unfinished partial implementation of SAP (Session Announcement Protocol)

python-sap.py

import socket
import time
import sdp_transform

# unfinished partial implementation of SAP (Session Announcement Protocol)
# https://datatracker.ietf.org/doc/html/rfc2974

MCAST_GRP = '239.255.255.255'
MCAST_PORT = 9875
MCAST_TTL = 255
SDP_FILE = '''v=0
o=- 3 0 IN IP4 10.49.51.51
s=CP950A 1-8
c=IN IP4 239.69.83.67/32
t=0 0
m=audio 6518 RTP/AVP 96
a=clock-domain:PTPv2 0
a=rtpmap:96 L24/48000/8
a=recvonly
a=framecount:48
a=sync-time:0
a=ptime:1
a=ts-refclk:ptp=IEEE1588-2008:00-60-DB-FF-FE-01-02-C8:0
a=mediaclk:direct=0
'''

def build_header(type, src_ip):
    if type == 'announce':
        # Flags
        x = 32
        header = x.to_bytes(1, 'big')

    else:
        pass

    # Authentication Length
    x = 0
    header += x.to_bytes(1, 'big')
    
    # header Identifier Hash
    x = 1
    header += x.to_bytes(2, 'big')

    # Originating Source
    # TODO: handle IPv6 source
    header += int(src_ip.split('.')[0]).to_bytes(1, 'big')
    header += int(src_ip.split('.')[1]).to_bytes(1, 'big')
    header += int(src_ip.split('.')[2]).to_bytes(1, 'big')
    header += int(src_ip.split('.')[3]).to_bytes(1, 'big')

    # Payload Type
    header += bytes('application/sdp', 'ascii')
    x = 0
    header += x.to_bytes(1, 'big')

    return header


def main():
    # simp
    try:
        sdp_dict = sdp_transform.parse(SDP_FILE)
    except Exception as e:
        print('Failed to parse SDP file', SDP_FILE, e)

    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
    sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, MCAST_TTL)

    header = build_header('announce', sdp_dict['origin']['address'])
    message = header

    # SDP
    message += SDP_FILE.encode('ascii')

    while True:
        print('Sending packet')
        sock.sendto(message, (MCAST_GRP, MCAST_PORT))
        #break # only run once for testing
        time.sleep(5)


if __name__ == "__main__":
    main()