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u-msgpack-python v2.0

u-msgpack-python is a lightweight MessagePack serializer and deserializer module written in pure Python, compatible with both Python 2 and 3, as well CPython and PyPy implementations of Python. u-msgpack-python is fully compliant with the latest MessagePack specification. In particular, it supports the new binary, UTF-8 string, and application-defined ext types.

u-msgpack-python is currently distributed on PyPI: https://pypi.python.org/pypi/u-msgpack-python and as a single file: umsgpack.py

Installation

With pip:

$ pip install u-msgpack-python

With easy_install:

$ easy_install u-msgpack-python

or simply drop umsgpack.py into your project!

$ wget https://raw.github.com/vsergeev/u-msgpack-python/master/umsgpack.py

Examples

Basic Example:

>>> import umsgpack
>>> umsgpack.packb({u"compact": True, u"schema": 0})
'\x82\xa7compact\xc3\xa6schema\x00'
>>> umsgpack.unpackb(_)
{u'compact': True, u'schema': 0}
>>>

A more complicated example:

>>> umsgpack.packb( [1, True, False, 0xffffffff, {u"foo": b"\x80\x01\x02",
                     u"bar": [1,2,3, {u"a": [1,2,3,{}]}]}, -1, 2.12345] )
'\x97\x01\xc3\xc2\xce\xff\xff\xff\xff\x82\xa3foo\xc4\x03\x80\x01
\x02\xa3bar\x94\x01\x02\x03\x81\xa1a\x94\x01\x02\x03\x80\xff\xcb
@\x00\xfc\xd3Z\x85\x87\x94'
>>> umsgpack.unpackb(_)
[1, True, False, 4294967295, {u'foo': '\x80\x01\x02',
 u'bar': [1, 2, 3, {u'a': [1, 2, 3, {}]}]}, -1, 2.12345]
>>>

Streaming serialization with file-like objects:

>>> f = open('test.bin', 'w')
>>> umsgpack.pack({u"compact": True, u"schema": 0}, f)
>>> umsgpack.pack([1,2,3], f)
>>> f.close()
>>> 
>>> f = open('test.bin')
>>> umsgpack.unpack(f)
{u'compact': True, u'schema': 0}
>>> umsgpack.unpack(f)
[1, 2, 3]
>>> f.close()
>>>

Encoding and decoding an application-defined ext type:

# Create an Ext object with type 0x05 and data b"\x01\x02\x03"
>>> foo = umsgpack.Ext(0x05, b"\x01\x02\x03")
>>> umsgpack.packb({u"special stuff": foo, u"awesome": True})
b'\x82\xadspecial stuff\xc7\x03\x05\x01\x02\x03\xa7awesome\xc3'
>>> bar = umsgpack.unpackb(_)
>>> print(bar["special stuff"])
Ext Object (Type: 0x05, Data: 01 02 03)
>>> bar["special stuff"].type
5
>>> bar["special stuff"].data
b'\x01\x02\x03'
>>>

Python standard library style names dump, dumps, load, loads are also available:

>>> import umsgpack
>>> umsgpack.dumps({u"compact": True, u"schema": 0})
'\x82\xa7compact\xc3\xa6schema\x00'
>>> umsgpack.loads(_)
{u'compact': True, u'schema': 0}
>>> 
>>> f = open('test.bin', 'w')
>>> umsgpack.dump({u"compact": True, u"schema": 0}, f)
>>> f.close()
>>> 
>>> f = open('test.bin')
>>> umsgpack.load(f)
{u'compact': True, u'schema': 0}
>>>

Streaming Serialization and Deserialization

The streaming pack()/dump() and unpack()/load() functions allow packing and unpacking objects directly to and from a stream, respectively. Streaming may be necessary when unpacking serialized bytes whose size is unknown in advance, or it may be more convenient and efficient when working directly with stream objects (e.g. files or stream sockets).

pack(obj, fp) / dump(obj, fp) serialize Python object obj to a .write() supporting file-like object fp.

>>> class Foo:
...     def write(self, data):
...         # write 'data' bytes
...         pass
... 
>>> f = Foo()
>>> umsgpack.pack({u"compact": True, u"schema": 0}, f)
>>>

unpack(fp) / load(fp) deserialize a Python object from a .read() supporting file-like object fp.

>>> class Bar:
...     def read(self, n):
...         # read and return 'n' number of bytes
...         return b"\x01"*n
... 
>>> f = Bar()
>>> umsgpack.unpack(f)
1
>>>

Compatibility Mode

u-msgpack-python offers a compatibility mode for the old specification to handle the old "raw" bytes msgpack type. When the compatibility mode is enabled, u-msgpack-python will serialize both unicode strings and bytes into the old "raw" msgpack type, and deserialize the "raw" msgpack type into bytes. To enable compatibility mode, simply set the compatibility boolean of the umsgpack module to True.

>>> umsgpack.compatibility = True
>>>
>>> umsgpack.packb([u"some string", b"some bytes"])
b'\x92\xabsome string\xaasome bytes'
>>> umsgpack.unpackb(_)
[b'some string', b'some bytes']
>>>

Exceptions

Packing Exceptions

If an error occurs during packing, umsgpack will raise an exception derived from umsgpack.PackException. All possible packing exceptions are described below.

  • UnsupportedTypeException: Object type not supported for packing.

    >>> # Attempt to pack set type
... umsgpack.packb(set([1,2,3]))
...
umsgpack.UnsupportedTypeException: unsupported type: <type 'set'>
>>> 

>>> # Attempt to pack > 64-bit unsigned int
... umsgpack.packb(2**64)
...
umsgpack.UnsupportedTypeException: huge unsigned int
>>>

Unpacking Exceptions

If a non-byte-string argument is passed to umsgpack.unpackb(), it will raise a TypeError exception. If an error occurs during unpacking, umsgpack will raise an exception derived from umsgpack.UnpackException. All possible unpacking exceptions are described below.

  • TypeError: Packed data is not type str (Python 2), or not type bytes (Python 3).

    # Attempt to unpack non-str type data in Python 2
>>> umsgpack.unpackb(u"no good")
...
TypeError: expected packed data as type 'str'
>>> 

# Attempt to unpack non-bytes type data in Python 3
>>> umsgpack.unpackb("no good")
...
TypeError: expected packed data as type 'bytes'
>>>

  • InsufficientDataException: Insufficient data to unpack the encoded object.

    # Attempt to unpack a cut-off encoded 32-bit unsigned int
>>> umsgpack.unpackb(b"\xce\xff\xff\xff")
...
umsgpack.InsufficientDataException
>>> 

# Attempt to unpack an array of length 2 missing the second item
>>> umsgpack.unpackb(b"\x92\xc2")
...
umsgpack.InsufficientDataException
>>>

  • InvalidStringException: Invalid UTF-8 string encountered during unpacking.

    String bytes are strictly decoded with UTF-8. This exception is thrown if UTF-8 decoding of string bytes fails.

    # Attempt to unpack the string b"\x80\x81"
>>> umsgpack.unpackb(b"\xa2\x80\x81")
...
umsgpack.InvalidStringException: unpacked string is not utf-8
>>>

  • ReservedCodeException: Reserved code encountered during unpacking.

    # Attempt to unpack reserved code 0xc1
>>> umsgpack.unpackb(b"\xc1")
...
umsgpack.ReservedCodeException: reserved code encountered: 0xc1
>>>

  • UnhashableKeyException: Unhashable key encountered during map unpacking. The packed map cannot be unpacked into a Python dictionary.

    Python dictionaries only support keys that are instances of collections.Hashable, so while the map { { u'abc': True } : 5 } has a msgpack encoding, it cannot be unpacked into a valid Python dictionary.

    # Attempt to unpack { {} : False }
>>> umsgpack.unpackb(b"\x82\x80\xc2")
...
umsgpack.UnhashableKeyException: encountered unhashable key type: {}, <type 'dict'>
>>>

  • DuplicateKeyException: Duplicate key encountered during map unpacking.

    Python dictionaries do not support duplicate keys, but msgpack maps may be encoded with duplicate keys.

    # Attempt to unpack { 1: True, 1: False }
>>> umsgpack.unpackb(b"\x82\x01\xc3\x01\xc2")
...
umsgpack.DuplicateKeyException: encountered duplicate key: 1, <type 'int'>
>>>

Behavior Notes

  • Python 2
    • unicode type objects are packed into, and unpacked from, the msgpack string format
    • str type objects are packed into, and unpacked from, the msgpack binary format
  • Python 3
    • str type objects are packed into, and unpacked from, the msgpack string format
    • bytes type objects are packed into, and unpacked from, the msgpack binary format
  • The msgpack string format is strictly decoded with UTF-8 -- an exception is thrown if the string bytes cannot be decoded into a valid UTF-8 string
  • The msgpack array format is unpacked into a Python list, unless it is the key of a map, in which case it is unpacked into a Python tuple
  • Python tuples and lists are both packed into the msgpack array format
  • Python float types are packed into the msgpack float32 or float64 format depending on the system's sys.float_info

Testing

u-msgpack-python's included unit tests may be run with test_umsgpack.py, under your favorite interpreter.

$ python2 test_umsgpack.py
$ python3 test_umsgpack.py
$ pypy test_umsgpack.py
$ pypy3 test_umsgpack.py

License

u-msgpack-python is MIT licensed. See the included LICENSE file for more details.