[Cppcms-users] How to combine SSE with the url dispatcher

[eric m. <mid...@gm...>]

Hello,

I'm trying to combine the features of the ticker example (
https://svn.code.sf.net/p/cppcms
/code/framework/trunk/contrib/server_side/sse/), i.e. streaming data from
the server to update a webpage with url dispatching instead of using the
default main function and a static html page.

So instead of the following code in ticker.cpp:

    void main(std::string /*url*/)
    {
        stream_->accept(release_context());
    }

I would like to use something like:

MyApp::MyApp(cppcms::service &service) : cppcms::application(service),
tm_(service.get_io_service()), price_(1.0)
{
    dispatcher().assign("/camerasettings",&MyApp::cameraSettings,this);
    mapper().assign("Camera Settings","/camerasettings");

    mapper().root("/robot");

    stream_ = sse::state_stream::create(service.get_io_service());
    wait();
}

void MyApp::cameraSettings()
{
    string page = FileSystem().readFileIntoString("the_ticker.html");
    response().out() << page.c_str();
    stream_->accept(release_context());
}

While having all the rest the same as in the ticker example.

I open the page with 127.0.0.1:8080/robot/camerasettings and the page is
displayed correctly but the stream keeps loading and is not being
displayed. After stopping the server, the data is displayed and looks like
this:
Stock Price

Price:
id:8 data:2.54208 id:9 data:2.97668 id:10 data:3.19061 id:11 data:2.67639
id:12 data:3.28474 id:13 data:3.08663 id:14 data:2.30425 id:15 data:1.74076
id:16 data:2.41898 id:17 data:2.01105 id:18 data:2.05962 id:19 data:3.00517
id:20 data:3.54789 id:21 data:4.08772 id:22 data:4.87077 id:23 data:4.57569
id:24 data:5.41374 id:25 data:6.3124

If on the other hand the stream is accepted before the response is sent,
like this

void MyApp::cameraSettings()
{
    string page = FileSystem().readFileIntoString("the_ticker.html");
    stream_->accept(release_context());
    response().out() << page.c_str();
}

an exception is thrown: cppcms, error: Caught exception [Access to
unassigned context] which seems to be kind of logical, the page does not
show, but after stopping the server, the browser displays the streamed data
as follows:

id:15
data:1.74076

id:16
data:2.41898

id:17
data:2.01105

id:18
data:2.05962

id:19
data:3.00517

id:20
data:3.54789

So I have two questions:

1) How do I combine server side events with url dispatching in cppcms?
As I would like to create and send the page to the browser from a
method and start to stream events after the page has loaded.

2) How do I stop the stream if the user switches to another page or
does it stop itself?

I can provide full sourcecode if necessary. Sofar I couldn't find
other comparable examples.

My guess is that it shouldn't be all that difficult once you know, but
currently I do not (-;

Any help is welcome here.

Best regards,
Eric