micropython-lib/python-ecosys/cbor2/cbor2/_decoder.py

"""
The MIT License (MIT)

Copyright (c) 2023 Arduino SA
Copyright (c) 2018 KPN (Jan Bogaerts)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
"""


import io
import struct


class CBORDecodeError(Exception):
    """Raised when an error occurs deserializing a CBOR datastream."""


break_marker = object()


class CBORSimpleValue(object):
    """
    Represents a CBOR "simple value".
    :param int value: the value (0-255)
    """

    def __init__(self, value):
        if value < 0 or value > 255:
            raise TypeError("simple value too big")
        self.value = value

    def __eq__(self, other):
        if isinstance(other, CBORSimpleValue):
            return self.value == other.value
        elif isinstance(other, int):
            return self.value == other
        return NotImplemented

    def __repr__(self):
        return "CBORSimpleValue({self.value})".format(self=self)


def decode_uint(decoder, subtype, allow_indefinite=False):
    # Major tag 0
    if subtype < 24:
        return subtype
    elif subtype == 24:
        return struct.unpack(">B", decoder.read(1))[0]
    elif subtype == 25:
        return struct.unpack(">H", decoder.read(2))[0]
    elif subtype == 26:
        return struct.unpack(">L", decoder.read(4))[0]
    elif subtype == 27:
        return struct.unpack(">Q", decoder.read(8))[0]
    elif subtype == 31 and allow_indefinite:
        return None
    else:
        raise CBORDecodeError("unknown unsigned integer subtype 0x%x" % subtype)


def decode_negint(decoder, subtype):
    # Major tag 1
    uint = decode_uint(decoder, subtype)
    return -uint - 1


def decode_bytestring(decoder, subtype):
    # Major tag 2
    length = decode_uint(decoder, subtype, allow_indefinite=True)
    if length is None:
        # Indefinite length
        buf = bytearray()
        while True:
            initial_byte = decoder.read(1)[0]
            if initial_byte == 255:
                return buf
            else:
                length = decode_uint(decoder, initial_byte & 31)
                value = decoder.read(length)
                buf.extend(value)
    else:
        return decoder.read(length)


def decode_string(decoder, subtype):
    # Major tag 3
    return decode_bytestring(decoder, subtype).decode("utf-8")


def decode_array(decoder, subtype):
    # Major tag 4
    items = []
    length = decode_uint(decoder, subtype, allow_indefinite=True)
    if length is None:
        # Indefinite length
        while True:
            value = decoder.decode()
            if value is break_marker:
                break
            else:
                items.append(value)
    else:
        for _ in range(length):
            item = decoder.decode()
            items.append(item)
    return items


def decode_map(decoder, subtype):
    # Major tag 5
    dictionary = {}
    length = decode_uint(decoder, subtype, allow_indefinite=True)
    if length is None:
        # Indefinite length
        while True:
            key = decoder.decode()
            if key is break_marker:
                break
            else:
                value = decoder.decode()
                dictionary[key] = value
    else:
        for _ in range(length):
            key = decoder.decode()
            value = decoder.decode()
            dictionary[key] = value

    return dictionary


def decode_special(decoder, subtype):
    # Simple value
    if subtype < 20:
        return CBORSimpleValue(subtype)

    # Major tag 7
    return special_decoders[subtype](decoder)


def decode_simple_value(decoder):
    return CBORSimpleValue(struct.unpack(">B", decoder.read(1))[0])


def decode_float16(decoder):
    payload = decoder.read(2)
    raise NotImplementedError  # no float16 unpack function


def decode_float32(decoder):
    return struct.unpack(">f", decoder.read(4))[0]


def decode_float64(decoder):
    return struct.unpack(">d", decoder.read(8))[0]


major_decoders = {
    0: decode_uint,
    1: decode_negint,
    2: decode_bytestring,
    3: decode_string,
    4: decode_array,
    5: decode_map,
    7: decode_special,
}

special_decoders = {
    20: lambda self: False,
    21: lambda self: True,
    22: lambda self: None,
    # 23 is undefined
    24: decode_simple_value,
    25: decode_float16,
    26: decode_float32,
    27: decode_float64,
    31: lambda self: break_marker,
}


class CBORDecoder(object):
    """
    Deserializes a CBOR encoded byte stream.
    """

    def __init__(self, fp):
        self.fp = fp

    def read(self, amount):
        """
        Read bytes from the data stream.
        :param int amount: the number of bytes to read
        """
        data = self.fp.read(amount)
        if len(data) < amount:
            raise CBORDecodeError(
                "premature end of stream (expected to read {} bytes, got {} instead)".format(
                    amount, len(data)
                )
            )

        return data

    def decode(self):
        """
        Decode the next value from the stream.
        :raises CBORDecodeError: if there is any problem decoding the stream
        """
        try:
            initial_byte = self.fp.read(1)[0]
            major_type = initial_byte >> 5
            subtype = initial_byte & 31
        except Exception as e:
            raise CBORDecodeError(
                "error reading major type at index {}: {}".format(self.fp.tell(), e)
            )

        decoder = major_decoders[major_type]
        try:
            return decoder(self, subtype)
        except CBORDecodeError:
            raise
        except Exception as e:
            raise CBORDecodeError(
                "error decoding value {}".format(e)
            )  # tell doesn't work on micropython at the moment


def loads(payload, **kwargs):
    """
    Deserialize an object from a bytestring.
    :param bytes payload: the bytestring to serialize
    :param kwargs: keyword arguments passed to :class:`~.CBORDecoder`
    :return: the deserialized object
    """
    fp = io.BytesIO(payload)
    return CBORDecoder(fp, **kwargs).decode()


def load(fp, **kwargs):
    """
    Deserialize an object from an open file.
    :param fp: the input file (any file-like object)
    :param kwargs: keyword arguments passed to :class:`~.CBORDecoder`
    :return: the deserialized object
    """
    return CBORDecoder(fp, **kwargs).decode()