lessons period 2

period_2/02-sockets/902/TxBlock.py

@@ -0,0 +1,60 @@
+from BlockChain import CBlock
+from Signature import generate_keys, sign, verify
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.backends import default_backend
+
+import random
+
+reward = 25.0
+leading_zeros = 2
+next_char_limit = 20
+
+class TxBlock(CBlock):
+
+    nonce = "A random nonce"
+
+    def __init__(self, previousBlock):
+        super(TxBlock, self).__init__([], previousBlock)
+
+    def addTx(self, Tx_in):
+        self.data.append(Tx_in)
+
+    def __count_totals(self):
+        total_in = 0
+        total_out = 0
+        for tx in self.data:
+            for addr, amt in tx.inputs:
+                total_in = total_in + amt
+            for addr, amt in tx.outputs:
+                total_out = total_out + amt
+        return total_in, total_out
+
+    def is_valid(self):
+        if not super(TxBlock, self).is_valid():
+            return False
+        for tx in self.data:
+            if not tx.is_valid():
+                return False
+        total_in, total_out = self.__count_totals()
+        if total_out - total_in - reward > 0.000000000001:
+            return False
+        return True
+
+    def good_nonce(self):
+        digest = hashes.Hash(hashes.SHA256(), backend=default_backend())
+        digest.update(bytes(str(self.data), 'utf8'))
+        digest.update(bytes(str(self.previousHash), 'utf8'))
+        digest.update(bytes(str(self.nonce), 'utf8'))
+        this_hash = digest.finalize()
+
+        if this_hash[:leading_zeros] != bytes(''.join(['\x4f' for i in range(leading_zeros)]), 'utf8'):
+            return False
+        return int(this_hash[leading_zeros]) < next_char_limit
+
+    def find_nonce(self):
+        for i in range(1000000):
+            self.nonce = ''.join([
+                chr(random.randint(0, 255)) for i in range(10*leading_zeros)])
+            if self.good_nonce():
+                return self.nonce
+        return None