flask/flask/json.py

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

    Implementation helpers for the JSON support in Flask.

    :copyright: (c) 2012 by Armin Ronacher.
    :license: BSD, see LICENSE for more details.
"""
import uuid
from datetime import datetime
from .globals import current_app, request

from werkzeug.http import http_date

# Use the same json implementation as itsdangerous on which we
# depend anyways.
from itsdangerous import simplejson as _json
import six


# figure out if simplejson escapes slashes.  This behavior was changed
# from one version to another without reason.
_slash_escape = '\\/' not in _json.dumps('/')


__all__ = ['dump', 'dumps', 'load', 'loads', 'htmlsafe_dump',
           'htmlsafe_dumps', 'JSONDecoder', 'JSONEncoder',
           'jsonify']


class JSONEncoder(_json.JSONEncoder):
    """The default Flask JSON encoder.  This one extends the default simplejson
    encoder by also supporting ``datetime`` objects, ``UUID`` as well as
    ``Markup`` objects which are serialized as RFC 822 datetime strings (same
    as the HTTP date format).  In order to support more data types override the
    :meth:`default` method.
    """

    def default(self, o):
        """Implement this method in a subclass such that it returns a
        serializable object for ``o``, or calls the base implementation (to
        raise a ``TypeError``).

        For example, to support arbitrary iterators, you could implement
        default like this::

            def default(self, o):
                try:
                    iterable = iter(o)
                except TypeError:
                    pass
                else:
                    return list(iterable)
                return JSONEncoder.default(self, o)
        """
        if isinstance(o, datetime):
            return http_date(o)
        if isinstance(o, uuid.UUID):
            return str(o)
        if hasattr(o, '__html__'):
            return six.text_type(o.__html__())
        return _json.JSONEncoder.default(self, o)


class JSONDecoder(_json.JSONDecoder):
    """The default JSON decoder.  This one does not change the behavior from
    the default simplejson encoder.  Consult the :mod:`json` documentation
    for more information.  This decoder is not only used for the load
    functions of this module but also :attr:`~flask.Request`.
    """


def _dump_arg_defaults(kwargs):
    """Inject default arguments for dump functions."""
    if current_app:
        kwargs.setdefault('cls', current_app.json_encoder)
        if not current_app.config['JSON_AS_ASCII']:
            kwargs.setdefault('ensure_ascii', False)


def _load_arg_defaults(kwargs):
    """Inject default arguments for load functions."""
    if current_app:
        kwargs.setdefault('cls', current_app.json_decoder)


def dumps(obj, **kwargs):
    """Serialize ``obj`` to a JSON formatted ``str`` by using the application's
    configured encoder (:attr:`~flask.Flask.json_encoder`) if there is an
    application on the stack.

    This function can return ``unicode`` strings or ascii-only bytestrings by
    default which coerce into unicode strings automatically.  That behavior by
    default is controlled by the ``JSON_AS_ASCII`` configuration variable
    and can be overriden by the simplejson ``ensure_ascii`` parameter.
    """
    _dump_arg_defaults(kwargs)
    return _json.dumps(obj, **kwargs)


def dump(obj, fp, **kwargs):
    """Like :func:`dumps` but writes into a file object."""
    _dump_arg_defaults(kwargs)
    return _json.dump(obj, fp, **kwargs)


def loads(s, **kwargs):
    """Unserialize a JSON object from a string ``s`` by using the application's
    configured decoder (:attr:`~flask.Flask.json_decoder`) if there is an
    application on the stack.
    """
    _load_arg_defaults(kwargs)
    return _json.loads(s, **kwargs)


def load(fp, **kwargs):
    """Like :func:`loads` but reads from a file object.
    """
    _load_arg_defaults(kwargs)
    return _json.load(fp, **kwargs)


def htmlsafe_dumps(obj, **kwargs):
    """Works exactly like :func:`dumps` but is safe for use in ``<script>``
    tags.  It accepts the same arguments and returns a JSON string.  Note that
    this is available in templates through the ``|tojson`` filter but it will
    have to be wrapped in ``|safe`` unless **true** XHTML is being used.
    """
    rv = dumps(obj, **kwargs)
    if _slash_escape:
        rv = rv.replace('/', '\\/')
    return rv.replace('<!', '<\\u0021')


def htmlsafe_dump(obj, fp, **kwargs):
    """Like :func:`htmlsafe_dumps` but writes into a file object."""
    fp.write(htmlsafe_dumps(obj, **kwargs))


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::
    
        from flask import jsonify

        @app.route('/_get_current_user')
        def get_current_user():
            return jsonify(username=g.user.username,
                           email=g.user.email,
                           id=g.user.id)

    This will send a JSON response like this to the browser::

        {
            "username": "admin",
            "email": "admin@localhost",
            "id": 42
        }

    For security reasons only objects are supported toplevel.  For more
    information about this, have a look at :ref:`json-security`.

    .. versionadded:: 0.2
    """
    return current_app.response_class(dumps(dict(*args, **kwargs),
        indent=None if request.is_xhr else 2),
        mimetype='application/json')