Многопоточный загрузчик файлов по ссылкам в txt файле

#include "C:\boost_1_68_0_VS2017\libs\beast\example\common\root_certificates.hpp"
 
#include <boost/beast/core.hpp>
#include <boost/beast/http.hpp>
#include <boost/beast/version.hpp>
#include <boost/asio/connect.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/ssl/error.hpp>
#include <boost/asio/ssl/stream.hpp>
#include <cstdlib>
#include <iostream>
#include <string>
#include <fstream>
 
using tcp = boost::asio::ip::tcp;       // from <boost/asio/ip/tcp.hpp>
namespace ssl = boost::asio::ssl;       // from <boost/asio/ssl.hpp>
namespace http = boost::beast::http;    // from <boost/beast/http.hpp>
 
// Performs an HTTP GET and prints the response
int main(int argc, char** argv)
{
    try
    {
        // Check command line arguments.
        if (argc != 4 && argc != 5)
        {
            std::cerr <<
                "Usage: http-client-sync-ssl <host> <port> <target> [<HTTP version: 1.0 or 1.1(default)>]\n" <<
                "Example:\n" <<
                "    http-client-sync-ssl www.example.com 443 /\n" <<
                "    http-client-sync-ssl www.example.com 443 / 1.0\n";
            //return EXIT_FAILURE;
        }
        auto const host = "www.boost.org";
        auto const port = "443";
        auto const target = "/LICENSE_1_0.txt";
        int version = argc == 5 && !std::strcmp("1.0", argv[4]) ? 10 : 11;
 
        // The io_context is required for all I/O
        boost::asio::io_context ioc;
 
        // The SSL context is required, and holds certificates
        ssl::context ctx{ ssl::context::sslv23_client };
 
        // This holds the root certificate used for verification
        load_root_certificates(ctx);
 
        // These objects perform our I/O
        tcp::resolver resolver{ ioc };
        ssl::stream<tcp::socket> stream{ ioc, ctx };
 
        // Set SNI Hostname (many hosts need this to handshake successfully)
        if (!SSL_set_tlsext_host_name(stream.native_handle(), host))
        {
            boost::system::error_code ec{ static_cast<int>(::ERR_get_error()), boost::asio::error::get_ssl_category() };
            throw boost::system::system_error{ ec };
        }
 
        // Look up the domain name
        auto const results = resolver.resolve(host, port);
 
        // Make the connection on the IP address we get from a lookup
        boost::asio::connect(stream.next_layer(), results.begin(), results.end());
 
        // Perform the SSL handshake
        stream.handshake(ssl::stream_base::client);
 
        // Set up an HTTP GET request message
        http::request<http::string_body> req{ http::verb::get, target, version };
        req.set(http::field::host, host);
        req.set(http::field::user_agent, BOOST_BEAST_VERSION_STRING);
 
        // Send the HTTP request to the remote host
        http::write(stream, req);
 
        // This buffer is used for reading and must be persisted
        boost::beast::flat_buffer buffer;
 
        // Declare a container to hold the response
        http::response<http::dynamic_body> res;
 
        // Receive the HTTP response
        http::read(stream, buffer, res);
 
        std::ofstream ofs{"out.txt"};
        ofs << res;
        ofs.close();
 
        // Write the message to standard out
        //std::cout << res << std::endl;
 
        // Gracefully close the stream
        boost::system::error_code ec;
        stream.shutdown(ec);
        if (ec == boost::asio::error::eof)
        {
            // Rationale:
            // http://stackoverflow.com/questions/25587403/boost-asio-ssl-async-shutdown-always-finishes-with-an-error
            ec.assign(0, ec.category());
        }
        if (ec)
            throw boost::system::system_error{ ec };
 
        // If we get here then the connection is closed gracefully
    }
    catch (std::exception const& e)
    {
        std::cerr << "Error: " << e.what() << std::endl;
        return EXIT_FAILURE;
    }
    return EXIT_SUCCESS;
}