Reading a .tar.xx file using a more C++ structured fashion via libarchive

CMakeLists.txt

cmake_minimum_required(VERSION 3.16)
project(read_archive)

set(CMAKE_CXX_STANDARD 14)
find_library(LibArchive  3.4.0)

add_executable(read_archive main.cpp)
target_link_libraries(read_archive archive)

main.cpp

#include <iostream>
#include <archive.h>
#include <archive_entry.h>
#include <fcntl.h>

template <size_t buffer_size = 1024>
class ReadArchiveBuffer {
    char buff[buffer_size];
    size_t size;
    struct archive *a;
    std::string path;

public:
    ReadArchiveBuffer(archive *a, const std::string& path) : a(a), path(path) { size = -1; }
    ReadArchiveBuffer() : ReadArchiveBuffer(nullptr, "") { size = 0; };
    ReadArchiveBuffer(const ReadArchiveBuffer&) = default;
    ReadArchiveBuffer& operator=(const ReadArchiveBuffer&) = default;

    bool readNext(struct iovec& data) {
        if (a) {
            size = archive_read_data(a, buff, 1024);
        }
        if (size <= 0) {
            data.iov_len = 0;
            data.iov_base = nullptr;
            return false;
        } else {
            data.iov_base = buff;
            data.iov_len = size;
            return true;
        }
    }

    std::string filename() const { return path; }

};

template <size_t buffer_size = 1024>
class ReadArchive {
public:

    ReadArchive(const std::string& file_name, size_t block_size = 10240) : ReadArchive{} {
        a = archive_read_new();
        archive_read_support_format_all(a);
        archive_read_support_compression_all(a);
        if ((r = archive_read_open_filename(a, file_name.c_str(), block_size)))
            throw std::runtime_error("Cannot read file: " + file_name);
        this->operator++();
    }

    ReadArchive() {
        a = nullptr;
        entry = nullptr;
        r = ARCHIVE_EOF;
    }

    ~ReadArchive() {
        archive_read_close(a);
        archive_read_free(a);
    }

    bool doStop() {
        return ((r == ARCHIVE_EOF) || (r < ARCHIVE_OK) || (r < ARCHIVE_WARN) || (archive_entry_size(entry) <= 0));
    }

    ReadArchive& operator++() {
        r = archive_read_next_header(a, &entry);
        while ((r != ARCHIVE_EOF) && (r >= ARCHIVE_OK) && (r >= ARCHIVE_WARN) && (archive_entry_size(entry) == 0)) {
            r = archive_read_next_header(a, &entry);
        }
    }

    ReadArchiveBuffer<buffer_size> operator*() {
        std::string filename = archive_entry_pathname(entry);
        return {a, filename};
    }

    ReadArchiveBuffer<buffer_size> operator->() {
        std::string filename = archive_entry_pathname(entry);
        return {a, filename};
    }

private:
    struct archive *a;
    struct archive_entry *entry;
    int r;
};


int main() {

    for (ReadArchive<> ra{"/path/to/some/file.tar.xz"}; !ra.doStop();  ++ra) {
        ReadArchiveBuffer<> buff = *ra;
        std::cout << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" << std::endl;
        std::cout << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" << std::endl;
        std::cout << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" << std::endl;
        std::cout << buff.filename() << std::endl;
        std::cout << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" << std::endl;
        std::cout << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" << std::endl;
        std::cout << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" << std::endl;
        struct iovec data;
        while (buff.readNext(data)) {
            std::cout << std::string((const char*)data.iov_base, data.iov_len); // Printing string data
        }
        std::cout << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" << std::endl;
        std::cout << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" << std::endl;
        std::cout << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" << std::endl;
    }
    return 0;
}