Support for Bluetooth LE L2CAP Connection-oriented channels through AF_BLUETOOTH/BTPROTO_L2CAP socket

[themadinventor]

Feature or enhancement

Proposal:

As has been discussed previously (69242, 70145), "new" fields have been added in sockaddr_l2, but are still not supported in CPython's socket implementation.

• The lack of l2_bdaddr_type prevents opening L2CAP connection-oriented channels to Bluetooth LE devices.
• Likewise, the missing l2_cid prevents raw access to e.g ATT.

My suggestion is to add support for a third and fourth optional element in the address tuple for l2_cid and l2_bdaddr_type respectively.

• Only one of psm and cid can be non-zero. This is enforced by the kernel.
• l2_bdaddr_type can take the value of BDADDR_LE_PUBLIC or BDADDR_LE_RANDOM. BDADDR_BREDR is implied if the element is missing, preserving compatibility with existing code.

I.e for LE CoC connection to PSM 0x80

sock = socket(AF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP)
sock.connect((bdaddr, 0x80, 0, BDADDR_LE_RANDOM))

For a raw LE ATT connection:

CID_ATT = 0x04
sock = socket(AF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP)
s.bind((BDADDR_ANY, 0, CID_ATT, BDADDR_LE_RANDOM))
s.connect((bdaddr, 0, CID_ATT, BDADDR_LE_RANDOM))

while keeping the existing format for classic BR/EDR L2CAP.

sock.connect((bdaddr, 0x80))

I have a working implementation of this locally (tested on Linux 6.11) and will file a PR for review as soon as I've got this issue number assigned.

This is my first attempt at contributing to CPython, so I apologize in advance for any mistakes in the process.

Edit 2025-01-26: Added CID field to proposal. PR to be updated.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

#69242
#70145

Linked PRs

• gh-129288: Add optional l2_cid and l2_bdaddr_type in BTPROTO_L2CAP socket address tuple #129293