x690 0.3.0

Pure Python X.690 implementation

Pure Python X.690 implementation

This module contains a pure Python implementation of the “x690” standard for BER encoding/decoding. Other encodings are currently unsupported but pull-requests are welcome.

Type Extensions

It allows defining and detecting new data-types by simply subclassing the base class x690.types.Type. An example for this can be seen in puresnmp

Examples

Encoding to bytes

Encoding to bytes can be done by simply calling the Python builting bytes() on instances from x690.types:

Encoding of a single value

import x690.types as t

>>> myvalue = t.Integer(12)
>>> asbytes = bytes(myvalue)
>>> repr(asbytes)
b'\x02\x01\x0c'

Encoding of a composite value using Sequence

import x690.types as t

>>> myvalue = t.Sequence(
...     t.Integer(12),
...     t.Integer(12),
...     t.Integer(12),
... )
>>> asbytes = bytes(myvalue)
>>> repr(asbytes)
b'0\t\x02\x01\x0c\x02\x01\x0c\x02\x01\x0c'

Decoding from bytes

Decode bytes by calling x690.types.pop_tlv on your byte data. This will return a tuple where the first value contains the decoded object, and the second one will contain any remaining bytes which were not decoded.

import x690.types as t
>>> data = b'0\t\x02\x01\x0c\x02\x01\x0c\x02\x01\x0c'
>>> decoded, remaining_bytes = t.pop_tlv(data)
>>> decoded
Sequence(Integer(12), Integer(12), Integer(12))
>>> remaining_bytes
b''

Type-Hinting & Enforcing

New in 0.3.0

When decoding bytes, it is possible to specify an expcted type which does two things: Firstly, it tells tools like mypy what the return type will be and secondly, it runs an internal type-check which ensures that the returned value is of the expected type. x690.exc.UnexpectedType is raised otherwise.

This does of course only work if you know the type in advance.

import x690.types as t
>>> data = b'0\t\x02\x01\x0c\x02\x01\x0c\x02\x01\x0c'
>>> decoded, remaining_bytes = t.pop_tlv(data, enforce_type=t.Sequence)
>>> decoded
Sequence(Integer(12), Integer(12), Integer(12))
>>> remaining_bytes
b''

Strict Decoding

New in 0.3.0

When decoding using pop_tlv and you don’t expect any remaining bytes, use strict=True which will raise x690.exc.IncompleteDecoding if there’s any remaining data.

import x690.types as t
>>> data = b'0\t\x02\x01\x0c\x02\x01\x0c\x02\x01\x0cjunk-bytes'
>>> decoded, remaining_bytes = t.pop_tlv(data, strict=True)
Traceback (most recent call last):
  ...
x690.exc.IncompleteDecoding: Strict decoding still had 10 remaining bytes!