"""Custom Crawl4AI logger that writes to stderr instead of stdout.
This is critical for MCP stdio transport compliance. The MCP specification states:
> The server MUST NOT write anything to its stdout that is not a valid MCP message.
> The server MAY write UTF-8 strings to its standard error (stderr) for logging purposes.
Crawl4AI's default AsyncLogger uses Rich Console which writes to stdout by default,
breaking MCP protocol. This module provides a logger that redirects all output to stderr.
"""
import sys
from typing import Any
from crawl4ai.async_logger import AsyncLogger
from rich.console import Console
class StderrAsyncLogger(AsyncLogger):
"""AsyncLogger that writes to stderr instead of stdout.
This ensures MCP stdio transport compliance by keeping stdout clean
for JSON-RPC messages only.
"""
def __init__(self, **kwargs: Any) -> None:
"""Initialize logger with stderr-based Console.
Args:
**kwargs: Arguments passed to AsyncLogger (log_file, log_level, etc.)
"""
super().__init__(**kwargs)
# Override console to use stderr instead of stdout
self.console = Console(file=sys.stderr, force_terminal=False)
