Oven logo

Oven

msgpack1.1.0

Published

MessagePack serializer

pip install msgpack

Package Downloads

Weekly DownloadsMonthly Downloads

Requires Python

>=3.8

Dependencies

    MessagePack for Python

    Build Status Documentation Status

    What's this

    MessagePack is an efficient binary serialization format. It lets you exchange data among multiple languages like JSON. But it's faster and smaller. This package provides CPython bindings for reading and writing MessagePack data.

    Install

    $ pip install msgpack
    

    Pure Python implementation

    The extension module in msgpack (msgpack._cmsgpack) does not support PyPy.

    But msgpack provides a pure Python implementation (msgpack.fallback) for PyPy.

    Windows

    When you can't use a binary distribution, you need to install Visual Studio or Windows SDK on Windows. Without extension, using pure Python implementation on CPython runs slowly.

    How to use

    One-shot pack & unpack

    Use packb for packing and unpackb for unpacking. msgpack provides dumps and loads as an alias for compatibility with json and pickle.

    pack and dump packs to a file-like object. unpack and load unpacks from a file-like object.

    >>> import msgpack
    >>> msgpack.packb([1, 2, 3])
    '\x93\x01\x02\x03'
    >>> msgpack.unpackb(_)
    [1, 2, 3]
    

    Read the docstring for options.

    Streaming unpacking

    Unpacker is a "streaming unpacker". It unpacks multiple objects from one stream (or from bytes provided through its feed method).

    import msgpack
    from io import BytesIO
    
    buf = BytesIO()
    for i in range(100):
       buf.write(msgpack.packb(i))
    
    buf.seek(0)
    
    unpacker = msgpack.Unpacker(buf)
    for unpacked in unpacker:
        print(unpacked)
    

    Packing/unpacking of custom data type

    It is also possible to pack/unpack custom data types. Here is an example for datetime.datetime.

    import datetime
    import msgpack
    
    useful_dict = {
        "id": 1,
        "created": datetime.datetime.now(),
    }
    
    def decode_datetime(obj):
        if '__datetime__' in obj:
            obj = datetime.datetime.strptime(obj["as_str"], "%Y%m%dT%H:%M:%S.%f")
        return obj
    
    def encode_datetime(obj):
        if isinstance(obj, datetime.datetime):
            return {'__datetime__': True, 'as_str': obj.strftime("%Y%m%dT%H:%M:%S.%f")}
        return obj
    
    
    packed_dict = msgpack.packb(useful_dict, default=encode_datetime)
    this_dict_again = msgpack.unpackb(packed_dict, object_hook=decode_datetime)
    

    Unpacker's object_hook callback receives a dict; the object_pairs_hook callback may instead be used to receive a list of key-value pairs.

    NOTE: msgpack can encode datetime with tzinfo into standard ext type for now. See datetime option in Packer docstring.

    Extended types

    It is also possible to pack/unpack custom data types using the ext type.

    >>> import msgpack
    >>> import array
    >>> def default(obj):
    ...     if isinstance(obj, array.array) and obj.typecode == 'd':
    ...         return msgpack.ExtType(42, obj.tostring())
    ...     raise TypeError("Unknown type: %r" % (obj,))
    ...
    >>> def ext_hook(code, data):
    ...     if code == 42:
    ...         a = array.array('d')
    ...         a.fromstring(data)
    ...         return a
    ...     return ExtType(code, data)
    ...
    >>> data = array.array('d', [1.2, 3.4])
    >>> packed = msgpack.packb(data, default=default)
    >>> unpacked = msgpack.unpackb(packed, ext_hook=ext_hook)
    >>> data == unpacked
    True
    

    Advanced unpacking control

    As an alternative to iteration, Unpacker objects provide unpack, skip, read_array_header and read_map_header methods. The former two read an entire message from the stream, respectively de-serialising and returning the result, or ignoring it. The latter two methods return the number of elements in the upcoming container, so that each element in an array, or key-value pair in a map, can be unpacked or skipped individually.

    Notes

    string and binary type in old msgpack spec

    Early versions of msgpack didn't distinguish string and binary types. The type for representing both string and binary types was named raw.

    You can pack into and unpack from this old spec using use_bin_type=False and raw=True options.

    >>> import msgpack
    >>> msgpack.unpackb(msgpack.packb([b'spam', 'eggs'], use_bin_type=False), raw=True)
    [b'spam', b'eggs']
    >>> msgpack.unpackb(msgpack.packb([b'spam', 'eggs'], use_bin_type=True), raw=False)
    [b'spam', 'eggs']
    

    ext type

    To use the ext type, pass msgpack.ExtType object to packer.

    >>> import msgpack
    >>> packed = msgpack.packb(msgpack.ExtType(42, b'xyzzy'))
    >>> msgpack.unpackb(packed)
    ExtType(code=42, data='xyzzy')
    

    You can use it with default and ext_hook. See below.

    Security

    To unpacking data received from unreliable source, msgpack provides two security options.

    max_buffer_size (default: 100*1024*1024) limits the internal buffer size. It is used to limit the preallocated list size too.

    strict_map_key (default: True) limits the type of map keys to bytes and str. While msgpack spec doesn't limit the types of the map keys, there is a risk of the hashdos. If you need to support other types for map keys, use strict_map_key=False.

    Performance tips

    CPython's GC starts when growing allocated object. This means unpacking may cause useless GC. You can use gc.disable() when unpacking large message.

    List is the default sequence type of Python. But tuple is lighter than list. You can use use_list=False while unpacking when performance is important.

    Major breaking changes in the history

    msgpack 0.5

    Package name on PyPI was changed from msgpack-python to msgpack from 0.5.

    When upgrading from msgpack-0.4 or earlier, do pip uninstall msgpack-python before pip install -U msgpack.

    msgpack 1.0

    • Python 2 support

      • The extension module does not support Python 2 anymore. The pure Python implementation (msgpack.fallback) is used for Python 2.

      • msgpack 1.0.6 drops official support of Python 2.7, as pip and GitHub Action (setup-python) no longer support Python 2.7.

    • Packer

      • Packer uses use_bin_type=True by default. Bytes are encoded in bin type in msgpack.
      • The encoding option is removed. UTF-8 is used always.
    • Unpacker

      • Unpacker uses raw=False by default. It assumes str types are valid UTF-8 string and decode them to Python str (unicode) object.
      • encoding option is removed. You can use raw=True to support old format (e.g. unpack into bytes, not str).
      • Default value of max_buffer_size is changed from 0 to 100 MiB to avoid DoS attack. You need to pass max_buffer_size=0 if you have large but safe data.
      • Default value of strict_map_key is changed to True to avoid hashdos. You need to pass strict_map_key=False if you have data which contain map keys which type is not bytes or str.