python / python/cpython

[socket] Support for Payload Protocol Identifier for SCTP sockets in standard socket library

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stdlib topic-socket type-feature
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Python
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Description

Feature or enhancement

Currently is there a way to specify the payload protocol identifier for an SCTP socket created using the socket library?

For example, the SCTP socket object created as sock_amf = socket.socket(socket.AF_INET, socket.SOCK_STREAM, socket.IPPROTO_SCTP) exposes sock_amf.send(bytes, flags) but has no way to mention the payload protocol identifier as mentioned in https://www.rfc-editor.org/rfc/rfc9260.html#section-3.3.1-3.20.1

Payload Protocol Identifier: 32 bits (unsigned integer)
This value represents an application (or upper layer) specified protocol identifier. This value is passed to SCTP by its upper layer and sent to its peer. This identifier is not used by SCTP but can be used by certain network entities, as well as by the peer application, to identify the type of information being carried in this DATA chunk. This field MUST be sent even in fragmented DATA chunks (to make sure it is available for agents in the middle of the network). Note that this field is not touched by an SCTP implementation; the upper layer is responsible for the host to network byte order conversion of this field.
The value 0 indicates that no application identifier is specified by the upper layer for this payload data.

At present the default value of 0 is being set when the data chunk is formed.

Sample packet capture for one such instance.

image

Pitch

If such an option was there, we could directly implement protocols that require specific ppid with the standard socket library (without having to depend on 3rd party bindings of SCTP C library).
Say for example the NGAP protocol used in 5G which uses

SCTP (IETF RFC 4960 [2]) shall be supported as the transport layer of NG-C signaling bearer. The Payload Protocol
Identifier (ppid) assigned by IANA to be used by SCTP for the application layer protocol NGAP is 60, and 66 for
DTLS over SCTP (IETF RFC 6083 [8])

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the standard socket.socket(..., IPPROTO_SCTP) and send(bytes, flags) entry points described in the issue, then read the referenced RFC 9260 PPID requirements. Determine how the standard socket API could accept a PPID and verify that the resulting SCTP DATA chunk carries it, including the NGAP values mentioned. No source files or tests are identified in the issue.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
networking
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
35/100

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