Complete section: The Cryptocurrency: Wallets, Keys, and Transactions

Author: 15Dkatz

backend/tests/wallet/test_transaction.py

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+import pytest
+
+from backend.wallet.transaction import Transaction
+from backend.wallet.wallet import Wallet
+
+def test_transaction():
+    sender_wallet = Wallet()
+    recipient = 'recipient'
+    amount = 50
+    transaction = Transaction(sender_wallet, recipient, amount)
+
+    assert transaction.output[recipient] == amount
+    assert transaction.output[sender_wallet.address] == sender_wallet.balance - amount
+
+    assert 'timestamp' in transaction.input
+    assert transaction.input['amount'] == sender_wallet.balance
+    assert transaction.input['address'] == sender_wallet.address
+    assert transaction.input['public_key'] == sender_wallet.public_key
+    assert Wallet.verify(
+        transaction.input['public_key'],
+        transaction.output,
+        transaction.input['signature']
+    )
+
+def test_transaction_exceeds_balance():
+    with pytest.raises(Exception, match='Amount exceeds balance'):
+        Transaction(Wallet(), 'recipient', 9001)
+
+def test_transaction_update_exceeds_balance():
+    sender_wallet = Wallet()
+    transaction = Transaction(sender_wallet, 'recipient', 50)
+
+    with pytest.raises(Exception, match='Amount exceeds balance'):
+        transaction.update(sender_wallet, 'new_recipient', 9001)
+
+def test_transaction_update():
+    sender_wallet = Wallet()
+    first_recipient = 'first_recipient'
+    first_amount = 50
+    transaction = Transaction(sender_wallet, first_recipient, first_amount)
+
+    next_recipient = 'next_recipient'
+    next_amount = 75
+    transaction.update(sender_wallet, next_recipient, next_amount)
+
+    assert transaction.output[next_recipient] == next_amount
+    assert transaction.output[sender_wallet.address] ==\
+        sender_wallet.balance - first_amount - next_amount
+    assert Wallet.verify(
+        transaction.input['public_key'],
+        transaction.output,
+        transaction.input['signature']
+    )
+
+    to_first_again_amount = 25
+    transaction.update(sender_wallet, first_recipient, to_first_again_amount)
+
+    assert transaction.output[first_recipient] == \
+        first_amount + to_first_again_amount
+    assert transaction.output[sender_wallet.address] ==\
+        sender_wallet.balance - first_amount - next_amount - to_first_again_amount
+    assert Wallet.verify(
+        transaction.input['public_key'],
+        transaction.output,
+        transaction.input['signature']
+    )
+
+def test_valid_transaction():
+    Transaction.is_valid_transaction(Transaction(Wallet(), 'recipient', 50))
+
+def test_valid_transaction_with_invalid_outputs():
+    sender_wallet = Wallet()
+    transaction = Transaction(sender_wallet, 'recipient', 50)
+    transaction.output[sender_wallet.address] = 9001
+
+    with pytest.raises(Exception, match='Invalid transaction output values'):
+        Transaction.is_valid_transaction(transaction)
+
+def test_valid_transaction_with_invalid_signature():
+    transaction = Transaction(Wallet(), 'recipient', 50)
+    transaction.input['signature'] = Wallet().sign(transaction.output)
+
+    with pytest.raises(Exception, match='Invalid signature'):
+        Transaction.is_valid_transaction(transaction)

backend/wallet/transaction.py

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+import time
+import uuid
+
+from backend.wallet.wallet import Wallet
+
+class Transaction:
+    """
+    Document of an exchange in currency from a sender to one
+    or more recipients.
+    """
+    def __init__(self, sender_wallet, recipient, amount):
+        self.id = str(uuid.uuid4())[0:8]
+        self.output = self.create_output(
+            sender_wallet,
+            recipient,
+            amount
+        )
+        self.input = self.create_input(sender_wallet, self.output)
+
+    def create_output(self, sender_wallet, recipient, amount):
+        """
+        Structure the output data for the transaction.
+        """
+        if amount > sender_wallet.balance:
+            raise Exception('Amount exceeds balance')
+
+        output = {}
+        output[recipient] = amount
+        output[sender_wallet.address] = sender_wallet.balance - amount
+
+        return output
+
+    def create_input(self, sender_wallet, output):
+        """
+        Structure the input data for the transaction.
+        Sign the transaction and include the sender's public key and address
+        """
+        return {
+            'timestamp': time.time_ns(),
+            'amount': sender_wallet.balance,
+            'address': sender_wallet.address,
+            'public_key': sender_wallet.public_key,
+            'signature': sender_wallet.sign(output)
+        }
+
+    def update(self, sender_wallet, recipient, amount):
+        """
+        Update the transaction with an existing or new recipient.
+        """
+        if amount > self.output[sender_wallet.address]:
+            raise Exception('Amount exceeds balance')
+
+        if recipient in self.output:
+            self.output[recipient] = self.output[recipient] + amount
+        else:
+            self.output[recipient] = amount
+
+        self.output[sender_wallet.address] = \
+            self.output[sender_wallet.address] - amount
+
+        self.input = self.create_input(sender_wallet, self.output)
+
+    @staticmethod
+    def is_valid_transaction(transaction):
+        """
+        Validate a transaction.
+        Raise an exception for invalid transactions.
+        """
+        output_total = sum(transaction.output.values())
+
+        if transaction.input['amount'] != output_total:
+            raise Exception('Invalid transaction output values')
+
+        if not Wallet.verify(
+            transaction.input['public_key'],
+            transaction.output,
+            transaction.input['signature']
+        ):
+            raise Exception('Invalid signature')
+
+def main():
+    transaction = Transaction(Wallet(), 'recipient', 15)
+    print(f'transaction.__dict__: {transaction.__dict__}')
+
+if __name__ == '__main__':
+    main()