PFCP
====
The system provides a python object :data:`alc.pfcp` to inspect and modify the PFCP packets.
.. _alc_dot_pfcp:
The :data:`alc.pfcp` object
---------------------------
Attributes
^^^^^^^^^^
The object exposes the header fields as attributes on the object.
.. list-table:: Attributes of alc.pfcp
:header-rows: 1
* - Attribute
- Description
- Access
- Type
* - flags
- Complete flags field as an 8-bit integer
- ro
- int
* - version
- PFCP version
- ro
- int
* - fo_flag
- FO flag (follow on) marking another PFCP message follows in the same UDP frame
- ro
- bool
* - mp_flag
- Flag marking if there is a msg_priority field
- ro
- bool
* - s_flag
- Flag marking if there is a SEID field
- ro
- bool
* - msg_type
- Message type
- ro
- int
* - msg_len
- Message length
- ro
- int
* - seid
- Session Endpoint Identifier; `None` if the header field is not present
- ro
- int|None
* - seq_number
- Sequence number
- ro
- int
* - msg_priority
- Message priority; `None` if the header field is not present
- ro
- int|None
Methods
^^^^^^^
.. method:: alc.Pfcp.drop()
Drops the packet.
.. method:: alc.Pfcp.get_ie_list()
Returns a list of IE-types that are present in the packet.
- The order of the elements is the same as they appear in the packet.
- If there are multiple instances of the same IE, the IE-type appears multiple times in the tuple.
:rtype: list
.. method:: alc.Pfcp.has(type, /)
Returns if an IE of the specified type is present at the top-level.
:param int type: IE-type to find
:rtype: bool
.. method:: alc.Pfcp.get(type, /)
Returns all values of the IEs with the specified type. The values are returned as the exact bytestrings as they appear in the packet.
- If the specified type does not exist, the result is an empty tuple: ()
- If a specific instance has zero length or no values, the corresponding bytestring is an empty bytestring: b""
:param int type: IE-type to fetch
:rtype: tuple of bytestrings
.. method:: alc.Pfcp.set(type, value, /)
Replaces the currently present IEs of the specific type with new ones. Multiple values can be specified in a tuple in which case one IE with the specified type is added for each item in the tuple.
:param int type: IE-type to set
:param bytes|tuple(bytes) value: value of the IE; length is computed from this value
.. method:: alc.Pfcp.clear(type, /)
Removes all IEs with the specified type.
:param int type: IE-type to clear
Constants
^^^^^^^^^
.. list-table:: Message type constants defined on alc.Pfcp
:header-rows: 1
* - Name
- Value
* - MSG_TYPE_HEARTBEAT_REQ
- 1
* - MSG_TYPE_HEARTBEAT_RESP
- 2
* - MSG_TYPE_PFD_MGMT_REQ
- 3
* - MSG_TYPE_PFD_MGMT_RESP
- 4
* - MSG_TYPE_ASSOC_SETUP_REQ
- 5
* - MSG_TYPE_ASSOC_SETUP_RESP
- 6
* - MSG_TYPE_ASSOC_UPDATE_REQ
- 7
* - MSG_TYPE_ASSOC_UPDATE_RESP
- 8
* - MSG_TYPE_ASSOC_RELEASE_REQ
- 9
* - MSG_TYPE_ASSOC_RELEASE_RESP
- 10
* - MSG_TYPE_VERSION_NOT_SUP_RESP
- 11
* - MSG_TYPE_NODE_REPORT_REQ
- 12
* - MSG_TYPE_NODE_REPORT_RESP
- 13
* - MSG_TYPE_SESSION_SET_DEL_REQ
- 14
* - MSG_TYPE_SESSION_SET_DEL_RESP
- 15
* - MSG_TYPE_SESSION_EST_REQ
- 50
* - MSG_TYPE_SESSION_EST_RESP
- 51
* - MSG_TYPE_SESSION_MOD_REQ
- 52
* - MSG_TYPE_SESSION_MOD_RESP
- 53
* - MSG_TYPE_SESSION_DEL_REQ
- 54
* - MSG_TYPE_SESSION_DEL_RESP
- 55
* - MSG_TYPE_SESSION_REPORT_REQ
- 56
* - MSG_TYPE_SESSION_REPORT_RESP
- 57
.. _alc_dot_pfcp_utils:
The :mod:`alc.pfcp_utils` module
---------------------------------
.. module:: alc.pfcp_utils
Decoded IE classes
^^^^^^^^^^^^^^^^^^
The module comes with a list of pre-defined classes which represent a decoded IE.
These classes known how to convert between a bytes-representation of a specific IE and a Python-object of that class that allows direct interaction with its value.
* :class:`AbstractIE`
* :class:`BasicIE`
* :class:`IntegerIE`
* :class:`StringIE`
* :class:`GroupedIE`
Other decoders can be created by subclassing the :class:`AbstractIE` class, providing a sensible `__init__` function and overriding the following two methods:
* :meth:`AbstractIE.encode`
* :meth:`AbstractIE.from_bytes`
.. autoclass:: AbstractIE
:members:
:special-members: __eq__
.. autoclass:: BasicIE
:members:
.. autoclass:: IntegerIE
:members:
.. autoclass:: StringIE
:members:
.. autoclass:: GroupedIE
:members:
Decoding
^^^^^^^^
The module provides a function to decode a bytes representation of the value of an IE.
This function can be passed in the result of a call to :meth:`alc.pfcp.get` as the value for the `iter_of_bytes` argument.
.. autofunction:: decode_ies
Examples
--------
Example 1: Adding and removing IEs
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
::
from alc import pfcp
from pfcp_utils import IntegerIE, GroupedIE, BasicIE, StringIE
# remove some IEs from the packet
pfcp.clear(17)
pfcp.clear(2)
# create new IEs and insert them
new_ies = [
IntegerIE(109, 4, 1),
BasicIE(25, b'\x00'),
GroupedIE(7, [qerid_ie, corrid_ie, gatestatus_ie])
]
for ie in new_ies:
pfcp.set(ie.type, ie.encode())
# add multiple IEs of the same type
pfcp.set(22, (StringIE(22, "ISP1"), StringIE(22, "ISP2")))
Example 2: Fetching and decoding IEs
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
::
from alc import pfcp
from pfcp_utils import IntegerIE, decode_ies
# fetch some IEs
# result will be a tuple of bytestrings
raw_qer_ies = pfcp.get(109)
# decode them using an IntegerIE decoder
qer_ies = decode_ies(109, raw_qer_ies, IntegerIE)
Example 3: Working with grouped IEs
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
::
from alc import pfcp
from pfcp_utils import IntegerIE, GroupedIE, BasicIE, StringIE, decode_ies
# Fetch a grouped IE and iterate its sub-IEs
create_pdrs = decode_ies(1, pfcp.get(1), GroupedIE)
for pdr in create_pdrs:
for ie in pdr.sub_ies:
print(ie)
# You can pass in extra info about sub-IEs that you want to be decoded automatically
# Notice that you can specify sub-IEs to be GroupedIE as well, which will cause the
# decoding to recurse even further.
sub_decoders = {2: GroupedIE, 20: IntegerIE}
create_pdrs = decode_ies(1, pfcp.get(1), GroupedIE, sub_decoders = sub_decoders)
# Find a specific sub-ie
for pdr in create_pdrs:
for pdi_ie in pdr.sub_ies_of_type(2):
print(ie)
# Find and modify specific sub-sub-ie:
for pdr in create_pdrs:
for pdi_ie in pdr.sub_ies_of_type(2):
for src_iface_ie in pdi_ie.sub_ies_of_type(20):
src_iface = src_iface_ie.value & 0x0f
if src_iface == 1:
src_iface = 2
# create a groupedIE
qerid_ie = IntegerIE(109, 4, 1)
corrid_ie = IntegerIE(28, 4, corrid)
gatestatus_ie = BasicIE(25, b'\x00')
qer_ie = GroupedIE(7, [qerid_ie, corrid_ie, gatestatus_ie])
# Add a sub-IE to an existing grouped IE:
for pdr in create_pdrs:
pdr.sub_ies.append(qerid_ie)
# In order to propagate these changes into the pfcp-packet, the outer
# GroupedIE needs to be encoded again and the resulting bytes has to be
# set on the packet.
alc.pfcp.set(1, tuple(ie.encode() for ie in create_pdrs))