Permalink
Fetching contributors…
Cannot retrieve contributors at this time
362 lines (244 sloc) 10.7 KB

Serialization

Serialization can be one of the most contentious areas of an API. Everyone has their own requirements, their own preferred output format & the desire to have control over what is returned.

As a result, Tastypie ships with a serializer that tries to meet the basic needs of most use cases, and the flexibility to go outside of that when you need to.

Usage

Using this class is simple. It is the default option on all Resource classes unless otherwise specified. The following code is identical to the defaults but demonstrate how you could use your own serializer:

from django.contrib.auth.models import User
from tastypie.resources import ModelResource
from tastypie.serializers import Serializer


class UserResource(ModelResource):
    class Meta:
        queryset = User.objects.all()
        resource_name = 'auth/user'
        excludes = ['email', 'password', 'is_superuser']
        # Add it here.
        serializer = Serializer()

Configuring Allowed Formats

The default Serializer supports the following formats:

Not everyone wants to install or support all the serialization options. If you would like to customize the list of supported formats for your entire site the :ref:`TASTYPIE_DEFAULT_FORMATS setting <settings.TASTYPIE_DEFAULT_FORMATS>` allows you to set the default format list site-wide.

If you wish to change the format list for a specific resource, you can pass the list of supported formats using the formats= kwarg. For example, to provide only JSON & binary plist serialization:

from django.contrib.auth.models import User
from tastypie.resources import ModelResource
from tastypie.serializers import Serializer


class UserResource(ModelResource):
    class Meta:
        queryset = User.objects.all()
        resource_name = 'auth/user'
        excludes = ['email', 'password', 'is_superuser']
        serializer = Serializer(formats=['json', 'plist'])

Enabling the built-in (but disabled by default) JSONP support looks like:

from django.contrib.auth.models import User
from tastypie.resources import ModelResource
from tastypie.serializers import Serializer


class UserResource(ModelResource):
    class Meta:
        queryset = User.objects.all()
        resource_name = 'auth/user'
        excludes = ['email', 'password', 'is_superuser']
        serializer = Serializer(formats=['json', 'jsonp', 'xml', 'yaml', 'plist'])

Serialization Security

Deserialization of input from unknown or untrusted sources is an intrinsically risky endeavor and vulnerabilities are regularly found in popular format libraries. Tastypie adopts and recommends the following approach:

  • Support the minimum required set of formats in your application. If you do not require a format, it's much safer to disable it completely. See :ref:`TASTYPIE_DEFAULT_FORMATS setting <settings.TASTYPIE_DEFAULT_FORMATS>`.

  • Some parsers offer additional safety check for use with untrusted content. The standard Tastypie Serializer attempts to be secure by default using features like PyYAML's safe_load function and the defusedxml security wrapper for popular Python XML libraries.

    Note

    Tastypie's precautions only apply to the default :class:`Serializer`. If you have written your own serializer subclass we strongly recommend that you review your code to ensure that it uses the same precautions.

    If backwards compatibility forces you to load files which require risky features we strongly recommend enabling those features only for the necessary resources and making your authorization checks as strict as possible. The :doc:`authentication` and :doc:`authorization` checks happen before deserialization so, for example, a resource which only allowed POST or PUT requests to be made by administrators is far less exposed than a general API open to the unauthenticated internet.

Implementing Your Own Serializer

There are several different use cases here. We'll cover simple examples of wanting a tweaked format & adding a different format.

To tweak a format, simply override it's to_<format> & from_<format> methods. So adding the server time to all output might look like so:

import time
import json
from django.core.serializers.json import DjangoJSONEncoder
from tastypie.serializers import Serializer

class CustomJSONSerializer(Serializer):
    def to_json(self, data, options=None):
        options = options or {}

        data = self.to_simple(data, options)

        # Add in the current time.
        data['requested_time'] = time.time()

        return json.dumps(data, cls=DjangoJSONEncoder, sort_keys=True)

    def from_json(self, content):
        data = json.loads(content)

        if 'requested_time' in data:
            # Log the request here...
            pass

        return data

In the case of adding a different format, let's say you want to add a CSV output option to the existing set. Your Serializer subclass might look like:

import csv
import StringIO
from tastypie.serializers import Serializer


class CSVSerializer(Serializer):
    formats = Serializer.formats + ['csv']

    content_types = dict(
        Serializer.content_types.items() +
        [('csv', 'text/csv')])

    def to_csv(self, data, options=None):
        options = options or {}
        data = self.to_simple(data, options)
        raw_data = StringIO.StringIO()
        if data['objects']:
            fields = data['objects'][0].keys()
            writer = csv.DictWriter(raw_data, fields,
                                    dialect="excel",
                                    extrasaction='ignore')
            header = dict(zip(fields, fields))
            writer.writerow(header)  # In Python 2.7: `writer.writeheader()`
            for item in data['objects']:
                writer.writerow(item)

        return raw_data.getvalue()

    def from_csv(self, content):
        raw_data = StringIO.StringIO(content)
        data = []
        # Untested, so this might not work exactly right.
        for item in csv.DictReader(raw_data):
            data.append(item)
        return data

Serializer Methods

A swappable class for serialization.

This handles most types of data as well as the following output formats:

* json
* jsonp
* xml
* yaml
* plist

It was designed to make changing behavior easy, either by overridding the various format methods (i.e. to_json), by changing the formats/content_types options or by altering the other hook methods.

get_mime_for_format

.. method:: Serializer.get_mime_for_format(self, format):

Given a format, attempts to determine the correct MIME type.

If not available on the current Serializer, returns application/json by default.

format_datetime

.. method:: Serializer.format_datetime(data):

A hook to control how datetimes are formatted.

Can be overridden at the Serializer level (datetime_formatting) or globally (via settings.TASTYPIE_DATETIME_FORMATTING).

Default is iso-8601, which looks like "2010-12-16T03:02:14".

format_date

.. method:: Serializer.format_date(data):

A hook to control how dates are formatted.

Can be overridden at the Serializer level (datetime_formatting) or globally (via settings.TASTYPIE_DATETIME_FORMATTING).

Default is iso-8601, which looks like "2010-12-16".

format_time

.. method:: Serializer.format_time(data):

A hook to control how times are formatted.

Can be overridden at the Serializer level (datetime_formatting) or globally (via settings.TASTYPIE_DATETIME_FORMATTING).

Default is iso-8601, which looks like "03:02:14".

serialize

.. method:: Serializer.serialize(self, bundle, format='application/json', options={}):

Given some data and a format, calls the correct method to serialize the data and returns the result.

deserialize

.. method:: Serializer.deserialize(self, content, format='application/json'):

Given some data and a format, calls the correct method to deserialize the data and returns the result.

to_simple

.. method:: Serializer.to_simple(self, data, options):

For a piece of data, attempts to recognize it and provide a simplified form of something complex.

This brings complex Python data structures down to native types of the serialization format(s).

to_etree

.. method:: Serializer.to_etree(self, data, options=None, name=None, depth=0):

Given some data, converts that data to an etree.Element suitable for use in the XML output.

from_etree

.. method:: Serializer.from_etree(self, data):

Not the smartest deserializer on the planet. At the request level, it first tries to output the deserialized subelement called "object" or "objects" and falls back to deserializing based on hinted types in the XML element attribute "type".

to_json

.. method:: Serializer.to_json(self, data, options=None):

Given some Python data, produces JSON output.

from_json

.. method:: Serializer.from_json(self, content):

Given some JSON data, returns a Python dictionary of the decoded data.

to_jsonp

.. method:: Serializer.to_jsonp(self, data, options=None):

Given some Python data, produces JSON output wrapped in the provided callback.

to_xml

.. method:: Serializer.to_xml(self, data, options=None):

Given some Python data, produces XML output.

from_xml

.. method:: Serializer.from_xml(self, content):

Given some XML data, returns a Python dictionary of the decoded data.

to_yaml

.. method:: Serializer.to_yaml(self, data, options=None):

Given some Python data, produces YAML output.

from_yaml

.. method:: Serializer.from_yaml(self, content):

Given some YAML data, returns a Python dictionary of the decoded data.

to_plist

.. method:: Serializer.to_plist(self, data, options=None):

Given some Python data, produces binary plist output.

from_plist

.. method:: Serializer.from_plist(self, content):

Given some binary plist data, returns a Python dictionary of the decoded data.