f3eade2f62
Drop the AGPL license in favor of a source-available license. See the blog post [1] for details. [1] https://www.scylladb.com/2024/12/18/why-were-moving-to-a-source-available-license/
119 lines
3.1 KiB
C++
119 lines
3.1 KiB
C++
/*
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* Copyright (C) 2019-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
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*/
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#pragma once
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#include <list>
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#include <fmt/format.h>
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#include <seastar/net/byteorder.hh>
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#include <seastar/util/backtrace.hh>
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#include "utils/fragment_range.hh"
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#include "utils/bit_cast.hh"
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namespace utils {
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// Facilitates transparently reading from a fragmented range.
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template<typename T, typename Exception = std::runtime_error>
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requires FragmentRange<T>
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class linearizing_input_stream {
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using iterator = typename T::iterator;
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using fragment_type = typename T::fragment_type;
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private:
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iterator _it;
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iterator _end;
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fragment_type _current;
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size_t _size;
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// We need stable addresses for the `bytes`, which, due to the small
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// value optimization, can invalidate any attached bytes_view on move.
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std::list<bytes> _linearized_values;
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private:
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size_t remove_current_prefix(size_t size) {
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if (size < _current.size()) {
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_current.remove_prefix(size);
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_size -= size;
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return size;
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}
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const auto ret = _current.size();
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_size -= ret;
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++_it;
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_current = (_it == _end) ? fragment_type{} : *_it;
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return ret;
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}
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void check_size(size_t size) const {
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if (size > _size) {
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seastar::throw_with_backtrace<Exception>(
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fmt::format("linearizing_input_stream::check_size() - not enough bytes (requested {:d}, got {:d})", size, _size));
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}
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}
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std::pair<bytes_view, bool> do_read(size_t size) {
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check_size(size);
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if (size <= _current.size()) {
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bytes_view ret(_current.begin(), size);
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remove_current_prefix(size);
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return {ret, false};
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}
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auto out = _linearized_values.emplace_back(bytes::initialized_later{}, size).begin();
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while (size) {
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out = std::copy_n(_current.begin(), std::min(size, _current.size()), out);
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size -= remove_current_prefix(size);
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}
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return {_linearized_values.back(), true};
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}
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public:
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explicit linearizing_input_stream(const T& fr)
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: _it(fr.begin())
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, _end(fr.end())
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, _current(*_it)
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, _size(fr.size_bytes()) {
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}
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// Not cheap to copy, would copy all linearized values.
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linearizing_input_stream(const linearizing_input_stream&) = delete;
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size_t size() const {
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return _size;
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}
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bool empty() const {
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return _size == 0;
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}
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// The returned view is only valid as long as the stream is alive.
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bytes_view read(size_t size) {
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return do_read(size).first;
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}
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template <typename Type>
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requires std::is_trivial_v<Type>
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Type read_trivial() {
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auto [bv, linearized] = do_read(sizeof(Type));
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auto ret = net::ntoh(::read_unaligned<net::packed<Type>>(bv.begin()));
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if (linearized) {
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_linearized_values.pop_back();
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}
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return ret;
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}
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void skip(size_t size) {
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check_size(size);
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while (size) {
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size -= remove_current_prefix(size);
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}
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}
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};
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} // namespace utils
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