Improve mine_block

Author: 15Dkatz

backend/blockchain/block.py

@@ -1,24 +1,29 @@
 import time
 
 from backend.util.crypto_hash import crypto_hash
+from backend.config import MINE_RATE
 
 GENESIS_DATA = {
     'timestamp': 1,
     'last_hash': 'genesis_last_hash',
     'hash': 'genesis_hash',
-    'data': []
+    'data': [],
+    'difficulty': 3,
+    'nonce': 'genesis_nonce'
 }
 
 class Block:
     """
     Block: a unit of storage.
     Store transactions in a blockchain that supports a cryptocurrency.
     """
-    def __init__(self, timestamp, last_hash, hash, data):
+    def __init__(self, timestamp, last_hash, hash, data, difficulty, nonce):
         self.timestamp = timestamp
         self.last_hash = last_hash
         self.hash = hash
         self.data = data
+        self.difficulty = difficulty
+        self.nonce = nonce
 
     def add_block(self, data):
         self.chain.append(Block(data))
@@ -29,33 +34,53 @@ def __repr__(self):
             f'timestamp: {self.timestamp}, '
             f'last_hash: {self.last_hash}, '
             f'hash: {self.hash}, '
-            f'data: {self.data})'
+            f'data: {self.data}, '
+            f'difficulty: {self.difficulty}, '
+            f'nonce: {self.nonce})'
         )
 
     @staticmethod
     def mine_block(last_block, data):
         """
-        Mine a block based on the given last_block and data.
+        Mine a block based on the given last_block and data, until a block hash
+        is found that meets the leading 0's proof of work requirement.
         """
         timestamp = time.time_ns()
         last_hash = last_block.hash
-        hash = crypto_hash(timestamp, last_hash, data)
+        difficulty = Block.adjust_difficulty(last_block, timestamp)
+        nonce = 0
+        hash = crypto_hash(timestamp, last_hash, data, difficulty, nonce)
 
-        return Block(timestamp, last_hash, hash, data)
+        while hash[0:difficulty] != '0' * difficulty:
+            nonce += 1
+            timestamp = time.time_ns()
+            difficulty = Block.adjust_difficulty(last_block, timestamp)
+            hash = crypto_hash(timestamp, last_hash, data, difficulty, nonce)
+
+        return Block(timestamp, last_hash, hash, data, difficulty, nonce)
 
     @staticmethod
     def genesis():
         """
         Generate the genesis block.
         """
-        # return Block(
-        #     timestamp=GENESIS_DATA['timestamp'],
-        #     last_hash=GENESIS_DATA['last_hash'],
-        #     hash=GENESIS_DATA['hash'],
-        #     data=GENESIS_DATA['data']
-        # )
         return Block(**GENESIS_DATA)
 
+    @staticmethod
+    def adjust_difficulty(last_block, new_timestamp):
+        """
+        Calculate the adjusted difficulty according to the MINE_RATE.
+        Increase the difficulty for slowly mined blocks.
+        Decrease the difficulty for slowly mined blocks.
+        """
+        if (new_timestamp - last_block.timestamp) < MINE_RATE:
+            return last_block.difficulty + 1
+
+        if (last_block.difficulty - 1) > 0:
+            return last_block.difficulty - 1
+
+        return 1
+
 def main():
     genesis_block = Block.genesis()
     block = Block.mine_block(genesis_block, 'foo')

backend/config.py

@@ -0,0 +1,6 @@
+NANOSECONDS = 1
+MICROSECONDS = 1000 * NANOSECONDS
+MILLISECONDS = 1000 * MICROSECONDS
+SECONDS = 1000 * MILLISECONDS
+
+MINE_RATE = 4 * SECONDS

backend/tests/blockchain/test_block.py

@@ -8,6 +8,7 @@ def test_mine_block():
     assert isinstance(block, Block)
     assert block.data == data
     assert block.last_hash == last_block.hash
+    assert block.hash[0:block.difficulty] == '0' * block.difficulty
 
 def test_genesis():
     genesis = Block.genesis()