Request/Response Patterns & NRC Handling

#!/usr/bin/env python3
# UDS timing model: P2, P2*, S3 — tester-side implementation

import time

P2_MAX_MS    = 50      # max wait for first response (default; ECU can reduce in 0x10 response)
P2STAR_MAX_MS = 5000   # max wait after NRC 0x78 (response pending)
S3_CLIENT_MS = 2000    # TesterPresent interval to maintain session

def send_request_with_timing(transport, request: bytes) -> bytes:
    transport.send(request)
    deadline = time.time() + P2_MAX_MS/1000

    while time.time() < deadline:
        response = transport.recv(timeout=P2_MAX_MS/1000)
        if not response:
            raise TimeoutError(f"No response within P2={P2_MAX_MS}ms")

        if response[0] == 0x7F and response[2] == 0x78:
            # NRC 0x78: requestCorrectlyReceivedResponsePending
            # ECU acknowledged receipt; will respond within P2*
            print(f"NRC 0x78: waiting up to {P2STAR_MAX_MS}ms for final response")
            deadline = time.time() + P2STAR_MAX_MS/1000
            continue  # keep waiting for final positive or negative response

        return response  # positive or non-pending negative response

    raise TimeoutError(f"No final response within P2*={P2STAR_MAX_MS}ms")