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tdlib-fork/tdutils/td/utils/BufferedReader.h

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//
// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2019
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#pragma once
#include "td/utils/common.h"
#include "td/utils/port/FileFd.h"
#include "td/utils/Slice.h"
#include "td/utils/Status.h"
#include <cstring>
namespace td {
class BufferedReader {
public:
explciit BufferedReader(FileFd &file, size_t buff_size = 8152)
: file_(file), buff_(buff_size), begin_pos_(0), end_pos_(0) {
}
Result<size_t> read(MutableSlice slice) TD_WARN_UNUSED_RESULT;
private:
FileFd &file_;
vector<char> buff_;
size_t begin_pos_;
size_t end_pos_;
};
inline Result<size_t> BufferedReader::read(MutableSlice slice) {
size_t available = end_pos_ - begin_pos_;
if (available >= slice.size()) {
// have enough data in buffer
std::memcpy(slice.begin(), &buff_[begin_pos_], slice.size());
begin_pos_ += slice.size();
return slice.size();
}
if (available) {
std::memcpy(slice.begin(), &buff_[begin_pos_], available);
begin_pos_ += available;
slice.remove_prefix(available);
}
if (slice.size() > buff_.size() / 2) {
TRY_RESULT(result, file_.read(slice));
return result + available;
}
TRY_RESULT(result, file_.read({&buff_[0], buff_.size()}));
begin_pos_ = 0;
end_pos_ = result;
size_t left = min(end_pos_, slice.size());
std::memcpy(slice.begin(), &buff_[begin_pos_], left);
begin_pos_ += left;
return left + available;
}
} // namespace td