example of using stdin and stdout as a message buffer:

selfdrive/manager/build.py

pandacan: pandacan is a user space library for talking to your car over USB or Wi-Fi from Python. It allows full read/write access to all the CAN and LIN buses. “pip install pandacan”

SocketCAN: SocketCAN is the Linux standard for CAN interfaces. The included driver allows panda to work with all SocketCAN tools, including can-utils and Wireshark.

SunnyPilot lfa btn:
class HyundaiFlagsSP(IntFlag):
  SP_ENHANCED_SCC = 1
  SP_CAN_LFA_BTN = 2
  SP_NAV_MSG = 4
LFA_Pressed
  188,47:       self.lkas_enabled = cp.vl["BCM_PO_11"]["LFA_Pressed"]