#!/usr/bin/env python3
# This script sends a multicast message and awaits responses by Sat>IP servers.
# returns the boolean variable 'satip_detected' as json
import json
import socket
import sys
import time

SSDP_ADDR = "239.255.255.250"
SSDP_PORT = 1900
# SSDP_MX = max delay for server response
# a value of 2s is recommended by the SAT>IP specification 1.2.2
SSDP_MX = 2
SSDP_ST = "urn:ses-com:device:SatIPServer:1"

ssdpRequest = "\r\n".join((
    "M-SEARCH * HTTP/1.1",
    "HOST: %s:%d" % (SSDP_ADDR, SSDP_PORT),
    "MAN: \"ssdp:discover\"",
    "MX: %d" % (SSDP_MX),
    "ST: %s" % (SSDP_ST),
    "\r\n"))

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
# according to Sat>IP Specification 1.2.2, p. 20
# a client should send three requests within 100 ms with a ttl of 2
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
sock.settimeout(SSDP_MX + 0.5)
for _ in range(3):
    sock.sendto(ssdpRequest.encode('ascii'), (SSDP_ADDR, SSDP_PORT))
    time.sleep(0.03)
try:
    response = sock.recv(1000).decode()
    if response and "SERVER:" in response:
        got_response = True
    else:
        raise ValueError('No satip server detected')
except (socket.timeout, ValueError):
    got_response = False
finally:
    print(json.dumps(
        {'satip_detected': got_response}
    ))