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import json
from django.conf import settings
from django.contrib.messages.storage.base import BaseStorage, Message
from django.http import SimpleCookie
from django.utils.crypto import constant_time_compare, salted_hmac
from django.utils.safestring import SafeData, mark_safe
class MessageEncoder(json.JSONEncoder):
"""
Compactly serialize instances of the ``Message`` class as JSON.
"""
message_key = '__json_message'
def default(self, obj):
if isinstance(obj, Message):
# Using 0/1 here instead of False/True to produce more compact json
is_safedata = 1 if isinstance(obj.message, SafeData) else 0
message = [self.message_key, is_safedata, obj.level, obj.message]
if obj.extra_tags:
message.append(obj.extra_tags)
return message
return super().default(obj)
class MessageDecoder(json.JSONDecoder):
"""
Decode JSON that includes serialized ``Message`` instances.
"""
def process_messages(self, obj):
if isinstance(obj, list) and obj:
if obj[0] == MessageEncoder.message_key:
if len(obj) == 3:
# Compatibility with previously-encoded messages
return Message(*obj[1:])
if obj[1]:
obj[3] = mark_safe(obj[3])
return Message(*obj[2:])
return [self.process_messages(item) for item in obj]
if isinstance(obj, dict):
return {key: self.process_messages(value)
for key, value in obj.items()}
return obj
def decode(self, s, **kwargs):
decoded = super().decode(s, **kwargs)
return self.process_messages(decoded)
class CookieStorage(BaseStorage):
"""
Store messages in a cookie.
"""
cookie_name = 'messages'
# uwsgi's default configuration enforces a maximum size of 4kb for all the
# HTTP headers. In order to leave some room for other cookies and headers,
# restrict the session cookie to 1/2 of 4kb. See #18781.
max_cookie_size = 2048
not_finished = '__messagesnotfinished__'
def _get(self, *args, **kwargs):
"""
Retrieve a list of messages from the messages cookie. If the
not_finished sentinel value is found at the end of the message list,
remove it and return a result indicating that not all messages were
retrieved by this storage.
"""
data = self.request.COOKIES.get(self.cookie_name)
messages = self._decode(data)
all_retrieved = not (messages and messages[-1] == self.not_finished)
if messages and not all_retrieved:
# remove the sentinel value
messages.pop()
return messages, all_retrieved
def _update_cookie(self, encoded_data, response):
"""
Either set the cookie with the encoded data if there is any data to
store, or delete the cookie.
"""
if encoded_data:
response.set_cookie(
self.cookie_name, encoded_data,
domain=settings.SESSION_COOKIE_DOMAIN,
secure=settings.SESSION_COOKIE_SECURE or None,
httponly=settings.SESSION_COOKIE_HTTPONLY or None,
samesite=settings.SESSION_COOKIE_SAMESITE,
)
else:
response.delete_cookie(self.cookie_name, domain=settings.SESSION_COOKIE_DOMAIN)
def _store(self, messages, response, remove_oldest=True, *args, **kwargs):
"""
Store the messages to a cookie and return a list of any messages which
could not be stored.
If the encoded data is larger than ``max_cookie_size``, remove
messages until the data fits (these are the messages which are
returned), and add the not_finished sentinel value to indicate as much.
"""
unstored_messages = []
encoded_data = self._encode(messages)
if self.max_cookie_size:
# data is going to be stored eventually by SimpleCookie, which
# adds its own overhead, which we must account for.
cookie = SimpleCookie() # create outside the loop
def stored_length(val):
return len(cookie.value_encode(val)[1])
while encoded_data and stored_length(encoded_data) > self.max_cookie_size:
if remove_oldest:
unstored_messages.append(messages.pop(0))
else:
unstored_messages.insert(0, messages.pop())
encoded_data = self._encode(messages + [self.not_finished],
encode_empty=unstored_messages)
self._update_cookie(encoded_data, response)
return unstored_messages
def _hash(self, value):
"""
Create an HMAC/SHA1 hash based on the value and the project setting's
SECRET_KEY, modified to make it unique for the present purpose.
"""
key_salt = 'django.contrib.messages'
return salted_hmac(key_salt, value).hexdigest()
def _encode(self, messages, encode_empty=False):
"""
Return an encoded version of the messages list which can be stored as
plain text.
Since the data will be retrieved from the client-side, the encoded data
also contains a hash to ensure that the data was not tampered with.
"""
if messages or encode_empty:
encoder = MessageEncoder(separators=(',', ':'))
value = encoder.encode(messages)
return '%s$%s' % (self._hash(value), value)
def _decode(self, data):
"""
Safely decode an encoded text stream back into a list of messages.
If the encoded text stream contained an invalid hash or was in an
invalid format, return None.
"""
if not data:
return None
bits = data.split('$', 1)
if len(bits) == 2:
hash, value = bits
if constant_time_compare(hash, self._hash(value)):
try:
# If we get here (and the JSON decode works), everything is
# good. In any other case, drop back and return None.
return json.loads(value, cls=MessageDecoder)
except json.JSONDecodeError:
pass
# Mark the data as used (so it gets removed) since something was wrong
# with the data.
self.used = True
return None