Background HTTP server in plugin

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Graham Parry

• January 11, 2023 11:48

Am trying to develop a plugin that can receive metadata via an HTTP server and then pass that data to the NX Server.

As a POC I'm just using Crow to test requests and responses.  The problem is this.  If I simply call the server from the DeviceAgent constructor the server works but my TestCamera video hangs.  If I try and put Crow into a separate thread, when I change the plugin and restart the NX Server service it keeps restarting every few seconds.

Here is my calling code

DeviceAgent::DeviceAgent(const nx::sdk::IDeviceInfo* deviceInfo) :
    // Call the DeviceAgent helper class constructor telling it to verbosely report to stderr.
    ConsumingDeviceAgent(deviceInfo, /*enableOutput*/ true)
{
    vnet * vnetptr;
    std::thread th(&vnet::InitialiseHTTPServer, vnetptr);
}

and here is the code being called in a class called vnet

void vnet::InitialiseHTTPServer()
        {

            crow::SimpleApp app; //define your crow application

            //define your endpoint at the root directory
            CROW_ROUTE(app, "/")([]() {
                return "Hello world";
                });

            //set the port, set the app to run on multiple threads, and run the app
            app.port(9090).run_async();

        }

Do you have a better method of utilising a small HTTP server within the plugin?

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• 

  Andrey Terentyev

  • January 11, 2023 18:27

  Hello,

  Could you please do the following?

  Take a sample_analytics_plugin in the Metadata SDK.
  Put your code dealing with HTTP server there.
  Try to reproduce the issue.
  Share the plugin code here. Just publish a link to the archive file.

   

   

   

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  Graham Parry

  • January 12, 2023 10:24

  Hi Andrey
  Will do that.  In principle though is there any reason why threading would upset the server service starting?  The plugin behaves OK if I don't try and run the mini server separately.

   

   

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  Andrey Terentyev

  • January 12, 2023 13:01

  Hi,

  In principle though is there any reason why threading would upset the server service starting?

  A bug in your code, most probably. Lost pointer or something similar.

  For example, in your code snippet, vnet * vnetptr is a local variable and is destroyed once the  DeviceAgent::DeviceAgent() method exits. Probably, you should declare and use a private member of the vnet * vnetptr type inside the DeviceAgent class.

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  Graham Parry

  • January 12, 2023 19:14

  Thanks.  Actually I may just have solved the issue I was inquiring about.  It's all a bit experimental at the moment as I find my way around the plugin, but I seem to have my server running again and the NX Server is stable.   Will obviously get back if I'm stuck, but I'll bear your thoughts in mind when doing any threading.

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