ping.pm

ARM上的如果你对底层感兴趣

        $chk += $short;
    }                                           # Add the odd byte in
    $chk += unpack("C", substr($msg, $len_msg - 1, 1)) if $len_msg % 2;
    $chk = ($chk >> 16) + ($chk & 0xffff);      # Fold high into low
    return(~(($chk >> 16) + $chk) & 0xffff);    # Again and complement
}

# Description:  Perform a tcp echo ping.  Since a tcp connection is
# host specific, we have to open and close each connection here.  We
# can't just leave a socket open.  Because of the robust nature of
# tcp, it will take a while before it gives up trying to establish a
# connection.  Therefore, we have to set the alarm to break out of the
# connection sooner if the timeout expires.  No data bytes are actually
# sent since the successful establishment of a connection is proof
# enough of the reachability of the remote host.  Also, tcp is
# expensive and doesn't need our help to add to the overhead.

sub ping_tcp
{
    my ($self,
        $ip,                # Packed IP number of the host
        $timeout            # Seconds after which ping times out
        ) = @_;
    my ($saddr,             # sockaddr_in with port and ip
        $ret                # The return value
        );
                            
    socket($self->{"fh"}, &PF_INET(), &SOCK_STREAM(), $self->{"proto_num"}) ||
        croak("tcp socket error - $!");
    $saddr = sockaddr_in($self->{"port_num"}, $ip);

    $SIG{'ALRM'} = sub { die };
    alarm($timeout);        # Interrupt connect() if we have to
            
    $ret = 0;               # Default to unreachable
    eval <<'EOM' ;
        return unless connect($self->{"fh"}, $saddr);
        $ret = 1;
EOM
    alarm(0);
    $self->{"fh"}->close();
    return($ret);
}

# Description:  Perform a udp echo ping.  Construct a message of
# at least the one-byte sequence number and any additional data bytes.
# Send the message out and wait for a message to come back.  If we
# get a message, make sure all of its parts match.  If they do, we are
# done.  Otherwise go back and wait for the message until we run out
# of time.  Return the result of our efforts.

sub ping_udp
{
    my ($self,
        $ip,                # Packed IP number of the host
        $timeout            # Seconds after which ping times out
        ) = @_;

    my $flags = 0;          # Nothing special on open

    my ($saddr,             # sockaddr_in with port and ip
        $ret,               # The return value
        $msg,               # Message to be echoed
        $finish_time,       # Time ping should be finished
        $done,              # Set to 1 when we are done pinging
        $rbits,             # Read bits, filehandles for reading
        $nfound,            # Number of ready filehandles found
        $from_saddr,        # sockaddr_in of sender
        $from_msg,          # Characters echoed by $host
        $from_port,         # Port message was echoed from
        $from_ip            # Packed IP number of sender
        );

    $saddr = sockaddr_in($self->{"port_num"}, $ip);
    $self->{"seq"} = ($self->{"seq"} + 1) % 256;    # Increment sequence
    $msg = chr($self->{"seq"}) . $self->{"data"};   # Add data if any
    send($self->{"fh"}, $msg, $flags, $saddr);      # Send it

    $rbits = "";
    vec($rbits, $self->{"fh"}->fileno(), 1) = 1;
    $ret = 0;                   # Default to unreachable
    $done = 0;
    $finish_time = time() + $timeout;       # Ping needs to be done by then
    while (!$done && $timeout > 0)
    {
        $nfound = select($rbits, undef, undef, $timeout); # Wait for response
        $timeout = $finish_time - time();   # Get remaining time

        if (!defined($nfound))  # Hmm, a strange error
        {
            $ret = undef;
            $done = 1;
        }
        elsif ($nfound)         # A packet is waiting
        {
            $from_msg = "";
            $from_saddr = recv($self->{"fh"}, $from_msg, 1500, $flags);
            ($from_port, $from_ip) = sockaddr_in($from_saddr);
            if (($from_ip eq $ip) &&        # Does the packet check out?
                ($from_port == $self->{"port_num"}) &&
                ($from_msg eq $msg))
            {
                $ret = 1;       # It's a winner
                $done = 1;
            }
        }
        else                    # Oops, timed out
        {
            $done = 1;
        }
    }
    return($ret);
}   

# Description:  Close the connection unless we are using the tcp
# protocol, since it will already be closed.

sub close
{
    my ($self) = @_;

    $self->{"fh"}->close() unless $self->{"proto"} eq "tcp";
}


1;
__END__

=head1 NAME

Net::Ping - check a remote host for reachability

=head1 SYNOPSIS

    use Net::Ping;

    $p = Net::Ping->new();
    print "$host is alive.\n" if $p->ping($host);
    $p->close();

    $p = Net::Ping->new("icmp");
    foreach $host (@host_array)
    {
        print "$host is ";
        print "NOT " unless $p->ping($host, 2);
        print "reachable.\n";
        sleep(1);
    }
    $p->close();
    
    $p = Net::Ping->new("tcp", 2);
    while ($stop_time > time())
    {
        print "$host not reachable ", scalar(localtime()), "\n"
            unless $p->ping($host);
        sleep(300);
    }
    undef($p);
    
    # For backward compatibility
    print "$host is alive.\n" if pingecho($host);

=head1 DESCRIPTION

This module contains methods to test the reachability of remote
hosts on a network.  A ping object is first created with optional
parameters, a variable number of hosts may be pinged multiple
times and then the connection is closed.

You may choose one of three different protocols to use for the ping.
With the "tcp" protocol the ping() method attempts to establish a
connection to the remote host's echo port.  If the connection is
successfully established, the remote host is considered reachable.  No
data is actually echoed.  This protocol does not require any special
privileges but has higher overhead than the other two protocols.

Specifying the "udp" protocol causes the ping() method to send a udp
packet to the remote host's echo port.  If the echoed packet is
received from the remote host and the received packet contains the
same data as the packet that was sent, the remote host is considered
reachable.  This protocol does not require any special privileges.

If the "icmp" protocol is specified, the ping() method sends an icmp
echo message to the remote host, which is what the UNIX ping program
does.  If the echoed message is received from the remote host and
the echoed information is correct, the remote host is considered
reachable.  Specifying the "icmp" protocol requires that the program
be run as root or that the program be setuid to root.

=head2 Functions

=over 4

=item Net::Ping->new([$proto [, $def_timeout [, $bytes]]]);

Create a new ping object.  All of the parameters are optional.  $proto
specifies the protocol to use when doing a ping.  The current choices
are "tcp", "udp" or "icmp".  The default is "udp".

If a default timeout ($def_timeout) in seconds is provided, it is used
when a timeout is not given to the ping() method (below).  The timeout
must be greater than 0 and the default, if not specified, is 5 seconds.

If the number of data bytes ($bytes) is given, that many data bytes
are included in the ping packet sent to the remote host. The number of
data bytes is ignored if the protocol is "tcp".  The minimum (and
default) number of data bytes is 1 if the protocol is "udp" and 0
otherwise.  The maximum number of data bytes that can be specified is
1024.

=item $p->ping($host [, $timeout]);

Ping the remote host and wait for a response.  $host can be either the
hostname or the IP number of the remote host.  The optional timeout
must be greater than 0 seconds and defaults to whatever was specified
when the ping object was created.  If the hostname cannot be found or
there is a problem with the IP number, undef is returned.  Otherwise,
1 is returned if the host is reachable and 0 if it is not.  For all
practical purposes, undef and 0 and can be treated as the same case.

=item $p->close();

Close the network connection for this ping object.  The network
connection is also closed by "undef $p".  The network connection is
automatically closed if the ping object goes out of scope (e.g. $p is
local to a subroutine and you leave the subroutine).

=item pingecho($host [, $timeout]);

To provide backward compatibility with the previous version of
Net::Ping, a pingecho() subroutine is available with the same
functionality as before.  pingecho() uses the tcp protocol.  The
return values and parameters are the same as described for the ping()
method.  This subroutine is obsolete and may be removed in a future
version of Net::Ping.

=back

=head1 WARNING

pingecho() or a ping object with the tcp protocol use alarm() to
implement the timeout.  So, don't use alarm() in your program while
you are using pingecho() or a ping object with the tcp protocol.  The
udp and icmp protocols do not use alarm() to implement the timeout.

=head1 NOTES

There will be less network overhead (and some efficiency in your
program) if you specify either the udp or the icmp protocol.  The tcp
protocol will generate 2.5 times or more traffic for each ping than
either udp or icmp.  If many hosts are pinged frequently, you may wish
to implement a small wait (e.g. 25ms or more) between each ping to
avoid flooding your network with packets.

The icmp protocol requires that the program be run as root or that it
be setuid to root.  The tcp and udp protocols do not require special
privileges, but not all network devices implement the echo protocol
for tcp or udp.

Local hosts should normally respond to pings within milliseconds.
However, on a very congested network it may take up to 3 seconds or
longer to receive an echo packet from the remote host.  If the timeout
is set too low under these conditions, it will appear that the remote
host is not reachable (which is almost the truth).

Reachability doesn't necessarily mean that the remote host is actually
functioning beyond its ability to echo packets.

Because of a lack of anything better, this module uses its own
routines to pack and unpack ICMP packets.  It would be better for a
separate module to be written which understands all of the different
kinds of ICMP packets.

=cut