + key_iterator out{*this}; + increment(); + return out; + } + + //! \pre `!is_end()` \return {current key, current value range} + value_type operator*() const + { + return {get_key(), make_value_range()}; + } + + //! \pre `!is_end()` \return Current key + K get_key() const noexcept + { + assert(!is_end()); + K out; + std::memcpy(std::addressof(out), key.data(), sizeof(out)); + return out; + } + + /*! + Return a C++ iterator over database values from current cursor + position that will reach `.is_end()` after the last duplicate key + record. Calling `make_iterator()` will return an iterator whose + `operator*` will return an entire value (`V`). + `make_iterator<MONERO_FIELD(account, id)>()` will return an + iterator whose `operator*` will return a `decltype(account.id)` + object - the other fields in the struct `account` are never copied + from the database. + + \throw std::system_error if LMDB has unexpected errors. + \return C++ iterator starting at current cursor position. + */ + 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}; + } + + /*! + Return a range from current cursor position until last duplicate + key record. Useful in for-each range loops or in templated code + expecting a range of elements. Calling `make_range()` will return + a range of `T` objects. `make_range<MONERO_FIELD(account, id)>()` + will return a range of `decltype(account.id)` objects - the other + fields in the struct `account` are never copied from the database. + + \throw std::system_error if LMDB has unexpected errors. + \return An InputIterator range over values at cursor position. + */ + 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>{}}; + } + }; + + /*! + C++ wrapper for a LMDB read-only cursor on a fixed-sized key `K` and + value `V`. + + \tparam K key type being stored by each record. + \tparam V value type being stored by each record. + \tparam D cleanup functor for the cursor; usually unique per db/table. + */ + template<typename K, typename V, typename D> + class key_stream + { + std::unique_ptr<MDB_cursor, D> cur; + public: + + //! Take ownership of `cur` without changing position. `nullptr` valid. + 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; + + /*! + Give up ownership of the cursor. `make_iterator()` and + `make_range()` can still be invoked, but return the empty set. + + \return Currently owned LMDB cursor. + */ + std::unique_ptr<MDB_cursor, D> give_cursor() noexcept + { + return {std::move(cur)}; + } + + /*! + Place the stream back at the first key/value. Newly created + iterators will start at the first value again. + + \note Invalidates all current iterators, including those created + with `make_iterator` or `make_range`. Also invalidates all + `value_iterator`s created with `key_iterator`. + */ + void reset() + { + if (cur) + lmdb::stream::get(*cur, MDB_FIRST, 0, 0); + } + + /*! + \throw std::system_error if LMDB has unexpected errors. + \return C++ iterator over database keys from current cursor + position that will reach `.is_end()` after the last key. + */ + key_iterator<K, V> make_iterator() const + { + return {cur.get()}; + } + + /*! + \throw std::system_error if LMDB has unexpected errors. + \return Range from current cursor position until last key record. + Useful in for-each range loops or in templated code + */ + 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 + |