make session serializer extensible

support serializing 1-item dicts with tag as key
refactor serializer into flask.json.tag module
continues #1452, closes #1438, closes #1908

CHANGES

@@ -65,6 +65,8 @@ Major release, unreleased
 - ``TRAP_BAD_REQUEST_ERRORS`` is enabled by default in debug mode.
   ``BadRequestKeyError`` has a message with the bad key in debug mode instead
   of the generic bad request message. (`#2348`_)
+- Allow registering new tags with ``TaggedJSONSerializer`` to support
+  storing other types in the session cookie. (`#2352`_)
 
 .. _#1489: https://github.com/pallets/flask/pull/1489
 .. _#1621: https://github.com/pallets/flask/pull/1621
@@ -84,6 +86,7 @@ Major release, unreleased
 .. _#2319: https://github.com/pallets/flask/pull/2319
 .. _#2326: https://github.com/pallets/flask/pull/2326
 .. _#2348: https://github.com/pallets/flask/pull/2348
+.. _#2352: https://github.com/pallets/flask/pull/2352
 
 Version 0.12.2
 --------------

flask/json/__init__.py

@@ -1,18 +1,9 @@
 # -*- coding: utf-8 -*-
-"""
-    flask.json
-    ~~~~~~~~~~
-
-    Implementation helpers for the JSON support in Flask.
-
-    :copyright: (c) 2015 by Armin Ronacher.
-    :license: BSD, see LICENSE for more details.
-"""
 import io
 import uuid
 from datetime import date
-from .globals import current_app, request
-from ._compat import text_type, PY2
+from flask.globals import current_app, request
+from flask._compat import text_type, PY2
 
 from werkzeug.http import http_date
 from jinja2 import Markup

flask/json/tag.py

@@ -0,0 +1,188 @@
+from base64 import b64decode, b64encode
+from datetime import datetime
+from uuid import UUID
+
+from jinja2 import Markup
+from werkzeug.http import http_date, parse_date
+
+from flask._compat import iteritems, text_type
+from flask.json import dumps, loads
+
+
+class JSONTag(object):
+    __slots__ = ()
+    key = None
+
+    def check(self, serializer, value):
+        raise NotImplementedError
+
+    def to_json(self, serializer, value):
+        raise NotImplementedError
+
+    def to_python(self, serializer, value):
+        raise NotImplementedError
+
+    def tag(self, serializer, value):
+        return {self.key: self.to_json(serializer, value)}
+
+
+class TagDict(JSONTag):
+    __slots__ = ()
+    key = ' di'
+
+    def check(self, serializer, value):
+        return isinstance(value, dict)
+
+    def to_json(self, serializer, value, key=None):
+        if key is not None:
+            return {key + '__': serializer._tag(value[key])}
+
+        return dict((k, serializer._tag(v)) for k, v in iteritems(value))
+
+    def to_python(self, serializer, value):
+        key = next(iter(value))
+        return {key[:-2]: value[key]}
+
+    def tag(self, serializer, value):
+        if len(value) == 1:
+            key = next(iter(value))
+
+            if key in serializer._tags:
+                return {self.key: self.to_json(serializer, value, key=key)}
+
+        return self.to_json(serializer, value)
+
+
+class TagTuple(JSONTag):
+    __slots__ = ()
+    key = ' t'
+
+    def check(self, serializer, value):
+        return isinstance(value, tuple)
+
+    def to_json(self, serializer, value):
+        return [serializer._tag(item) for item in value]
+
+    def to_python(self, serializer, value):
+        return tuple(value)
+
+
+class PassList(JSONTag):
+    __slots__ = ()
+
+    def check(self, serializer, value):
+        return isinstance(value, list)
+
+    def to_json(self, serializer, value):
+        return [serializer._tag(item) for item in value]
+
+    tag = to_json
+
+
+class TagBytes(JSONTag):
+    __slots__ = ()
+    key = ' b'
+
+    def check(self, serializer, value):
+        return isinstance(value, bytes)
+
+    def to_json(self, serializer, value):
+        return b64encode(value).decode('ascii')
+
+    def to_python(self, serializer, value):
+        return b64decode(value)
+
+
+class TagMarkup(JSONTag):
+    __slots__ = ()
+    key = ' m'
+
+    def check(self, serializer, value):
+        return callable(getattr(value, '__html__', None))
+
+    def to_json(self, serializer, value):
+        return text_type(value.__html__())
+
+    def to_python(self, serializer, value):
+        return Markup(value)
+
+
+class TagUUID(JSONTag):
+    __slots__ = ()
+    key = ' u'
+
+    def check(self, serializer, value):
+        return isinstance(value, UUID)
+
+    def to_json(self, serializer, value):
+        return value.hex
+
+    def to_python(self, serializer, value):
+        return UUID(value)
+
+
+class TagDateTime(JSONTag):
+    __slots__ = ()
+    key = ' d'
+
+    def check(self, serializer, value):
+        return isinstance(value, datetime)
+
+    def to_json(self, serializer, value):
+        return http_date(value)
+
+    def to_python(self, serializer, value):
+        return parse_date(value)
+
+
+class TaggedJSONSerializer(object):
+    __slots__ = ('_tags', '_order')
+    _default_tags = [
+        TagDict(), TagTuple(), PassList(), TagBytes(), TagMarkup(), TagUUID(),
+        TagDateTime(),
+    ]
+
+    def __init__(self):
+        self._tags = {}
+        self._order = []
+
+        for tag in self._default_tags:
+            self.register(tag)
+
+    def register(self, tag, force=False, index=-1):
+        key = tag.key
+
+        if key is not None:
+            if not force and key in self._tags:
+                raise KeyError("Tag '{0}' is already registered.".format(key))
+
+            self._tags[key] = tag
+
+        if index == -1:
+            self._order.append(tag)
+        else:
+            self._order.insert(index, tag)
+
+    def _tag(self, value):
+        for tag in self._order:
+            if tag.check(self, value):
+                return tag.tag(self, value)
+
+        return value
+
+    def _untag(self, value):
+        if len(value) != 1:
+            return value
+
+        key = next(iter(value))
+
+        if key not in self._tags:
+            return value
+
+        return self._tags[key].to_python(self, value[key])
+
+    def dumps(self, value):
+        return dumps(self._tag(value), separators=(',', ':'))
+
+    def loads(self, value):
+        return loads(value, object_hook=self._untag)

flask/sessions.py

@@ -9,18 +9,14 @@
     :license: BSD, see LICENSE for more details.
 """
 import hashlib
-import uuid
 import warnings
-from base64 import b64decode, b64encode
 from datetime import datetime
 
 from itsdangerous import BadSignature, URLSafeTimedSerializer
 from werkzeug.datastructures import CallbackDict
-from werkzeug.http import http_date, parse_date
 
-from . import Markup, json
-from ._compat import iteritems, text_type
-from .helpers import is_ip, total_seconds
+from flask.helpers import is_ip, total_seconds
+from flask.json.tag import TaggedJSONSerializer
 
 
 class SessionMixin(object):
@@ -57,126 +53,6 @@ class SessionMixin(object):
     #: from being served the same cache.
     accessed = True
 
-class TaggedJSONSerializer(object):
-    """A customized JSON serializer that supports a few extra types that
-    we take for granted when serializing (tuples, markup objects, datetime).
-    """
-
-    def __init__(self):
-        self.conversions = [
-            {
-                'check': lambda value: self._is_dict_with_used_key(value),
-                'tag': lambda value: self._tag_dict_used_with_key(value),
-                'untag': lambda value: self._untag_dict_used_with_key(value),
-                'key': ' di',
-            },
-            {
-                'check': lambda value: isinstance(value, tuple),
-                'tag': lambda value: [self._tag(x) for x in value],
-                'untag': lambda value: tuple(value),
-                'key': ' t',
-            },
-            {
-                'check': lambda value: isinstance(value, uuid.UUID),
-                'tag': lambda value: value.hex,
-                'untag': lambda value: uuid.UUID(value),
-                'key': ' u',
-            },
-            {
-                'check': lambda value: isinstance(value, bytes),
-                'tag': lambda value: b64encode(value).decode('ascii'),
-                'untag': lambda value: b64decode(value),
-                'key': ' b',
-            },
-            {
-                'check': lambda value: callable(getattr(value, '__html__',
-                                                        None)),
-                'tag': lambda value: text_type(value.__html__()),
-                'untag': lambda value: Markup(value),
-                'key': ' m',
-            },
-            {
-                'check': lambda value: isinstance(value, list),
-                'tag': lambda value: [self._tag(x) for x in value],
-            },
-            {
-                'check': lambda value: isinstance(value, datetime),
-                'tag': lambda value: http_date(value),
-                'untag': lambda value: parse_date(value),
-                'key': ' d',
-            },
-            {
-                'check': lambda value: isinstance(value, dict),
-                'tag': lambda value: dict((k, self._tag(v)) for k, v in
-                                          iteritems(value)),
-            },
-            {
-                'check': lambda value: isinstance(value, str),
-                'tag': lambda value: self._tag_string(value),
-            }
-        ]
-
-    @property
-    def keys(self):
-        return [c['key'] for c in self.conversions if c.get('key')]
-
-    def _get_conversion_untag(self, key):
-        return next(
-            (c['untag'] for c in self.conversions if c.get('key') == key),
-            lambda v: None
-        )
-
-    def _is_dict_with_used_key(self, v):
-        return isinstance(v, dict) and len(v) == 1 and list(v)[0] in self.keys
-
-    def _was_dict_with_used_key(self, k):
-        return k.endswith('__') and k[:-2] in self.keys
-
-    def _tag_string(self, value):
-        try:
-            return text_type(value)
-        except UnicodeError:
-            from flask.debughelpers import UnexpectedUnicodeError
-            raise UnexpectedUnicodeError(u'A byte string with '
-                u'non-ASCII data was passed to the session system '
-                u'which can only store unicode strings.  Consider '
-                u'base64 encoding your string (String was %r)' % value)
-
-    def _tag_dict_used_with_key(self, value):
-        k, v = next(iteritems(value))
-        return {'%s__' % k: v}
-
-    def _tag(self, value):
-        for tag_ops in self.conversions:
-            if tag_ops['check'](value):
-                tag = tag_ops.get('key')
-                if tag:
-                    return {tag: tag_ops['tag'](value)}
-                return tag_ops['tag'](value)
-        return value
-
-    def _untag_dict_used_with_key(self, the_value):
-        k, v = next(iteritems(the_value))
-        if self._was_dict_with_used_key(k):
-            return {k[:-2]: self._untag(v)}
-
-    def _untag(self, obj):
-        if len(obj) != 1:
-            return obj
-        the_key, the_value = next(iteritems(obj))
-        untag = self._get_conversion_untag(the_key)
-        new_value = untag(the_value)
-        return new_value if new_value else obj
-
-    def dumps(self, value):
-        return json.dumps(self._tag(value), separators=(',', ':'))
-
-    def loads(self, value):
-        return json.loads(value, object_hook=self._untag)
-
-
-session_json_serializer = TaggedJSONSerializer()
-
 
 class SecureCookieSession(CallbackDict, SessionMixin):
     """Base class for sessions based on signed cookies."""
@@ -284,10 +160,10 @@ class SessionInterface(object):
 
     def get_cookie_domain(self, app):
         """Returns the domain that should be set for the session cookie.
-        
+
         Uses ``SESSION_COOKIE_DOMAIN`` if it is configured, otherwise
         falls back to detecting the domain based on ``SERVER_NAME``.
-        
+
         Once detected (or if not set at all), ``SESSION_COOKIE_DOMAIN`` is
         updated to avoid re-running the logic.
         """
@@ -377,7 +253,7 @@ class SessionInterface(object):
         has been modified, the cookie is set. If the session is permanent and
         the ``SESSION_REFRESH_EACH_REQUEST`` config is true, the cookie is
         always set.
-        
+
         This check is usually skipped if the session was deleted.
 
         .. versionadded:: 0.11
@@ -404,6 +280,9 @@ class SessionInterface(object):
         raise NotImplementedError()
 
 
+session_json_serializer = TaggedJSONSerializer()
+
+
 class SecureCookieSessionInterface(SessionInterface):
     """The default session interface that stores sessions in signed cookies
     through the :mod:`itsdangerous` module.