C++ Header-only event driven communication between jQuery in a web-browser via the nginx web-server. This can implement, for example, a RESTful API for fast sensor data transfer.

This was developed because of a lack of a lightweight jQuery to C++ communication. It's a small helper which can easily be included in any C++ application which needs to talk to a web page where realtime data needs to be exchanged.

Works alongside PHP as nginx can serve both!

apt-get install libfcgi-dev
apt-get install libjsoncpp-dev
apt-get install nginx-core

This is a pure header based library. All the code is in json_fastcgi_web_api.h. Just type:

sudo make install json_fastcgi_web_api.h

to install the header in the system-wide include dir.

The only file you need is:

json_fastcgi_web_api.h

The file json_fastcgi_web_api.h has extensive inline documentation. Its doxygen generated online documentation is here: https://berndporr.github.io/fastcgi_json_cpp_api/

This is the callback which sends JSON packets to the client (website, phone app, etc):

	class GETCallback {
	public:
		/**
		 * Needs to return the JSON data sent to the web browser.
		 **/
		virtual std::string getJSONString() = 0;
	};

Overload getJSONString() and return JSON. The recommended way of generating JSON is with the jsoncpp library which is part of all major Linux distros.

This handler receives the JSON from jQuery POST command from the website for example when the user presses a button. Implement the callback:

	class POSTCallback {
	public:
		/**
		 * Receives the data from the web browser in JSON format.
		 **/
		virtual void postString(std::string arg) = 0;
	};

Overload postString(std::string arg) with a function which decodes the received POST data.

The start method takes as arguments the GET callback, the POST callback and the path to the fastCGI socket:

JSONCGIHandler jsoncgihandler;
jsoncgihandler.start(GETCallback* argGetCallback,
                     POSTCallback* argPostCallback = nullptr,
		     const char socketpath[] = "/tmp/fastcgisocket");

Just call jsoncgihandler.stop() to shut down the communication.

The subdir fake_sensor_demo contains a demo_sensor_server which fakes a temperature sensor and its readings are plotted in a web browser. The nginx config file and the website are in the website directory.

The subdir ads1115_demo contains a demo where the channel one from a real ADS1115 ADC chip is plotted in a web browser. You need an ADS1115 ADC for this demo.

The subdir usbdux_demo contains a demo where the temperature from an LM35 is digitised with a USB-DUX and then plotted in a web browser. You need an USB-DUX (sigma or D) for this demo.

Bernd Porr, [email protected]

if you have no static IP address you can use the the "afraid" dynamic DNS service: Free DNS