Added logging support.

CHANGES

@@ -9,6 +9,10 @@ Version 0.5
 Release date to be announced
 
 - added support for categories for flashed messages.
+- the application now configures a :class:`logging.Handler` and will
+  log request handling exceptions to that logger when not in debug
+  mode.  This makes it possible to receive mails on server errors
+  for example.
 
 Version 0.2
 -----------

flask.py

@@ -21,7 +21,7 @@ from werkzeug import Request as RequestBase, Response as ResponseBase, \
      LocalStack, LocalProxy, create_environ, SharedDataMiddleware, \
      ImmutableDict, cached_property, wrap_file, Headers
 from werkzeug.routing import Map, Rule
-from werkzeug.exceptions import HTTPException
+from werkzeug.exceptions import HTTPException, InternalServerError
 from werkzeug.contrib.securecookie import SecureCookie
 
 # try to load the best simplejson implementation available.  If JSON
@@ -659,6 +659,18 @@ class Flask(_PackageBoundObject):
     #: .. versionadded:: 0.2
     use_x_sendfile = False
 
+    #: the logging format used for the debug logger.  This is only used when
+    #: the application is in debug mode, otherwise the attached logging
+    #: handler does the formatting.
+    #:
+    #: .. versionadded:: 0.5
+    debug_log_format = (
+        '-' * 80 + '\n' +
+        '%(levelname)s in %(module)s, %(filename)s:%(lineno)d]:\n' +
+        '%(message)s\n' +
+        '-' * 80
+    )
+
     #: options that are passed directly to the Jinja2 environment
     jinja_options = ImmutableDict(
         autoescape=True,
@@ -753,6 +765,24 @@ class Flask(_PackageBoundObject):
         )
         self.jinja_env.filters['tojson'] = _tojson_filter
 
+    @cached_property
+    def logger(self):
+        """A :class:`logging.Logger` object for this application.  The
+        default configuration is to log to stderr if the application is
+        in debug mode.
+        """
+        from logging import getLogger, StreamHandler, Formatter, DEBUG
+        class DebugHandler(StreamHandler):
+            def emit(x, record):
+                if self.debug:
+                    StreamHandler.emit(x, record)
+        handler = DebugHandler()
+        handler.setLevel(DEBUG)
+        handler.setFormatter(Formatter(self.debug_log_format))
+        logger = getLogger(self.import_name)
+        logger.addHandler(handler)
+        return logger
+
     def create_jinja_loader(self):
         """Creates the Jinja loader.  By default just a package loader for
         the configured package is returned that looks up templates in the
@@ -1010,6 +1040,38 @@ class Flask(_PackageBoundObject):
         self.template_context_processors[None].append(f)
         return f
 
+    def handle_http_exception(self, e):
+        """Handles an HTTP exception.  By default this will invoke the
+        registered error handlers and fall back to returning the
+        exception as response.
+
+        .. versionadded: 0.5
+        """
+        handler = self.error_handlers.get(e.code)
+        if handler is None:
+            return e
+        return handler(e)
+
+    def handle_exception(self, e):
+        """Default exception handling that kicks in when an exception
+        occours that is not catched.  In debug mode the exception will
+        be re-raised immediately, otherwise it is logged an the handler
+        for an 500 internal server error is used.  If no such handler
+        exists, a default 500 internal server error message is displayed.
+
+        .. versionadded: 0.5
+        """
+        handler = self.error_handlers.get(500)
+        if self.debug:
+            raise
+        self.logger.exception('Exception on %s [%s]' % (
+            request.path,
+            request.method
+        ))
+        if handler is None:
+            return InternalServerError()
+        return handler(e)
+
     def dispatch_request(self):
         """Does the request dispatching.  Matches the URL and returns the
         return value of the view or error handler.  This does not have to
@@ -1022,15 +1084,9 @@ class Flask(_PackageBoundObject):
                 raise req.routing_exception
             return self.view_functions[req.endpoint](**req.view_args)
         except HTTPException, e:
-            handler = self.error_handlers.get(e.code)
-            if handler is None:
-                return e
-            return handler(e)
+            return self.handle_http_exception(e)
         except Exception, e:
-            handler = self.error_handlers.get(500)
-            if self.debug or handler is None:
-                raise
-            return handler(e)
+            return self.handle_exception(e)
 
     def make_response(self, rv):
         """Converts the return value from a view function to a real

tests/flask_tests.py

@@ -16,6 +16,7 @@ import sys
 import flask
 import unittest
 import tempfile
+from contextlib import contextmanager
 from datetime import datetime
 from werkzeug import parse_date, parse_options_header
 from cStringIO import StringIO
@@ -26,6 +27,16 @@ sys.path.append(os.path.join(example_path, 'flaskr'))
 sys.path.append(os.path.join(example_path, 'minitwit'))
 
 
+@contextmanager
+def catch_stderr():
+    old_stderr = sys.stderr
+    sys.stderr = rv = StringIO()
+    try:
+        yield rv
+    finally:
+        sys.stderr = old_stderr
+
+
 class ContextTestCase(unittest.TestCase):
 
     def test_context_binding(self):
@@ -585,6 +596,56 @@ class SendfileTestCase(unittest.TestCase):
             assert options['filename'] == 'index.txt'
 
 
+class LoggingTestCase(unittest.TestCase):
+
+    def test_debug_log(self):
+        app = flask.Flask(__name__)
+        app.debug = True
+        @app.route('/')
+        def index():
+            app.logger.warning('the standard library is dead')
+            return ''
+
+        @app.route('/exc')
+        def exc():
+            1/0
+        c = app.test_client()
+
+        with catch_stderr() as err:
+            rv = c.get('/')
+            out = err.getvalue()
+            assert 'WARNING in flask_tests, flask_tests.py' in out
+            assert 'the standard library is dead' in out
+
+        with catch_stderr() as err:
+            try:
+                c.get('/exc')
+            except ZeroDivisionError:
+                pass
+            else:
+                assert False, 'debug log ate the exception'
+
+    def test_exception_logging(self):
+        from logging import StreamHandler
+        out = StringIO()
+        app = flask.Flask(__name__)
+        app.logger.addHandler(StreamHandler(out))
+
+        @app.route('/')
+        def index():
+            1/0
+
+        rv = app.test_client().get('/')
+        assert rv.status_code == 500
+        assert 'Internal Server Error' in rv.data
+
+        err = out.getvalue()
+        assert 'Exception on / [GET]' in err
+        assert 'Traceback (most recent call last):' in err
+        assert '1/0' in err
+        assert 'ZeroDivisionError:' in err
+
+
 def suite():
     from minitwit_tests import MiniTwitTestCase
     from flaskr_tests import FlaskrTestCase
@@ -592,8 +653,9 @@ def suite():
     suite.addTest(unittest.makeSuite(ContextTestCase))
     suite.addTest(unittest.makeSuite(BasicFunctionalityTestCase))
     suite.addTest(unittest.makeSuite(TemplatingTestCase))
-    suite.addTest(unittest.makeSuite(SendfileTestCase))
     suite.addTest(unittest.makeSuite(ModuleTestCase))
+    suite.addTest(unittest.makeSuite(SendfileTestCase))
+    suite.addTest(unittest.makeSuite(LoggingTestCase))
     if flask.json_available:
         suite.addTest(unittest.makeSuite(JSONTestCase))
     suite.addTest(unittest.makeSuite(MiniTwitTestCase))