Implement the wallet software

wallet.py

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+#! /usr/bin/env python3
+
+import base64, socket, sys, time
+from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey, Ed25519PublicKey
+
+def format_address(raw_address):
+    return base64.b64encode(raw_address).decode()
+
+def format_amount(amount, show_plus = True):
+    color_prefix = ""
+    color_suffix = ""
+    sign = "+ " if show_plus else ""
+    if amount < 0:
+        color_prefix = "\x1b[31m"
+        color_suffix = "\x1b[0m"
+        sign = "- "
+        amount = -amount
+    coins = amount / 100
+    return f"{color_prefix}{sign}{coins:.02f} cc{color_suffix}"
+
+def write_transaction(timestamp, message, amount):
+    formatted_time = time.strftime("%d.%m.%Y %H:%M:%S", time.localtime(timestamp))
+    print(f"{formatted_time}  {message:<44}  {format_amount(amount):>14}")
+
+def show_balance(public_key):
+    public_key_raw = public_key.public_bytes_raw()
+    with open("blockchain", "rb") as f:
+        total_amount = 0
+        while True:
+            block = f.read(292)
+            if len(block) != 292:
+                break
+            miner = block[180:212]
+            timestamp = int.from_bytes(block[244:252], "big")
+            if block[0:148] != 148 * b"\0":
+                sender = block[4:36]
+                receiver = block[36:68]
+                amount = int.from_bytes(block[68:76], "big")
+                fee = int.from_bytes(block[76:84], "big")
+                if sender == public_key_raw:
+                    write_transaction(timestamp, format_address(receiver), - amount - fee)
+                    total_amount -= (amount + fee)
+                if receiver == public_key_raw:
+                    write_transaction(timestamp, format_address(sender), amount)
+                    total_amount += amount
+            else:
+                fee = 0
+            if miner == public_key_raw:
+                write_transaction(timestamp, "mining reward", 100 + fee)
+                total_amount += 100 + fee
+        print(81 * "\u2500")
+        amount_string = f"\U0001f955 \x1b[1;37m{format_amount(total_amount, False)}\x1b[0m"
+        print(21 * " " + f"\x1b[1;37mYour balance:\x1b[0m{amount_string:>57}")
+
+def parse_amount(amount):
+    amount = amount.replace(",", ".")
+    parts = amount.split(".")
+    if len(parts) == 1:
+        return int(parts[0]) * 100
+    elif len(parts) == 2:
+        if len(parts[1]) > 2:
+            raise Exception(f"Invalid amount: {amount}")
+        coins = int(parts[0])
+        cents = int(parts[1])
+        return coins * 100 + cents
+    raise Exception(f"Invalid amount: {amount}")
+
+def parse_amount_checked(amount):
+    amount = parse_amount(amount)
+    if amount < 0:
+        raise Exception("amount must not be negative")
+    if amount >= 2**64:
+        raise Exception("amount is too large")
+    return amount
+
+def find_free_id(public_key_raw):
+    try:
+        with open("blockchain", "rb") as f:
+            used_ids = set()
+            while True:
+                block = f.read(292)
+                if len(block) != 292:
+                    break
+                if block[0:148] != 148 * b"\0":
+                    transaction_id = int.from_bytes(block[0:4], "big")
+                    sender = block[4:36]
+                    if sender == public_key_raw:
+                        used_ids.add(transaction_id)
+            for possible_id in range(0, 2**32):
+                if possible_id not in used_ids:
+                    return possible_id
+            raise Exception("No transaction id available")
+    except FileNotFoundError:
+        return 0
+
+def send_payment(private_key, target, amount, fee):
+    target_raw = base64.b64decode(target.encode())
+    if len(target_raw) != 32:
+        raise Exception(f"Invalid target address: {target}")
+    amount = parse_amount_checked(amount)
+    if amount == 0:
+        raise Exception("Amount must not be zero")
+    fee = parse_amount_checked(fee)
+    public_key_raw = private_key.public_key().public_bytes_raw()
+    transaction_id = find_free_id(public_key_raw)
+    transaction_prefix = transaction_id.to_bytes(4, "big") + \
+        public_key_raw + \
+        target_raw + \
+        amount.to_bytes(8, "big") + \
+        fee.to_bytes(8, "big")
+    signature = private_key.sign(transaction_prefix)
+    transaction = transaction_prefix + signature
+    request = b"\0\0\0\0\x09" + transaction
+
+    s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
+    try:
+        s.connect(("::1", 62039))
+        s.settimeout(1)
+        for _ in range(10):
+            s.send(request)
+            try:
+                response = s.recv(1024)
+                if response == b"\0\0\0\0\x0a":
+                    print("Payment has been transmitted to the node")
+                    return
+            except TimeoutError:
+                pass
+        print("node did not respond")
+    except ConnectionRefusedError:
+        print("node is not running")
+
+def usage_info():
+    print("Usage:", file=sys.stderr)
+    print("  ./wallet.py # see your past transactions and balance", file=sys.stderr)
+    print("  ./wallet.py pay <target> <amount> <fee> # send carrotcoins to someone else", file=sys.stderr)
+
+def main():
+    try:
+        with open("wallet-key", "rb") as f:
+            private_key_raw = f.read()
+        private_key = Ed25519PrivateKey.from_private_bytes(private_key_raw)
+    except FileNotFoundError:
+        private_key = Ed25519PrivateKey.generate()
+        private_key_raw = private_key.private_bytes_raw()
+        with open("wallet-key", "wb") as f:
+            f.write(private_key_raw)
+
+    public_key = private_key.public_key()
+    wallet_addr = format_address(public_key.public_bytes_raw())
+    print(f"Your wallet address: {wallet_addr}\n")
+
+    if len(sys.argv) == 1:
+        show_balance(public_key)
+    elif len(sys.argv) == 5 and sys.argv[1] == "pay":
+        send_payment(private_key, *sys.argv[2:5])
+    else:
+        usage_info()
+        exit(1)
+
+if __name__ == '__main__':
+    main()