packeteer 0.4

Light-weight packet serializer

Packeteer: The packet serializer

Packeteer is a light-weight packet serializer capable of translating between raw bytes and custom packet objects; Objects which are easier to understand, display, and work with

import socket
from packeteer import packets, fields

HOST = '127.0.0.1'
PORT = '1234'

class Request(packets.BigEndian):
    """ Request packet """
    fields = [
        fields.UInt8('type'),
        fields.UInt8('size'),
        fields.Raw('data', size='size')
    ]

class Response(packets.BigEndian):
    """ Response packet """
    fields = [
        fields.Bool('success'),
        fields.Uint32('transfered'),
    ]

if __name__ == '__main__':
    data = b'Hello World'
    request = RequestPacket(type=0, data=data)
    response = ResponsePacket()

    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.connect()
        s.sendall(request)
        raw = s.recv(response.size())
        response.unpack(raw)

    print(repr(response))

# <Packet: Response packet>
#   success: True
#   transfered: 11

Installation

Packeteer is available on PyPi, and can be installed with pip directly

$ pip install packeteer

Requirements

Operating systems

Packeteer has no OS dependencies, and should be compatible wherever python can run; However, it is only verified for Ubuntu 18.04. If you discover any issues in other environments, please open a new issue or submit a pull request.

Python

Packeteer was developed and tested against python 2.7, 3.5, 3.6, and 3.7.

Dependencies

Packeteer depends on the following packages:

• future
• six

For development and testing, these optional dependencies are also required:

• pytest
• pytest-cov
• tox

Documentation

Defining packets

Defining packets is as simple as deriving a new class from either packets.BigEndian or packets.LittleEndian (Depending on the byte ordering of your packet structure)

import copy
from packeteer import packets, fields

class MyPacketBE(packets.BigEndian):
    name = 'Custom (Big Endian)'
    fields = [
        fields.Bool('OK'),
        fields.Int32('value', default=42)
    ]

class MyPacketLE(packets.LittleEndian):
    """ Custom (Little Endian) """
    fields = copy.deepcopy(MyPacketBE.fields)

Take notice that the packet definition is built using the fields variable, and the built-in field types; Field types and there options are explained in the fields section of the documentation.

The packet name is an optional value that can be set directly, otherwise it will be coppied from the classes doc-string. If no name is found, the name will be given a default value. The name is only used for human readibility when using repr()

Working with packets

Creating new instances

When packet objects are constructed without any parameters, their default values are stored in each field

from packeteer import packets, fields

class MyPacket(packets.BigEndian):
    """ Custom (Big Endian) """
    fields = [
        fields.Bool('OK'),
        fields.Int32('value', default=42)
    ]

packet = MyPacket()
print(repr(packet))
# <Packet: Custom (Big Endian)>
#   OK: False
#   value: 42

Packets can also be constructed with non-default values by using the field names to set values

packet = MyPacket(OK=True)
print(repr(packet))
# <Packet: Custom (Big Endian)>
#   OK: True
#   value: 42

packet2 = MyPacket(value=100)
print(repr(packet2))
# <Packet: Custom (Big Endian)>
#   OK: False
#   value: 100

Working with packet values

Field values can be accessed like a list (By index) or like a dictionary (By key)

packet = MyPacket()
print(packet[0], packet[1])
# False 42

print(packet['OK'], packet['value'])
# False 42

Values can also be set in the same fashion

packet = MyPacket()
packet[0] = True
packet[1] = 100

print(packet['OK'], packet['value'])
# True 100

Packing/Unpacking

The entire purpose of this library is to work with bytes, so it should come to no surprise that packet instances can be serialized into their raw bytes and back.

packet = MyPacket()

raw = b'\x01\x00\x00\x00\xFF'
packet.unpack(raw)
print(repr(packet))
# <Packet: Custom (Big Endian)>
#   OK: True
#   value: 255

raw2 = packet.pack()
print(raw == raw2)
# True

Packet instances can be constructed directly from bytes as well using the from_raw() call

packet = MyPacket.from_raw(b'\x01\x00\x00\x00\xFF')
print(repr(packet))
# <Packet: Custom (Big Endian)>
#   OK: True
#   value: 255

Fields

The different components of the packet are referred to as fields, which are a collection of the associated value, meta data, and supporting functions.

Packeteer comes with the following field types:

• fields.Padding: (1 Byte) N/A
• fields.Bool: (1 Byte) Boolean
• fields.Char: (1 Byte) Character
• fields.Int8: (1 Byte) Signed Integer
• fields.UInt8: (1 Byte) Unsigned Integer
• fields.Int16: (2 Byte) Signed Integer
• fields.UInt16: (2 Byte) Unsigned Integer
• fields.Int32: (4 Byte) Signed Integer
• fields.UInt32: (4 Byte) Unsigned Integer
• fields.Int64: (8 Byte) Signed Integer
• fields.UInt64: (8 Byte) Unsigned Integer
• fields.Float: (4 Byte) Float value
• fields.Double (8 Byte) Float value
• fields.Raw: (n Byte) Raw byte data as a single value
• fields.String: (n Bytes) Unicode String as a single value

The majority of the types are self explanatory and work identically to the others, but some like padding, string, and raw behave differently and are looked at further in the following sections

Padding

fields.Padding is a special field type that is 1 byte wide per character.

Padding bytes are nameless and not associated with any value; They can't be accessed, but they are counted when packing and unpacking.

from packeteer import packets, fields

class PaddedPacket(packets.BigEndian):
    """ Padded """
    fields = [
        fields.Padding(),
        fields.UInt8('value'),
        fields.Padding(default=b'\xff')
    ]

packet = PaddedPacket(value=170)
print(repr(packet))
# <Packet: Padded>
#   value: 170

print(packet[0])
# 170

print(packet[1])
# IndexError

raw = packet.pack()
print(repr(raw))
# '\x00\xAA\xFF'

packet.unpack(b'\x00\x7f\xff')
print(repr(packet))
# <Packet: Padded>
#   value: 127

Raw data and strings

fields.Raw is a raw byte store of a given size (The size argument is required). If the data is too large for the field, it will be truncated to fit. Likewise if it is too short, it will be padded with null bytes.

fields.String is an extension of fields.Raw that stores it's internal value as a unicode string with the encoding of your choosing (Defaults to utf8). The internal value has any trailing null byte padding removed until it is serialized.

from packeteer import packets, fields

class DataPacket(packets.BigEndian):
    """ Data Packet """
    fields = [
        fields.Raw('raw', size=12),
        fields.String('string', size=12, encoding='utf8')
    ]

packet = DataPacket(raw=b'Hello World', string='Hello World')
print(repr(packet))
# <Packet: Raw Packet>
#   raw: b'Hello World\x00'
#   string: u'Hellow World'

List fields

There are often times when you need to have a variable list of values in a packet (Think about a repeating set of values depending on a given count value). fields.List takes care of this. fields.List requires an additional argument of the field the list contains, with the rest of the arguments given as keywords that the underlying field type requires.

from packeteer import packets, fields

class ListPacket(packets.BigEndian):
    """ List Packet """
    fields = [
        fields.UInt8('count')
        fields.List('messages', fields.String, size=128),
    ]

messages = ['foo', 'bar', 'Hello World']
packet = ListPacket(count=len(messages), messages=messages)
print(repr(packet))
# <Packet: List Packet>
#   count: 3
#   messages: [u'foo', u'bar', u'Hello World']