This Node.js application, utilising the Express framework, will launch a web server (listening on port 4000 by default). Once called by a client (e.g. a Web Browser), it will execute a Python script, and return the output of that script to the client.
Follow these instructions to run the example codebase locally on your computer.
You need the following installed on your computer:
Node.js (https://nodejs.org/en/download/)
Clone this repo:
git clone https://github.com/ibm-cork-coderdojo-projects/ArduinoPiExpressSample.git
cd ArduinoPiExpressSample
Alternatively, if Git is not installed, a Zip file can be downloaded from GitHub, and extracted on the computer (https://github.com/ibm-cork-coderdojo-projects/ArduinoPiExpressSample/archive/master.zip)
Next, the Node.js module dependencies must be installed using npm, the Node Package Manager. There is one important dependency: the Express framework!
npm install
This will download and install the dependencies into a new node_modules folder in your project directory.
Finally, launch the application server with:
npm start
This launches app.js. To view the application in action, open your web browser, and navigate to http://localhost:4000.
Next, in your browser navigate to http://localhost:4000/button.html. This webpage contains a button that, when clicked, will send a HTTP GET request (by using AJAX) to app.js at htttp://localhost:4000. The response output will be written onto the webpage beneath the button.
app.js starts up a web server on port 4000, initialised with the Express framework. The code listens for incoming HTTP GET requests to the root of the application /, i.e. no other path. The incoming HTTP requests are represented by the req object.
When a request is received (all HTTP requests sent from your web browser from the address bar are GET requests), spawn will launch a child process on the server, to start python, and execute my_script.py, located in the code folder.
The output of the script is stored in the variable pyProg. This is eventually returned to the calling client in the HTTP response object, res.
Note: Python scripts in the code folder need to have executable permissions to run! e.g. chmod +x code/my_script.py