ping.py

#!/usr/bin/env python

"""
    A pure python ping implementation using raw socket.
 
 
    Note that ICMP messages can only be sent from processes running as root.
 
 
    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.
 
    Original Version from Matthew Dixon Cowles:
      -> ftp://ftp.visi.com/users/mdc/ping.py
 
    Rewrite by Jens Diemer:
      -> http://www.python-forum.de/post-69122.html#69122
 
    Rewrite by George Notaras:
      -> http://www.g-loaded.eu/2009/10/30/python-ping/
 
    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.
    
    May 30, 2007
    ------------
    little rewrite by Jens Diemer:
     -  change socket asterisk import to a normal import
     -  replace time.time() with time.clock()
     -  delete "return None" (or change to "return" only)
     -  in checksum() rename "str" to "source_string"
    
    November 8, 2009
    ----------------
    Improved compatibility with GNU/Linux systems.
 
    Fixes by:
     * George Notaras -- http://www.g-loaded.eu
    Reported by:
     * Chris Hallman -- http://cdhallman.blogspot.com
 
    Changes in this release:
     - Re-use time.time() instead of time.clock(). The 2007 implementation
       worked only under Microsoft Windows. Failed on GNU/Linux.
       time.clock() behaves differently under the two OSes[1].
 
    [1] http://docs.python.org/library/time.html#time.clock
    
    December 25, 2012 
    ----------------- 
    Christopher J. Hanks <develop@cjhanks.name>
    -   Remove redundant operations and variables.  
    -   Added TimeoutException for errors. 
    -   Brought code much closer to PEP8 standard (9.55 / 10)  
"""
 
#
# see: /usr/include/linux/icmp.h 
# to understand 'magic numbers' 
#
# struct icmphdr {
#     __u8        type; 
#     __u8        code; 
#     __sum16     checksum;
#     union {
#          struct {
#                  __be16 id; 
#                  __be16 sequence; 
#           } echo;
#          struct {
#                  __be16 __unused; 
#                  __be16 mtu;
#          } frag;
#     } un;
# }
# 

from   socket import (socket, gethostbyname, getprotobyname, htons, AF_INET, 
                      SOCK_RAW)
from   select import select 
from   os     import getpid 
from   struct import pack, unpack, calcsize 
from   time   import time 


ICMP_ECHO_REQUEST = 8 

class TimeoutException(RuntimeError):
    """
    :class TimeoutException: 
    """
    def __init__(self, timeout, msg = ''):
        RuntimeError.__init__(self, msg) 
        self.timeout = timeout 


def _checksum(src):
    """
    Checksum derived from in_cksum in ping.c 
    """
    sss      = 0
    count_to = int(len(src)) 
    count    = 0

    while count < count_to:
        sss += ord(src[count + 1]) * 256 + ord(src[count])  
        sss &= 0xffffffff 

        count += 2

    if count_to < len(src):
        sss += ord(src[-1:])
        sss &= 0xffffffff

    sss  = (sss >> 16) + (sss & 0xffff)
    sss += (sss >> 16) 

    ret = ~sss & 0xffff 
    ret = ret >> 8 | (ret << 8 & 0xff00) 

    return ret 


def _recv_ping(sock, msg_id, timeout):
    """ 
    Receive a single ping from the socket which has an ID matching msg_id 

    :param sock:    Socket to act only
    :type  sock:    socket.socket() 

    :param msg_id:  Packet message ID to listen for. 
    :type  msg_id:  str() 

    :param timeout: Ping RTT timeout 
    :type  timeout: int() 
    """
    select_wait = timeout 

    while True:
        s_start = time() 
        s_stats = select([sock], [], [], select_wait)
        s_time  = time() - s_start 

        if not len(s_stats[0]):
            raise TimeoutException(timeout)

        t_recv      = time() 
        recv_packet = sock.recvfrom(1024)[0] 
        icmp_header = recv_packet[20:28] 
        pkt_id      = unpack('bbHHh', icmp_header)[3]

        if pkt_id == msg_id:
            return t_recv - unpack('d', recv_packet[28:28 + calcsize('d')])[0]
        
        select_wait -= s_time 

        if select_wait <= 0:
            raise TimeoutException(timeout)


def _send_ping(sock, dest, msg_id):
    """
    Send a single ping. 

    :param sock:    Socket to act only
    :type  sock:    socket.socket() 
    
    :param dest:    Destination to send to.
    :type  dest:    str() 

    :param msg_id:  Message id to send and watch for in return. 
    :type  msg_id:  str() 
    """
    # create faux header : create data item : create real header 
    header = pack('bbHHh', ICMP_ECHO_REQUEST, 0, 0, msg_id, 1)
    msgdat = pack('d', time()) + ((192 - calcsize('d')) * 'Q') 
    header = pack(
             'bbHHh', ICMP_ECHO_REQUEST, 0, htons(_checksum(header + msgdat)), 
             msg_id, 1
             )
    
    try:
        sock.sendto(header + msgdat, (gethostbyname(dest), 1))
    except Exception as (errno, errstr):
        raise RuntimeError('errno = %i : %s' % (errno, errstr))


def _ping(destination, timeout):
    """
    Implementation for single ping 

    :param destination: Location to send ping to. 
    :type  destination: str() 

    :param timeout: Ping RTT timeout 
    :type  timeout: int() 
    """
    try:
        sock = socket(AF_INET, SOCK_RAW, getprotobyname('icmp'))
    except tuple as (errno, msg):
        if 1 == errno:
            raise RuntimeError('uid != 0')
        else:
            raise RuntimeError('unknown error [%i]: %s' % (errno, msg))

    msg_id = getpid() & 0xFFFF 

    _send_ping(sock, destination, msg_id) 
    period = _recv_ping(sock, msg_id, timeout) 
    
    sock.close() 

    return period * 1000  


def ping(destination, timeout = 4, count = 1):
    """
    Send ping(s) to a destination and return the mean RTT. 
    raises RuntimeError if ping times out. 

    :param destination: Web-address to ping. 
    :type  destination: str() 

    :param timeout:     Maximum timeout per-ping 
    :type  timeout:     int() 

    :param count:       Number of pings to send and test 
    :type  count:       int() 

    :return:    Mean round trip time in ms  
    :type  :    float() 
    """
    rets = list()

    for _ in xrange(count):
        rets.append(_ping(destination, timeout))
    
    return sum(rets) / len(rets)



if __name__ == '__main__':
    #
    #Create a more useful basic test case 
    #
    import sys 
    from time import sleep 

    if len(sys.argv) < 2: 
        print(
            'Usage: ./ping.py hostname ping_count'
            )

        exit(1) 
    
    host = sys.argv[1] 
    cnt  = 1 if len(sys.argv) < 3 else int(sys.argv[2])
    
    try:
        print(
            'PING %s (%s)' % (host, gethostbyname(host))
            ) 
    except tuple as err:
        print(
            'PING %s (%s)' % (host, 'UNKNOWN HOST')
            ) 

    
    for i in xrange(cnt):
        try:
            print(
                'icmp_req=%02i  time=%03f ms' % (i, ping(host))
                )
        except TimeoutException as err:
            print(
                'icmp_req=%02i  time=timeout' % i
                ) 
        except RuntimeError as err:
            print( 
                'icmp_req=%02i  time=ERROR [%s]' % (i, str(err))
                ) 

        sleep(1)