streaming-json-encoder

.gitignore

*.pyc

/bin
/include
/lib

README.rst

streaming-json-encoder

This is a JSON encoder based on the pure-Python one in Django's django.utils.simplejson. The big new feature is the ability to encode Python generators as JSON lists. When using streamingjson.JSONEncoder.iterencode(), the output is streamed while the generator is being read.

See the tests.py file for example usage.

To return streaming JSON from a Django view, do something similar to this:

from streamingjson import JSONEncoder()

def streaming_json_view(request):
    data = {'items': (x for x in xrange(1000000))}
    return HttpResponse(JSONEncoder().iterencode(data),
                        content_type='application/json')

Make sure that no middleware slurps all the data and prevents streaming to the client. See Django's ticket #7581 and Stack Overflow question How to stream an HttpResponse with Django for more information.

This code is licensed under Django's original 3-clause BSD license.

LICENSE

Copyright (c) Django Software Foundation and individual contributors.
All rights reserved.

Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice, 
       this list of conditions and the following disclaimer.
    
    2. Redistributions in binary form must reproduce the above copyright 
       notice, this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.

    3. Neither the name of Django nor the names of its contributors may be used
       to endorse or promote products derived from this software without
       specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

streamingjson.py

from django.utils import simplejson
from django.utils.simplejson.encoder import (
    encode_basestring, encode_basestring_ascii, FLOAT_REPR, INFINITY)
from types import GeneratorType


class JSONEncoder(simplejson.JSONEncoder):
    def iterencode(self, o, _one_shot=False):
        """Encode the given object and yield each string
        representation as available.

        For example::

            for chunk in JSONEncoder().iterencode(bigobject):
                mysocket.write(chunk)

        This method is a verbatim copy of
        :meth:`django.utils.simplejson.encoder.JSONEncoder.iterencode`.  It is
        needed because we need to call our patched
        :func:`streamingjson._make_iterencode`.
        """
        if self.check_circular:
            markers = {}
        else:
            markers = None
        if self.ensure_ascii:
            _encoder = encode_basestring_ascii
        else:
            _encoder = encode_basestring
        if self.encoding != 'utf-8':
            def _encoder(o, _orig_encoder=_encoder, _encoding=self.encoding):
                if isinstance(o, str):
                    o = o.decode(_encoding)
                return _orig_encoder(o)

        def floatstr(o, allow_nan=self.allow_nan, _repr=FLOAT_REPR, _inf=INFINITY, _neginf=-INFINITY):
            # Check for specials.  Note that this type of test is processor- and/or
            # platform-specific, so do tests which don't depend on the internals.

            if o != o:
                text = 'NaN'
            elif o == _inf:
                text = 'Infinity'
            elif o == _neginf:
                text = '-Infinity'
            else:
                return _repr(o)

            if not allow_nan:
                raise ValueError("Out of range float values are not JSON compliant: %r"
                    % (o,))

            return text

        _iterencode = _make_iterencode(
            markers, self.default, _encoder, self.indent, floatstr,
            self.key_separator, self.item_separator, self.sort_keys,
            self.skipkeys, _one_shot)
        return _iterencode(o, 0)


def _make_iterencode(markers, _default, _encoder, _indent, _floatstr, _key_separator, _item_separator, _sort_keys, _skipkeys, _one_shot,
        ## HACK: hand-optimized bytecode; turn globals into locals
        False=False,
        True=True,
        ValueError=ValueError,
        basestring=basestring,
        dict=dict,
        float=float,
        GeneratorType=GeneratorType,
        id=id,
        int=int,
        isinstance=isinstance,
        list=list,
        long=long,
        str=str,
        tuple=tuple,
    ):
    """
    This is a patched version of
    :func:`django.utils.simplejson.encoder.iterencode`.  Whenever it encounters
    a generator in the data structure, it encodes it as a JSON list.
    """
    def _iterencode_list(lst, _current_indent_level):
        if not lst:
            # note: empty generators aren't caught here, see below
            yield '[]'
            return
        if markers is not None:
            markerid = id(lst)
            if markerid in markers:
                raise ValueError("Circular reference detected")
            markers[markerid] = lst
        buf = '['
        if _indent is not None:
            _current_indent_level += 1
            newline_indent = '\n' + (' ' * (_indent * _current_indent_level))
            separator = _item_separator + newline_indent
            buf += newline_indent
        else:
            newline_indent = None
            separator = _item_separator
        first = True
        for value in lst:
            if first:
                first = False
            else:
                buf = separator
            if isinstance(value, basestring):
                yield buf + _encoder(value)
            elif value is None:
                yield buf + 'null'
            elif value is True:
                yield buf + 'true'
            elif value is False:
                yield buf + 'false'
            elif isinstance(value, (int, long)):
                yield buf + str(value)
            elif isinstance(value, float):
                yield buf + _floatstr(value)
            else:
                yield buf
                if isinstance(value, (list, tuple, GeneratorType)):
                    chunks = _iterencode_list(value, _current_indent_level)
                elif isinstance(value, dict):
                    chunks = _iterencode_dict(value, _current_indent_level)
                else:
                    chunks = _iterencode(value, _current_indent_level)
                for chunk in chunks:
                    yield chunk
        if first:
            # we had an empty generator
            yield buf
        if newline_indent is not None:
            _current_indent_level -= 1
            yield '\n' + (' ' * (_indent * _current_indent_level))
        yield ']'
        if markers is not None:
            del markers[markerid]

    def _iterencode_dict(dct, _current_indent_level):
        if not dct:
            yield '{}'
            return
        if markers is not None:
            markerid = id(dct)
            if markerid in markers:
                raise ValueError("Circular reference detected")
            markers[markerid] = dct
        yield '{'
        if _indent is not None:
            _current_indent_level += 1
            newline_indent = '\n' + (' ' * (_indent * _current_indent_level))
            item_separator = _item_separator + newline_indent
            yield newline_indent
        else:
            newline_indent = None
            item_separator = _item_separator
        first = True
        if _sort_keys:
            items = dct.items()
            items.sort(key=lambda kv: kv[0])
        else:
            items = dct.iteritems()
        for key, value in items:
            if isinstance(key, basestring):
                pass
            # JavaScript is weakly typed for these, so it makes sense to
            # also allow them.  Many encoders seem to do something like this.
            elif isinstance(key, float):
                key = _floatstr(key)
            elif isinstance(key, (int, long)):
                key = str(key)
            elif key is True:
                key = 'true'
            elif key is False:
                key = 'false'
            elif key is None:
                key = 'null'
            elif _skipkeys:
                continue
            else:
                raise TypeError("key %r is not a string" % (key,))
            if first:
                first = False
            else:
                yield item_separator
            yield _encoder(key)
            yield _key_separator
            if isinstance(value, basestring):
                yield _encoder(value)
            elif value is None:
                yield 'null'
            elif value is True:
                yield 'true'
            elif value is False:
                yield 'false'
            elif isinstance(value, (int, long)):
                yield str(value)
            elif isinstance(value, float):
                yield _floatstr(value)
            else:
                if isinstance(value, (list, tuple, GeneratorType)):
                    chunks = _iterencode_list(value, _current_indent_level)
                elif isinstance(value, dict):
                    chunks = _iterencode_dict(value, _current_indent_level)
                else:
                    chunks = _iterencode(value, _current_indent_level)
                for chunk in chunks:
                    yield chunk
        if newline_indent is not None:
            _current_indent_level -= 1
            yield '\n' + (' ' * (_indent * _current_indent_level))
        yield '}'
        if markers is not None:
            del markers[markerid]

    def _iterencode(o, _current_indent_level):
        if isinstance(o, basestring):
            yield _encoder(o)
        elif o is None:
            yield 'null'
        elif o is True:
            yield 'true'
        elif o is False:
            yield 'false'
        elif isinstance(o, (int, long)):
            yield str(o)
        elif isinstance(o, float):
            yield _floatstr(o)
        elif isinstance(o, (list, tuple, GeneratorType)):
            for chunk in _iterencode_list(o, _current_indent_level):
                yield chunk
        elif isinstance(o, dict):
            for chunk in _iterencode_dict(o, _current_indent_level):
                yield chunk
        else:
            if markers is not None:
                markerid = id(o)
                if markerid in markers:
                    raise ValueError("Circular reference detected")
                markers[markerid] = o
            o = _default(o)
            for chunk in _iterencode(o, _current_indent_level):
                yield chunk
            if markers is not None:
                del markers[markerid]

    return _iterencode

tests.py

from streamingjson import JSONEncoder
from django.utils.simplejson import loads


def encode_and_decode(data):
    jsonstr = ''.join(JSONEncoder().iterencode(data))
    decoded = loads(jsonstr)


def test_empty_generator():
    data = {'items': (x for x in ())}
    encode_and_decode(data)


def test_nested_generators():
    SIZE = 500
    data = {
        'batches': (
            {'title': 'batch #%d' % y,
             'items': (SIZE * y + x
                       for x in xrange(SIZE))
            }
            for y in xrange(SIZE))
    }
    encode_and_decode(data)