Reliable UDP

listener.py

import socket
import struct
import sys

if (len(sys.argv) < 3):
    print "arguments needed: <port> <filename>"
    exit()


UDP_IP = ''
UDP_PORT = int(sys.argv[1])
FILE = sys.argv[2]

sock = socket.socket( socket.AF_INET, socket.SOCK_DGRAM )
sock.bind( (UDP_IP, UDP_PORT) )

packets = {}

while True:
    data, addr = sock.recvfrom( 2048 ) # buffer size is 2048 bytes
    syn, total, msg = struct.unpack('!II1400s', data)
    sock.sendto( struct.pack('4sI', 'ack:', syn), (addr[0], UDP_PORT + 1) )
    print "received packet " + str(syn) + " of " + str(total)
    print "sent ack for packet " + str(syn)
    packets[syn] = msg
    if len(packets) == total:
        print "got all packets"
        break

print "writing to file"

f = open(FILE, "wb")
try:
    for syn, data in sorted(packets.iteritems()):
      f.write(data)
except:
    print "Error writing file"
finally:
    f.close()

print "done."

talker.py

import threading
import socket
import struct
import sys
from time import sleep, time

if (len(sys.argv) < 4):
    print "arguments needed: <hostname> <port> <filename>"
    exit()

UDP_IP =  socket.gethostbyname(sys.argv[1])
UDP_PORT = int(sys.argv[2])
FILE = sys.argv[3]

print "UDP target IP:", UDP_IP
print "UDP target port:", UDP_PORT

PACKET_SIZE = 1400

packets = {}

f = open(FILE, "rb")
try:
    bytes = f.read(PACKET_SIZE)
    i = 0
    while bytes != "":
        packets[i] = bytes
        bytes = f.read(PACKET_SIZE)
        i = i + 1
except:
    print "Error reading file"
finally:
    f.close()

print "preparing to send " + str(len(packets)) + " packets..."

sock = socket.socket( socket.AF_INET, # Internet
                      socket.SOCK_DGRAM ) # UDP

acked_packets = set()

class AckListener(threading.Thread):
    def __init__(self, ip, port):
        threading.Thread.__init__(self)
        self.sock = socket.socket( socket.AF_INET, socket.SOCK_DGRAM )
        self.ip = ip
        self.port = port
    def run(self):
        sock.bind( (self.ip, self.port) )
        print 'listening for acks...'
        while len(acked_packets) < len(packets):
            data, addr = sock.recvfrom(1024)
            msg, syn = struct.unpack('4sI', data)
            if msg == 'ack:':
                acked_packets.add(syn)
                print "got ack for packet " + str(syn)

listener = AckListener('', UDP_PORT + 1)
listener.start()

start = time()

sent_packets = set()
while len(acked_packets) < len(packets):
    # until all the packets have been acked, keep sending all the packets that haven't been acked
    for syn, data in packets.iteritems():
        if syn not in acked_packets:
            packed = struct.pack('!II1400s', syn, len(packets), data)
            print "sending packet " + str(syn)
            sock.sendto( packed, (UDP_IP, UDP_PORT) )
            sent_packets.add(syn)
            timeout = 0
            while len(sent_packets) - len(acked_packets) > 60:
                timeout += 1
                sleep(0.001)
                if timeout >= 5000:
                    break

listener.join()

end = time()
elapsed = end - start

print "done in " + str(elapsed) + " seconds"
print "throughput is " + str(10485760 / elapsed) + " bytes / second"