jQuery <--> C++ fastcgi web API

C++ Header-only event driven communication between jQuery in a web-browser via nginx.

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.

Prerequisites

apt-get install libfcgi-dev
apt-get install libcurl4-openssl-dev

Installation

This is a pure header based libary. 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.

Howto

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/json_fastcgi_web_api/

Implement the GET callback (server -> client)

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

	class GETCallback {
	public:
		/**
		 * Needs to return the payload data sent to the web browser.
		 * Use the JSON generator class or an external json generator.
		 **/
		virtual std::string getJSONString() = 0;
	};

Overload getJSONString() and return JSON. You can use the class JSONGenerator to generate the JSON data: Use the add methods to add key/value pairs and then get the json with the method getJSON().

Implement the POST callback (client -> server, optional)

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.
		 * Use postDecoder() to decode the JSON or use an external
		 * library.
		 **/
		virtual void postString(std::string arg) = 0;
	};

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

postDecoder(std::string s)

which returns a std::map of key/value pairs.

Start the communication

The constructor takes as arguments the GET callback, the POST callback and the path to the fastCGI socket. As soon as the constructor is instantiated the communication starts.

       /**
         * Constructor which inits it and starts the main thread.
         * Provide an instance of the callback handler which provides the
         * payload data in return. The optional socketpath variable
         * can be set to another path for the socket which talks to the
         * webserver. postCallback is the callback which returns
         * received json packets as a map.
         **/
        JSONCGIHandler(GETCallback* argGetCallback,
                       POSTCallback* argPostCallback = nullptr,
		       const char socketpath[] = "/tmp/fastcgisocket");

Stop the communication

This is done by deleting the instance.

Example code

Fake sensor demo

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

Real ADC realtime demo

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.

Credit

Bernd Porr, [email protected]