Proof-of-Work Based Blockchain

Python based decentralised blockchain application using a P2P network to distribute the ledger and a flask interface to probe the network.

Usage

Run the flask interface:

python main.py

Run a few P2P nodes:

python server.py 5001
python server.py 5002
python server.py 5003

Probe the network using the flask interface:

#todo

The servers will auto synchronise to the longest valid chain

Blockchain

implemented with a python deque collection as it's optimised for pop/push (perfect for blockchain)

Block

Genesis Block

Origin of the blockchain. A genesis block is available as a property. Our genesis block is hardcoded with dummy values for the timestamp, nonce, data and prev_hash.

@property
def genesis_block(self):
    if not hasattr(self, '_genesis_block'):
        genesis_block = Block(prev_hash='0000', data={})
        setattr(self, '_genesis_block', genesis_block)
    return getattr(self, '_genesis_block')

Block Fields

index:	current block's chain index
timestamp:	(req) UTC TimeZone - string format: "%d/%m/%Y, %H:%M:%S"
nonce:	(req) Integer value added to the hashed block so that, when rehashed, meets the difficulty level restrictions
previous hash:	(req) Hash value of the previous block in the chain
current hash:	Used for debugging - next block will compute this block's hash instead of assessing this field
data:	(req) JSON formatted, sorted by key name, data to be stored in the blockchain

Peer-to-Peer Network

The peer-to-peer network is comprised of multiple servers (server.py) interconnected using sockets and a flask interface that is used to probe individual nodes in the network.

Each node in the peer-to-peer network will subscribe itself to the list of running nodes in the network for as long as the server is running and unsubscribe itself if gracefully terminated.

The nodes in the network will send/receive utf-8 encoded bytes where the first 10 characters are reserved for the header and indicate the message size.

valid_message = bytes('13        Valid message', 'utf-8'))

HEADER_SIZE = 10

client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client.connect(('localhost', 5001))

msg = repr(blockchain)
msg = f'{len(msg):<{HEADER_SIZE}}{msg}'

client.send(bytes(msg, 'utf-8'))
msg = client.recv(1024)

Flask API

# Mining a new block
@app.route('/mine_block/<port>', methods=['POST'])

# Getting the full Blockchain
@app.route('/get_chain/<port>', methods=['GET'])

# Checking if the Blockchain is valid
@app.route('/validate/<port>', methods=['GET'])

# Shutdown a node
@app.route('/shutdown/<port>', methods=['GET'])