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https://github.com/berndporr/fastcgi_json_cpp_api

Header-only JSON event driven communication between jQuery and C++ via nginx
https://github.com/berndporr/fastcgi_json_cpp_api

cpp fastcgi jquery json nginx real-time realtime

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Header-only JSON event driven communication between jQuery and C++ via nginx

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# jQuery <--> C++ JSON communication



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!



![alt tag](dataflow.png)



## Prerequisites



```

apt-get install libfcgi-dev

apt-get install libjsoncpp-dev

apt-get install nginx-core

```



## Installation



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.



## 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/fastcgi_json_cpp_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 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](https://github.com/open-source-parsers/jsoncpp)

library which is part of all major Linux distros.



### 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.

		 **/

		virtual void postString(std::string arg) = 0;

	};

```

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



### Start the communication



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");

```



### Stop the communication



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



## 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 browser. The nginx

config file and the website are in the `website`

directory.



### Real ADC ADS1115 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.



### Real USB-DUX realtime demo

The subdir `usbdux_demo` contains a demo where the temperature from an LM35 is digitised

with a [USB-DUX](https://github.com/glasgowneuro/usbdux) and then plotted in a web browser.

You need an USB-DUX (sigma or D) for this demo.



## Credit



Bernd Porr, [email protected]



## Dynamic DNS

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

[Free DNS](http://freedns.afraid.org/)