62 lines
1.5 KiB
C++
62 lines
1.5 KiB
C++
//
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// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2020
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#pragma once
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#include "td/utils/common.h"
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#include "td/utils/port/FileFd.h"
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#include "td/utils/Slice.h"
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#include "td/utils/Status.h"
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namespace td {
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class BufferedReader {
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public:
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explicit BufferedReader(FileFd &file, size_t buff_size = 8152)
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: file_(file), buff_(buff_size), begin_pos_(0), end_pos_(0) {
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}
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Result<size_t> read(MutableSlice slice) TD_WARN_UNUSED_RESULT;
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private:
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FileFd &file_;
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vector<char> buff_;
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size_t begin_pos_;
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size_t end_pos_;
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};
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inline Result<size_t> BufferedReader::read(MutableSlice slice) {
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size_t available = end_pos_ - begin_pos_;
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if (available >= slice.size()) {
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// have enough data in buffer
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slice.copy_from({&buff_[begin_pos_], slice.size()});
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begin_pos_ += slice.size();
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return slice.size();
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}
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if (available) {
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slice.copy_from({&buff_[begin_pos_], available});
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begin_pos_ += available;
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slice.remove_prefix(available);
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}
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if (slice.size() > buff_.size() / 2) {
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TRY_RESULT(result, file_.read(slice));
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return result + available;
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}
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TRY_RESULT(result, file_.read({&buff_[0], buff_.size()}));
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begin_pos_ = 0;
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end_pos_ = result;
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size_t left = min(end_pos_, slice.size());
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slice.copy_from({&buff_[0], left});
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begin_pos_ = left;
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return left + available;
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}
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} // namespace td
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