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new debug/test preserve context implementation

This commit is contained in:
David Lord 2022-06-29 21:02:44 -07:00
parent 3635583ce2
commit 84c722044a
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10 changed files with 84 additions and 220 deletions
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12
CHANGES.rst
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@ -42,6 +42,18 @@ Unreleased
them in a ``Response``. :pr:`4629`
- Add ``stream_template`` and ``stream_template_string`` functions to
render a template as a stream of pieces. :pr:`4629`
- A new implementation of context preservation during debugging and
testing. :pr:`4666`
- ``request``, ``g``, and other context-locals point to the
correct data when running code in the interactive debugger
console. :issue:`2836`
- Teardown functions are always run at the end of the request,
even if the context is preserved. They are also run after the
preserved context is popped.
- ``stream_with_context`` preserves context separately from a
``with client`` block. It will be cleaned up when
``response.get_data()`` or ``response.close()`` is called.
Version 2.1.3

11
docs/config.rst
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@ -126,14 +126,6 @@ The following configuration values are used internally by Flask:
Default: ``None``
.. py:data:: PRESERVE_CONTEXT_ON_EXCEPTION
Don't pop the request context when an exception occurs. If not set, this
is true if ``DEBUG`` is true. This allows debuggers to introspect the
request data on errors, and should normally not need to be set directly.
Default: ``None``
.. py:data:: TRAP_HTTP_EXCEPTIONS
If there is no handler for an ``HTTPException``-type exception, re-raise it
@ -392,6 +384,9 @@ The following configuration values are used internally by Flask:
Added :data:`MAX_COOKIE_SIZE` to control a warning from Werkzeug.
.. versionchanged:: 2.2
Removed ``PRESERVE_CONTEXT_ON_EXCEPTION``.
Configuring from Python Files
-----------------------------

19
docs/reqcontext.rst
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@ -219,25 +219,6 @@ sent:
:meth:`~Flask.teardown_request` functions are called.
Context Preservation on Error
-----------------------------
At the end of a request, the request context is popped and all data
associated with it is destroyed. If an error occurs during development,
it is useful to delay destroying the data for debugging purposes.
When the development server is running in development mode (the
``--env`` option is set to ``'development'``), the error and data will
be preserved and shown in the interactive debugger.
This behavior can be controlled with the
:data:`PRESERVE_CONTEXT_ON_EXCEPTION` config. As described above, it
defaults to ``True`` in the development environment.
Do not enable :data:`PRESERVE_CONTEXT_ON_EXCEPTION` in production, as it
will cause your application to leak memory on exceptions.
.. _notes-on-proxies:
Notes On Proxies

23
src/flask/app.py
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@ -331,7 +331,6 @@ class Flask(Scaffold):
"DEBUG": None,
"TESTING": False,
"PROPAGATE_EXCEPTIONS": None,
"PRESERVE_CONTEXT_ON_EXCEPTION": None,
"SECRET_KEY": None,
"PERMANENT_SESSION_LIFETIME": timedelta(days=31),
"USE_X_SENDFILE": False,
@ -583,19 +582,6 @@ class Flask(Scaffold):
return rv
return self.testing or self.debug
@property
def preserve_context_on_exception(self) -> bool:
"""Returns the value of the ``PRESERVE_CONTEXT_ON_EXCEPTION``
configuration value in case it's set, otherwise a sensible default
is returned.
.. versionadded:: 0.7
"""
rv = self.config["PRESERVE_CONTEXT_ON_EXCEPTION"]
if rv is not None:
return rv
return self.debug
@locked_cached_property
def logger(self) -> logging.Logger:
"""A standard Python :class:`~logging.Logger` for the app, with
@ -2301,9 +2287,14 @@ class Flask(Scaffold):
raise
return response(environ, start_response)
finally:
if self.should_ignore_error(error):
if "werkzeug.debug.preserve_context" in environ:
environ["werkzeug.debug.preserve_context"](_app_ctx_stack.top)
environ["werkzeug.debug.preserve_context"](_request_ctx_stack.top)
if error is not None and self.should_ignore_error(error):
error = None
ctx.auto_pop(error)
ctx.pop(error)
def __call__(self, environ: dict, start_response: t.Callable) -> t.Any:
"""The WSGI server calls the Flask application object as the

67
src/flask/ctx.py
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@ -289,20 +289,12 @@ class RequestContext:
functions registered on the application for teardown execution
(:meth:`~flask.Flask.teardown_request`).
The request context is automatically popped at the end of the request
for you. In debug mode the request context is kept around if
exceptions happen so that interactive debuggers have a chance to
introspect the data. With 0.4 this can also be forced for requests
that did not fail and outside of ``DEBUG`` mode. By setting
``'flask._preserve_context'`` to ``True`` on the WSGI environment the
context will not pop itself at the end of the request. This is used by
the :meth:`~flask.Flask.test_client` for example to implement the
deferred cleanup functionality.
You might find this helpful for unittests where you need the
information from the context local around for a little longer. Make
sure to properly :meth:`~werkzeug.LocalStack.pop` the stack yourself in
that situation, otherwise your unittests will leak memory.
The request context is automatically popped at the end of the
request. When using the interactive debugger, the context will be
restored so ``request`` is still accessible. Similarly, the test
client can preserve the context after the request ends. However,
teardown functions may already have closed some resources such as
database connections.
"""
def __init__(
@ -330,14 +322,6 @@ class RequestContext:
# one is created implicitly so for each level we add this information
self._implicit_app_ctx_stack: t.List[t.Optional["AppContext"]] = []
# indicator if the context was preserved. Next time another context
# is pushed the preserved context is popped.
self.preserved = False
# remembers the exception for pop if there is one in case the context
# preservation kicks in.
self._preserved_exc = None
# Functions that should be executed after the request on the response
# object. These will be called before the regular "after_request"
# functions.
@ -400,19 +384,6 @@ class RequestContext:
self.request.routing_exception = e
def push(self) -> None:
"""Binds the request context to the current context."""
# If an exception occurs in debug mode or if context preservation is
# activated under exception situations exactly one context stays
# on the stack. The rationale is that you want to access that
# information under debug situations. However if someone forgets to
# pop that context again we want to make sure that on the next push
# it's invalidated, otherwise we run at risk that something leaks
# memory. This is usually only a problem in test suite since this
# functionality is not active in production environments.
top = _request_ctx_stack.top
if top is not None and top.preserved:
top.pop(top._preserved_exc)
# Before we push the request context we have to ensure that there
# is an application context.
app_ctx = _app_ctx_stack.top
@ -454,8 +425,6 @@ class RequestContext:
try:
if not self._implicit_app_ctx_stack:
self.preserved = False
self._preserved_exc = None
if exc is _sentinel:
exc = sys.exc_info()[1]
self.app.do_teardown_request(exc)
@ -481,12 +450,17 @@ class RequestContext:
), f"Popped wrong request context. ({rv!r} instead of {self!r})"
def auto_pop(self, exc: t.Optional[BaseException]) -> None:
if self.request.environ.get("flask._preserve_context") or (
exc is not None and self.app.preserve_context_on_exception
):
self.preserved = True
self._preserved_exc = exc # type: ignore
else:
"""
.. deprecated:: 2.2
Will be removed in Flask 2.3.
"""
import warnings
warnings.warn(
"'ctx.auto_pop' is deprecated and will be removed in Flask 2.3.",
DeprecationWarning,
stacklevel=2,
)
self.pop(exc)
def __enter__(self) -> "RequestContext":
@ -499,12 +473,7 @@ class RequestContext:
exc_value: t.Optional[BaseException],
tb: t.Optional[TracebackType],
) -> None:
# do not pop the request stack if we are in debug mode and an
# exception happened. This will allow the debugger to still
# access the request object in the interactive shell. Furthermore
# the context can be force kept alive for the test client.
# See flask.testing for how this works.
self.auto_pop(exc_value)
self.pop(exc_value)
def __repr__(self) -> str:
return (

7
src/flask/scaffold.py
View File

@ -600,13 +600,6 @@ class Scaffold:
be passed an error object.
The return values of teardown functions are ignored.
.. admonition:: Debug Note
In debug mode Flask will not tear down a request on an exception
immediately. Instead it will keep it alive so that the interactive
debugger can still access it. This behavior can be controlled
by the ``PRESERVE_CONTEXT_ON_EXCEPTION`` configuration variable.
"""
self.teardown_request_funcs.setdefault(None, []).append(f)
return f

43
src/flask/testing.py
View File

@ -1,5 +1,6 @@
import typing as t
from contextlib import contextmanager
from contextlib import ExitStack
from copy import copy
from types import TracebackType
@ -108,10 +109,12 @@ class FlaskClient(Client):
"""
application: "Flask"
preserve_context = False
def __init__(self, *args: t.Any, **kwargs: t.Any) -> None:
super().__init__(*args, **kwargs)
self.preserve_context = False
self._new_contexts: t.List[t.ContextManager[t.Any]] = []
self._context_stack = ExitStack()
self.environ_base = {
"REMOTE_ADDR": "127.0.0.1",
"HTTP_USER_AGENT": f"werkzeug/{werkzeug.__version__}",
@ -173,11 +176,12 @@ class FlaskClient(Client):
self.cookie_jar.extract_wsgi(c.request.environ, headers)
def _copy_environ(self, other):
return {
**self.environ_base,
**other,
"flask._preserve_context": self.preserve_context,
}
out = {**self.environ_base, **other}
if self.preserve_context:
out["werkzeug.debug.preserve_context"] = self._new_contexts.append
return out
def _request_from_builder_args(self, args, kwargs):
kwargs["environ_base"] = self._copy_environ(kwargs.get("environ_base", {}))
@ -214,12 +218,24 @@ class FlaskClient(Client):
# request is None
request = self._request_from_builder_args(args, kwargs)
return super().open(
# Pop any previously preserved contexts. This prevents contexts
# from being preserved across redirects or multiple requests
# within a single block.
self._context_stack.close()
response = super().open(
request,
buffered=buffered,
follow_redirects=follow_redirects,
)
# Re-push contexts that were preserved during the request.
while self._new_contexts:
cm = self._new_contexts.pop()
self._context_stack.enter_context(cm)
return response
def __enter__(self) -> "FlaskClient":
if self.preserve_context:
raise RuntimeError("Cannot nest client invocations")
@ -233,18 +249,7 @@ class FlaskClient(Client):
tb: t.Optional[TracebackType],
) -> None:
self.preserve_context = False
# Normally the request context is preserved until the next
# request in the same thread comes. When the client exits we
# want to clean up earlier. Pop request contexts until the stack
# is empty or a non-preserved one is found.
while True:
top = _request_ctx_stack.top
if top is not None and top.preserved:
top.pop()
else:
break
self._context_stack.close()
class FlaskCliRunner(CliRunner):

56
tests/test_basic.py
View File

@ -928,14 +928,9 @@ def test_baseexception_error_handling(app, client):
def broken_func():
raise KeyboardInterrupt()
with client:
with pytest.raises(KeyboardInterrupt):
client.get("/")
ctx = flask._request_ctx_stack.top
assert ctx.preserved
assert type(ctx._preserved_exc) is KeyboardInterrupt
def test_before_request_and_routing_errors(app, client):
@app.before_request
@ -1769,57 +1764,6 @@ def test_route_decorator_custom_endpoint(app, client):
assert client.get("/bar/123").data == b"123"
def test_preserve_only_once(app, client):
app.debug = True
@app.route("/fail")
def fail_func():
1 // 0
for _x in range(3):
with pytest.raises(ZeroDivisionError):
client.get("/fail")
assert flask._request_ctx_stack.top is not None
assert flask._app_ctx_stack.top is not None
# implicit appctx disappears too
flask._request_ctx_stack.top.pop()
assert flask._request_ctx_stack.top is None
assert flask._app_ctx_stack.top is None
def test_preserve_remembers_exception(app, client):
app.debug = True
errors = []
@app.route("/fail")
def fail_func():
1 // 0
@app.route("/success")
def success_func():
return "Okay"
@app.teardown_request
def teardown_handler(exc):
errors.append(exc)
# After this failure we did not yet call the teardown handler
with pytest.raises(ZeroDivisionError):
client.get("/fail")
assert errors == []
# But this request triggers it, and it's an error
client.get("/success")
assert len(errors) == 2
assert isinstance(errors[0], ZeroDivisionError)
# At this point another request does nothing.
client.get("/success")
assert len(errors) == 3
assert errors[1] is None
def test_get_method_on_g(app_ctx):
assert flask.g.get("x") is None
assert flask.g.get("x", 11) == 11

22
tests/test_signals.py
View File

@ -123,8 +123,7 @@ def test_request_exception_signal():
flask.got_request_exception.disconnect(record, app)
def test_appcontext_signals():
app = flask.Flask(__name__)
def test_appcontext_signals(app, client):
recorded = []
def record_push(sender, **kwargs):
@ -140,10 +139,8 @@ def test_appcontext_signals():
flask.appcontext_pushed.connect(record_push, app)
flask.appcontext_popped.connect(record_pop, app)
try:
with app.test_client() as c:
rv = c.get("/")
rv = client.get("/")
assert rv.data == b"Hello"
assert recorded == ["push"]
assert recorded == ["push", "pop"]
finally:
flask.appcontext_pushed.disconnect(record_push, app)
@ -174,12 +171,12 @@ def test_flash_signal(app):
flask.message_flashed.disconnect(record, app)
def test_appcontext_tearing_down_signal():
app = flask.Flask(__name__)
def test_appcontext_tearing_down_signal(app, client):
app.testing = False
recorded = []
def record_teardown(sender, **kwargs):
recorded.append(("tear_down", kwargs))
def record_teardown(sender, exc):
recorded.append(exc)
@app.route("/")
def index():
@ -187,10 +184,9 @@ def test_appcontext_tearing_down_signal():
flask.appcontext_tearing_down.connect(record_teardown, app)
try:
with app.test_client() as c:
rv = c.get("/")
rv = client.get("/")
assert rv.status_code == 500
assert recorded == []
assert recorded == [("tear_down", {"exc": None})]
assert len(recorded) == 1
assert isinstance(recorded[0], ZeroDivisionError)
finally:
flask.appcontext_tearing_down.disconnect(record_teardown, app)

34
tests/test_testing.py
View File

@ -187,7 +187,6 @@ def test_session_transactions(app, client):
def test_session_transactions_no_null_sessions():
app = flask.Flask(__name__)
app.testing = True
with app.test_client() as c:
with pytest.raises(RuntimeError) as e:
@ -254,29 +253,6 @@ def test_reuse_client(client):
assert client.get("/").status_code == 404
def test_test_client_calls_teardown_handlers(app, client):
called = []
@app.teardown_request
def remember(error):
called.append(error)
with client:
assert called == []
client.get("/")
assert called == []
assert called == [None]
del called[:]
with client:
assert called == []
client.get("/")
assert called == []
client.get("/")
assert called == [None]
assert called == [None, None]
def test_full_url_request(app, client):
@app.route("/action", methods=["POST"])
def action():
@ -412,13 +388,15 @@ def test_cli_custom_obj(app):
def test_client_pop_all_preserved(app, req_ctx, client):
@app.route("/")
def index():
# stream_with_context pushes a third context, preserved by client
return flask.Response(flask.stream_with_context("hello"))
# stream_with_context pushes a third context, preserved by response
return flask.stream_with_context("hello")
# req_ctx fixture pushed an initial context, not marked preserved
# req_ctx fixture pushed an initial context
with client:
# request pushes a second request context, preserved by client
client.get("/")
rv = client.get("/")
# close the response, releasing the context held by stream_with_context
rv.close()
# only req_ctx fixture should still be pushed
assert flask._request_ctx_stack.top is req_ctx