python_blockchain_app

A simple tutorial for developing a blockchain application from scratch in Python.

What is blockchain? How it is implemented? And how it works?

Blockchain is a system of recording information in a way that makes it difficult or impossible to change, hack, or cheat the system.

A blockchain is essentially a digital ledger of transactions that is duplicated and distributed across the entire network of computer systems on the blockchain.

Instructions to run

Clone the project,

$ git clone https://github.com/arjunsundaram4/pythonBlockchain.git

Install the dependencies,

```sh
$ cd python_blockchain_app
$ pip install -r requirements.txt

Start a blockchain node server,

# Windows users can follow this: https://flask.palletsprojects.com/en/1.1.x/cli/#application-discovery
$ export FLASK_APP=node_server.py
$ flask run --port 8000

One instance of our blockchain node is now up and running at port 8000.

Run the application on a different terminal session,

$ python run_app.py

To play around by spinning off multiple custom nodes, use the register_with/ endpoint to register a new node.

Here's a sample scenario that you might wanna try,

# Make sure you set the FLASK_APP environment variable to node_server.py before running these nodes
# already running
$ flask run --port 8000 &
# spinning up new nodes
$ flask run --port 8001 &
$ flask run --port 8002 &

You can use the following cURL requests to register the nodes at port 8001 and 8002 with the already running 8000.

curl -X POST \
  http://127.0.0.1:8001/register_with \
  -H 'Content-Type: application/json' \
  -d '{"node_address": "http://127.0.0.1:8000"}'
curl -X POST \
  http://127.0.0.1:8002/register_with \
  -H 'Content-Type: application/json' \
  -d '{"node_address": "http://127.0.0.1:8000"}'

This will make the node at port 8000 aware of the nodes at port 8001 and 8002, and make the newer nodes sync the chain with the node 8000, so that they are able to actively participate in the mining process post registration.

To update the node with which the frontend application syncs (default is localhost port 8000), change CONNECTED_NODE_ADDRESS field in the views.py file.

Once you do all this, you can run the application, create transactions (post messages via the web inteface), and once you mine the transactions, all the nodes in the network will update the chain. The chain of the nodes can also be inspected by inovking /chain endpoint using cURL.

$ curl -X GET http://localhost:8001/chain
$ curl -X GET http://localhost:8002/chain