django-rest-framework/djangorestframework/parsers.py

"""
Django supports parsing the content of an HTTP request, but only for form POST requests.
That behavior is sufficient for dealing with standard HTML forms, but it doesn't map well
to general HTTP requests.

We need a method to be able to:

1) Determine the parsed content on a request for methods other than POST (eg typically also PUT)
2) Determine the parsed content on a request for media types other than application/x-www-form-urlencoded
   and multipart/form-data.  (eg also handle multipart/json)
"""

from django.http.multipartparser import MultiPartParser as DjangoMultiPartParser
from django.utils import simplejson as json
from djangorestframework import status
from djangorestframework.compat import parse_qs
from djangorestframework.response import ErrorResponse
from djangorestframework.utils import as_tuple
from djangorestframework.utils.mediatypes import media_type_matches

__all__ = (
    'BaseParser',
    'JSONParser',
    'PlainTextParser',
    'FormParser',
    'MultiPartParser'
)


class BaseParser(object):
    """
    All parsers should extend BaseParser, specifying a media_type attribute,
    and overriding the parse() method.
    """
    media_type = None

    def __init__(self, view):
        """
        Initialize the parser with the ``View`` instance as state,
        in case the parser needs to access any metadata on the ``View`` object.
        """
        self.view = view
    
    def can_handle_request(self, content_type):
        """
        Returns `True` if this parser is able to deal with the given media type.
        
        The default implementation for this function is to check the ``media_type``
        argument against the ``media_type`` attribute set on the class to see if
        they match.
        
        This may be overridden to provide for other behavior, but typically you'll
        instead want to just set the ``media_type`` attribute on the class.
        """
        return media_type_matches(content_type, self.media_type)

    def parse(self, stream):
        """
        Given a stream to read from, return the deserialized output.
        Should return a 2-tuple of (data, files).
        """
        raise NotImplementedError("BaseParser.parse() Must be overridden to be implemented.")


class JSONParser(BaseParser):
    media_type = 'application/json'

    def parse(self, stream):
        try:
            return (json.load(stream), None)
        except ValueError, exc:
            raise ErrorResponse(status.HTTP_400_BAD_REQUEST,
                                {'detail': 'JSON parse error - %s' % unicode(exc)})


class DataFlatener(object):
    """Utility object for flattening dictionaries of lists. Useful for "urlencoded" decoded data."""

    def flatten_data(self, data):
        """Given a data dictionary {<key>: <value_list>}, returns a flattened dictionary
        with information provided by the method "is_a_list"."""
        flatdata = dict()
        for key, val_list in data.items():
            if self.is_a_list(key, val_list):
                flatdata[key] = val_list
            else:
                if val_list:
                    flatdata[key] = val_list[0]
                else:
                    # If the list is empty, but the parameter is not a list,
                    # we strip this parameter.
                    data.pop(key)
        return flatdata

    def is_a_list(self, key, val_list):
        """Returns True if the parameter with name *key* is expected to be a list, or False otherwise.
        *val_list* which is the received value for parameter *key* can be used to guess the answer."""
        return False


class PlainTextParser(BaseParser):
    """
    Plain text parser.
    
    Simply returns the content of the stream.
    """
    media_type = 'text/plain'

    def parse(self, stream):
        return (stream.read(), None)


class FormParser(BaseParser, DataFlatener):
    """
    The default parser for form data.
    Return a dict containing a single value for each non-reserved parameter.

    In order to handle select multiple (and having possibly more than a single value for each parameter),
    you can customize the output by subclassing the method 'is_a_list'."""

    media_type = 'application/x-www-form-urlencoded'

    """The value of the parameter when the select multiple is empty.
    Browsers are usually stripping the select multiple that have no option selected from the parameters sent.
    A common hack to avoid this is to send the parameter with a value specifying that the list is empty.
    This value will always be stripped before the data is returned.
    """
    EMPTY_VALUE = '_empty'
    RESERVED_FORM_PARAMS = ('csrfmiddlewaretoken',)

    def parse(self, stream):
        data = parse_qs(stream.read(), keep_blank_values=True)

        # removing EMPTY_VALUEs from the lists and flatening the data 
        for key, val_list in data.items():
            self.remove_empty_val(val_list)
        data = self.flatten_data(data)

        # Strip any parameters that we are treating as reserved
        for key in data.keys():
            if key in self.RESERVED_FORM_PARAMS:
                data.pop(key)

        return (data, None)

    def remove_empty_val(self, val_list):
        """ """
        while(1): # Because there might be several times EMPTY_VALUE in the list
            try: 
                ind = val_list.index(self.EMPTY_VALUE)
            except ValueError:
                break
            else:
                val_list.pop(ind) 


class MultiPartParser(BaseParser, DataFlatener):
    media_type = 'multipart/form-data'
    RESERVED_FORM_PARAMS = ('csrfmiddlewaretoken',)

    def parse(self, stream):
        upload_handlers = self.view.request._get_upload_handlers()
        django_parser = DjangoMultiPartParser(self.view.request.META, stream, upload_handlers)
        data, files = django_parser.parse()

        # Flatening data, files and combining them
        data = self.flatten_data(dict(data.iterlists()))
        files = self.flatten_data(dict(files.iterlists()))

        # Strip any parameters that we are treating as reserved
        for key in data.keys():
            if key in self.RESERVED_FORM_PARAMS:
                data.pop(key)
        
        return (data, files)