#!/usr/bin/env python

# Derived from ping.c distributed in Linux's netkit. That code is
# copyright (c) 1989 by The Regents of the University of California.
# That code is in turn derived from code written by Mike Muuss of the
# US Army Ballistic Research Laboratory in December, 1983 and
# placed in the public domain. They have my thanks.

# Bugs are naturally mine. I'd be glad to hear about them. There are
# certainly word-size dependenceies here.

# Copyright (c) Matthew Dixon Cowles, <http://www.visi.com/~mdc/>.
# Distributable under the terms of the GNU General Public License
# version 2. Provided with no warranties of any sort.

# Note that ICMP messages can only be sent from processes running
# as root.

# Revision history:
#
# November 22, 1997
# Initial hack. Doesn't do much, but rather than try to guess
# what features I (or others) will want in the future, I've only
# put in what I need now.
#
# December 16, 1997
# For some reason, the checksum bytes are in the wrong order when
# this is run under Solaris 2.X for SPARC but it works right under
# Linux x86. Since I don't know just what's wrong, I'll swap the
# bytes always and then do an htons().
#
# December 4, 2000
# Changed the struct.pack() calls to pack the checksum and ID as
# unsigned. My thanks to Jerome Poincheval for the fix.
#

import os
from socket import *
import struct
import select
import time
import sys

# From /usr/include/linux/icmp.h; your milage may vary.
ICMP_ECHO_REQUEST=8 # Seems to be the same on Solaris.

# I'm not too confident that this is right but testing seems
# to suggest that it gives the same answers as in_cksum in ping.c
def checksum(str):
  sum=0
  countTo=(len(str)/2)*2
  count=0
  while count<countTo:
    thisVal=ord(str[count+1])*256+ord(str[count])
    sum=sum+thisVal
    sum=sum & 0xffffffff # Necessary?
    count=count+2

  if countTo<len(str):
    sum=sum+ord(str[len(str)-1])
    sum=sum & 0xffffffff # Necessary?

  sum=(sum >> 16) + (sum & 0xffff)
  sum=sum+(sum >> 16)
  answer=~sum
  answer=answer & 0xffff

  # Swap bytes. Bugger me if I know why.
  answer=answer >> 8 | (answer << 8 & 0xff00)
  
  return answer

def receiveOnePing(mySocket,ID,timeout):
  timeLeft=timeout
  while 1:
    startedSelect=time.time()
    whatReady=select.select([mySocket],[],[],timeLeft)
    howLongInSelect=(time.time()-startedSelect)
    if whatReady[0]==[]: # Timeout
      return None
    timeReceived=time.time()
    recPacket,addr=mySocket.recvfrom(1024)
    icmpHeader=recPacket[20:28]
    type,code,checksum,packetID,sequence=struct.unpack("bbHHh",icmpHeader)
    if packetID==ID:
      bytesInDouble=struct.calcsize("d")
      timeSent=struct.unpack("d",recPacket[28:28+bytesInDouble])[0]
      return timeReceived-timeSent
      
    timeLeft=timeLeft-howLongInSelect
    if timeLeft<=0:
      return None

def sendOnePing(mySocket,destAddr,ID):
  # Header is type (8), code (8), checksum (16), id (16), sequence (16)
  myChecksum=0
  # Make a dummy heder with a 0 checksum.
  header=struct.pack("bbHHh",ICMP_ECHO_REQUEST,0,myChecksum,ID,1)
  bytesInDouble=struct.calcsize("d")
  data=(192-bytesInDouble) * "Q"
  data=struct.pack("d",time.time())+data
  # Calculate the checksum on the data and the dummy header.
  myChecksum=checksum(header+data)
  # Now that we have the right checksum, we put that in. It's just easier
  # to make up a new header than to stuff it into the dummy.
  header=struct.pack("bbHHh",ICMP_ECHO_REQUEST,0,htons(myChecksum),ID,1)
  packet=header+data
  mySocket.sendto(packet,(destAddr,1)) # Don't know about the 1 
  return None
  
def doOne(destAddr,timeout=10):
  # Returns either the delay (in seconds) or none on timeout.
  icmp=getprotobyname("icmp")
  mySocket=socket(AF_INET,SOCK_RAW,icmp)
  myID=os.getpid() & 0xFFFF
  sendOnePing(mySocket,destAddr,myID)
  delay=receiveOnePing(mySocket,myID,timeout)
  mySocket.close()
  return delay

def main():
  if len(sys.argv)<2:
    print "Usage: %s hostname" % os.path.basename(sys.argv[0])
    sys.exit(1)

  dest=gethostbyname(sys.argv[1])
  delay=doOne(dest)
  print delay
  return None

if __name__=='__main__':
  main()
  sys.exit(0)