LlamaFirewallProvider unable to run due to nested asyncio event loops

[xp4u1]

I encountered an issue with the LlamaFirewall Guardrail-Provider and am a bit confused about its origin. Initially, I suspected it might be due to my setup, but after some investigation, it seems this issue should be affecting everyone.

ERROR:llama_firewall_provider:Error in LlamaFirewallProvider.check_tool_response
Traceback (most recent call last):
  File "xxx/mcp-context-protector/src/contextprotector/guardrail_providers/llama_firewall.py", line 124, in check_tool_response
    result = lf.scan(message)
             ^^^^^^^^^^^^^^^^
  File "xxx/mcp-context-protector/.venv/lib/python3.11/site-packages/llamafirewall/llamafirewall.py", line 122, in scan
    scanner_result = asyncio.run(scanner_instance.scan(input, trace))
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/asyncio/runners.py", line 186, in run
    raise RuntimeError(
RuntimeError: asyncio.run() cannot be called from a running event loop
WARNING:mcp_wrapper:Guardrail alert triggered for tool 'get_alerts': Error checking tool response: asyncio.run()
                    cannot be called from a running event loop

The following code causes this error, since asyncio does not allow nested event loops.

# external llamafirewall/llamafirewall.py
for scanner_type in scanners:
    scanner_instance = create_scanner(scanner_type)
    LOG.debug(
        f"[LlamaFirewall] Scanning with {scanner_instance.name}, for the input {str(input.content)[:20]}"
    )
    scanner_result = asyncio.run(scanner_instance.scan(input, trace)) # <-- this call fails

# src/contextprotector/__main__.py
def main() -> None:
    """Launch async main function."""
    asyncio.run(main_async()) # <-- entire mcp-context-protector already inside an event loop

The llamafirewall library includes a scan_async function. However, after a brief review of the codebase, it seems that some refactoring is necessary, as many functions need to be marked as async.

---

To reproduce the issue, use the official demo repo and run it using the inspector:

npx @modelcontextprotocol/inspector bash $PWD/mcp-context-protector.sh \
	--guardrail-provider LlamaFirewall --command-args $(which uv) run \
	--directory xxx/mcp-quickstart-resources/weather-server-python/ weather.py