fix: logging to file with structlog (#3425)

fix: structlog file logging

Fixes issue where adding a file handle to the config object would cause it to fail on call to `configure()`.

- add e2e test for logging to file w/ structlog

litestar/logging/config.py

@@ -2,13 +2,14 @@
 
 import sys
 from abc import ABC, abstractmethod
-from dataclasses import asdict, dataclass, field, fields
+from dataclasses import dataclass, field, fields
 from importlib.util import find_spec
 from logging import INFO
 from typing import TYPE_CHECKING, Any, Callable, Literal, cast
 
 from litestar.exceptions import ImproperlyConfiguredException, MissingDependencyException
 from litestar.serialization.msgspec_hooks import _msgspec_json_encoder
+from litestar.utils.dataclass import simple_asdict
 from litestar.utils.deprecation import deprecated
 
 __all__ = ("BaseLoggingConfig", "LoggingConfig", "StructLoggingConfig")
@@ -313,7 +314,9 @@ def stdlib_json_serializer(value: EventDict, **_: Any) -> str:  # pragma: no cov
     return _msgspec_json_encoder.encode(value).decode("utf-8")
 
 
-def default_structlog_processors(as_json: bool = True) -> list[Processor]:  # pyright: ignore
+def default_structlog_processors(
+    as_json: bool = True, json_serializer: Callable[[Any], Any] = default_json_serializer
+) -> list[Processor]:  # pyright: ignore
     """Set the default processors for structlog.
 
     Returns:
@@ -329,7 +332,7 @@ def default_structlog_processors(as_json: bool = True) -> list[Processor]:  # py
                 structlog.processors.add_log_level,
                 structlog.processors.format_exc_info,
                 structlog.processors.TimeStamper(fmt="iso"),
-                structlog.processors.JSONRenderer(serializer=default_json_serializer),
+                structlog.processors.JSONRenderer(serializer=json_serializer),
             ]
         return [
             structlog.contextvars.merge_contextvars,
@@ -465,7 +468,7 @@ def configure(self) -> GetLogger:
         structlog.configure(
             **{
                 k: v
-                for k, v in asdict(self).items()
+                for k, v in simple_asdict(self).items()
                 if k
                 not in (
                     "standard_lib_logging_config",

tests/e2e/test_logging/test_structlog_to_file.py

@@ -0,0 +1,85 @@
+from __future__ import annotations
+
+import json
+from pathlib import Path
+from typing import TYPE_CHECKING
+from unittest.mock import ANY
+
+import pytest
+import structlog
+
+from litestar import Litestar, get
+from litestar.logging import StructLoggingConfig
+from litestar.logging.config import default_json_serializer, default_structlog_processors
+from litestar.plugins.structlog import StructlogConfig, StructlogPlugin
+from litestar.testing import TestClient
+
+if TYPE_CHECKING:
+    from collections.abc import Iterator
+
+
+@pytest.fixture(autouse=True)
+def structlog_reset() -> Iterator[None]:
+    try:
+        yield
+    finally:
+        structlog.reset_defaults()
+
+
+def test_structlog_to_file(tmp_path: Path) -> None:
+    log_file = tmp_path / "log.log"
+
+    logging_config = StructlogConfig(
+        structlog_logging_config=StructLoggingConfig(
+            logger_factory=structlog.WriteLoggerFactory(file=log_file.open("wt")),
+            processors=default_structlog_processors(
+                json_serializer=lambda v, **_: str(default_json_serializer(v), "utf-8")
+            ),
+        ),
+    )
+
+    logger = structlog.get_logger()
+
+    @get("/")
+    def handler() -> str:
+        logger.info("handled", hello="world")
+        return "hello"
+
+    app = Litestar(route_handlers=[handler], plugins=[StructlogPlugin(config=logging_config)], debug=True)
+
+    with TestClient(app) as client:
+        resp = client.get("/")
+        assert resp.text == "hello"
+
+    logged_data = [json.loads(line) for line in log_file.read_text().splitlines()]
+    assert logged_data == [
+        {
+            "path": "/",
+            "method": "GET",
+            "content_type": ["", {}],
+            "headers": {
+                "host": "testserver.local",
+                "accept": "*/*",
+                "accept-encoding": "gzip, deflate, br",
+                "connection": "keep-alive",
+                "user-agent": "testclient",
+            },
+            "cookies": {},
+            "query": {},
+            "path_params": {},
+            "body": None,
+            "event": "HTTP Request",
+            "level": "info",
+            "timestamp": ANY,
+        },
+        {"hello": "world", "event": "handled", "level": "info", "timestamp": ANY},
+        {
+            "status_code": 200,
+            "cookies": {},
+            "headers": {"content-type": "text/plain; charset=utf-8", "content-length": "5"},
+            "body": "hello",
+            "event": "HTTP Response",
+            "level": "info",
+            "timestamp": ANY,
+        },
+    ]