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POE::Component::Client::Ping.3pm

NAME

POE::Component::Client::Ping - a non-blocking ICMP ping client

SYNOPSIS

   use POE qw(Component::Client::Ping);
 
 

   POE::Component::Client::Ping->spawn(
     Alias     => "pingthing",  # defaults to "pinger"
     Timeout   => 10,           # defaults to 1 second
     OneReply  => 1             # defaults to disabled
   );
 
 

   sub some_event_handler {
     $kernel->post(
       "pingthing", # Post the request to the "pingthing" component.
       "ping",      # Ask it to "ping" an address.
       "pong",      # Have it post an answer as a "pong" event.
       $address,    # This is the address we want to ping.
       $timeout,    # Optional timeout.  It overrides the default.
     );
   }
 
 

   # This is the sub which is called when the session receives a "pong"
   # event.  It handles responses from the Ping component.
   sub got_pong {
     my ($request, $response) = @_[ARG0, ARG1];
 
 

     my ($req_address, $req_timeout, $req_time)      = @$request;
     my ($resp_address, $roundtrip_time, $resp_time) = @$response;
 
 

     # The response address is defined if this is a response.
     if (defined $resp_address) {
       printf(
         "ping to %-15.15s at %10d. pong from %-15.15s in %6.3f s\n",
         $req_address, $req_time,
         $resp_address, $roundtrip_time,
       );
       return;
     }
 
 

     # Otherwise the timeout period has ended.
     printf(
       "ping to %-15.15s is done.\n", $req_address,
     );
   }
 
 

   or
 
 

   use POE::Component::Client::Ping ":const";
 
 

   # Post an array ref as the callback to get data back to you
   $kernel->post("pinger", "ping", [ "pong", $user_data ]);
 
 

   # use the REQ_USER_ARGS constant to get to your data
   sub got_pong {
       my ($request, $response) = @_[ARG0, ARG1];
       my $user_data = $request->[REQ_USER_ARGS];
       ...;
   }
 
 

DESCRIPTION

POE::Component::Client::Ping is non-blocking ICMP ping client. It lets several other sessions ping through it in parallel, and it lets them continue doing other things while they wait for responses.

Ping client components are not proper objects. Instead of being created, as most objects are, they are ``spawned'' as separate sessions. To avoid confusion (and hopefully not cause other confusion), they must be spawned with a "spawn" method, not created anew with a "new" one.

PoCo::Client::Ping's "spawn" method takes a few named parameters:

Alias => $session_alias

"Alias" sets the component's alias. It is the target of post() calls. See the synopsis. The alias defaults to ``pinger''.

Socket => $raw_socket

"Socket" allows developers to open an existing raw socket rather than letting the component attempt opening one itself. If omitted, the component will create its own raw socket.

This is useful for people who would rather not perform a security audit on POE, since it allows them to create a raw socket in their own code and then run POE at reduced privileges.

Timeout => $ping_timeout

"Timeout" sets the default amount of time a Ping component will wait for an ICMP echo reply, in seconds. It is 1 by default. It's possible and meaningful to set the timeout to a fractional number of seconds.

This default timeout is only used for ping requests that don't include their own timeouts.

OneReply => 0|1

Set "OneReply" to prevent the Ping component from waiting the full timeout period for replies. Normally the ICMP protocol allows for multiple replies to a single request, so it's proper to wait for late responses. This option disables the wait, ending the ping transaction at the first response. Any subsequent responses will be silently ignored.

"OneReply" is disabled by default, and a single successful request will generate at least two responses. The first response is a successful ICMP ECHO REPLY event. The second is an undefined response event, signifying that the timeout period has ended.

A ping request will generate exactly one reply when "OneReply" is enabled. This reply will represent either the first ICMP ECHO REPLY to arrive or that the timeout period has ended.

Sessions communicate asynchronously with the Client::Ping component. They post ping requests to it, and they receive pong events back.

Requests are posted to the component's ``ping'' handler. They include the name of an event to post back, an address to ping, and an optional amount of time to wait for responses. The address may be a numeric dotted quad, a packed inet_aton address, or a host name. Host names are not recommended: they must be looked up for every ping request, and DNS lookups can be very slow. The optional timeout overrides the one set when "spawn" is called.

Ping responses come with two array references:

   my ($request, $response) = @_[ARG0, ARG1];
 
 

$request contains information about the original request:

   my (
     $req_address, $req_timeout, $req_time, $req_user_args,
   ) = @$request;
 
 

$req_address

This is the original request address. It matches the address posted along with the original ``ping'' request.

It is useful along with $req_user_args for pairing requests with their corresponding responses.

$req_timeout

This is the original request timeout. It's either the one passed with the ``ping'' request or the default timeout set with "spawn".

$req_time

This is the time that the ``ping'' event was received by the Ping component. It is a real number based on the current system's time() epoch.

$req_user_args

This is a scalar containing arbitrary data that can be sent along with a request. It's often used to provide continuity between requests and their responses. $req_user_args may contain a reference to some larger data structure.

To use it, replace the response event with an array reference in the original request. The array reference should contain two items: the actual response event and a scalar with the context data the program needs back. See the SYNOPSIS for an example.

$response contains information about the ICMP ping response. There may be multiple responses for a single request.

   my ($response_address, $roundtrip_time, $reply_time) = @$response;
 
 

$response_address

This is the address that responded to the ICMP echo request. It may be different than $request_address, especially if the request was sent to a broadcast address.

$response_address will be undefined if $request_timeout seconds have elapsed. This marks the end of responses for a given request. Programs can assume that no more responses will be sent for the request address. They may use this marker to initiate another ping request.

$roundtrip_time

This is the number of seconds that elapsed between the ICMP echo request's transmission and its corresponding response's receipt. It's a real number.

$reply_time

This is the time when the ICMP echo response was received. It is a real number based on the current system's time() epoch.

If the ``:const'' tagset is imported the following constants will be exported:

REQ_ADDRESS, REQ_TIMEOUT, REQ_TIME REQ_USER_ARGS, RES_ADDRESS, RES_ROUNDTRIP, RES_TIME

SEE ALSO

This component's ICMP ping code was lifted from Net::Ping, which is an excellent module when you only need to ping one host at a time.

See POE, of course, which includes a lot of documentation about how POE works.

Also see the test program, t/01_ping.t, in the component's distribution.

BUGS

None currently known.

AUTHOR & COPYRIGHTS

POE::Component::Client::Ping is Copyright 1999-2004 by Rocco Caputo. All rights are reserved. POE::Component::Client::Ping is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

Rocco may be contacted by e-mail via <rcaputo@cpan.org>.

You can learn more about POE at <http://poe.perl.org/>.