Add default logging handler to web.run_app (#3243)

CHANGES/3324.feature

@@ -0,0 +1,3 @@
+Add default logging handler to web.run_app
+
+If the `Application.debug` flag is set and the default logger `aiohttp.access` is used, access logs will now be output using a `stderr` `StreamHandler` if no handlers are attached. Furthermore, if the default logger has no log level set, the log level will be set to `DEBUG`.

CONTRIBUTORS.txt

@@ -30,6 +30,7 @@ Andrej Antonov
 Andrew Leech
 Andrew Lytvyn
 Andrew Svetlov
+Andrew Zhou
 Andrii Soldatenko
 Antoine Pietri
 Anton Kasyanov

aiohttp/log.py

@@ -7,3 +7,5 @@
 server_logger = logging.getLogger('aiohttp.server')
 web_logger = logging.getLogger('aiohttp.web')
 ws_logger = logging.getLogger('aiohttp.websocket')
+
+default_handler = logging.StreamHandler()

aiohttp/web.py

@@ -9,7 +9,7 @@
 from . import (helpers, web_app, web_exceptions, web_fileresponse,
                web_middlewares, web_protocol, web_request, web_response,
                web_routedef, web_runner, web_server, web_urldispatcher, web_ws)
-from .log import access_logger
+from .log import access_logger, default_handler
 from .web_app import *  # noqa
 from .web_exceptions import *  # noqa
 from .web_fileresponse import *  # noqa
@@ -52,6 +52,13 @@ def run_app(app, *, host=None, port=None, path=None, sock=None,
     if asyncio.iscoroutine(app):
         app = loop.run_until_complete(app)
 
+    # Configure if and only if in debugging mode and using the default logger
+    if app.debug and access_log is access_logger:
+        if access_log.level == logging.NOTSET:
+            access_log.setLevel(logging.DEBUG)
+        if not access_log.hasHandlers():
+            access_log.addHandler(default_handler)
+
     runner = AppRunner(app, handle_signals=handle_signals,
                        access_log_class=access_log_class,
                        access_log_format=access_log_format,

docs/logging.rst

@@ -28,8 +28,11 @@ configuring whole loggers in your application.
 Access logs
 -----------
 
-Access log by default is switched on and uses ``'aiohttp.access'``
-logger name.
+Access logs are enabled by default. If the `debug` flag is set, and the default
+logger ``'aiohttp.access'`` is used, access logs will be output to
+:obj:`~sys.stderr` if no handlers are attached.
+Furthermore, if the default logger has no log level set, the log level will be
+set to :obj:`logging.DEBUG`.
 
 The log may be controlled by :meth:`aiohttp.web.AppRunner` and
 :func:`aiohttp.web.run_app`.