Make session serializer extensible

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.py → 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 +1,253 @@
+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):
+    """Base class for defining type tags for :class:`TaggedJSONSerializer`."""
+
+    __slots__ = ('serializer',)
+    key = None
+    """The tag to mark the serialized object with. If ``None``, this tag is
+    only used as an intermediate step during tagging."""
+
+    def __init__(self, serializer):
+        """Create a tagger for the given serializer."""
+
+        self.serializer = serializer
+
+    def check(self, value):
+        """Check if the given value should be tagged by this tag."""
+
+        raise NotImplementedError
+
+    def to_json(self, value):
+        """Convert the Python object to an object that is a valid JSON type.
+        The tag will be added later."""
+
+        raise NotImplementedError
+
+    def to_python(self, value):
+        """Convert the JSON representation back to the correct type. The tag
+        will already be removed."""
+
+        raise NotImplementedError
+
+    def tag(self, value):
+        """Convert the value to a valid JSON type and add the tag structure
+        around it."""
+
+        return {self.key: self.to_json(value)}
+
+
+class TagDict(JSONTag):
+    """Tag for 1-item dicts whose only key matches a registered tag.
+
+    Internally, the dict key is suffixed with `__`, and the suffix is removed
+    when deserializing.
+    """
+
+    __slots__ = ('serializer',)
+    key = ' di'
+
+    def check(self, value):
+        return (
+            isinstance(value, dict)
+            and len(value) == 1
+            and next(iter(value)) in self.serializer.tags
+        )
+
+    def to_json(self, value):
+        key = next(iter(value))
+        return {key + '__': self.serializer.tag(value[key])}
+
+    def to_python(self, value):
+        key = next(iter(value))
+        return {key[:-2]: value[key]}
+
+
+class PassDict(JSONTag):
+    __slots__ = ('serializer',)
+
+    def check(self, value):
+        return isinstance(value, dict)
+
+    def to_json(self, value):
+        # JSON objects may only have string keys, so don't bother tagging the
+        # key here.
+        return dict((k, self.serializer.tag(v)) for k, v in iteritems(value))
+
+    tag = to_json
+
+
+class TagTuple(JSONTag):
+    __slots__ = ('serializer',)
+    key = ' t'
+
+    def check(self, value):
+        return isinstance(value, tuple)
+
+    def to_json(self, value):
+        return [self.serializer.tag(item) for item in value]
+
+    def to_python(self, value):
+        return tuple(value)
+
+
+class PassList(JSONTag):
+    __slots__ = ('serializer',)
+
+    def check(self, value):
+        return isinstance(value, list)
+
+    def to_json(self, value):
+        return [self.serializer.tag(item) for item in value]
+
+    tag = to_json
+
+
+class TagBytes(JSONTag):
+    __slots__ = ('serializer',)
+    key = ' b'
+
+    def check(self, value):
+        return isinstance(value, bytes)
+
+    def to_json(self, value):
+        return b64encode(value).decode('ascii')
+
+    def to_python(self, value):
+        return b64decode(value)
+
+
+class TagMarkup(JSONTag):
+    """Serialize anything matching the :class:`~markupsafe.Markup` API by
+    having a ``__html__`` method to the result of that method. Always
+    deserializes to an instance of :class:`~markupsafe.Markup`."""
+
+    __slots__ = ('serializer',)
+    key = ' m'
+
+    def check(self, value):
+        return callable(getattr(value, '__html__', None))
+
+    def to_json(self, value):
+        return text_type(value.__html__())
+
+    def to_python(self, value):
+        return Markup(value)
+
+
+class TagUUID(JSONTag):
+    __slots__ = ('serializer',)
+    key = ' u'
+
+    def check(self, value):
+        return isinstance(value, UUID)
+
+    def to_json(self, value):
+        return value.hex
+
+    def to_python(self, value):
+        return UUID(value)
+
+
+class TagDateTime(JSONTag):
+    __slots__ = ('serializer',)
+    key = ' d'
+
+    def check(self, value):
+        return isinstance(value, datetime)
+
+    def to_json(self, value):
+        return http_date(value)
+
+    def to_python(self, value):
+        return parse_date(value)
+
+
+class TaggedJSONSerializer(object):
+    """Serializer that uses a tag system to compactly represent objects that
+    are not JSON types. Passed as the intermediate serializer to
+    :class:`itsdangerous.Serializer`."""
+
+    __slots__ = ('tags', 'order')
+    default_tags = [
+        TagDict, PassDict, TagTuple, PassList, TagBytes, TagMarkup, TagUUID,
+        TagDateTime,
+    ]
+    """Tag classes to bind when creating the serializer. Other tags can be
+    added later using :meth:`~register`."""
+
+    def __init__(self):
+        self.tags = {}
+        self.order = []
+
+        for cls in self.default_tags:
+            self.register(cls)
+
+    def register(self, tag_class, force=False, index=-1):
+        """Register a new tag with this serializer.
+
+        :param tag_class: tag class to register. Will be instantiated with this
+            serializer instance.
+        :param force: overwrite an existing tag. If false (default), a
+            :exc:`KeyError` is raised.
+        :param index: index to insert the new tag in the tag order. Useful when
+            the new tag is a special case of an existing tag. If -1 (default),
+            the tag is appended to the end of the order.
+
+        :raise KeyError: if the tag key is already registered and ``force`` is
+            not true.
+        """
+
+        tag = tag_class(self)
+        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):
+        """Convert a value to a tagged representation if necessary."""
+
+        for tag in self.order:
+            if tag.check(value):
+                return tag.tag(value)
+
+        return value
+
+    def untag(self, value):
+        """Convert a tagged representation back to the original type."""
+
+        if len(value) != 1:
+            return value
+
+        key = next(iter(value))
+
+        if key not in self.tags:
+            return value
+
+        return self.tags[key].to_python(value[key])
+
+    def dumps(self, value):
+        """Tag the value and dump it to a compact JSON string."""
+
+        return dumps(self.tag(value), separators=(',', ':'))
+
+    def loads(self, value):
+        """Load data from a JSON string and deserialized any tagged objects."""
+        return loads(value, object_hook=self.untag)