client_saw.py

#!/usr/bin/env python3
#
# Author: K. Walsh <kwalsh@cs.holycross.edu>
# Date: 4 April 2017
#
# Stop-and-wait client for a simple TCP-like semi-reliable protocol on top of UDP. 
#
# What it does: This implements the stop-and-wait protocol, mostly. It sends one UDP packet,
# waits for an ACK, sends one more, waits for an ACK, etc. A sequence number is
# included in each packet, so the server can detect duplicates, detect missing
# packets, and sort any mis-ordered packets back into the correct order. A
# "magic" integer (0xBAADCAFE) is also included with each packet, for no reason
# at all (you can replace it with something else, or remove it entirely).
#
# What it doesn't do: There are no NACKs or timeouts, so if any packet is lost,
# the protocol will deadlock. The ACK numbers are also completely ignored, so if
# there packets get duplicated in the network, things will probably go haywire.
#
# Run the program like this:
#   python3 client_saw.py 1.2.3.4 6000
# This will send data to a UDP server at IP address 1.2.3.4 port 6000.

import socket
import sys
import time
import struct
import datasource
import trace

# setting verbose = 0 turns off most printing
# setting verbose = 1 turns on a little bit of printing
# setting verbose = 2 turns on a lot of printing
# setting verbose = 3 turns on all printing
verbose = 2

# setting tracefile = None disables writing a trace file for the client
# tracefile = None
tracefile = "client_saw_packets.csv"

magic = 0xBAADCAFE

def main(host, port):
    print("Sending UDP packets to %s:%d" % (host, port))
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) # Makes a UDP socket!

    trace.init(tracefile,
            "Log of all packets sent and ACKs received by client", 
            "SeqNo", "TimeSent", "AckNo", "timeACKed")

    start = time.time()
    for seqno in range(0, 180000):
        # get some example data to send
        body = datasource.wait_for_data(seqno)

        # make a header, create a packet, and send it
        hdr = bytearray(struct.pack(">II", magic, seqno))
        pkt = hdr + body
        tSend = time.time()
        s.sendto(pkt, (host, port))
        if verbose >= 3 or (verbose >= 1 and seqno < 5 or seqno % 1000 == 0):
            print("Sent packet with seqno %d" % (seqno))

        # wait for an ACK
        (ack, addr) = s.recvfrom(100)
        tRecv = time.time()

        # unpack integers from the ACK packet, then print some messages
        (magack, ackno) = struct.unpack(">II", ack)
        if verbose >= 3 or (verbose >= 1 and seqno < 5 or seqno % 1000 == 0):
            print("Got ack with seqno %d" % (ackno))

        # write info about the packet and the ACK to the log file
        trace.write(seqno, tSend - start, ackno, tRecv - start)

    end = time.time()
    elapsed = end - start
    print("Finished sending all packets!")
    print("Elapsed time: %0.4f s" % (elapsed))
    trace.close()


if __name__ == "__main__":
    if len(sys.argv) <= 2:
        print("To send data to the server at 1.2.3.4 port 6000, try running:")
        print("   python3 %s 1.2.3.4 6000" % (sys.argv[0]))
        sys.exit(0)
    host = sys.argv[1]
    port = int(sys.argv[2])
    main(host, port)