test: Check snapshot file with wrong number of coins

Also, fix a bug in an assert_debug_log call.

Author: MarcoFalke

test/functional/feature_assumeutxo.py

@@ -40,7 +40,7 @@
     assert_equal,
     assert_raises_rpc_error,
 )
-
+import struct
 
 START_HEIGHT = 199
 SNAPSHOT_BASE_HEIGHT = 299
@@ -68,23 +68,35 @@ def setup_network(self):
 
     def test_invalid_snapshot_scenarios(self, valid_snapshot_path):
         self.log.info("Test different scenarios of loading invalid snapshot files")
-        self.log.info("  - snapshot file refering to a block that is not in the assumeutxo parameters")
         with open(valid_snapshot_path, 'rb') as f:
             valid_snapshot_contents = f.read()
+        bad_snapshot_path = valid_snapshot_path + '.mod'
 
+        self.log.info("  - snapshot file refering to a block that is not in the assumeutxo parameters")
         # we can only test this with a block that is already known, as otherwise the `loadtxoutset` RPC
         # would time out (waiting to see the hash in the headers chain), rather than error immediately
         bad_snapshot_height = SNAPSHOT_BASE_HEIGHT - 1
-        bad_snapshot_path = valid_snapshot_path + '.mod'
         with open(bad_snapshot_path, 'wb') as f:
             bad_snapshot_block_hash = self.nodes[0].getblockhash(bad_snapshot_height)
             # block hash of the snapshot base is stored right at the start (first 32 bytes)
             f.write(bytes.fromhex(bad_snapshot_block_hash)[::-1] + valid_snapshot_contents[32:])
 
         expected_log = f"assumeutxo height in snapshot metadata not recognized ({bad_snapshot_height}) - refusing to load snapshot"
-        with self.nodes[1].assert_debug_log(expected_log):
+        with self.nodes[1].assert_debug_log([expected_log]):
             assert_raises_rpc_error(-32603, "Unable to load UTXO snapshot", self.nodes[1].loadtxoutset, bad_snapshot_path)
 
+        self.log.info("  - snapshot file with wrong number of coins")
+        valid_num_coins = struct.unpack("<I", valid_snapshot_contents[32:32 + 4])[0]
+        for off in [-1, +1]:
+            with open(bad_snapshot_path, 'wb') as f:
+                f.write(valid_snapshot_contents[:32])
+                f.write(struct.pack("<I", valid_num_coins + off))
+                f.write(valid_snapshot_contents[32 + 4:])
+
+            expected_log = f"bad snapshot - coins left over after deserializing 298 coins" if off == -1 else f"bad snapshot format or truncated snapshot after deserializing 299 coins"
+            with self.nodes[1].assert_debug_log([expected_log]):
+                assert_raises_rpc_error(-32603, "Unable to load UTXO snapshot", self.nodes[1].loadtxoutset, bad_snapshot_path)
+
     def run_test(self):
         """
         Bring up two (disconnected) nodes, mine some new blocks on the first,