GzipFileReader.hpp

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#ifndef BYTEME_GZIP_FILE_READER_HPP
#define BYTEME_GZIP_FILE_READER_HPP
 
#include <cstddef>
#include <stdexcept>
#include <vector>
#include <optional>
 
#include "zlib.h"
 
#include "check_buffer_size.hpp"
#include "SelfClosingGzFile.hpp"
#include "Reader.hpp"
 
namespace byteme {
 
struct GzipFileReaderOptions {
    std::size_t buffer_size = 65536;
 
    std::optional<unsigned> gzbuffer_size;
};
 
class GzipFileReader final : public Reader {
public:
    GzipFileReader(const char* path, const GzipFileReaderOptions& options) : 
        my_gzfile(path, "rb"),
        my_buffer(
            check_buffer_size<int>( // constrained for the gzread return type.
                check_buffer_size<unsigned>( // constrained for the gzread argument type.
                    check_buffer_size(options.buffer_size)
                )
            )
        )
    {
        set_optional_gzbuffer_size(my_gzfile, options.gzbuffer_size);
    }
 
public:
    bool load() {
        if (my_finished) {
            // We need to check the status explicitly because gzread()
            // doesn't return an error for a truncated file.
            check_status();
            return false;
        }
 
        const std::size_t bufsize = my_buffer.size();
        auto ret = gzread(my_gzfile.handle, my_buffer.data(), bufsize);
        if (ret < 0) {
            check_status();
            return false;
        }
 
        my_read = ret;
        my_finished = (my_read < bufsize);
        return true;
    }
 
    const unsigned char* buffer() const {
        return my_buffer.data();
    }
 
    std::size_t available() const {
        return my_read;
    }
 
private:
    SelfClosingGzFile my_gzfile;
    std::vector<unsigned char> my_buffer;
    std::size_t my_read = 0;
    bool my_finished = false;
 
    void check_status() {
        int status;
        auto msg = gzerror(my_gzfile.handle, &status);
        if (status != Z_OK) {
            throw std::runtime_error(msg);
        }
    }
 
};
 
}
 
#endif