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@schlamar
Created April 20, 2012 12:45
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Simple Python SSDP discovery
import socket
import struct
import sys
from httplib import HTTPResponse
from BaseHTTPServer import BaseHTTPRequestHandler
from StringIO import StringIO
import gtk
import gobject
LIB_ID = 'my_library'
MCAST_GRP = '239.255.255.250'
MCAST_PORT = 1900
SERVICE_LOCS = {'id1': '127.0.0.1:7766', 'id2': '127.0.0.1:7766'}
DISCOVERY_MSG = ('M-SEARCH * HTTP/1.1\r\n' +
'ST: %(library)s:%(service)s\r\n' +
'MX: 3\r\n' +
'MAN: "ssdp:discover"\r\n' +
'HOST: 239.255.255.250:1900\r\n\r\n')
LOCATION_MSG = ('HTTP/1.1 200 OK\r\n' +
'ST: %(library)s:%(service)s\r\n'
'USN: %(service)s\r\n'
'Location: %(loc)s\r\n'
'Cache-Control: max-age=900\r\n\r\n')
class Request(BaseHTTPRequestHandler):
def __init__(self, request_text):
self.rfile = StringIO(request_text)
self.raw_requestline = self.rfile.readline()
self.error_code = self.error_message = None
self.parse_request()
def send_error(self, code, message):
self.error_code = code
self.error_message = message
class Response(HTTPResponse):
def __init__(self, response_text):
self.fp = StringIO(response_text)
self.debuglevel = 0
self.strict = 0
self.msg = None
self._method = None
self.begin()
def interface_addresses(family=socket.AF_INET):
for fam, _, _, _, sockaddr in socket.getaddrinfo('', None):
if family == fam:
yield sockaddr[0]
def client(timeout=1, retries=5):
socket.setdefaulttimeout(timeout)
for _ in xrange(retries):
for addr in interface_addresses():
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
sock.bind((addr, 0))
msg = DISCOVERY_MSG % dict(service='id1', library=LIB_ID)
for _ in xrange(2):
# sending it more than once will
# decrease the probability of a timeout
sock.sendto(msg, (MCAST_GRP, MCAST_PORT))
try:
data = sock.recv(1024)
except socket.timeout:
pass
else:
response = Response(data)
print response.getheader('Location')
return
def server(timeout=5):
socket.setdefaulttimeout(timeout)
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
sock.bind(('', MCAST_PORT))
mreq = struct.pack('4sl', socket.inet_aton(MCAST_GRP), socket.INADDR_ANY)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
cond = gobject.IO_IN | gobject.IO_HUP
gobject.io_add_watch(sock, cond, handle_requests)
gtk.main()
def handle_requests(sock, _):
data, addr = sock.recvfrom(4096)
request = Request(data)
if not request.error_code and \
request.command == 'M-SEARCH' and \
request.path == '*' and \
request.headers['ST'].startswith(LIB_ID) and \
request.headers['MAN'] == '"ssdp:discover"':
service = request.headers['ST'].split(':', 2)[1]
if service in SERVICE_LOCS:
loc = SERVICE_LOCS[service]
msg = LOCATION_MSG % dict(service=service, loc=loc, library=LIB_ID)
sock.sendto(msg, addr)
return True
if __name__ == '__main__':
if len(sys.argv) > 1 and 'client' in sys.argv[1]:
client()
else:
server()
@philip-goh
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I'm trying to adapt this code to write a simple SSDP client and I've run into a couple of issues.

The line socket.getaddrinfo('', None) throws the exception socket.gaierror: [Errno 8] nodename nor servname provided, or not known. It looks like getaddrinfo isn't happy with passing in a blank string as the hostname.

So I changed it to socket.getaddrinfo('localhost', None) and it happily returns "127.0.0.1" which allows the client to carry on.

The next issue I run into is this statement sock.sendto(msg, (MCAST_GRP, MCAST_PORT)) throws an exception socket.error: [Errno 51] Network is unreachable and this has me totally lost.

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