cc6e619aa9
This method takes a data_source and returns another data_source that returns data from the input source but in chunks of limited size. Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
75 lines
2.5 KiB
C++
75 lines
2.5 KiB
C++
/*
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* Copyright (C) 2017 ScyllaDB
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "limiting_data_source.hh"
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#include <seastar/core/iostream.hh>
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#include <seastar/core/temporary_buffer.hh>
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#include <cstdint>
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using namespace seastar;
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class limiting_data_source_impl final : public data_source_impl {
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data_source _src;
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seastar::noncopyable_function<size_t()> _limit_generator;
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temporary_buffer<char> _buf;
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future<temporary_buffer<char>> do_get() {
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uint64_t size = std::min(_limit_generator(), _buf.size());
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auto res = _buf.share(0, size);
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_buf.trim_front(size);
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return make_ready_future<temporary_buffer<char>>(std::move(res));
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}
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public:
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limiting_data_source_impl(data_source&& src, seastar::noncopyable_function<size_t()>&& limit_generator)
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: _src(std::move(src))
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, _limit_generator(std::move(limit_generator))
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{}
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limiting_data_source_impl(limiting_data_source_impl&&) noexcept = default;
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limiting_data_source_impl& operator=(limiting_data_source_impl&&) noexcept = default;
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virtual future<temporary_buffer<char>> get() override {
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if (_buf.empty()) {
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_buf.release();
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return _src.get().then([this] (auto&& buf) {
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_buf = std::move(buf);
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return do_get();
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});
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}
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return do_get();
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}
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virtual future<temporary_buffer<char>> skip(uint64_t n) override {
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if (n < _buf.size()) {
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_buf.trim_front(n);
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return do_get();
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}
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n -= _buf.size();
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_buf.release();
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return _src.skip(n).then([this] (auto&& buf) {
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_buf = std::move(buf);
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return do_get();
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});
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}
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};
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data_source make_limiting_data_source(data_source&& src, seastar::noncopyable_function<size_t()>&& limit_generator) {
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return data_source{std::make_unique<limiting_data_source_impl>(std::move(src), std::move(limit_generator))};
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}
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