From 5a11d22973c18f2d9d6df3a1c635fc099120c600 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C5=91rinc?= <pap.lorinc@gmail.com>
Date: Fri, 19 Dec 2025 18:19:39 +0100
Subject: [PATCH] test: add test for coins database read error handling

The error was also reworded to avoid the leading repetition (see expected stderr).

### Reproducers
The test failure can be triggered manually by:
```patch
std::optional<Coin> CCoinsViewErrorCatcher::GetCoin(const COutPoint& outpoint) const
{
-    return ExecuteBackedWrapper<std::optional<Coin>>([&]() { return CCoinsViewBacked::GetCoin(outpoint); }, m_err_callbacks);
+    return CCoinsViewBacked::GetCoin(outpoint);
}
```

### Notes
Note that CCoinsViewErrorCatcher::HaveCoin failure isn't tested since it doesn't seem to be used in production code, all tests pass with:
```patch
bool CCoinsViewErrorCatcher::HaveCoin(const COutPoint& outpoint) const
{
-    return ExecuteBackedWrapper<bool>([&]() { return CCoinsViewBacked::HaveCoin(outpoint); }, m_err_callbacks);
+    throw "CCoinsViewBacked::HaveCoin";
}
```

### Context:

On 64-bit systems, LevelDB uses mmap which reflects file changes immediately.
On 32-bit systems (i686, armhf), mmap is disabled (kDefaultMmapLimit=0 in leveldb/util/env_posix.cc), so LevelDB uses block cache which serves stale data.
The node must be restarted after corruption to clear the cache.

Corruption is placed at the middle to avoid LevelDB's paranoid_checks verification during database open, and -checkblocks=0 -checklevel=0 skips Bitcoin's block verification.

Co-authored-by: MarcoFalke <*~=`'#}+{/-|&$^_@721217.xyz>
---
 src/init.cpp                                  |  2 +-
 test/functional/feature_coinsdb_read_error.py | 48 +++++++++++++++++++
 test/functional/test_runner.py                |  1 +
 3 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100755 test/functional/feature_coinsdb_read_error.py

diff --git a/src/init.cpp b/src/init.cpp
index f2af858eb46c..79e163756f59 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1364,7 +1364,7 @@ static ChainstateLoadResult InitAndLoadChainstate(
     options.require_full_verification = args.IsArgSet("-checkblocks") || args.IsArgSet("-checklevel");
     options.coins_error_cb = [] {
         uiInterface.ThreadSafeMessageBox(
-            _("Error reading from database, shutting down."),
+            _("Cannot read from database, shutting down."),
             "", CClientUIInterface::MSG_ERROR);
     };
     uiInterface.InitMessage(_("Loading block index…"));
diff --git a/test/functional/feature_coinsdb_read_error.py b/test/functional/feature_coinsdb_read_error.py
new file mode 100755
index 000000000000..e257ed103a3f
--- /dev/null
+++ b/test/functional/feature_coinsdb_read_error.py
@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+# Copyright (c) 2025-present The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+"""Test that coins database read errors trigger a shutdown message."""
+import http
+import subprocess
+
+from test_framework.test_framework import BitcoinTestFramework
+
+
+class CoinsDBReadErrorTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = False
+        self.num_nodes = 1
+
+    def run_test(self):
+        node = self.nodes[0]
+
+        # Stop node to clear LevelDB block cache (required for 32-bit where mmap is disabled)
+        self.stop_node(0)
+
+        for ldb_path in (node.chain_path / "chainstate").glob("*.ldb"):
+            with open(ldb_path, "r+b") as f:
+                f.seek(ldb_path.stat().st_size // 2)
+                f.write(b'\xff')
+
+        self.start_node(0, extra_args=["-checkblocks=0", "-checklevel=0"])
+
+        with node.assert_debug_log(["block checksum mismatch"]):
+            try:
+                for height in range(1, node.getblockcount() + 1):
+                    txid = node.getblock(node.getblockhash(height))["tx"][0]
+                    node.gettxout(txid, 0)
+            except (subprocess.CalledProcessError,
+                    http.client.CannotSendRequest,
+                    http.client.RemoteDisconnected,
+                    ConnectionResetError):
+                pass
+
+        node.wait_until(lambda: node.process.poll())
+        assert node.is_node_stopped(expected_stderr="Error: Cannot read from database, shutting down.",
+                                    expected_ret_code=node.process.returncode)
+
+
+if __name__ == '__main__':
+    CoinsDBReadErrorTest(__file__).main()
diff --git a/test/functional/test_runner.py b/test/functional/test_runner.py
index a4af55784685..23c0f3312460 100755
--- a/test/functional/test_runner.py
+++ b/test/functional/test_runner.py
@@ -323,6 +323,7 @@
     'p2p_fingerprint.py',
     'feature_uacomment.py',
     'feature_init.py',
+    'feature_coinsdb_read_error.py',
     'wallet_coinbase_category.py',
     'feature_filelock.py',
     'feature_loadblock.py',