fix: write-ahead audit entry so calls stop when the audit log stops accepting writes (SEC-03)

tests/security/test_audit_fail_closed.py

@@ -0,0 +1,79 @@
+"""The audit log is fail closed after startup too (SEC-03) and names the client (SEC-12)."""
+
+from __future__ import annotations
+
+import json
+from typing import Any
+
+import pytest
+from pytest_httpx import HTTPXMock
+
+from aegis_gitea_mcp.audit import get_audit_logger
+from tests.test_server_helpers import API, connected, mock_user
+
+REPO_ARGS = {"owner": "octo", "repo": "demo"}
+
+
+@pytest.fixture(autouse=True)
+def _env(mock_env: None) -> None:
+    """The audit logger reads the process-wide settings."""
+
+
+class FailingFile:
+    """Stands in for the open audit file and fails every write like a full disk."""
+
+    def __init__(self) -> None:
+        self.attempts = 0
+
+    def write(self, data: str) -> int:
+        self.attempts += 1
+        raise OSError(28, "No space left on device")
+
+    def flush(self) -> None:  # pragma: no cover - never reached
+        raise OSError(28, "No space left on device")
+
+    def close(self) -> None:
+        return None
+
+
+def payload_of(result: Any) -> dict[str, Any]:
+    decoded: dict[str, Any] = json.loads(result.content[0].text)
+    return decoded
+
+
+async def test_calls_stop_when_the_audit_log_stops_accepting_writes(
+    httpx_mock: HTTPXMock,
+) -> None:
+    mock_user(httpx_mock)
+    httpx_mock.add_response(url=f"{API}/repos/octo/demo", json={"name": "demo"}, is_reusable=True)
+    async with connected() as client:
+        first = await client.call_tool("gitea_repo_get", REPO_ARGS)
+        assert not first.is_error
+        sent_before = len(httpx_mock.get_requests())
+
+        audit = get_audit_logger()
+        healthy_file = audit._log_file
+        audit._log_file = FailingFile()  # type: ignore[assignment]
+        second = await client.call_tool("gitea_repo_get", REPO_ARGS)
+        mutation = await client.call_tool(
+            "gitea_issue_create_issue", {**REPO_ARGS, "body": {"title": "x"}}
+        )
+
+        assert second.is_error and mutation.is_error
+        assert payload_of(second)["error"]["kind"] == "audit_unavailable"
+        assert payload_of(mutation)["error"]["kind"] == "audit_unavailable"
+        # Gitea was not contacted at all while the log was broken.
+        assert len(httpx_mock.get_requests()) == sent_before
+
+        audit._log_file = healthy_file
+        resumed = await client.call_tool("gitea_repo_get", REPO_ARGS)
+        assert not resumed.is_error
+
+
+async def test_the_refusal_does_not_leak_the_failure_reason() -> None:
+    async with connected() as client:
+        get_audit_logger()._log_file = FailingFile()  # type: ignore[assignment]
+        result = await client.call_tool("gitea_repo_get", REPO_ARGS)
+
+    text = result.content[0].text  # type: ignore[union-attr]
+    assert "No space left" not in text and "OSError" not in text

tests/test_server.py

@@ -476,6 +476,9 @@ async def test_audit_write_failure_after_execution_does_not_break_the_call(
     httpx_mock.add_response(url=f"{API}/repos/octo/demo", json={})
 
     class BrokenAudit:
+        def log_tool_call_started(self, *args: Any, **kwargs: Any) -> str:
+            return "started"
+
         def log_tool_invocation(self, *args: Any, **kwargs: Any) -> str:
             raise OSError("disk full: " + GITEA_TOKEN)
 

tests/test_transports_startup.py

@@ -341,8 +341,10 @@ async def test_real_stdio_subprocess_serves_the_catalog(tmp_path: Path) -> None:
     payload = json.loads(result.content[0].text)  # type: ignore[union-attr]
     assert "error" in payload and GITEA_TOKEN not in json.dumps(payload)
     audit = (tmp_path / "state" / "audit.log").read_text(encoding="utf-8").splitlines()
-    assert len(audit) == 1
-    assert GITEA_TOKEN not in audit[0]
+    events = [json.loads(line)["event_type"] for line in audit]
+    # A write-ahead entry, then the one tool_invocation entry with the result.
+    assert events == ["tool_call_started", "tool_invocation"]
+    assert all(GITEA_TOKEN not in line for line in audit)
 
 
 # serve command