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ssdp_discover.py
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ssdp_discover.py
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import logging
import socket
from http.client import HTTPResponse
DISCOVERY_MSG = (b'M-SEARCH * HTTP/1.1\r\n' +
b'ST: urn:flamenco:manager:0\r\n' +
b'MX: 3\r\n' +
b'MAN: "ssdp:discover"\r\n' +
b'HOST: 239.255.255.250:1900\r\n\r\n')
# We use site-local multicast, both in IPv6 and IPv4.
DESTINATIONS = {
socket.AF_INET6: 'FF05::C',
socket.AF_INET: '239.255.255.250',
}
log = logging.getLogger(__name__)
class DiscoveryFailed(Exception):
"""Raised when we cannot find a Manager through SSDP."""
class Response(HTTPResponse):
# noinspection PyMissingConstructor
def __init__(self, payload: bytes):
from io import BytesIO
self.fp = BytesIO(payload)
self.debuglevel = 0
self.strict = 0
self.headers = self.msg = None
self._method = None
self.begin()
def interface_addresses():
for dest in ('0.0.0.0', '::'):
for family, _, _, _, _ in socket.getaddrinfo(dest, None):
yield family
def find_flamenco_manager(timeout=1, retries=5):
log.info('Finding Flamenco Manager through UPnP/SSDP discovery.')
families_and_addresses = set(interface_addresses())
for _ in range(retries):
failed_families = 0
for family in families_and_addresses:
try:
dest = DESTINATIONS[family]
except KeyError:
log.warning('Unknown address family %s, skipping', family)
continue
log.debug('Sending to %s, dest=%s', family, dest)
sock = socket.socket(family, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.settimeout(timeout)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
if hasattr(socket, 'SO_REUSEPORT'): # on macOS
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
try:
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 32)
except OSError:
# Not supported on Windows and AF_INET6.
pass
sock.bind(('', 1901))
try:
for _ in range(2):
# sending it more than once will
# decrease the probability of a timeout
sock.sendto(DISCOVERY_MSG, (dest, 1900))
except PermissionError:
log.info('Failed sending UPnP/SSDP discovery message to %s, dest=%s', family, dest)
failed_families += 1
continue
try:
data = sock.recv(1024)
except socket.timeout:
pass
else:
response = Response(data)
return response.getheader('Location')
if failed_families >= len(families_and_addresses):
log.error('Failed to send UPnP/SSDP discovery message '
'to every address family (IPv4/IPv6)')
break
raise DiscoveryFailed('Unable to find Flamenco Manager after %i tries' % retries)
if __name__ == '__main__':
logging.basicConfig(level=logging.DEBUG)
location = find_flamenco_manager()
print('Found the service at %s' % location)

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