Package list python-cbor / debian/0.1.24-1 cbor / tagmap.py
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try:
    # try C library _cbor.so
    from ._cbor import loads, dumps, load, dump
except:
    # fall back to 100% python implementation
    from .cbor import loads, dumps, load, dump

from .cbor import Tag, CBOR_TAG_CBOR, _IS_PY3


class ClassTag(object):
    '''
    For some CBOR tag_number, encode/decode Python class_type.
    class_type manily used for isintance(foo, class_type)
    Call encode_function() taking a Python instance and returning CBOR primitive types.
    Call decode_function() on CBOR primitive types and return an instance of the Python class_type (a factory function).
    '''
    def __init__(self, tag_number, class_type, encode_function, decode_function):
        self.tag_number = tag_number
        self.class_type = class_type
        self.encode_function = encode_function
        self.decode_function = decode_function


# TODO: This would be more efficient if it moved into cbor.py and
# cbormodule.c, happening inline so that there is only one traversal
# of the objects. But that would require two implementations. When
# this API has been used more and can be considered settled I should
# do that. -- Brian Olson 20140917_172229
class TagMapper(object):
    '''
    Translate Python objects and CBOR tagged data.
    Use the CBOR TAG system to note that some data is of a certain class.
    Dump while translating Python objects into a CBOR compatible representation.
    Load and translate CBOR primitives back into Python objects.
    '''
    def __init__(self, class_tags=None, raise_on_unknown_tag=False):
        '''
        class_tags: list of ClassTag objects
        '''
        self.class_tags = class_tags
        self.raise_on_unknown_tag = raise_on_unknown_tag

    def encode(self, obj):
        for ct in self.class_tags:
            if (ct.class_type is None) or (ct.encode_function is None):
                continue
            if isinstance(obj, ct.class_type):
                return Tag(ct.tag_number, ct.encode_function(obj))
        if isinstance(obj, (list, tuple)):
            return [self.encode(x) for x in obj]
        if isinstance(obj, dict):
            # assume key is a primitive
            # can't do this in Python 2.6:
            #return {k:self.encode(v) for k,v in obj.iteritems()}
            out = {}
            if _IS_PY3:
                items = obj.items()
            else:
                items = obj.iteritems()
            for k,v in items:
                out[k] = self.encode(v)
            return out
        # fall through, let underlying cbor.dump decide if it can encode object
        return obj

    def decode(self, obj):
        if isinstance(obj, Tag):
            for ct in self.class_tags:
                if ct.tag_number == obj.tag:
                    return ct.decode_function(obj.value)
            # unknown Tag
            if self.raise_on_unknown_tag:
                raise UnknownTagException(str(obj.tag))
            # otherwise, pass it through
            return obj
        if isinstance(obj, list):
            # update in place. cbor only decodes to list, not tuple
            for i,v in enumerate(obj):
                obj[i] = self.decode(v)
            return obj
        if isinstance(obj, dict):
            # update in place
            if _IS_PY3:
                items = obj.items()
            else:
                items = obj.iteritems()
            for k,v in items:
                # assume key is a primitive
                obj[k] = self.decode(v)
            return obj
        # non-recursive object (num,bool,blob,string)
        return obj

    def dump(self, obj, fp):
        dump(self.encode(obj), fp)

    def dumps(self, obj):
        return dumps(self.encode(obj))

    def load(self, fp):
        return self.decode(load(fp))

    def loads(self, blob):
        return self.decode(loads(blob))


class WrappedCBOR(ClassTag):
    """Handles Tag 24, where a byte array is sub encoded CBOR.
    Unpacks sub encoded object on finding such a tag.
    Does not convert anyting into such a tag.

    Usage:
>>> import cbor
>>> import cbor.tagmap
>>> tm=cbor.TagMapper([cbor.tagmap.WrappedCBOR()])
>>> x = cbor.dumps(cbor.Tag(24, cbor.dumps({"a":[1,2,3]})))
>>> x
'\xd8\x18G\xa1Aa\x83\x01\x02\x03'
>>> tm.loads(x)
{'a': [1L, 2L, 3L]}
>>> cbor.loads(x)
Tag(24L, '\xa1Aa\x83\x01\x02\x03')
"""
    def __init__(self):
        super(WrappedCBOR, self).__init__(CBOR_TAG_CBOR, None, None, loads)

    @staticmethod
    def wrap(ob):
        return Tag(CBOR_TAG_CBOR, dumps(ob))

    @staticmethod
    def dump(ob, fp):
        return dump(Tag(CBOR_TAG_CBOR, dumps(ob)), fp)

    @staticmethod
    def dumps(ob):
        return dumps(Tag(CBOR_TAG_CBOR, dumps(ob)))


class UnknownTagException(BaseException):
    pass