1 files changed, 140 insertions, 0 deletions
diff --git a/assignment5/traceroute.py b/assignment5/traceroute.py
new file mode 100755
index 0000000..68f2d36
--- /dev/null
+++ b/assignment5/traceroute.py
@@ -0,0 +1,140 @@
+#!/usr/bin/env python
+"""Python implementation of the Unix traceroute program"""
+import argparse
+import os
+import socket
+import struct
+import sys
+import time
+
+ICMP_ECHO_REQUEST = 8
+ICMP_ECHO_REPLY = 0
+ICMP_TIME_EXCEEDED = 11
+
+
+def checksum(str_):
+    """The ICMP checksum as defined in RFC 792"""
+    str_ = bytearray(str_)
+    csum = 0
+    count_to = (len(str_) // 2) * 2
+
+    for count in range(0, count_to, 2):
+        this_val = str_[count+1] * 256 + str_[count]
+        csum = csum + this_val
+        csum = csum & 0xffffffff
+
+    if count_to < len(str_):
+        csum = csum + str_[-1]
+        csum = csum & 0xffffffff
+
+    csum = (csum >> 16) + (csum & 0xffff)
+    csum = csum + (csum >> 16)
+    answer = ~csum
+    answer = answer & 0xffff
+    answer = answer >> 8 | (answer << 8 & 0xff00)
+    return answer
+
+
+def receive_one_ping(my_socket, rec_id, timeout):
+    """Attempt to receive a ping.
+
+    Arguments:
+    my_socket -- a Python socket to receive from
+    rec_id -- only receive packets with this identifier (in case of echo reply)
+    timeout -- timeout in seconds
+
+    Return value:
+    A tuple (responding server, icmp message type)
+    """
+    start_time = time.time()
+
+    while (start_time + timeout - time.time()) > 0:
+        try:
+            rec_packet, _ = my_socket.recvfrom(1024)
+        except socket.timeout:
+            break  # timed out
+
+        # Fetch the ICMPHeader fromt the IP
+        icmp_header = rec_packet[20:28]
+        source_ip = '%d.%d.%d.%d' % struct.unpack("BBBB", rec_packet[12:16])
+
+        icmp_type, _, _, packet_id, _ = struct.unpack("bbHHh", icmp_header)
+
+        if icmp_type == ICMP_TIME_EXCEEDED or \
+                icmp_type == ICMP_ECHO_REPLY and packet_id == rec_id:
+            return (source_ip, icmp_type)
+
+    return None, None
+
+def send_one_ping(my_socket, dest_addr, snd_id, ttl=30):
+    """Send an ICMP echo message"""
+    # Make a dummy packet with a 0 checksum
+    header = struct.pack("bbHHh", ICMP_ECHO_REQUEST, 0, 0, snd_id, 1)
+    data = struct.pack("d", time.time())
+
+    # Calculate the checksum on the data and the dummy header.
+    my_checksum = socket.htons(checksum(header + data))
+    if sys.platform == 'darwin':
+        my_checksum = my_checksum & 0xffff
+
+    header = struct.pack("bbHHh", ICMP_ECHO_REQUEST, 0, my_checksum, snd_id, 1)
+    packet = header + data
+
+    my_socket.setsockopt(socket.SOL_IP, socket.IP_TTL, ttl)
+    my_socket.sendto(packet, (dest_addr, 1))
+
+
+def do_one_ping(dest_addr, timeout, ttl=30):
+    """Send one echo and receive either an echo reply or a time exceeded msg"""
+    icmp = socket.getprotobyname("icmp")
+
+    my_socket = socket.socket(socket.AF_INET, socket.SOCK_RAW, icmp)
+    my_socket.settimeout(timeout)
+
+    my_id = os.getpid() & 0xffff
+    send_one_ping(my_socket, dest_addr, my_id, ttl)
+    response = receive_one_ping(my_socket, my_id, timeout)
+
+    my_socket.close()
+    return response
+
+
+def traceroute(host, timeout=1.0, hops=10):
+    """Python version of the Unix traceroute program"""
+    dest = socket.gethostbyname(host)
+    print 'traceroute to %s (%s), %d hops max' % (host, dest, hops)
+
+    i = 0
+    while i < hops:
+        i += 1
+        address, icmp_type = do_one_ping(dest, timeout, ttl=i)
+        if address == None:
+            print '%2d  *' % i
+        else:
+            name, _, _ = socket.gethostbyaddr(address)
+            print '%2d  %s (%s)' % (i, name, address)
+
+            if icmp_type == ICMP_ECHO_REPLY:
+                break
+
+
+def main():
+    """Wrapper for traceroute to get host from the command line"""
+    parser = argparse.ArgumentParser(description='Traceroute')
+    parser.add_argument(
+        'host', metavar='HOST', type=str, nargs=1,
+        help='The host to traceroute to')
+    parser.add_argument(
+        '--timeout', type=float, default=1.0,
+        help='Number of seconds to wait for response to a probe (default 1.0)')
+    parser.add_argument(
+        '--hops', type=int, default=10,
+        help='Maximum number of hops (default 10)')
+
+    args = parser.parse_args()
+    traceroute(args.host[0], timeout=args.timeout, hops=args.hops)
+
+
+if __name__ == '__main__':
+    main()
+