#!/usr/bin/env python3
# PC-side control experiment (no device involved; lives in MDK-ARM/bench_diag/).
# Question: is "sendall(4096) then close()" against a SLOW receiver (small SO_RCVBUF,
# no prompt read) lossless on a normal TCP stack?  If yes here but lossy against the
# device, the loss is device-side; if lossy here too, it is generic TCP/client behaviour.
import socket, sys, threading, time

def log(m):
    sys.stdout.write(m + "\n"); sys.stdout.flush()

def run(rcvbuf, read_delay, send_size=4096):
    srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    srv.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, rcvbuf)
    srv.bind(("127.0.0.1", 0))
    srv.listen(1)
    port = srv.getsockname()[1]
    got = bytearray()
    res = {}

    def server():
        c, _ = srv.accept()
        if read_delay:
            time.sleep(read_delay)          # receiver does not read promptly
        c.settimeout(3.0)
        try:
            while True:
                b = c.recv(65536)
                if not b:
                    break
                got.extend(b)
        except Exception as e:
            res["err"] = repr(e)
        res["n"] = len(got)
        c.close()

    t = threading.Thread(target=server, daemon=True)
    t.start()
    time.sleep(0.15)
    cli = socket.create_connection(("127.0.0.1", port), timeout=5.0)
    cli.sendall(bytes([(i * 13 + 5) & 0xFF for i in range(send_size)]))
    cli.close()                              # close immediately after sendall
    t.join(timeout=8)
    srv.close()
    ok = res.get("n") == send_size
    log("  PC-control rcvbuf=%-6d read_delay=%-4s sent=%d received=%s %s %s"
        % (rcvbuf, read_delay, send_size, res.get("n"),
           "OK" if ok else "LOSS", res.get("err", "")))
    return res.get("n")

log("=== PC-side reference (loopback): does an immediate close() lose data when the")
log("=== receiver reads late / has a tiny buffer?  Expected on a correct stack: no loss.")
run(2048, 0.0)
run(2048, 1.5)
run(65536, 0.0)
run(65536, 1.5)