decoder.py

"""
Implementation of JSONDecoder
"""
import re
import sys

from simplejson.scanner import Scanner, pattern
try:
    from simplejson._speedups import scanstring as c_scanstring
except ImportError:
    pass

FLAGS = re.VERBOSE | re.MULTILINE | re.DOTALL

def _floatconstants():
    import struct
    import sys
    _BYTES = '7FF80000000000007FF0000000000000'.decode('hex')
    if sys.byteorder != 'big':
        _BYTES = _BYTES[:8][::-1] + _BYTES[8:][::-1]
    nan, inf = struct.unpack('dd', _BYTES)
    return nan, inf, -inf

NaN, PosInf, NegInf = _floatconstants()


def linecol(doc, pos):
    lineno = doc.count('\n', 0, pos) + 1
    if lineno == 1:
        colno = pos
    else:
        colno = pos - doc.rindex('\n', 0, pos)
    return lineno, colno


def errmsg(msg, doc, pos, end=None):
    lineno, colno = linecol(doc, pos)
    if end is None:
        return '%s: line %d column %d (char %d)' % (msg, lineno, colno, pos)
    endlineno, endcolno = linecol(doc, end)
    return '%s: line %d column %d - line %d column %d (char %d - %d)' % (
        msg, lineno, colno, endlineno, endcolno, pos, end)


_CONSTANTS = {
    '-Infinity': NegInf,
    'Infinity': PosInf,
    'NaN': NaN,
    'true': True,
    'false': False,
    'null': None,
}

def JSONConstant(match, context, c=_CONSTANTS):
    s = match.group(0)
    fn = getattr(context, 'parse_constant', None)
    if fn is None:
        rval = c[s]
    else:
        rval = fn(s)
    return rval, None
pattern('(-?Infinity|NaN|true|false|null)')(JSONConstant)


def JSONNumber(match, context):
    match = JSONNumber.regex.match(match.string, *match.span())
    integer, frac, exp = match.groups()
    if frac or exp:
        fn = getattr(context, 'parse_float', None) or float
        res = fn(integer + (frac or '') + (exp or ''))
    else:
        fn = getattr(context, 'parse_int', None) or int
        res = fn(integer)
    return res, None
pattern(r'(-?(?:0|[1-9]\d*))(\.\d+)?([eE][-+]?\d+)?')(JSONNumber)


STRINGCHUNK = re.compile(r'(.*?)(["\\\x00-\x1f])', FLAGS)
BACKSLASH = {
    '"': u'"', '\\': u'\\', '/': u'/',
    'b': u'\b', 'f': u'\f', 'n': u'\n', 'r': u'\r', 't': u'\t',
}

DEFAULT_ENCODING = "utf-8"

def py_scanstring(s, end, encoding=None, strict=True, _b=BACKSLASH, _m=STRINGCHUNK.match):
    if encoding is None:
        encoding = DEFAULT_ENCODING
    chunks = []
    _append = chunks.append
    begin = end - 1
    while 1:
        chunk = _m(s, end)
        if chunk is None:
            raise ValueError(
                errmsg("Unterminated string starting at", s, begin))
        end = chunk.end()
        content, terminator = chunk.groups()
        if content:
            if not isinstance(content, unicode):
                content = unicode(content, encoding)
            _append(content)
        if terminator == '"':
            break
        elif terminator != '\\':
            if strict:
                raise ValueError(errmsg("Invalid control character %r at", s, end))
            else:
                _append(terminator)
                continue
        try:
            esc = s[end]
        except IndexError:
            raise ValueError(
                errmsg("Unterminated string starting at", s, begin))
        if esc != 'u':
            try:
                m = _b[esc]
            except KeyError:
                raise ValueError(
                    errmsg("Invalid \\escape: %r" % (esc,), s, end))
            end += 1
        else:
            esc = s[end + 1:end + 5]
            next_end = end + 5
            msg = "Invalid \\uXXXX escape"
            try:
                if len(esc) != 4:
                    raise ValueError
                uni = int(esc, 16)
                if 0xd800 <= uni <= 0xdbff and sys.maxunicode > 65535:
                    msg = "Invalid \\uXXXX\\uXXXX surrogate pair"
                    if not s[end + 5:end + 7] == '\\u':
                        raise ValueError
                    esc2 = s[end + 7:end + 11]
                    if len(esc2) != 4:
                        raise ValueError
                    uni2 = int(esc2, 16)
                    uni = 0x10000 + (((uni - 0xd800) << 10) | (uni2 - 0xdc00))
                    next_end += 6
                m = unichr(uni)
            except ValueError:
                raise ValueError(errmsg(msg, s, end))
            end = next_end
        _append(m)
    return u''.join(chunks), end


# Use speedup
try:
    scanstring = c_scanstring
except NameError:
    scanstring = py_scanstring

def JSONString(match, context):
    encoding = getattr(context, 'encoding', None)
    strict = getattr(context, 'strict', True)
    return scanstring(match.string, match.end(), encoding, strict)
pattern(r'"')(JSONString)


WHITESPACE = re.compile(r'\s*', FLAGS)

def JSONObject(match, context, _w=WHITESPACE.match):
    pairs = {}
    s = match.string
    end = _w(s, match.end()).end()
    nextchar = s[end:end + 1]
    # Trivial empty object
    if nextchar == '}':
        return pairs, end + 1
    if nextchar != '"':
        raise ValueError(errmsg("Expecting property name", s, end))
    end += 1
    encoding = getattr(context, 'encoding', None)
    strict = getattr(context, 'strict', True)
    iterscan = JSONScanner.iterscan
    while True:
        key, end = scanstring(s, end, encoding, strict)
        end = _w(s, end).end()
        if s[end:end + 1] != ':':
            raise ValueError(errmsg("Expecting : delimiter", s, end))
        end = _w(s, end + 1).end()
        try:
            value, end = iterscan(s, idx=end, context=context).next()
        except StopIteration:
            raise ValueError(errmsg("Expecting object", s, end))
        pairs[key] = value
        end = _w(s, end).end()
        nextchar = s[end:end + 1]
        end += 1
        if nextchar == '}':
            break
        if nextchar != ',':
            raise ValueError(errmsg("Expecting , delimiter", s, end - 1))
        end = _w(s, end).end()
        nextchar = s[end:end + 1]
        end += 1
        if nextchar != '"':
            raise ValueError(errmsg("Expecting property name", s, end - 1))
    object_hook = getattr(context, 'object_hook', None)
    if object_hook is not None:
        pairs = object_hook(pairs)
    return pairs, end
pattern(r'{')(JSONObject)


def JSONArray(match, context, _w=WHITESPACE.match):
    values = []
    s = match.string
    end = _w(s, match.end()).end()
    # Look-ahead for trivial empty array
    nextchar = s[end:end + 1]
    if nextchar == ']':
        return values, end + 1
    iterscan = JSONScanner.iterscan
    while True:
        try:
            value, end = iterscan(s, idx=end, context=context).next()
        except StopIteration:
            raise ValueError(errmsg("Expecting object", s, end))
        values.append(value)
        end = _w(s, end).end()
        nextchar = s[end:end + 1]
        end += 1
        if nextchar == ']':
            break
        if nextchar != ',':
            raise ValueError(errmsg("Expecting , delimiter", s, end))
        end = _w(s, end).end()
    return values, end
pattern(r'\[')(JSONArray)


ANYTHING = [
    JSONObject,
    JSONArray,
    JSONString,
    JSONConstant,
    JSONNumber,
]

JSONScanner = Scanner(ANYTHING)


class JSONDecoder(object):
    """
    Simple JSON <http://json.org> decoder

    Performs the following translations in decoding by default:
    
    +---------------+-------------------+
    | JSON          | Python            |
    +===============+===================+
    | object        | dict              |
    +---------------+-------------------+
    | array         | list              |
    +---------------+-------------------+
    | string        | unicode           |
    +---------------+-------------------+
    | number (int)  | int, long         |
    +---------------+-------------------+
    | number (real) | float             |
    +---------------+-------------------+
    | true          | True              |
    +---------------+-------------------+
    | false         | False             |
    +---------------+-------------------+
    | null          | None              |
    +---------------+-------------------+

    It also understands ``NaN``, ``Infinity``, and ``-Infinity`` as
    their corresponding ``float`` values, which is outside the JSON spec.
    """

    _scanner = Scanner(ANYTHING)
    __all__ = ['__init__', 'decode', 'raw_decode']

    def __init__(self, encoding=None, object_hook=None, parse_float=None,
            parse_int=None, parse_constant=None, strict=True):
        """
        ``encoding`` determines the encoding used to interpret any ``str``
        objects decoded by this instance (utf-8 by default).  It has no
        effect when decoding ``unicode`` objects.
        
        Note that currently only encodings that are a superset of ASCII work,
        strings of other encodings should be passed in as ``unicode``.

        ``object_hook``, if specified, will be called with the result
        of every JSON object decoded and its return value will be used in
        place of the given ``dict``.  This can be used to provide custom
        deserializations (e.g. to support JSON-RPC class hinting).

        ``parse_float``, if specified, will be called with the string
        of every JSON float to be decoded. By default this is equivalent to
        float(num_str). This can be used to use another datatype or parser
        for JSON floats (e.g. decimal.Decimal).

        ``parse_int``, if specified, will be called with the string
        of every JSON int to be decoded. By default this is equivalent to
        int(num_str). This can be used to use another datatype or parser
        for JSON integers (e.g. float).

        ``parse_constant``, if specified, will be called with one of the
        following strings: -Infinity, Infinity, NaN, null, true, false.
        This can be used to raise an exception if invalid JSON numbers
        are encountered.
        """
        self.encoding = encoding
        self.object_hook = object_hook
        self.parse_float = parse_float
        self.parse_int = parse_int
        self.parse_constant = parse_constant
        self.strict = strict

    def decode(self, s, _w=WHITESPACE.match):
        """
        Return the Python representation of ``s`` (a ``str`` or ``unicode``
        instance containing a JSON document)
        """
        obj, end = self.raw_decode(s, idx=_w(s, 0).end())
        end = _w(s, end).end()
        if end != len(s):
            raise ValueError(errmsg("Extra data", s, end, len(s)))
        return obj

    def raw_decode(self, s, **kw):
        """
        Decode a JSON document from ``s`` (a ``str`` or ``unicode`` beginning
        with a JSON document) and return a 2-tuple of the Python
        representation and the index in ``s`` where the document ended.

        This can be used to decode a JSON document from a string that may
        have extraneous data at the end.
        """
        kw.setdefault('context', self)
        try:
            obj, end = self._scanner.iterscan(s, **kw).next()
        except StopIteration:
            raise ValueError("No JSON object could be decoded")
        return obj, end

__all__ = ['JSONDecoder']