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A simple package to simplify conversion between binary data and python objects

Project description

This package allows quick and simple creation of protocol-handling classes. It consists of two maintypes - Struct and Parser - where Struct represent an object with fields and a Parser is used to parse said fields from and into binary buffers; the package also includes some basic Parsers and Structs which can be dynamically built to fit the developer's needs.

Usage

Structs

The class generic_struct.structs.Struct is the basic protocol-handling class. it has members to represent the different fields in the protocol and the API to write buffers from its fields and read its fields from buffers. All protocol-handling classes created using generic_struct are derived from Struct.

The methods of Struct:

  • get_buffer() - create a binary buffer (a bytes object) representing the current fields of the struct
  • read_buffer(buffer) - read a binary buffer into the fields of the struct
  • get_buffer_size() - get the length of the corresponding binary buffer

How to create a Struct class

The current version includes two types of Structs which can be created

generic_struct.structs.GenericStruct

This type of Struct has fields of varying types and generates buffers using each field's corresponding Parser.

To create a Struct of that type you can use the class-decorator generic_struct.structs.GenericStruct.build_struct:

from generic_struct.structs.GenericStruct import build_struct

@build_struct
class MyStruct():
    <field_name> = <field_parser>
    <field_name> = <field_parser>   
    ...

object of this type of Struct can be converted to dict

generic_struct.structs.Flags

This type of Struct handles flags fields. Each field is a bool object and has a designated bit in the serialized buffer.

A Struct of this type is created usnig the class-decorator generic_struct.structs.Flags.build_flags:

from generic_struct.structs.Flags import build_flags

@build_flags
class MyFlags():
    FIELDS = ['list', 'of', 'field', 'names']

Where The first element in the FIELDS list is the most significant bit of the first byte in the buffer, and so on.

To have more control over the positions of the bits in the buffer, you can insert generic_struct.structs.Flags.RESERVED to represent one unused bit or generic_struct.structs.Flags.ReservedBits(n) to represent n unused bits. unused bits in the buffer are Always 0.

from generic_struct.structs.Flags import build_flags, RESERVED, ReservedBits

@build_flags
class MyFlags():
    FIELDS = [ReservedBits(5), 'some', 'bits', 'are', RESERVED , 'bits']

object of this type of Struct can be converted to dict

Parsers

A Parser class is responsible to converting between a specific type and a binary buffer in a specific way; converting between int and an unsigned big-endian 4-bytes integer, for example.

Parsers are mainly used in the creation of Struct classes.

The more complicated Parsers use other Parsers in order to do their work.

This package contains a bunch of common useful Parsers:

Parser Supported Types Buffer type
generic_struct.parsers.StaticField.StaticFieldParser int, bool, float, bytes simple conversion using the struct module
generic_struct.parsers.StaticSizeBuffer.StaticSizeBufferParser str a buffer with a pre-determined size
generic_struct.parsers.DynamicSizeBuffer.DynamicSizeBufferParser str length of the buffer, then the buffer
generic_struct.parsers.StaticSizeList.StaticSizeListParser list every element of a pre-defined size list, parsed with a Parser for the elements
generic_struct.parsers.DynamicSizeList.DynamicSizeListParser list length of the list, then the elements of the list
generic_struct.parsers.DelimitedBuffer.DelimitedBufferParser str a buffer with a delimiter buffer/byte at its end
generic_struct.parsers.DelimitedList.DelimitedListParser str a list with a delimiter object at its end
generic_struct.parsers.StructParser Struct a parser for a specific type of Struct
generic_struct.parsers.Union.UnionParser any one of a list of Structs a number which defines the parsed type, then the parsed object

generic_struct.parsers.StaticField.StaticFieldParser

The most simple Parser is ``. This Parser wraps the functionality of `struct.pack()` and `struct.unpack_from()`, although meant to handle mainly `int` and `float`.

The generic_struct.parsers.StaticField module also contains wrappers for the different types StaticFieldParser can handle: SignedIntFormats, UnsignedIntFormats, FloatFormats, CHAR_FORMAT, and BOOL_FORMAT.

Example: The parser StaticFieldParser(SignedIntFormats.BE_DWORD) would serialize 11 as b'\x00\x00\x00\x11'

generic_struct.parsers.StaticSizeBuffer.StaticSizeBufferParser

This parser packs a str into a buffer of a static size. Too short strings are padded with b'\x00'. For example, the string 'some txt' will be converted to b'some txt\x00\x00'.

Note: trailing b'\x00's are not automatically removed by StaticSizeBufferParser.parse(). The buffer b'some txt\x00\x00' is parsed as the string 'some txt\x00\x00'.

generic_struct.parsers.DynamicSizeBuffer.DynamicSizeBufferParser

This parser packs a str into a dynamic sized buffer. The buffer begins with the length of the string, serialized by a Parser that can serialize the type int, and then the string itself.

Example: the parser DynamicSizeBufferParser(StaticFieldParser(UnsignedIntFormats.BYTE)) serializes the string 'some string' as the buffer b'\x0bsome string', while the parser DynamicSizeBufferParser(StaticFieldParser(UnsignedIntFormats.LE_DWORD)) serializes it as b'\x0b\x00\x00\x00some string'

generic_struct.parsers.StaticSizeList.StaticSizeListParser

This parser packs a static-sized list into a buffer, with the elements packed by a Parser that can parse all the elements in the list.

Example: the parser StaticSizeListParser(element_parser=StaticFieldParser(SignedIntFormats.LE_WORD), size=3) serializes the list [3,-1,5] as b'\x03\x00\xff\xff\x05\x00'

generic_struct.parsers.DynamicSizeList.DynamicSizeListParser

This parser packs a dynamic-sized list into a buffer similarly to generic_struct.parsers.StaticSizeList.StaticSizeListParser, except that the size of the list is added at the beginning of the buffer

Example: the parser

DynamicSizeListParser(element_parser=StaticFieldParser(SignedIntFormats.LE_WORD),
                      size_parser=StaticFieldParser(SignedIntFormats.BYTE))

serializes the list [3,-1,5] as b'\x03\x03\x00\xff\xff\x05\x00'

generic_struct.parsers.DelimitedBuffer.DelimitedBufferParser

This parser packs a string as a buffer with a delimiter. The delimiter is a bytes of any length

Example: the parser DelimitedBufferParser(b'\x93) serializes the string 'some_string' as b'some_string\x93'

generic_struct.parsers.DelimitedList.DelimitedListParser

This parser packs a list as a buffer with a delimiter: The elements packed by a Parser that can parse all the elements in the list, and then a delimiter with its own Parser

Example: the parser

DelimitedListParser(element_parser=StaticFieldParser(SignedIntFormats.LE_WORD),
                    delimiter=700,
                    delimiter_parser=StaticFieldParser(UnsignedIntFormats.BE_DWORD))

serializes the list [3,-1,5] as b'\x03\x00\xff\xff\x05\x00\x00\x00\x02\xbc'

generic_struct.parsers.StructParser

This parser packs a child-class of Struct. it is useful when one wishes one of the fields in their Struct to be a Struct.

generic_struct.parsers.Union.UnionParser

This parser packs one of a list of types, and adds a type identifier field packed with its own parser at the beginning of the buffer.

Example: The parser

UnionParser(type_enum_parser=StaticFieldParser(UnsignedIntFormats.BYTE),
            type_parsers=[StaticFieldParser(FloatFormats.BE_QWORD),
            DelimitedBufferParser(b'\x00')])

serializes:

  • 124.34 as b'\x00@_\x15\xc2\x8f\\(\xf6'
  • 'some string' as b'\x01some string\x00'

Example

from generic_struct.parsers import StructParser
from generic_struct.parsers.DelimitedBuffer import DelimitedBufferParser
from generic_struct.parsers.DelimitedList import DelimitedListParser
from generic_struct.parsers.DynamicSizeBuffer import DynamicSizeBufferParser
from generic_struct.parsers.StaticField import StaticFieldParser, UnsignedIntFormats, CHAR_FORMAT
from generic_struct.parsers.StaticSizeList import StaticSizeListParser
from generic_struct.parsers.Union import UnionParser
from generic_struct.structs.Flags import ReservedBits, build_flags
from generic_struct.structs.GenericStruct import build_struct


@build_flags
class MyFlags(object):
    FIELDS = [ReservedBits(5), 'bool_a', 'bool_b', 'bool_c']


@build_struct
class MyStruct(object):
    word_int = StaticFieldParser(UnsignedIntFormats.BE_WORD)
    byte_int = DynamicSizeBufferParser(StaticFieldParser(UnsignedIntFormats.BYTE))
    delim_list = DelimitedListParser(element_parser=DelimitedBufferParser(b'::'),
                                     delimiter=b'$',
                                     delimiter_parser=StaticFieldParser(CHAR_FORMAT))
    union = UnionParser(StaticFieldParser(UnsignedIntFormats.BYTE),
                        [StructParser(MyFlags),
                         StaticSizeListParser(StaticFieldParser(UnsignedIntFormats.BE_DWORD), 4),
                         DelimitedBufferParser(b';')])


def main():
    struct1 = MyStruct(word_int=4,
                       byte_int='some_ string',
                       delim_list=['some', 'list', 'of', 'strings'],
                       union=MyFlags(bool_a=False, bool_b=False, bool_c=True))

    print('struct1:', dict(struct1))
    print('struct1.union:', dict(struct1.union))

    buffer1 = struct1.get_buffer()
    print('serialized:', buffer1)
    print()
    struct2 = MyStruct()
    struct2.read_buffer(buffer1)

    struct2.union = 'this is a string now'
    buffer2 = struct2.get_buffer()
    print('struct2:', dict(struct2))
    print('serialized:', buffer2)


if __name__ == '__main__':
    main()

the output would be:

struct1: {'word_int': 4, 'byte_int': 'some_ string', 'delim_list': ['some', 'list', 'of', 'strings'], 'union': <generic_struct.structs.Flags.flags.<locals>.Flags object at 0x03304810>}
struct1.union: {'bool_a': False, 'bool_b': False, 'bool_c': True}
serialized: b'\x00\x04\x0csome_ stringsome::list::of::strings::$\x00\x01'

struct2: {'word_int': 4, 'byte_int': 'some_ string', 'delim_list': ['some', 'list', 'of', 'strings'], 'union': 'this is a string now'}
serialized: b'\x00\x04\x0csome_ stringsome::list::of::strings::$\x02this is a string now;'

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