persist blockchain across sessions via save/load

minichain/__init__.py

@@ -6,6 +6,7 @@
 from .contract import ContractMachine
 from .p2p import P2PNetwork
 from .mempool import Mempool
+from .persistence import save, load
 
 __all__ = [
     "mine_block",
@@ -18,4 +19,6 @@
     "ContractMachine",
     "P2PNetwork",
     "Mempool",
+    "save",
+    "load",
 ]

minichain/persistence.py

@@ -0,0 +1,140 @@
+"""
+Chain persistence: save and load the blockchain and state to/from JSON.
+
+Design:
+  - blockchain.json  holds the full list of serialized blocks
+  - state.json       holds the accounts dict
+
+Usage:
+    from minichain.persistence import save, load
+
+    save(blockchain, path="data/")
+    blockchain = load(path="data/")
+"""
+
+import json
+import os
+import logging
+from .block import Block
+from .transaction import Transaction
+from .chain import Blockchain
+
+logger = logging.getLogger(__name__)
+
+_CHAIN_FILE = "blockchain.json"
+_STATE_FILE = "state.json"
+
+
+# Public API
+
+def save(blockchain: Blockchain, path: str = ".") -> None:
+    """
+    Persist the blockchain and account state to two JSON files inside `path`.
+
+    Args:
+        blockchain: The live Blockchain instance to save.
+        path:       Directory to write blockchain.json and state.json into.
+    """
+    os.makedirs(path, exist_ok=True)
+
+    _write_json(
+        os.path.join(path, _CHAIN_FILE),
+        [block.to_dict() for block in blockchain.chain],
+    )
+
+    _write_json(
+        os.path.join(path, _STATE_FILE),
+        blockchain.state.accounts,
+    )
+
+    logger.info(
+        "Saved %d blocks and %d accounts to '%s'",
+        len(blockchain.chain),
+        len(blockchain.state.accounts),
+        path,
+    )
+
+
+def load(path: str = ".") -> Blockchain:
+    """
+    Restore a Blockchain from JSON files inside `path`.
+
+    Returns a fully initialised Blockchain whose chain and state match
+    what was previously saved with save().
+
+    Raises:
+        FileNotFoundError: if blockchain.json or state.json are missing.
+        ValueError:        if the data is structurally invalid.
+    """
+    chain_path = os.path.join(path, _CHAIN_FILE)
+    state_path = os.path.join(path, _STATE_FILE)
+
+    raw_blocks = _read_json(chain_path)
+    raw_accounts = _read_json(state_path)
+
+    if not isinstance(raw_blocks, list) or not raw_blocks:
+        raise ValueError(f"Invalid or empty chain data in '{chain_path}'")
+
+    blockchain = Blockchain.__new__(Blockchain)   # skip __init__ (no genesis)
+    import threading
+    from .state import State
+    from .contract import ContractMachine
+
+    blockchain._lock = threading.RLock()
+    blockchain.chain = [_deserialize_block(b) for b in raw_blocks]
+
+    blockchain.state = State.__new__(State)
+    blockchain.state.accounts = raw_accounts
+    blockchain.state.contract_machine = ContractMachine(blockchain.state)
+
+    logger.info(
+        "Loaded %d blocks and %d accounts from '%s'",
+        len(blockchain.chain),
+        len(blockchain.state.accounts),
+        path,
+    )
+    return blockchain
+
+
+# Helpers
+
+def _write_json(filepath: str, data) -> None:
+    with open(filepath, "w", encoding="utf-8") as f:
+        json.dump(data, f, indent=2)
+
+
+def _read_json(filepath: str):
+    if not os.path.exists(filepath):
+        raise FileNotFoundError(f"Persistence file not found: '{filepath}'")
+    with open(filepath, "r", encoding="utf-8") as f:
+        return json.load(f)
+
+
+def _deserialize_block(data: dict) -> Block:
+    """Reconstruct a Block (including its transactions) from a plain dict."""
+    transactions = [
+        Transaction(
+            sender=tx["sender"],
+            receiver=tx["receiver"],
+            amount=tx["amount"],
+            nonce=tx["nonce"],
+            data=tx.get("data"),
+            signature=tx.get("signature"),
+            timestamp=tx["timestamp"],
+        )
+        for tx in data.get("transactions", [])
+    ]
+
+    block = Block(
+        index=data["index"],
+        previous_hash=data["previous_hash"],
+        transactions=transactions,
+        timestamp=data["timestamp"],
+        difficulty=data.get("difficulty"),
+    )
+    block.nonce = data["nonce"]
+    block.hash = data["hash"]
+    # Preserve the stored merkle root rather than recomputing to guard against
+    # any future change in the hash algorithm.
+    block.merkle_root = data.get("merkle_root")
+    return block

tests/test_persistence.py

@@ -0,0 +1,174 @@
+"""
+Tests for chain persistence (save / load round-trip).
+"""
+
+import os
+import tempfile
+import unittest
+
+from nacl.signing import SigningKey
+from nacl.encoding import HexEncoder
+
+from minichain import Blockchain, Transaction, Block, mine_block
+from minichain.persistence import save, load
+
+
+def _make_keypair():
+    sk = SigningKey.generate()
+    pk = sk.verify_key.encode(encoder=HexEncoder).decode()
+    return sk, pk
+
+
+class TestPersistence(unittest.TestCase):
+
+    def setUp(self):
+        self.tmpdir = tempfile.mkdtemp()
+
+    # Helpers
+
+    def _chain_with_tx(self):
+        """Return a Blockchain that has one mined block with a transfer."""
+        bc = Blockchain()
+        alice_sk, alice_pk = _make_keypair()
+        _, bob_pk = _make_keypair()
+
+        bc.state.credit_mining_reward(alice_pk, 100)
+
+        tx = Transaction(alice_pk, bob_pk, 30, 0)
+        tx.sign(alice_sk)
+
+        block = Block(
+            index=1,
+            previous_hash=bc.last_block.hash,
+            transactions=[tx],
+            difficulty=1,
+        )
+        mine_block(block, difficulty=1)
+        bc.add_block(block)
+        return bc, alice_pk, bob_pk
+
+    # Tests
+
+    def test_save_creates_files(self):
+        bc = Blockchain()
+        save(bc, path=self.tmpdir)
+
+        self.assertTrue(os.path.exists(os.path.join(self.tmpdir, "blockchain.json")))
+        self.assertTrue(os.path.exists(os.path.join(self.tmpdir, "state.json")))
+
+    def test_chain_length_preserved(self):
+        bc, _, _ = self._chain_with_tx()
+        save(bc, path=self.tmpdir)
+
+        restored = load(path=self.tmpdir)
+        self.assertEqual(len(restored.chain), len(bc.chain))
+
+    def test_block_hashes_preserved(self):
+        bc, _, _ = self._chain_with_tx()
+        save(bc, path=self.tmpdir)
+
+        restored = load(path=self.tmpdir)
+        for original, loaded in zip(bc.chain, restored.chain):
+            self.assertEqual(original.hash, loaded.hash)
+            self.assertEqual(original.index, loaded.index)
+            self.assertEqual(original.previous_hash, loaded.previous_hash)
+
+    def test_account_balances_preserved(self):
+        bc, alice_pk, bob_pk = self._chain_with_tx()
+        save(bc, path=self.tmpdir)
+
+        restored = load(path=self.tmpdir)
+        self.assertEqual(
+            bc.state.get_account(alice_pk)["balance"],
+            restored.state.get_account(alice_pk)["balance"],
+        )
+        self.assertEqual(
+            bc.state.get_account(bob_pk)["balance"],
+            restored.state.get_account(bob_pk)["balance"],
+        )
+
+    def test_account_nonces_preserved(self):
+        bc, alice_pk, _ = self._chain_with_tx()
+        save(bc, path=self.tmpdir)
+
+        restored = load(path=self.tmpdir)
+        self.assertEqual(
+            bc.state.get_account(alice_pk)["nonce"],
+            restored.state.get_account(alice_pk)["nonce"],
+        )
+
+    def test_transaction_data_preserved(self):
+        bc, _, _ = self._chain_with_tx()
+        save(bc, path=self.tmpdir)
+
+        restored = load(path=self.tmpdir)
+        original_tx = bc.chain[1].transactions[0]
+        loaded_tx = restored.chain[1].transactions[0]
+
+        self.assertEqual(original_tx.sender, loaded_tx.sender)
+        self.assertEqual(original_tx.receiver, loaded_tx.receiver)
+        self.assertEqual(original_tx.amount, loaded_tx.amount)
+        self.assertEqual(original_tx.nonce, loaded_tx.nonce)
+        self.assertEqual(original_tx.signature, loaded_tx.signature)
+
+    def test_loaded_chain_can_add_new_block(self):
+        """Restored chain must still accept new valid blocks."""
+        bc, alice_pk, bob_pk = self._chain_with_tx()
+        save(bc, path=self.tmpdir)
+
+        restored = load(path=self.tmpdir)
+
+        # Build a second transfer on top of the loaded chain
+        alice_sk, alice_pk2 = _make_keypair()
+        _, carol_pk = _make_keypair()
+        restored.state.credit_mining_reward(alice_pk2, 50)
+
+        tx2 = Transaction(alice_pk2, carol_pk, 10, 0)
+        tx2.sign(alice_sk)
+
+        block2 = Block(
+            index=len(restored.chain),
+            previous_hash=restored.last_block.hash,
+            transactions=[tx2],
+            difficulty=1,
+        )
+        mine_block(block2, difficulty=1)
+
+        self.assertTrue(restored.add_block(block2))
+        self.assertEqual(len(restored.chain), len(bc.chain) + 1)
+
+    def test_load_missing_file_raises(self):
+        with self.assertRaises(FileNotFoundError):
+            load(path=self.tmpdir)  # nothing saved yet
+
+    def test_genesis_only_chain(self):
+        bc = Blockchain()
+        save(bc, path=self.tmpdir)
+        restored = load(path=self.tmpdir)
+
+        self.assertEqual(len(restored.chain), 1)
+        self.assertEqual(restored.chain[0].hash, "0" * 64)
+
+    def test_contract_storage_preserved(self):
+        """Contract accounts and storage survive a save/load cycle."""
+        from minichain import State, Transaction as Tx
+        bc = Blockchain()
+
+        deployer_sk, deployer_pk = _make_keypair()
+        bc.state.credit_mining_reward(deployer_pk, 100)
+
+        code = "storage['hits'] = storage.get('hits', 0) + 1"
+        tx_deploy = Tx(deployer_pk, None, 0, 0, data=code)
+        tx_deploy.sign(deployer_sk)
+        contract_addr = bc.state.apply_transaction(tx_deploy)
+        self.assertIsInstance(contract_addr, str)
+
+        save(bc, path=self.tmpdir)
+        restored = load(path=self.tmpdir)
+
+        contract = restored.state.get_account(contract_addr)
+        self.assertEqual(contract["code"], code)
+
+
+if __name__ == "__main__":
+    unittest.main()