# -*- coding: utf-8 -*-
# mypy: disable-error-code=dict-item
"""UDP - User Datagram Protocol
==================================
.. module:: pcapkit.protocols.transport.udp
:mod:`pcapkit.protocols.transport.udp` contains
:class:`~pcapkit.protocols.transport.udp.UDP` only,
which implements the extractor for User Datagram Protocol
(UDP) [*]_, whose structure is described as below:
======= ========= ===================== ===============================
Octets Bits Name Description
======= ========= ===================== ===============================
0 0 ``udp.srcport`` Source Port
2 16 ``udp.dstport`` Destination Port
4 32 ``udp.len`` Length (header included)
6 48 ``udp.checksum`` Checksum
======= ========= ===================== ===============================
.. [*] https://en.wikipedia.org/wiki/User_Datagram_Protocol
"""
import collections
from typing import TYPE_CHECKING
from pcapkit.const.reg.apptype import TransportProtocol as Enum_TransportProtocol
from pcapkit.const.reg.transtype import TransType as Enum_TransType
from pcapkit.corekit.module import ModuleDescriptor
from pcapkit.protocols.data.transport.udp import UDP as Data_UDP
from pcapkit.protocols.schema.transport.udp import UDP as Schema_UDP
from pcapkit.protocols.transport.transport import Transport
if TYPE_CHECKING:
from typing import Any, Optional
from typing_extensions import Literal
from pcapkit.const.reg.apptype import AppType as Enum_AppType
from pcapkit.protocols.protocol import ProtocolBase
from pcapkit.protocols.schema.schema import Schema
__all__ = ['UDP']
[docs]
class UDP(Transport[Data_UDP, Schema_UDP],
schema=Schema_UDP, data=Data_UDP):
"""This class implements User Datagram Protocol.
This class supports parsing of the following protocols, which are
registered in the :attr:`self.__proto__ <pcapkit.protocols.transport.udp.UDP.__proto__>`
attribute:
.. list-table::
:header-rows: 1
* - Port Number
- Protocol
* - 80
- :class:`pcapkit.protocols.application.http.HTTP`
* - 1701
- :class:`pcapkit.protocols.link.l2tpv2.L2TPv2`
* - 8080
- :class:`pcapkit.protocols.application.http.HTTP`
Note:
The HTTP ports resolve to
:class:`pcapkit.protocols.application.http.HTTP`, which identifies the
version from the payload and delegates.
:attr:`TCP.__proto__ <pcapkit.protocols.transport.tcp.TCP.__proto__>`
binds the same class for its HTTP ports.
.. versionchanged:: 1.5.0
:meth:`make` takes ``total_length``, which a
:meth:`~pcapkit.protocols.protocol.Protocol.from_data` rebuild
passes so that a truncated capture keeps its declared Length
(:issue:`1155`), and ``trailer``, so that the octets past the Length
field rebuild as captured (:issue:`1461`).
"""
##########################################################################
# Defaults.
##########################################################################
#: Protocol index mapping for decoding next layer, see
#: :meth:`self._decode_next_layer
#: <pcapkit.protocols.transport.transport.Transport._decode_next_layer>` &
#: :meth:`self._import_next_layer
#: <pcapkit.protocols.protocol.Protocol._import_next_layer>`.
__proto__ = collections.defaultdict(
lambda: ModuleDescriptor('pcapkit.protocols.misc.raw', 'Raw'),
{
# Ports are IANA service-name registry assignments, quoting that
# registry's own service name and description:
#
# 80 http World Wide Web HTTP
# 1701 l2tp l2tp
# 8080 http-alt HTTP Alternate (see port 80)
#
# The HTTP entries bind the version-dispatching
# :class:`pcapkit.protocols.application.http.HTTP`, as TCP's table
# does. See the note in the class docstring.
80: ModuleDescriptor('pcapkit.protocols.application.http', 'HTTP'),
8080: ModuleDescriptor('pcapkit.protocols.application.http', 'HTTP'),
# L2TPv2 (RFC 2661) is UDP-borne, and v2 is the only version
# implemented, so the concrete class is bound rather than the
# abstract L2TP base. IANA protocol number 115 (L2TPv3, RFC 3931)
# stays unbound because that version has no class; once it has,
# it takes 115 and this entry becomes a version switch on the Ver
# nibble. See pcapkit.protocols.link.l2tp.
1701: ModuleDescriptor('pcapkit.protocols.link.l2tpv2', 'L2TPv2'),
},
)
##########################################################################
# Properties.
##########################################################################
@property
def name(self) -> 'Literal["User Datagram Protocol"]':
"""Name of current protocol."""
return 'User Datagram Protocol'
@property
def length(self) -> 'Literal[8]':
"""Header length of current protocol."""
return 8
@property
def src(self) -> 'Enum_AppType':
"""Source port."""
return self._info.srcport
@property
def dst(self) -> 'Enum_AppType':
"""Destination port."""
return self._info.dstport
##########################################################################
# Methods.
##########################################################################
[docs]
def read(self, length: 'Optional[int]' = None, **kwargs: 'Any') -> 'Data_UDP': # pylint: disable=unused-argument
"""Read User Datagram Protocol (UDP).
Structure of UDP header [:rfc:`768`]:
.. code-block:: text
0 7 8 15 16 23 24 31
+--------+--------+--------+--------+
| Source | Destination |
| Port | Port |
+--------+--------+--------+--------+
| | |
| Length | Checksum |
+--------+--------+--------+--------+
|
| data octets ...
+---------------- ...
Args:
length: Length of packet data.
**kwargs: Arbitrary keyword arguments.
Returns:
Parsed packet data.
"""
if length is None:
length = len(self)
schema = self.__header__
udp = Data_UDP(
srcport=schema.srcport,
dstport=schema.dstport,
len=schema.len,
checksum=schema.checksum,
)
# NOTE: Octets captured past the Length field belong to this layer,
# since its own length field is what leaves them out of the payload,
# and the rebuild keeps them as captured (#1461).
if schema.trailer:
udp.__update__([
('trailer', schema.trailer),
])
return self._decode_next_layer(udp, (udp.srcport.port, udp.dstport.port), udp.len - 8)
[docs]
def make(self,
srcport: 'Enum_AppType | int' = 0,
dstport: 'Enum_AppType | int' = 0,
checksum: 'bytes' = b'\x00\x00',
total_length: 'Optional[int]' = None,
payload: 'bytes | Schema | ProtocolBase' = b'',
trailer: 'bytes' = b'',
**kwargs: 'Any') -> 'Schema_UDP':
"""Make (construct) packet data.
Args:
srcport: Source port.
dstport: Destination port.
checksum: Checksum.
total_length: Length of the datagram, header included; computed from
the header and the payload when omitted.
payload: Payload data.
trailer: Octets after the datagram, outside the Length field;
written as is and not counted in a computed ``total_length``.
**kwargs: Arbitrary keyword arguments.
Returns:
Constructed packet data.
.. versionchanged:: 1.5.0
An out-of-range ``srcport`` or ``dstport`` raises
:exc:`ValueError` rather than being accepted (:issue:`758`).
``total_length`` sits before ``payload`` (:issue:`1155`), so a
caller passing ``payload`` positionally sets ``total_length``
instead.
"""
# NOTE: An explicit ``total_length`` is written as given, so that a
# ``from_data`` rebuild of a capture truncated by snaplen keeps the
# length the sender declared instead of the one that was recorded
# (#1155). Computed from the octets at hand otherwise, which is
# what a plain ``UDP(payload=...)`` wants.
if total_length is None:
total_length = 8 + len(payload)
return Schema_UDP(
srcport=self._make_port(srcport, Enum_TransportProtocol.udp),
dstport=self._make_port(dstport, Enum_TransportProtocol.udp),
len=total_length,
checksum=checksum,
payload=payload,
trailer=trailer,
)
##########################################################################
# Data models.
##########################################################################
def __length_hint__(self) -> 'Literal[8]':
"""Return an estimated length for the object."""
return 8
[docs]
@classmethod
def __index__(cls) -> 'Enum_TransType': # pylint: disable=invalid-index-returned
"""Numeral registry index of the protocol.
Returns:
Numeral registry index of the protocol in `IANA`_.
.. _IANA: https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml
"""
return Enum_TransType.UDP # type: ignore[return-value]
##########################################################################
# Utilities.
##########################################################################
[docs]
@classmethod
def _make_data(cls, data: 'Data_UDP') -> 'dict[str, Any]': # type: ignore[override]
"""Create key-value pairs from ``data`` for protocol construction.
Args:
data: protocol data
Returns:
Key-value pairs for protocol construction.
"""
return {
'srcport': data.srcport,
'dstport': data.dstport,
'checksum': data.checksum,
# NOTE: The parsed length is passed through rather than left to
# ``make`` to recompute, so that a truncated capture rebuilds with
# the length that was on the wire (#1155).
'total_length': data.len,
'payload': cls._make_payload(data),
# NOTE: And the octets captured past the Length field (#1461).
'trailer': data.get('trailer', b''),
}