flask/flask/ctx.py

# -*- coding: utf-8 -*-
"""
    flask.ctx
    ~~~~~~~~~

    Implements the objects required to keep the context.

    :copyright: (c) 2015 by Armin Ronacher.
    :license: BSD, see LICENSE for more details.
"""

import sys
from functools import update_wrapper

from werkzeug.exceptions import HTTPException

from .globals import _request_ctx_stack, _app_ctx_stack
from .signals import appcontext_pushed, appcontext_popped
from ._compat import BROKEN_PYPY_CTXMGR_EXIT, reraise


# a singleton sentinel value for parameter defaults
_sentinel = object()


class _AppCtxGlobals(object):
    """A plain object."""

    def get(self, name, default=None):
        return self.__dict__.get(name, default)

    def pop(self, name, default=_sentinel):
        if default is _sentinel:
            return self.__dict__.pop(name)
        else:
            return self.__dict__.pop(name, default)

    def setdefault(self, name, default=None):
        return self.__dict__.setdefault(name, default)

    def __contains__(self, item):
        return item in self.__dict__

    def __iter__(self):
        return iter(self.__dict__)

    def __repr__(self):
        top = _app_ctx_stack.top
        if top is not None:
            return '<flask.g of %r>' % top.app.name
        return object.__repr__(self)


def after_this_request(f):
    """Executes a function after this request.  This is useful to modify
    response objects.  The function is passed the response object and has
    to return the same or a new one.

    Example::

        @app.route('/')
        def index():
            @after_this_request
            def add_header(response):
                response.headers['X-Foo'] = 'Parachute'
                return response
            return 'Hello World!'

    This is more useful if a function other than the view function wants to
    modify a response.  For instance think of a decorator that wants to add
    some headers without converting the return value into a response object.

    .. versionadded:: 0.9
    """
    _request_ctx_stack.top._after_request_functions.append(f)
    return f


def copy_current_request_context(f):
    """A helper function that decorates a function to retain the current
    request context.  This is useful when working with greenlets.  The moment
    the function is decorated a copy of the request context is created and
    then pushed when the function is called.

    Example::

        import gevent
        from flask import copy_current_request_context

        @app.route('/')
        def index():
            @copy_current_request_context
            def do_some_work():
                # do some work here, it can access flask.request like you
                # would otherwise in the view function.
                ...
            gevent.spawn(do_some_work)
            return 'Regular response'

    .. versionadded:: 0.10
    """
    top = _request_ctx_stack.top
    if top is None:
        raise RuntimeError('This decorator can only be used at local scopes '
            'when a request context is on the stack.  For instance within '
            'view functions.')
    reqctx = top.copy()
    def wrapper(*args, **kwargs):
        with reqctx:
            return f(*args, **kwargs)
    return update_wrapper(wrapper, f)


def has_request_context():
    """If you have code that wants to test if a request context is there or
    not this function can be used.  For instance, you may want to take advantage
    of request information if the request object is available, but fail
    silently if it is unavailable.

    ::

        class User(db.Model):

            def __init__(self, username, remote_addr=None):
                self.username = username
                if remote_addr is None and has_request_context():
                    remote_addr = request.remote_addr
                self.remote_addr = remote_addr

    Alternatively you can also just test any of the context bound objects
    (such as :class:`request` or :class:`g` for truthness)::

        class User(db.Model):

            def __init__(self, username, remote_addr=None):
                self.username = username
                if remote_addr is None and request:
                    remote_addr = request.remote_addr
                self.remote_addr = remote_addr

    .. versionadded:: 0.7
    """
    return _request_ctx_stack.top is not None


def has_app_context():
    """Works like :func:`has_request_context` but for the application
    context.  You can also just do a boolean check on the
    :data:`current_app` object instead.

    .. versionadded:: 0.9
    """
    return _app_ctx_stack.top is not None


class AppContext(object):
    """The application context binds an application object implicitly
    to the current thread or greenlet, similar to how the
    :class:`RequestContext` binds request information.  The application
    context is also implicitly created if a request context is created
    but the application is not on top of the individual application
    context.
    """

    def __init__(self, app):
        self.app = app
        self.url_adapter = app.create_url_adapter(None)
        self.g = app.app_ctx_globals_class()

        # Like request context, app contexts can be pushed multiple times
        # but there a basic "refcount" is enough to track them.
        self._refcnt = 0

    def push(self):
        """Binds the app context to the current context."""
        self._refcnt += 1
        if hasattr(sys, 'exc_clear'):
            sys.exc_clear()
        _app_ctx_stack.push(self)
        appcontext_pushed.send(self.app)

    def pop(self, exc=_sentinel):
        """Pops the app context."""
        try:
            self._refcnt -= 1
            if self._refcnt <= 0:
                if exc is _sentinel:
                    exc = sys.exc_info()[1]
                self.app.do_teardown_appcontext(exc)
        finally:
            rv = _app_ctx_stack.pop()
        assert rv is self, 'Popped wrong app context.  (%r instead of %r)' \
            % (rv, self)
        appcontext_popped.send(self.app)

    def __enter__(self):
        self.push()
        return self

    def __exit__(self, exc_type, exc_value, tb):
        self.pop(exc_value)

        if BROKEN_PYPY_CTXMGR_EXIT and exc_type is not None:
            reraise(exc_type, exc_value, tb)


class RequestContext(object):
    """The request context contains all request relevant information.  It is
    created at the beginning of the request and pushed to the
    `_request_ctx_stack` and removed at the end of it.  It will create the
    URL adapter and request object for the WSGI environment provided.

    Do not attempt to use this class directly, instead use
    :meth:`~flask.Flask.test_request_context` and
    :meth:`~flask.Flask.request_context` to create this object.

    When the request context is popped, it will evaluate all the
    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.
    """

    def __init__(self, app, environ, request=None):
        self.app = app
        if request is None:
            request = app.request_class(environ)
        self.request = request
        self.url_adapter = app.create_url_adapter(self.request)
        self.flashes = None
        self.session = None

        # Request contexts can be pushed multiple times and interleaved with
        # other request contexts.  Now only if the last level is popped we
        # get rid of them.  Additionally if an application context is missing
        # one is created implicitly so for each level we add this information
        self._implicit_app_ctx_stack = []

        # 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.
        self._after_request_functions = []

        self.match_request()

    def _get_g(self):
        return _app_ctx_stack.top.g
    def _set_g(self, value):
        _app_ctx_stack.top.g = value
    g = property(_get_g, _set_g)
    del _get_g, _set_g

    def copy(self):
        """Creates a copy of this request context with the same request object.
        This can be used to move a request context to a different greenlet.
        Because the actual request object is the same this cannot be used to
        move a request context to a different thread unless access to the
        request object is locked.

        .. versionadded:: 0.10
        """
        return self.__class__(self.app,
            environ=self.request.environ,
            request=self.request
        )

    def match_request(self):
        """Can be overridden by a subclass to hook into the matching
        of the request.
        """
        try:
            url_rule, self.request.view_args = \
                self.url_adapter.match(return_rule=True)
            self.request.url_rule = url_rule
        except HTTPException as e:
            self.request.routing_exception = e

    def push(self):
        """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
        if app_ctx is None or app_ctx.app != self.app:
            app_ctx = self.app.app_context()
            app_ctx.push()
            self._implicit_app_ctx_stack.append(app_ctx)
        else:
            self._implicit_app_ctx_stack.append(None)

        if hasattr(sys, 'exc_clear'):
            sys.exc_clear()

        _request_ctx_stack.push(self)

        # Open the session at the moment that the request context is
        # available. This allows a custom open_session method to use the
        # request context (e.g. code that access database information
        # stored on `g` instead of the appcontext).
        self.session = self.app.open_session(self.request)
        if self.session is None:
            self.session = self.app.make_null_session()

    def pop(self, exc=_sentinel):
        """Pops the request context and unbinds it by doing that.  This will
        also trigger the execution of functions registered by the
        :meth:`~flask.Flask.teardown_request` decorator.

        .. versionchanged:: 0.9
           Added the `exc` argument.
        """
        app_ctx = self._implicit_app_ctx_stack.pop()

        try:
            clear_request = False
            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)

                # If this interpreter supports clearing the exception information
                # we do that now.  This will only go into effect on Python 2.x,
                # on 3.x it disappears automatically at the end of the exception
                # stack.
                if hasattr(sys, 'exc_clear'):
                    sys.exc_clear()

                request_close = getattr(self.request, 'close', None)
                if request_close is not None:
                    request_close()
                clear_request = True
        finally:
            rv = _request_ctx_stack.pop()

            # get rid of circular dependencies at the end of the request
            # so that we don't require the GC to be active.
            if clear_request:
                rv.request.environ['werkzeug.request'] = None

            # Get rid of the app as well if necessary.
            if app_ctx is not None:
                app_ctx.pop(exc)

            assert rv is self, 'Popped wrong request context.  ' \
                '(%r instead of %r)' % (rv, self)

    def auto_pop(self, exc):
        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
        else:
            self.pop(exc)

    def __enter__(self):
        self.push()
        return self

    def __exit__(self, exc_type, exc_value, tb):
        # 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)

        if BROKEN_PYPY_CTXMGR_EXIT and exc_type is not None:
            reraise(exc_type, exc_value, tb)

    def __repr__(self):
        return '<%s \'%s\' [%s] of %s>' % (
            self.__class__.__name__,
            self.request.url,
            self.request.method,
            self.app.name,
        )