Corrections

blockchain.py

@@ -1,53 +1,105 @@
 import hashlib
 import json
-
 from time import time
+from urllib.parse import urlparse
 from uuid import uuid4
 
-from flask import Flask
+from flask import Flask, jsonify, request
+
 
-class Blockchain(object):
+class Blockchain:
     def __init__(self):
-        self.chain = []
         self.current_transactions = []
+        self.chain = []
+        self.nodes = set()
 
         # Create the genesis block
-        self.new_block(previous_hash=1, proof=100)
+        self.new_block(previous_hash='1', proof=100)
 
-    def proof_of_work(self, last_proof):
+    def register_node(self, address):
         """
-        Simple Proof of Work Algorithm:
-         - Find a number p' such that hash(pp') contains leading 4 zeroes, where p is the previous p'
-         - p is the previous proof, and p' is the new proof
-        :param last_proof: <int>
-        :return: <int>
+        Add a new node to the list of nodes
+        :param address: Address of node. Eg. 'http://192.168.0.5:5000'
         """
 
-        proof = 0
-        while self.valid_proof(last_proof, proof) is False:
-            proof += 1
+        parsed_url = urlparse(address)
+        if parsed_url.netloc:
+            self.nodes.add(parsed_url.netloc)
+        elif parsed_url.path:
+            # Accepts an URL without scheme like '192.168.0.5:5000'.
+            self.nodes.add(parsed_url.path)
+        else:
+            raise ValueError('Invalid URL')
 
-        return proof
 
-    @staticmethod
-    def valid_proof(last_proof, proof):
+    def valid_chain(self, chain):
         """
-        Validates the Proof: Does hash(last_proof, proof) contain 4 leading zeroes?
-        :param last_proof: <int> Previous Proof
-        :param proof: <int> Current Proof
-        :return: <bool> True if correct, False if not.
+        Determine if a given blockchain is valid
+        :param chain: A blockchain
+        :return: True if valid, False if not
         """
 
-        guess = f'{last_proof}{proof}'.encode()
-        guess_hash = hashlib.sha256(guess).hexdigest()
-        return guess_hash[:4] == "0000"
+        last_block = chain[0]
+        current_index = 1
+
+        while current_index < len(chain):
+            block = chain[current_index]
+            print(f'{last_block}')
+            print(f'{block}')
+            print("\n-----------\n")
+            # Check that the hash of the block is correct
+            last_block_hash = self.hash(last_block)
+            if block['previous_hash'] != last_block_hash:
+                return False
 
-    def new_block(self, proof, previous_hash=None):
+            # Check that the Proof of Work is correct
+            if not self.valid_proof(last_block['proof'], block['proof'], last_block_hash):
+                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: 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
+
+    def new_block(self, proof, previous_hash):
         """
         Create a new Block in the Blockchain
-        :param proof: <int> The proof given by the Proof of Work algorithm
-        :param previous_hash: (Optional) <str> Hash of previous Block
-        :return: <dict> New Block
+        :param proof: The proof given by the Proof of Work algorithm
+        :param previous_hash: Hash of previous Block
+        :return: New Block
         """
 
         block = {
@@ -67,10 +119,10 @@ def new_block(self, proof, previous_hash=None):
     def new_transaction(self, sender, recipient, amount):
         """
         Creates a new transaction to go into the next mined Block
-        :param sender: <str> Address of the Sender
-        :param recipient: <str> Address of the Recipient
-        :param amount: <int> Amount
-        :return: <int> The index of the Block that will hold this transaction
+        :param sender: Address of the Sender
+        :param recipient: Address of the Recipient
+        :param amount: Amount
+        :return: The index of the Block that will hold this transaction
         """
         self.current_transactions.append({
             'sender': sender,
@@ -88,32 +140,48 @@ def last_block(self):
     def hash(block):
         """
         Creates a SHA-256 hash of a Block
-        :param block: <dict> Block
-        :return: <str>
+        :param block: Block
         """
 
         # We must make sure that the Dictionary is Ordered, or we'll have inconsistent hashes
         block_string = json.dumps(block, sort_keys=True).encode()
         return hashlib.sha256(block_string).hexdigest()
 
-    def new_transaction(self, sender, recipient, amount):
+    def proof_of_work(self, last_block):
         """
-        Creates a new transaction to go into the next mined Block
-        :param sender: <str> Address of the Sender
-        :param recipient: <str> Address of the Recipient
-        :param amount: <int> Amount
-        :return: <int> The index of the Block that will hold this transaction
+        Simple Proof of Work Algorithm:
+         - Find a number p' such that hash(pp') contains leading 4 zeroes
+         - Where p is the previous proof, and p' is the new proof
+
+        :param last_block: <dict> last Block
+        :return: <int>
         """
 
-        self.current_transactions.append({
-            'sender': sender,
-            'recipient': recipient,
-            'amount': amount,
-        })
+        last_proof = last_block['proof']
+        last_hash = self.hash(last_block)
+
+        proof = 0
+        while self.valid_proof(last_proof, proof, last_hash) is False:
+            proof += 1
+
+        return proof
+
+    @staticmethod
+    def valid_proof(last_proof, proof, last_hash):
+        """
+        Validates the Proof
+        :param last_proof: <int> Previous Proof
+        :param proof: <int> Current Proof
+        :param last_hash: <str> The hash of the Previous Block
+        :return: <bool> True if correct, False if not.
+        """
 
-        return self.last_block['index'] + 1    
+        guess = f'{last_proof}{proof}{last_hash}'.encode()
+        guess_hash = hashlib.sha256(guess).hexdigest()
+        return guess_hash[:4] == "0000"
 
-# Instantiate our Node
+
+# Instantiate the Node
 app = Flask(__name__)
 
 # Generate a globally unique address for this node
@@ -125,22 +193,31 @@ def new_transaction(self, sender, recipient, amount):
 
 @app.route('/mine', methods=['GET'])
 def mine():
-    return "We'll mine a new Block"
-
-@app.route('/transactions/new', methods=['POST'])
-def new_transaction():
-    return "We'll add a new transaction"
+    # We run the proof of work algorithm to get the next proof...
+    last_block = blockchain.last_block
+    proof = blockchain.proof_of_work(last_block)
+
+    # We must receive a reward for finding the proof.
+    # The sender is "0" to signify that this node has mined a new coin.
+    blockchain.new_transaction(
+        sender="0",
+        recipient=node_identifier,
+        amount=1,
+    )
+
+    # Forge the new Block by adding it to the chain
+    previous_hash = blockchain.hash(last_block)
+    block = blockchain.new_block(proof, previous_hash)
 
-@app.route('/chain', methods=['GET'])
-def full_chain():
     response = {
-        'chain': blockchain.chain,
-        'length': len(blockchain.chain),
+        'message': "New Block Forged",
+        'index': block['index'],
+        'transactions': block['transactions'],
+        'proof': block['proof'],
+        'previous_hash': block['previous_hash'],
     }
     return jsonify(response), 200
 
-if __name__ == '__main__':
-    app.run(host='0.0.0.0', port=5000)
 
 @app.route('/transactions/new', methods=['POST'])
 def new_transaction():
@@ -155,33 +232,60 @@ def new_transaction():
     index = blockchain.new_transaction(values['sender'], values['recipient'], values['amount'])
 
     response = {'message': f'Transaction will be added to Block {index}'}
-    return jsonify(response), 201        
-
-@app.route('/mine', methods=['GET'])
-def mine():
-    # We run the proof of work algorithm to get the next proof...
-    last_block = blockchain.last_block
-    last_proof = last_block['proof']
-    proof = blockchain.proof_of_work(last_proof)
+    return jsonify(response), 201
 
-    # We must receive a reward for finding the proof.
-    # The sender is "0" to signify that this node has mined a new coin.
-    blockchain.new_transaction(
-        sender="0",
-        recipient=node_identifier,
-        amount=1,
-    )
 
-    # Forge the new Block by adding it to the chain
-    previous_hash = blockchain.hash(last_block)
-    block = blockchain.new_block(proof, previous_hash)
+@app.route('/chain', methods=['GET'])
+def full_chain():
+    response = {
+        'chain': blockchain.chain,
+        'length': len(blockchain.chain),
+    }
+    return jsonify(response), 200
+
+
+@app.route('/nodes/register', methods=['POST'])
+def register_nodes():
+    values = request.get_json()
+
+    nodes = values.get('nodes')
+    if nodes is None:
+        return "Error: Please supply a valid list of nodes", 400
+
+    for node in nodes:
+        blockchain.register_node(node)
 
     response = {
-        'message': "New Block Forged",
-        'index': block['index'],
-        'transactions': block['transactions'],
-        'proof': block['proof'],
-        'previous_hash': block['previous_hash'],
+        'message': 'New nodes have been added',
+        'total_nodes': list(blockchain.nodes),
     }
+    return jsonify(response), 201
+
+
+@app.route('/nodes/resolve', methods=['GET'])
+def consensus():
+    replaced = blockchain.resolve_conflicts()
+
+    if replaced:
+        response = {
+            'message': 'Our chain was replaced',
+            'new_chain': blockchain.chain
+        }
+    else:
+        response = {
+            'message': 'Our chain is authoritative',
+            'chain': blockchain.chain
+        }
+
+    return jsonify(response), 200
+
+
+if __name__ == '__main__':
+    from argparse import ArgumentParser
+
+    parser = ArgumentParser()
+    parser.add_argument('-p', '--port', default=5000, type=int, help='port to listen on')
+    args = parser.parse_args()
+    port = args.port
 
-    return jsonify(response), 200
+    app.run(host='0.0.0.0', port=port)