using boost::asio with boost::context::callcc

simple-http-server.cc

#include <iostream>
#include <utility>
#include <boost/context/all.hpp>
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

namespace spawn {
  namespace asio = boost::asio;
  namespace ctx = boost::context;

  template <typename F>
  struct yield_context {
    F f;
    ctx::continuation c1;
    ctx::continuation c2;
    yield_context(F&& f) : f(std::move(f)){}
  };

  template <typename F>
  struct yield_handler {
    std::shared_ptr<yield_context<F>> y;
    template <typename... T>
    void operator()(T...) {y->c1 = y->c1.resume();}
    void resume() {y->c2 = y->c2.resume();}
  };
  
  template <typename F>
  void spawn(asio::io_service& ios, F&& f) {
    auto yc = std::make_shared<yield_context<F>>(std::move(f));
    ios.post([yc] {
      yc->c1 = ctx::callcc([yc](auto&& cc) {
        yc->c2 = std::move(cc);
        yield_handler<F> yh{yc};
        yc->f(yh);
        return std::move(yc->c2);
      });
    });
  }
};

namespace boost::asio {  
  template <typename F>
  class async_result<::spawn::yield_handler<F>> {
  public:
    ::spawn::yield_handler<F> y;
    using type = void;
    explicit async_result(::spawn::yield_handler<F>& _y) : y(_y) {}
    type get() {y.resume();}
  };
}

int main(void) {
  namespace asio = boost::asio;
  using tcp = boost::asio::ip::tcp;

  asio::io_service ios;
  spawn::spawn(ios, [&](auto&& yield) {
    tcp::acceptor acceptor{ios, {tcp::v4(), 1024}};
    for (;;) {
      tcp::socket sock{ios};
      acceptor.async_accept(sock, yield);
      spawn::spawn(ios, [&,sock=std::move(sock)](auto&& yield) mutable {
        char buf[1024];
        sock.async_read_some(asio::buffer(buf), yield);
        std::cout << buf;
        asio::deadline_timer t{ios};
        t.expires_from_now(boost::posix_time::milliseconds{100});
        t.async_wait(yield);
        asio::async_write(sock, asio::buffer("HTTP/1.1 200 OK\r\nContent-Length: 14\r\n\r\nHello, World!\n"), yield);
        sock.close();
      });
    }
  });

  ios.run();
  return 0;
}