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Last active May 22, 2020 14:11
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Step 11: Implementing Consensus Algorithm
import requests
class Blockchain(object)
def valid_chain(self, chain):
Determine if a given blockchain is valid
:param chain: <list> A blockchain
:return: <bool> True if valid, False if not
last_block = chain[0]
current_index = 1
while current_index < len(chain):
block = chain[current_index]
# Check that the hash of the block is correct
if block['previous_hash'] != self.hash(last_block):
return False
# Check that the Proof of Work is correct
if not self.valid_proof(last_block['proof'], block['proof']):
return False
last_block = block
current_index += 1
return True
def resolve_conflicts(self):
This is our Consensus Algorithm, it resolves conflicts
by replacing our chain with the longest one in the network.
:return: <bool> True if our chain was replaced, False if not
neighbours = self.nodes
new_chain = None
# We're only looking for chains longer than ours
max_length = len(self.chain)
# Grab and verify the chains from all the nodes in our network
for node in neighbours:
response = requests.get(f'http://{node}/chain')
if response.status_code == 200:
length = response.json()['length']
chain = response.json()['chain']
# Check if the length is longer and the chain is valid
if length > max_length and self.valid_chain(chain):
max_length = length
new_chain = chain
# Replace our chain if we discovered a new, valid chain longer than ours
if new_chain:
self.chain = new_chain
return True
return False
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