jsonutil.py

"""Utilities to manipulate JSON objects."""

# Copyright (c) IPython Development Team.
# Distributed under the terms of the Modified BSD License.

import math
import re
import types
from datetime import datetime

try:
    # base64.encodestring is deprecated in Python 3.x
    from base64 import encodebytes
except ImportError:
    # Python 2.x
    from base64 import encodestring as encodebytes

from IPython.utils import py3compat
from IPython.utils.py3compat import string_types, unicode_type, iteritems
from IPython.utils.encoding import DEFAULT_ENCODING
next_attr_name = '__next__' if py3compat.PY3 else 'next'

#-----------------------------------------------------------------------------
# Globals and constants
#-----------------------------------------------------------------------------

# timestamp formats
ISO8601 = "%Y-%m-%dT%H:%M:%S.%f"
ISO8601_PAT=re.compile(r"^(\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2})(\.\d{1,6})?Z?([\+\-]\d{2}:?\d{2})?$")

# holy crap, strptime is not threadsafe.
# Calling it once at import seems to help.
datetime.strptime("1", "%d")

#-----------------------------------------------------------------------------
# Classes and functions
#-----------------------------------------------------------------------------

def rekey(dikt):
    """Rekey a dict that has been forced to use str keys where there should be
    ints by json."""
    for k in list(dikt):
        if isinstance(k, string_types):
            nk = None
            try:
                nk = int(k)
            except ValueError:
                try:
                    nk = float(k)
                except ValueError:
                    continue
            if nk in dikt:
                raise KeyError("already have key %r" % nk)
            dikt[nk] = dikt.pop(k)
    return dikt

def parse_date(s):
    """parse an ISO8601 date string
    
    If it is None or not a valid ISO8601 timestamp,
    it will be returned unmodified.
    Otherwise, it will return a datetime object.
    """
    if s is None:
        return s
    m = ISO8601_PAT.match(s)
    if m:
        # FIXME: add actual timezone support
        # this just drops the timezone info
        notz, ms, tz = m.groups()
        if not ms:
            ms = '.0'
        notz = notz + ms
        return datetime.strptime(notz, ISO8601)
    return s

def extract_dates(obj):
    """extract ISO8601 dates from unpacked JSON"""
    if isinstance(obj, dict):
        new_obj = {} # don't clobber
        for k,v in iteritems(obj):
            new_obj[k] = extract_dates(v)
        obj = new_obj
    elif isinstance(obj, (list, tuple)):
        obj = [ extract_dates(o) for o in obj ]
    elif isinstance(obj, string_types):
        obj = parse_date(obj)
    return obj

def squash_dates(obj):
    """squash datetime objects into ISO8601 strings"""
    if isinstance(obj, dict):
        obj = dict(obj) # don't clobber
        for k,v in iteritems(obj):
            obj[k] = squash_dates(v)
    elif isinstance(obj, (list, tuple)):
        obj = [ squash_dates(o) for o in obj ]
    elif isinstance(obj, datetime):
        obj = obj.isoformat()
    return obj

def date_default(obj):
    """default function for packing datetime objects in JSON."""
    if isinstance(obj, datetime):
        return obj.isoformat()
    else:
        raise TypeError("%r is not JSON serializable"%obj)


# constants for identifying png/jpeg data
PNG = b'\x89PNG\r\n\x1a\n'
# front of PNG base64-encoded
PNG64 = b'iVBORw0KG'
JPEG = b'\xff\xd8'
# front of JPEG base64-encoded
JPEG64 = b'/9'
# front of PDF base64-encoded
PDF64 = b'JVBER'

def encode_images(format_dict):
    """b64-encodes images in a displaypub format dict

    Perhaps this should be handled in json_clean itself?

    Parameters
    ----------

    format_dict : dict
        A dictionary of display data keyed by mime-type

    Returns
    -------

    format_dict : dict
        A copy of the same dictionary,
        but binary image data ('image/png', 'image/jpeg' or 'application/pdf')
        is base64-encoded.

    """
    encoded = format_dict.copy()

    pngdata = format_dict.get('image/png')
    if isinstance(pngdata, bytes):
        # make sure we don't double-encode
        if not pngdata.startswith(PNG64):
            pngdata = encodebytes(pngdata)
        encoded['image/png'] = pngdata.decode('ascii')

    jpegdata = format_dict.get('image/jpeg')
    if isinstance(jpegdata, bytes):
        # make sure we don't double-encode
        if not jpegdata.startswith(JPEG64):
            jpegdata = encodebytes(jpegdata)
        encoded['image/jpeg'] = jpegdata.decode('ascii')

    pdfdata = format_dict.get('application/pdf')
    if isinstance(pdfdata, bytes):
        # make sure we don't double-encode
        if not pdfdata.startswith(PDF64):
            pdfdata = encodebytes(pdfdata)
        encoded['application/pdf'] = pdfdata.decode('ascii')

    return encoded


def json_clean(obj):
    """Clean an object to ensure it's safe to encode in JSON.

    Atomic, immutable objects are returned unmodified.  Sets and tuples are
    converted to lists, lists are copied and dicts are also copied.

    Note: dicts whose keys could cause collisions upon encoding (such as a dict
    with both the number 1 and the string '1' as keys) will cause a ValueError
    to be raised.

    Parameters
    ----------
    obj : any python object

    Returns
    -------
    out : object

      A version of the input which will not cause an encoding error when
      encoded as JSON.  Note that this function does not *encode* its inputs,
      it simply sanitizes it so that there will be no encoding errors later.

    """
    # types that are 'atomic' and ok in json as-is.
    atomic_ok = (unicode_type, type(None))

    # containers that we need to convert into lists
    container_to_list = (tuple, set, types.GeneratorType)

    if isinstance(obj, float):
        # cast out-of-range floats to their reprs
        if math.isnan(obj) or math.isinf(obj):
            return repr(obj)
        return float(obj)
    
    if isinstance(obj, int):
        # cast int to int, in case subclasses override __str__ (e.g. boost enum, #4598)
        if isinstance(obj, bool):
            # bools are ints, but we don't want to cast them to 0,1
            return obj
        return int(obj)

    if isinstance(obj, atomic_ok):
        return obj

    if isinstance(obj, bytes):
        return obj.decode(DEFAULT_ENCODING, 'replace')

    if isinstance(obj, container_to_list) or (
        hasattr(obj, '__iter__') and hasattr(obj, next_attr_name)):
        obj = list(obj)

    if isinstance(obj, list):
        return [json_clean(x) for x in obj]

    if isinstance(obj, dict):
        # First, validate that the dict won't lose data in conversion due to
        # key collisions after stringification.  This can happen with keys like
        # True and 'true' or 1 and '1', which collide in JSON.
        nkeys = len(obj)
        nkeys_collapsed = len(set(map(unicode_type, obj)))
        if nkeys != nkeys_collapsed:
            raise ValueError('dict cannot be safely converted to JSON: '
                             'key collision would lead to dropped values')
        # If all OK, proceed by making the new dict that will be json-safe
        out = {}
        for k,v in iteritems(obj):
            out[unicode_type(k)] = json_clean(v)
        return out

    # If we get here, we don't know how to handle the object, so we just get
    # its repr and return that.  This will catch lambdas, open sockets, class
    # objects, and any other complicated contraption that json can't encode
    return repr(obj)