Add Proof of work as last 4 hash digits should be 0

app/managers/block.py

@@ -2,6 +2,7 @@
 import json
 from datetime import datetime
 from app.models.block import Block
+from config import NUM_ZEROS
 
 
 def save_block(block):
@@ -16,12 +17,16 @@ def mine(last_block):
     # random string for now
     data = "I block #%s" % (int(last_block.index) + 1)
     prev_hash = last_block.hash
-    block_hash = calculate_hash(index, prev_hash, data, timestamp)
-
+    nonce = 0
+    block_hash = calculate_hash(index, prev_hash, data, timestamp, nonce)
+    while str(block_hash[0:NUM_ZEROS]) != '0' * NUM_ZEROS:
+        nonce += 1
+        block_hash = calculate_hash(index, prev_hash, data, timestamp, nonce)
     block_data = {}
     block_data['index'] = int(last_block.index) + 1
-    block_data['timestamp'] = calculate_hash
+    block_data['timestamp'] = timestamp
     block_data['data'] = "I block #%s" % last_block.index
     block_data['prev_hash'] = last_block.hash
     block_data['hash'] = block_hash
+    block_data['nonce'] = nonce
     return Block(block_data)

app/managers/common.py

@@ -1,20 +1,20 @@
 import os
-from config import blockchain_dir
+from config import DATA_DIR
 import hashlib
 
 
 def get_data_directory():
     return os.path.abspath(
         os.path.join(os.path.dirname(__file__), '../')
-    ) + blockchain_dir
+    ) + DATA_DIR
 
 
-def generate_header(index, prev_hash, data, timestamp):
-    return str(index) + prev_hash + data + str(timestamp)
+def generate_header(index, prev_hash, data, timestamp, nonce):
+    return str(index) + prev_hash + data + str(timestamp) + str(nonce)
 
 
-def calculate_hash(index, prev_hash, data, timestamp):
-    header_string = generate_header(index, prev_hash, data, timestamp)
+def calculate_hash(index, prev_hash, data, timestamp, nonce):
+    header_string = generate_header(index, prev_hash, data, timestamp, nonce)
     sha = hashlib.sha256()
     sha.update(header_string)
     return sha.hexdigest()

app/models/block.py

@@ -13,12 +13,15 @@ def __init__(self, **kwargs):
         :type index: str (json)
         :param prev_hash: The hash for the previous block in the chain
         :type index: str
+        :param nonce: Counter used for the proof of work implementation
+        :type index: int
         """
         self.index = kwargs.get('index')
         self.hash = kwargs.get('hash')
         self.timestamp = kwargs.get('timestamp')
         self.data = kwargs.get('data')
         self.prev_hash = kwargs.get('prev_hash')
+        self.nonce = kwargs.get('nonce')
 
     def __dict__(self):
         return {

config.py

@@ -1 +1,2 @@
 blockchain_dir = 'data'
+NUM_ZEROS = 4

scripts/test.py

@@ -1,7 +1,8 @@
 from app.models.block import Block
 from datetime import datetime
 import os
-from app.managers.common import get_data_directory
+from app.managers.common import get_data_directory, calculate_hash
+from app.managers.block import save_block
 
 
 def initialize_block():
@@ -11,6 +12,9 @@ def initialize_block():
     block_data['timestamp'] = datetime.now()
     block_data['data'] = 'First block data'
     block_data['prev_hash'] = None
+    block_data['hash'] = calculate_hash(
+        0, None, block_data['data'], block_data['timestamp'], 0
+    )
     block = Block(block_data)
     return block
 
@@ -29,4 +33,4 @@ def save_to_file():
     if os.listdir(directory) == []:
         # create first block
         first_block = initialize_block()
-        # first_block.save()
+        save_block(first_block)