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# -*- coding: utf-8 -*-
Implements various helpers.
:copyright: (c) 2010 by Armin Ronacher.
:license: BSD, see LICENSE for more details.
import os
import sys
import posixpath
import mimetypes
from time import time
from zlib import adler32
# try to load the best simplejson implementation available. If JSON
# is not installed, we add a failing class.
json_available = True
json = None
import simplejson as json
except ImportError:
import json
except ImportError:
# Google Appengine offers simplejson via django
from django.utils import simplejson as json
except ImportError:
json_available = False
from werkzeug import Headers, wrap_file, cached_property
from werkzeug.exceptions import NotFound
from jinja2 import FileSystemLoader
from .globals import session, _request_ctx_stack, current_app, request
def _assert_have_json():
"""Helper function that fails if JSON is unavailable."""
if not json_available:
raise RuntimeError('simplejson not installed')
# figure out if simplejson escapes slashes. This behaviour was changed
# from one version to another without reason.
if not json_available or '\\/' not in json.dumps('/'):
def _tojson_filter(*args, **kwargs):
if __debug__:
return json.dumps(*args, **kwargs).replace('/', '\\/')
_tojson_filter = json.dumps
# what separators does this operating system provide that are not a slash?
# this is used by the send_from_directory function to ensure that nobody is
# able to access files from outside the filesystem.
_os_alt_seps = list(sep for sep in [os.path.sep, os.path.altsep]
if sep not in (None, '/'))
def _endpoint_from_view_func(view_func):
"""Internal helper that returns the default endpoint for a given
function. This always is the function name.
assert view_func is not None, 'expected view func if endpoint ' \
'is not provided.'
return view_func.__name__
def jsonify(*args, **kwargs):
"""Creates a :class:`~flask.Response` with the JSON representation of
the given arguments with an `application/json` mimetype. The arguments
to this function are the same as to the :class:`dict` constructor.
Example usage::
def get_current_user():
return jsonify(username=g.user.username,,
This will send a JSON response like this to the browser::
"username": "admin",
"email": "admin@localhost",
"id": 42
This requires Python 2.6 or an installed version of simplejson. For
security reasons only objects are supported toplevel. For more
information about this, have a look at :ref:`json-security`.
.. versionadded:: 0.2
if __debug__:
return current_app.response_class(json.dumps(dict(*args, **kwargs),
indent=None if request.is_xhr else 2), mimetype='application/json')
def make_response(*args):
"""Sometimes it is necessary to set additional headers in a view. Because
views do not have to return response objects but can return a value that
is converted into a response object by Flask itself, it becomes tricky to
add headers to it. This function can be called instead of using a return
and you will get a response object which you can use to attach headers.
If view looked like this and you want to add a new header::
def index():
return render_template('index.html', foo=42)
You can now do something like this::
def index():
response = make_response(render_template('index.html', foo=42))
response.headers['X-Parachutes'] = 'parachutes are cool'
return response
This function accepts the very same arguments you can return from a
view function. This for example creates a response with a 404 error
response = make_response(render_template('not_found.html'), 404)
Internally this function does the following things:
- if no arguments are passed, it creates a new response argument
- if one argument is passed, :meth:`flask.Flask.make_response`
is invoked with it.
- if more than one argument is passed, the arguments are passed
to the :meth:`flask.Flask.make_response` function as tuple.
.. versionadded:: 0.6
if not args:
return current_app.response_class()
if len(args) == 1:
args = args[0]
return current_app.make_response(args)
def url_for(endpoint, **values):
"""Generates a URL to the given endpoint with the method provided.
The endpoint is relative to the active module if modules are in use.
Here are some examples:
==================== ======================= =============================
Active Module Target Endpoint Target Function
==================== ======================= =============================
`None` ``'index'`` `index` of the application
`None` ``'.index'`` `index` of the application
``'admin'`` ``'index'`` `index` of the `admin` module
any ``'.index'`` `index` of the application
any ``'admin.index'`` `index` of the `admin` module
==================== ======================= =============================
Variable arguments that are unknown to the target endpoint are appended
to the generated URL as query arguments.
For more information, head over to the :ref:`Quickstart <url-building>`.
:param endpoint: the endpoint of the URL (name of the function)
:param values: the variable arguments of the URL rule
:param _external: if set to `True`, an absolute URL is generated.
ctx =
if '.' not in endpoint:
mod = ctx.request.module
if mod is not None:
endpoint = mod + '.' + endpoint
elif endpoint.startswith('.'):
endpoint = endpoint[1:]
external = values.pop('_external', False)
return, values, force_external=external)
def get_template_attribute(template_name, attribute):
"""Loads a macro (or variable) a template exports. This can be used to
invoke a macro from within Python code. If you for example have a
template named `_cider.html` with the following contents:
.. sourcecode:: html+jinja
{% macro hello(name) %}Hello {{ name }}!{% endmacro %}
You can access this from Python code like this::
hello = get_template_attribute('_cider.html', 'hello')
return hello('World')
.. versionadded:: 0.2
:param template_name: the name of the template
:param attribute: the name of the variable of macro to acccess
return getattr(current_app.jinja_env.get_template(template_name).module,
def flash(message, category='message'):
"""Flashes a message to the next request. In order to remove the
flashed message from the session and to display it to the user,
the template has to call :func:`get_flashed_messages`.
.. versionchanged: 0.3
`category` parameter added.
:param message: the message to be flashed.
:param category: the category for the message. The following values
are recommended: ``'message'`` for any kind of message,
``'error'`` for errors, ``'info'`` for information
messages and ``'warning'`` for warnings. However any
kind of string can be used as category.
session.setdefault('_flashes', []).append((category, message))
def get_flashed_messages(with_categories=False):
"""Pulls all flashed messages from the session and returns them.
Further calls in the same request to the function will return
the same messages. By default just the messages are returned,
but when `with_categories` is set to `True`, the return value will
be a list of tuples in the form ``(category, message)`` instead.
Example usage:
.. sourcecode:: html+jinja
{% for category, msg in get_flashed_messages(with_categories=true) %}
<p class=flash-{{ category }}>{{ msg }}
{% endfor %}
.. versionchanged:: 0.3
`with_categories` parameter added.
:param with_categories: set to `True` to also receive categories.
flashes =
if flashes is None: = flashes = session.pop('_flashes', [])
if not with_categories:
return [x[1] for x in flashes]
return flashes
def send_file(filename_or_fp, mimetype=None, as_attachment=False,
attachment_filename=None, add_etags=True,
cache_timeout=60 * 60 * 12, conditional=False):
"""Sends the contents of a file to the client. This will use the
most efficient method available and configured. By default it will
try to use the WSGI server's file_wrapper support. Alternatively
you can set the application's :attr:`~Flask.use_x_sendfile` attribute
to ``True`` to directly emit an `X-Sendfile` header. This however
requires support of the underlying webserver for `X-Sendfile`.
By default it will try to guess the mimetype for you, but you can
also explicitly provide one. For extra security you probably want
to send certain files as attachment (HTML for instance). The mimetype
guessing requires a `filename` or an `attachment_filename` to be
Please never pass filenames to this function from user sources without
checking them first. Something like this is usually sufficient to
avoid security problems::
if '..' in filename or filename.startswith('/'):
.. versionadded:: 0.2
.. versionadded:: 0.5
The `add_etags`, `cache_timeout` and `conditional` parameters were
added. The default behaviour is now to attach etags.
.. versionchanged:: 0.7
mimetype guessing and etag support for file objects was
deprecated because it was unreliable. Pass a filename if you are
able to, otherwise attach an etag yourself. This functionality
will be removed in Flask 1.0
:param filename_or_fp: the filename of the file to send. This is
relative to the :attr:`~Flask.root_path` if a
relative path is specified.
Alternatively a file object might be provided
in which case `X-Sendfile` might not work and
fall back to the traditional method. Make sure
that the file pointer is positioned at the start
of data to send before calling :func:`send_file`.
:param mimetype: the mimetype of the file if provided, otherwise
auto detection happens.
:param as_attachment: set to `True` if you want to send this file with
a ``Content-Disposition: attachment`` header.
:param attachment_filename: the filename for the attachment if it
differs from the file's filename.
:param add_etags: set to `False` to disable attaching of etags.
:param conditional: set to `True` to enable conditional responses.
:param cache_timeout: the timeout in seconds for the headers.
mtime = None
if isinstance(filename_or_fp, basestring):
filename = filename_or_fp
file = None
from warnings import warn
file = filename_or_fp
filename = getattr(file, 'name', None)
# XXX: this behaviour is now deprecated because it was unreliable.
# removed in Flask 1.0
if not attachment_filename and not mimetype \
and isinstance(filename, basestring):
warn(DeprecationWarning('The filename support for file objects '
'passed to send_file is not deprecated. Pass an '
'attach_filename if you want mimetypes to be guessed.'),
if add_etags:
warn(DeprecationWarning('In future flask releases etags will no '
'longer be generated for file objects passed to the send_file '
'function because this behaviour was unreliable. Pass '
'filenames instead if possible, otherwise attach an etag '
'yourself based on another value'), stacklevel=2)
if filename is not None:
if not os.path.isabs(filename):
filename = os.path.join(current_app.root_path, filename)
if mimetype is None and (filename or attachment_filename):
mimetype = mimetypes.guess_type(filename or attachment_filename)[0]
if mimetype is None:
mimetype = 'application/octet-stream'
headers = Headers()
if as_attachment:
if attachment_filename is None:
if filename is None:
raise TypeError('filename unavailable, required for '
'sending as attachment')
attachment_filename = os.path.basename(filename)
headers.add('Content-Disposition', 'attachment',
if current_app.use_x_sendfile and filename:
if file is not None:
headers['X-Sendfile'] = filename
data = None
if file is None:
file = open(filename, 'rb')
mtime = os.path.getmtime(filename)
data = wrap_file(request.environ, file)
rv = current_app.response_class(data, mimetype=mimetype, headers=headers,
# if we know the file modification date, we can store it as the
# the time of the last modification.
if mtime is not None:
rv.last_modified = int(mtime)
rv.cache_control.public = True
if cache_timeout:
rv.cache_control.max_age = cache_timeout
rv.expires = int(time() + cache_timeout)
if add_etags and filename is not None:
rv.set_etag('flask-%s-%s-%s' % (
adler32(filename) & 0xffffffff
if conditional:
rv = rv.make_conditional(request)
# make sure we don't send x-sendfile for servers that
# ignore the 304 status code for x-sendfile.
if rv.status_code == 304:
rv.headers.pop('x-sendfile', None)
return rv
def send_from_directory(directory, filename, **options):
"""Send a file from a given directory with :func:`send_file`. This
is a secure way to quickly expose static files from an upload folder
or something similar.
Example usage::
def download_file(filename):
return send_from_directory(app.config['UPLOAD_FOLDER'],
filename, as_attachment=True)
.. admonition:: Sending files and Performance
It is strongly recommended to activate either `X-Sendfile` support in
your webserver or (if no authentication happens) to tell the webserver
to serve files for the given path on its own without calling into the
web application for improved performance.
.. versionadded:: 0.5
:param directory: the directory where all the files are stored.
:param filename: the filename relative to that directory to
:param options: optional keyword arguments that are directly
forwarded to :func:`send_file`.
filename = posixpath.normpath(filename)
for sep in _os_alt_seps:
if sep in filename:
raise NotFound()
if os.path.isabs(filename) or filename.startswith('../'):
raise NotFound()
filename = os.path.join(directory, filename)
if not os.path.isfile(filename):
raise NotFound()
return send_file(filename, conditional=True, **options)
def _get_package_path(name):
"""Returns the path to a package or cwd if that cannot be found."""
return os.path.abspath(os.path.dirname(sys.modules[name].__file__))
except (KeyError, AttributeError):
return os.getcwd()
class _PackageBoundObject(object):
def __init__(self, import_name):
#: The name of the package or module. Do not change this once
#: it was set by the constructor.
self.import_name = import_name
#: Where is the app root located?
self.root_path = _get_package_path(self.import_name)
def has_static_folder(self):
"""This is `True` if the package bound object's container has a
folder named ``'static'``.
.. versionadded:: 0.5
return os.path.isdir(os.path.join(self.root_path, 'static'))
def jinja_loader(self):
"""The Jinja loader for this package bound object.
.. versionadded:: 0.5
return FileSystemLoader(os.path.join(self.root_path, 'templates'))
def send_static_file(self, filename):
"""Function used internally to send static files from the static
folder to the browser.
.. versionadded:: 0.5
return send_from_directory(os.path.join(self.root_path, 'static'),
def open_resource(self, resource):
"""Opens a resource from the application's resource folder. To see
how this works, consider the following folder structure::
If you want to open the `schema.sql` file you would do the
with app.open_resource('schema.sql') as f:
contents =
:param resource: the name of the resource. To access resources within
subfolders use forward slashes as separator.
return open(os.path.join(self.root_path, resource), 'rb')
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