range_reader.hpp

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#pragma once
 
#include <fcb/error.hpp>
 
#include <cstdint>
#include <fstream>
#include <memory>
#include <string>
#include <vector>
 
namespace fcb {
 
struct RangeRequest {
    std::uint64_t offset;
    std::uint64_t length;
    std::vector<std::uint8_t> data;
};
 
class RangeReader {
  public:
    virtual ~RangeReader() = default;
 
    virtual std::uint64_t total_size() = 0;
 
    virtual std::vector<std::uint8_t> read(std::uint64_t offset, std::uint64_t length) = 0;
 
    virtual void read_batch(std::vector<RangeRequest>& requests);
};
 
class FileRangeReader : public RangeReader {
  public:
    explicit FileRangeReader(const std::string& path);
 
    std::uint64_t total_size() override;
    std::vector<std::uint8_t> read(std::uint64_t offset, std::uint64_t length) override;
 
  private:
    std::string path_;
    std::ifstream stream_;
    std::uint64_t size_;
};
 
class BufferedRangeReader : public RangeReader {
  public:
    BufferedRangeReader(std::shared_ptr<RangeReader> inner, std::uint64_t min_req_size);
 
    std::uint64_t total_size() override;
    std::vector<std::uint8_t> read(std::uint64_t offset, std::uint64_t length) override;
    void read_batch(std::vector<RangeRequest>& requests) override;
 
  private:
    bool covers(std::uint64_t offset, std::uint64_t length) const;
    std::uint64_t clamped_fetch(std::uint64_t offset, std::uint64_t length);
    std::vector<std::uint8_t> slice_from_buffer(std::uint64_t offset, std::uint64_t length) const;
 
    std::shared_ptr<RangeReader> inner_;
    std::uint64_t min_req_size_;
    std::uint64_t buf_offset_ = 0;
    std::vector<std::uint8_t> buf_;
};
 
}  // namespace fcb