[Python-Dev] socket.setsockopt() with optval=NULL

[Christian Heimes]

Hi,

the socket.setsockopt(level, optname, value) method has two calling
variants. When it is called with a buffer-like object as value, it calls
the C API function setsockopt() with optval=buffer.buf and
optlen=buffer.len. When value is an integer, setsockopt() packs it as
int32 and sends it with optlen=4.

---
# example.py
import socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR,
    b'\x00\x00\x00\x00')
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
---

$ strace -e setsockopt ./python example.py
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [0], 4) = 0
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0


For AF_ALG (Linux Kernel crypto) I need a way to call the C API function
setsockopt() with optval=NULL and optlen as any arbitrary number. I have
been playing with multiple ideas. So far I liked the idea of
value=(None, int) most.

setsockopt(socket.SOL_ALG, socket.ALG_SET_AEAD_AUTHSIZE, (None, taglen))

What do you think?

Christian