Boost SSL handshake(http_server_sync_ssl) : still reachable memory keeps increasing

//
// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
//
// 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)
//
// Official repository: https://github.com/boostorg/beast
//

//------------------------------------------------------------------------------
//
// Example: HTTP SSL server, synchronous
//
//------------------------------------------------------------------------------

//#include "example/common/server_certificate.hpp"

#include <boost/beast/core.hpp>
#include <boost/beast/http.hpp>
#include <boost/beast/ssl.hpp>
#include <boost/beast/version.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/ssl/stream.hpp>
#include <boost/config.hpp>
#include <cstdlib>
#include <iostream>
#include <memory>
#include <string>
#include <thread>

namespace beast = boost::beast;         // from <boost/beast.hpp>
namespace http = beast::http;           // from <boost/beast/http.hpp>
namespace net = boost::asio;            // from <boost/asio.hpp>
namespace ssl = boost::asio::ssl;       // from <boost/asio/ssl.hpp>
using tcp = boost::asio::ip::tcp;       // from <boost/asio/ip/tcp.hpp>

// Return a reasonable mime type based on the extension of a file.
beast::string_view
mime_type(beast::string_view path)
{
    using beast::iequals;
    auto const ext = [&path]
    {
        auto const pos = path.rfind(".");
        if(pos == beast::string_view::npos)
            return beast::string_view{};
        return path.substr(pos);
    }();
    if(iequals(ext, ".htm"))  return "text/html";
    if(iequals(ext, ".html")) return "text/html";
    if(iequals(ext, ".php"))  return "text/html";
    if(iequals(ext, ".css"))  return "text/css";
    if(iequals(ext, ".txt"))  return "text/plain";
    if(iequals(ext, ".js"))   return "application/javascript";
    if(iequals(ext, ".json")) return "application/json";
    if(iequals(ext, ".xml"))  return "application/xml";
    if(iequals(ext, ".swf"))  return "application/x-shockwave-flash";
    if(iequals(ext, ".flv"))  return "video/x-flv";
    if(iequals(ext, ".png"))  return "image/png";
    if(iequals(ext, ".jpe"))  return "image/jpeg";
    if(iequals(ext, ".jpeg")) return "image/jpeg";
    if(iequals(ext, ".jpg"))  return "image/jpeg";
    if(iequals(ext, ".gif"))  return "image/gif";
    if(iequals(ext, ".bmp"))  return "image/bmp";
    if(iequals(ext, ".ico"))  return "image/vnd.microsoft.icon";
    if(iequals(ext, ".tiff")) return "image/tiff";
    if(iequals(ext, ".tif"))  return "image/tiff";
    if(iequals(ext, ".svg"))  return "image/svg+xml";
    if(iequals(ext, ".svgz")) return "image/svg+xml";
    return "application/text";
}

// Append an HTTP rel-path to a local filesystem path.
// The returned path is normalized for the platform.
std::string
path_cat(
    beast::string_view base,
    beast::string_view path)
{
    if(base.empty())
        return std::string(path);
    std::string result(base);
#ifdef BOOST_MSVC
    char constexpr path_separator = '\\';
    if(result.back() == path_separator)
        result.resize(result.size() - 1);
    result.append(path.data(), path.size());
    for(auto& c : result)
        if(c == '/')
            c = path_separator;
#else
    char constexpr path_separator = '/';
    if(result.back() == path_separator)
        result.resize(result.size() - 1);
    result.append(path.data(), path.size());
#endif
    return result;
}

// This function produces an HTTP response for the given
// request. The type of the response object depends on the
// contents of the request, so the interface requires the
// caller to pass a generic lambda for receiving the response.
template<
    class Body, class Allocator,
    class Send>
void
handle_request(
    http::request<Body, http::basic_fields<Allocator>>&& req,
    Send&& send,
    int payloadProcessStatus)
{
    // Returns a bad request response
    auto const bad_request =
    [&req](beast::string_view why)
    {
        http::response<http::string_body> res;
        res.version(11);
        res.result(http::status::bad_request);
        res.set(http::field::server, BOOST_BEAST_VERSION_STRING);
        res.set(http::field::content_type, "text/html");
        res.keep_alive(req.keep_alive());
        res.body() = std::string(why);
        res.prepare_payload();
        return res;
    };

    // Returns a server error response
    auto const server_error =
    [&req](beast::string_view what)
    {
        http::response<http::string_body> res;
        res.version(11);
        res.result(http::status::internal_server_error);
        res.set(http::field::server, BOOST_BEAST_VERSION_STRING);
        res.set(http::field::content_type, "text/html");
        res.keep_alive(req.keep_alive());
        res.body() = "An error occurred: '" + std::string(what) + "'";
        res.prepare_payload();
        return res;
    };

    // Make sure we can handle the method
    if( req.method() != http::verb::post )
        return send(bad_request("Unknown HTTP-method"));

    if (payloadProcessStatus == -1)
        return send(server_error("Internal server error"));

    http::response<http::string_body> res;
    res.version(11);
    res.result(http::status::ok);
    res.set(http::field::server, BOOST_BEAST_VERSION_STRING);
    res.set(http::field::content_type, "application/text");
    res.keep_alive(req.keep_alive());
    res.body() = "Collection request succeeded";
    res.prepare_payload(); 
    return send(std::move(res));
}

//------------------------------------------------------------------------------

// Report a failure
void
fail(beast::error_code ec, char const* what)
{
    std::cerr << what << ": " << ec.message() << "\n";
}

// This is the C++11 equivalent of a generic lambda.
// The function object is used to send an HTTP message.
template<class Stream>
struct send_lambda
{
    Stream& stream_;
    bool& close_;
    beast::error_code& ec_;

    explicit
    send_lambda(
        Stream& stream,
        bool& close,
        beast::error_code& ec)
        : stream_(stream)
        , close_(close)
        , ec_(ec)
    {
    }

    template<bool isRequest, class Body, class Fields>
    void
    operator()(http::message<isRequest, Body, Fields>&& msg) const
    {
        // Determine if we should close the connection after
        close_ = msg.need_eof();

        // We need the serializer here because the serializer requires
        // a non-const file_body, and the message oriented version of
        // http::write only works with const messages.
        http::serializer<isRequest, Body, Fields> sr{msg};
        http::write(stream_, sr, ec_);
    }
};

// Handles an HTTP server connection
void
do_session(
    tcp::socket& socket,
    ssl::context& ctx,
    std::shared_ptr<std::string const> const& doc_root)
{
    bool close = false;
    beast::error_code ec;

    // Construct the stream around the socket
    beast::ssl_stream<tcp::socket&> stream{socket, ctx};

    // Perform the SSL handshake
    stream.handshake(ssl::stream_base::server, ec);
    if(ec)
        return fail(ec, "handshake");

    // This buffer is required to persist across reads
    beast::flat_buffer buffer;

    // This lambda is used to send messages
    send_lambda<beast::ssl_stream<tcp::socket&>> lambda{stream, close, ec};

    for(;;)
    {
        // Read a request
        http::request<http::string_body> req;
        http::read(stream, buffer, req, ec);
        if(ec == http::error::end_of_stream)
            break;
        if(ec)
            return fail(ec, "read");

        std::string payload = req.body();
        std::cout<<"Payload : "<<payload<<std::endl;
        int r = 0;
        // Send the response
        handle_request(std::move(req), lambda, r);
        if(ec)
            return fail(ec, "write");
        if(close)
        {
            // This means we should close the connection, usually because
            // the response indicated the "Connection: close" semantic.
            break;
        }
    }

    // Perform the SSL shutdown
    std::cout<<"Shutting down stream"<<std::endl;
    stream.shutdown(ec);
    if(ec)
        return fail(ec, "shutdown");
    OPENSSL_thread_stop(); 
    // At this point the connection is closed gracefully
}

//------------------------------------------------------------------------------

int main(int argc, char* argv[])
{
    try
    {
        // Check command line arguments.
        if (argc != 4)
        {
            std::cerr <<
                "Usage: http-server-sync-ssl <address> <port> <doc_root>\n" <<
                "Example:\n" <<
                "    http-server-sync-ssl 0.0.0.0 8080 .\n";
            return EXIT_FAILURE;
        }
        auto const address = net::ip::make_address(argv[1]);
        auto const port = static_cast<unsigned short>(std::atoi(argv[2]));
        auto const doc_root = std::make_shared<std::string>(argv[3]);

        // The io_context is required for all I/O
        net::io_context ioc{1};

        // The SSL context is required, and holds certificates
        ssl::context ctx{ssl::context::tlsv12};

        ctx.load_verify_file("/tmp/ca.crt"); 
        ctx.use_certificate_file("/tmp/server.crt", ssl::context::file_format::pem);
        ctx.use_rsa_private_key_file("/tmp/server.key", ssl::context::file_format::pem);
        

        // The acceptor receives incoming connections
        tcp::acceptor acceptor{ioc, {address, port}};
        for(;;)
        {
            // This will receive the new connection
            tcp::socket socket{ioc};

            // Block until we get a connection
            acceptor.accept(socket);

            // Launch the session, transferring ownership of the socket
            std::thread{std::bind(
                &do_session,
                std::move(socket),
                std::ref(ctx),
                doc_root)}.detach();
        }
    }
    catch (const std::exception& e)
    {
        std::cerr << "Error: " << e.what() << std::endl;
        return EXIT_FAILURE;
    }
}