From 05881a94507a2b70b26093d48c5361ed3a19fc4c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lukas=20F=C3=BCrderer?= <l.fuerderer@gmail.com>
Date: Sun, 17 Mar 2024 17:43:59 +0100
Subject: [PATCH] Persist blocks locally in a file

---
 .gitignore    |  1 +
 blockchain.py | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/.gitignore b/.gitignore
index 0d20b64..1deed07 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 *.pyc
+/blockchain
diff --git a/blockchain.py b/blockchain.py
index 3f4c191..6f8e38f 100644
--- a/blockchain.py
+++ b/blockchain.py
@@ -64,6 +64,7 @@ class Block:
     balances: dict
     # (sender_pubkey, id) tuples
     used_transaction_ids: set
+    block_number: int
     valid: bool
 
     def from_bytes(block_raw):
@@ -84,6 +85,7 @@ class Block:
             own_hash = hashlib.sha256(block_raw).digest(),
             balances = None,
             used_transaction_ids = None,
+            block_number = None,
             valid = False,
         )
     def validate(self, blockchain):
@@ -122,6 +124,7 @@ class Block:
         if self.valid:
             self.calculate_balances(prev_block)
             self.calculate_used_transaction_ids(prev_block)
+            self.calculate_block_number(prev_block)
         return self.valid
     def calculate_balances(self, prev_block):
         if prev_block is None:
@@ -147,6 +150,11 @@ class Block:
         if t is not None:
             used_transaction_ids.add((t.sender, t.id))
         self.used_transaction_ids = used_transaction_ids
+    def calculate_block_number(self, prev_block):
+        if prev_block is None:
+            self.block_number = 0
+        else:
+            self.block_number = prev_block.block_number + 1
     def get_difficulty_info(self, steps, blockchain):
         if steps == 0:
             return self.difficulty_sum, self.timestamp
@@ -162,8 +170,7 @@ class Block:
             transaction = 148 * b"\0"
         else:
             transaction = self.transaction.get_transaction_raw()
-        return
-            transaction + \
+        return transaction + \
             self.message + \
             self.miner_pubkey + \
             self.previous_hash + \
@@ -177,6 +184,22 @@ class Blockchain:
         self.__block_map = {}
         self.__latest_block_hash = None
         self.__lock = Lock()
+        self.__load_blocks_from_disk()
+    def __load_blocks_from_disk(self):
+        block_obj = None
+        try:
+            with open("blockchain", "rb") as f:
+                while True:
+                    block = f.read(292)
+                    if len(block) < 292:
+                        break
+                    block_obj = self.add_block(block)
+                    if not block_obj.validate(self):
+                        break
+        except FileNotFoundError:
+            pass
+        if block_obj is not None:
+            self.set_latest_block(block_obj.own_hash)
     def set_latest_block(self, block_hash):
         new_block = self.get_block(block_hash)
         assert new_block is not None
@@ -190,11 +213,33 @@ class Blockchain:
                 new_difficulty_sum = new_block.get_difficulty_info(1, self)[0]
                 if new_difficulty_sum <= current_difficulty_sum:
                     return False
+            else:
+                latest_block = None
             with self.__lock:
                 if self.__latest_block_hash != latest_block_hash:
                     continue
                 self.__latest_block_hash = block_hash
+                self.__persist_block_update(latest_block, new_block)
             return True
+    def __persist_block_update(self, old_block, new_block):
+        if old_block is not None:
+            while old_block.block_number > new_block.block_number:
+                old_block = self.__block_map[old_block.previous_hash]
+        block_list = []
+        while new_block is not old_block:
+            block_list.append(new_block)
+            if new_block.previous_hash == 32 * b"\0":
+                break
+            new_block = self.__block_map[new_block.previous_hash]
+            if old_block is not None and old_block.block_number > new_block.block_number:
+                old_block = self.__block_map[old_block.previous_hash]
+        start_block_number = block_list[-1].block_number
+        start_addr = start_block_number * 292
+        open_mode = "wb" if start_addr == 0 else "r+b"
+        with open("blockchain", open_mode) as f:
+            f.seek(start_addr)
+            for block in reversed(block_list):
+                f.write(block.get_block_raw())
     def add_block(self, block_raw):
         with self.__lock:
             block = Block.from_bytes(block_raw)