[Cppcms-users] async_flush_output and multipart/x_mixed_replace

[Tobias R. <rei...@go...>]

Hello,

I'm trying to get a multipart response by doing a single request. The motivation
behind is a big computation which gives some progress feedback. So far I
stumbled over "context::async_flush_output" which (given that name) should flush
the responding data. Simulating the computational part by using a timer, I
expect to get five distinct responses, each in a second (see following code).
Instead, I get the whole response after the five seconds en bloc. Did I miss
something?


class Application : public cppcms::application
{
    int counter_;
    booster::aio::deadline_timer timer_;
    booster::shared_ptr<cppcms::http::context> context_;
    boost::thread thread_;

public:
    Application(cppcms::service &srv)
        : cppcms::application(srv)
    {
        timer_.set_io_service(service().get_io_service());
        dispatcher().assign("^/compute$", &Application::compute, this);
    }

    void async_handler(cppcms::http::context::complition_type t)
    {
        timer_.expires_from_now(booster::ptime::seconds(1));
        timer_.async_wait(boost::bind(&Application::compute_thread,
booster::intrusive_ptr<Application>(this)));
    }

    void flush_output()
    {
        context_->async_flush_output(boost::bind(&Application::async_handler,
booster::intrusive_ptr<Application>(this), _1));
    }

    void compute_thread()
    {
        std::ostream& o = context_->response().out();
        if (counter_++ < 5)
        {
            o << "Content-type: text/plain\n\n";
            o << "count: " << counter_ << std::endl;
            o << "--progress-token\n";
//            flush_output();
            service().post(boost::bind(&Application::flush_output,
booster::intrusive_ptr<Application>(this)));
            return;
        }
        o << "Content-type: text/plain\n\n";
        o << "Computation finished\n";
        o << "--progress-token\n";
        context_->async_complete_response();
    }

    void compute()
    {
        context_ = release_context();
        context_->response().set_content_header("multipart/x-mixed-replace;
boundary=progress-token");
        context_->response().out() << "--progress-token\n";
        counter_ = 0;
//        compute_thread();
        thread_ = boost::thread(boost::bind(&Application::compute_thread,
booster::intrusive_ptr<Application>(this)));
    }

};

int main(int argc, char** argv)  
{  
    try {  
        cppcms::service srv(argc, argv);
        booster::intrusive_ptr<Application> app = new Application(srv);
        srv.applications_pool().mount(app, cppcms::mount_point("/counter"));
        srv.run();  
    }  
    catch(std::exception const& e) {  
        std::cerr << e.what() << std::endl;  
    }  
}


On the client side I have a simple Javascript:

    var xmlHttp = new XMLHttpRequest();
    xmlHttp.multipart = true;
    xmlHttp.open('GET', 'counter/compute', true);
    xmlHttp.onreadystatechange = function (event)
    {
        console.log("readystate = " + event.target.readyState + ": " +
event.target.responseText + "\n");
    }
    xmlHttp.send(null);


Best regards,

Tobias