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.\" ========================================================================
.\"
.IX Title "POE::Component::Client::Ping 3pm"
.TH POE::Component::Client::Ping 3pm "2021-02-15" "perl v5.32.1" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
POE::Component::Client::Ping \- a non\-blocking ICMP ping client
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  use POE qw(Component::Client::Ping);
\&
\&  POE::Component::Client::Ping\->spawn(
\&    Alias               => "pingthing",  # defaults to "pinger"
\&    Timeout             => 10,           # defaults to 1 second
\&    Retry               => 3,            # defaults to 1 attempt
\&    OneReply            => 1,            # defaults to disabled
\&    Parallelism         => 64,           # defaults to autodetect
\&    BufferSize          => 65536,        # defaults to undef
\&    AlwaysDecodeAddress => 1,            # defaults to 0
\&  );
\&
\&  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.
\&      $retry,      # Optional retries. It overrides the default.
\&    );
\&  }
\&
\&  # This is the sub which is called when the session receives a "pong"
\&  # event.  It handles responses from the Ping component.
\&  sub got_pong {
\&    my ($request, $response) = @_[ARG0, ARG1];
\&
\&    my ($req_address, $req_timeout, $req_time)      = @$request;
\&    my ($resp_address, $roundtrip_time, $resp_time, $resp_ttl) = @$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\en",
\&        $req_address, $req_time,
\&        $resp_address, $roundtrip_time,
\&      );
\&      return;
\&    }
\&
\&    # Otherwise the timeout period has ended.
\&    printf(
\&      "ping to %\-15.15s is done.\en", $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];
\&      ...;
\&  }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
POE::Component::Client::Ping is non-blocking \s-1ICMP\s0 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.
.PP
Ping client components are not proper objects.  Instead of being
created, as most objects are, they are \*(L"spawned\*(R" as separate sessions.
To avoid confusion (and hopefully not cause other confusion), they
must be spawned with a \f(CW\*(C`spawn\*(C'\fR method, not created anew with a \f(CW\*(C`new\*(C'\fR
one.
.PP
PoCo::Client::Ping's \f(CW\*(C`spawn\*(C'\fR method takes a few named parameters:
.ie n .IP "Alias => $session_alias" 2
.el .IP "Alias => \f(CW$session_alias\fR" 2
.IX Item "Alias => $session_alias"
\&\f(CW\*(C`Alias\*(C'\fR sets the component's alias.  It is the target of \fBpost()\fR
calls.  See the synopsis.  The alias defaults to \*(L"pinger\*(R".
.ie n .IP "Socket => $raw_socket" 2
.el .IP "Socket => \f(CW$raw_socket\fR" 2
.IX Item "Socket => $raw_socket"
\&\f(CW\*(C`Socket\*(C'\fR 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.
.Sp
This is useful for people who would rather not perform a security
audit on \s-1POE,\s0 since it allows them to create a raw socket in their own
code and then run \s-1POE\s0 at reduced privileges.
.ie n .IP "Timeout => $ping_timeout" 2
.el .IP "Timeout => \f(CW$ping_timeout\fR" 2
.IX Item "Timeout => $ping_timeout"
\&\f(CW\*(C`Timeout\*(C'\fR sets the default amount of time (in seconds) a Ping
component will wait for a single \s-1ICMP\s0 echo reply before retrying.  It
is 1 by default.  It is possible and meaningful to set the timeout to
a fractional number of seconds.
.Sp
This default timeout is only used for ping requests that don't include
their own timeouts.
.ie n .IP "Retry => $ping_attempts" 2
.el .IP "Retry => \f(CW$ping_attempts\fR" 2
.IX Item "Retry => $ping_attempts"
\&\f(CW\*(C`Retry\*(C'\fR sets the default number of attempts a ping will be sent
before it should be considered failed. It is 1 by default.
.IP "OneReply => 0|1" 2
.IX Item "OneReply => 0|1"
Set \f(CW\*(C`OneReply\*(C'\fR to prevent the Ping component from waiting the full
timeout period for replies.  Normally the \s-1ICMP\s0 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.
.Sp
\&\f(CW\*(C`OneReply\*(C'\fR is disabled by default, and a single successful request
will generate at least two responses.  The first response is a
successful \s-1ICMP ECHO REPLY\s0 event.  The second is an undefined response
event, signifying that the timeout period has ended.
.Sp
A ping request will generate exactly one reply when \f(CW\*(C`OneReply\*(C'\fR is
enabled.  This reply will represent either the first \s-1ICMP ECHO REPLY\s0
to arrive or that the timeout period has ended.
.ie n .IP "Parallelism => $limit" 2
.el .IP "Parallelism => \f(CW$limit\fR" 2
.IX Item "Parallelism => $limit"
Parallelism sets POE::Component::Client::Ping's maximum number of
simultaneous \s-1ICMP\s0 requests.  Higher numbers speed up the processing of
large host lists, up to the point where the operating system or
network becomes oversaturated and begin to drop packets.
.Sp
The difference can be dramatic.  A tuned Parallelism can enable
responses down to 1ms, depending on the network, although it will take
longer to get through the hosts list.
.Sp
.Vb 5
\&  Pinging 762 hosts at Parallelism=64
\&  Starting to ping hosts.
\&  Pinged 10.0.0.25       \- Response from 10.0.0.25       in  0.002s
\&  Pinged 10.0.0.200      \- Response from 10.0.0.200      in  0.003s
\&  Pinged 10.0.0.201      \- Response from 10.0.0.201      in  0.001s
\&
\&  real  1m1.923s
\&  user  0m2.584s
\&  sys   0m0.207s
.Ve
.Sp
Responses will take significantly longer with an untuned Parallelism,
but the total run time will be quicker.
.Sp
.Vb 5
\&  Pinging 762 hosts at Parallelism=500
\&  Starting to ping hosts.
\&  Pinged 10.0.0.25       \- Response from 10.0.0.25       in  3.375s
\&  Pinged 10.0.0.200      \- Response from 10.0.0.200      in  1.258s
\&  Pinged 10.0.0.201      \- Response from 10.0.0.201      in  2.040s
\&
\&  real  0m13.410s
\&  user  0m6.390s
\&  sys   0m0.290s
.Ve
.Sp
Excessively high parallelism values may saturate the \s-1OS\s0 or network,
resulting in few or no responses.
.Sp
.Vb 2
\&  Pinging 762 hosts at Parallelism=1000
\&  Starting to ping hosts.
\&
\&  real  0m20.520s
\&  user  0m7.896s
\&  sys   0m0.297s
.Ve
.Sp
By default, POE::Component::Client::Ping will guess at an optimal
Parallelism value based on the raw socket receive buffer size and the
operating system's nominal \s-1ICMP\s0 packet size.  The latter figure is
3000 octets for Linux and 100 octets for other systems.  \s-1ICMP\s0 packets
are generally under 90 bytes, but operating systems may use
alternative numbers when calculating buffer capacities.  The component
tries to mimic calculations observed in the wild.
.Sp
When in doubt, experiment with different Parallelism values and use
the one that works best.
.ie n .IP "BufferSize => $bytes" 2
.el .IP "BufferSize => \f(CW$bytes\fR" 2
.IX Item "BufferSize => $bytes"
If set, then the size of the receive buffer of the raw socket will be
modified to the given value. The default size of the receive buffer is
operating system dependent. If the buffer cannot be set to the given
value, a warning will be generated but the system will continue
working. Note that if the buffer is set too small and too many ping
replies arrive at the same time, then the operating system may discard
the ping replies and mistakenly cause this component to believe the
ping to have timed out. In this case, you will typically see discards
being noted in the counters displayed by 'netstat \-s'.
.Sp
Increased BufferSize values can expand the practical limit for
Parallelism.
.IP "AlwaysDecodeAddress => 0|1" 2
.IX Item "AlwaysDecodeAddress => 0|1"
If set, then any input addresses will always be looked up,
even if the hostname happens to be only 4 characters in size.
Ideally, you should be passing addresses in to the system to
avoid slow hostname lookups, but if you must use hostnames
and there is a possibility that you might have short
hostnames, then you should set this.
.ie n .IP "Payload => $bytes" 2
.el .IP "Payload => \f(CW$bytes\fR" 2
.IX Item "Payload => $bytes"
Sets the \s-1ICMP\s0 payload (data bytes).  Otherwise the component generates
56 data bytes internally.  Note that some firewalls will discard \s-1ICMP\s0
packets with nonstandard payload sizes.
.PP
Sessions communicate asynchronously with the Client::Ping component.
They post ping requests to it, and they receive pong events back.
.PP
Requests are posted to the component's \*(L"ping\*(R" handler.  They include
the name of an event to post back, an address to ping, and an optional
amount of time to wait for responses.  The address may be a numeric
dotted quad, a packed inet_aton address, or a host name.  Host names
are not recommended: they must be looked up for every ping request,
and \s-1DNS\s0 lookups can be very slow.  The optional timeout overrides the
one set when \f(CW\*(C`spawn\*(C'\fR is called.
.PP
Ping responses come with two array references:
.PP
.Vb 1
\&  my ($request, $response) = @_[ARG0, ARG1];
.Ve
.PP
\&\f(CW$request\fR contains information about the original request:
.PP
.Vb 3
\&  my (
\&    $req_address, $req_timeout, $req_time, $req_user_args,
\&  ) = @$request;
.Ve
.ie n .IP "$req_address" 2
.el .IP "\f(CW$req_address\fR" 2
.IX Item "$req_address"
This is the original request address.  It matches the address posted
along with the original \*(L"ping\*(R" request.
.Sp
It is useful along with \f(CW$req_user_args\fR for pairing requests with
their corresponding responses.
.ie n .IP "$req_timeout" 2
.el .IP "\f(CW$req_timeout\fR" 2
.IX Item "$req_timeout"
This is the original request timeout.  It's either the one passed with
the \*(L"ping\*(R" request or the default timeout set with \f(CW\*(C`spawn\*(C'\fR.
.ie n .IP "$req_time" 2
.el .IP "\f(CW$req_time\fR" 2
.IX Item "$req_time"
This is the time that the \*(L"ping\*(R" event was received by the Ping
component.  It is a real number based on the current system's \fBtime()\fR
epoch.
.ie n .IP "$req_user_args" 2
.el .IP "\f(CW$req_user_args\fR" 2
.IX Item "$req_user_args"
This is a scalar containing arbitrary data that can be sent along with
a request.  It's often used to provide continuity between requests and
their responses.  \f(CW$req_user_args\fR may contain a reference to some
larger data structure.
.Sp
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 \s-1SYNOPSIS\s0 for an example.
.PP
\&\f(CW$response\fR contains information about the \s-1ICMP\s0 ping response.  There
may be multiple responses for a single request.
.PP
.Vb 2
\&  my ($response_address, $roundtrip_time, $reply_time, $reply_ttl) =
\&  @$response;
.Ve
.ie n .IP "$response_address" 2
.el .IP "\f(CW$response_address\fR" 2
.IX Item "$response_address"
This is the address that responded to the \s-1ICMP\s0 echo request.  It may
be different than \f(CW$request_address\fR, especially if the request was
sent to a broadcast address.
.Sp
\&\f(CW$response_address\fR will be undefined if \f(CW$request_timeout\fR 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.
.ie n .IP "$roundtrip_time" 2
.el .IP "\f(CW$roundtrip_time\fR" 2
.IX Item "$roundtrip_time"
This is the number of seconds that elapsed between the \s-1ICMP\s0 echo
request's transmission and its corresponding response's receipt.  It's
a real number. This is purely the trip time and does *not* include any
time spent queueing if the system's parallelism limit caused the ping
transmission to be delayed.
.ie n .IP "$reply_time" 2
.el .IP "\f(CW$reply_time\fR" 2
.IX Item "$reply_time"
This is the time when the \s-1ICMP\s0 echo response was received.  It is a
real number based on the current system's \fBtime()\fR epoch.
.ie n .IP "$reply_ttl" 2
.el .IP "\f(CW$reply_ttl\fR" 2
.IX Item "$reply_ttl"
This is the ttl for the echo response packet we received.
.PP
If the \*(L":const\*(R" tagset is imported the following constants will be
exported:
.PP
\&\s-1REQ_ADDRESS, REQ_TIMEOUT, REQ_TIME REQ_USER_ARGS,
RES_ADDRESS, RES_ROUNDTRIP, RES_TIME, RES_TTL\s0
.SH "SEE ALSO"
.IX Header "SEE ALSO"
This component's \s-1ICMP\s0 ping code was lifted from Net::Ping, which is an
excellent module when you only need to ping one host at a time.
.PP
See \s-1POE,\s0 of course, which includes a lot of documentation about how
\&\s-1POE\s0 works.
.PP
Also see the test program, t/01_ping.t, in the component's
distribution.
.SH "BUG TRACKER"
.IX Header "BUG TRACKER"
https://rt.cpan.org/Dist/Display.html?Queue=POE\-Component\-Client\-Ping
.SH "REPOSITORY"
.IX Header "REPOSITORY"
http://github.com/rcaputo/poe\-component\-client\-ping/
.SH "OTHER RESOURCES"
.IX Header "OTHER RESOURCES"
http://search.cpan.org/dist/POE\-Component\-Client\-Ping/
.SH "AUTHOR & COPYRIGHTS"
.IX Header "AUTHOR & COPYRIGHTS"
POE::Component::Client::Ping is Copyright 1999\-2020 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.
.PP
You can learn more about \s-1POE\s0 at http://poe.perl.org/