POE::Component::Client::TCP(3p)

NAME
POE::Component::Client::TCP - a simplified TCP client

SYNOPSIS
  #!perl

  use warnings;
  use strict;

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

  POE::Component::Client::TCP->new(
    RemoteAddress => "yahoo.com",
    RemotePort    => 80,
    Connected     => sub {
      $_[HEAP]{server}->put("HEAD /");
    },
    ServerInput   => sub {
      my $input = $_[ARG0];
      print "from server: $input\n";
    },
  );

  POE::Kernel->run();
  exit;

DESCRIPTION
POE::Component::Client::TCP implements a generic single-Session client. Internally it uses POE::Wheel::SocketFactory to establish the connection and POE::Wheel::ReadWrite to interact with the server.

POE::Component::Client::TCP is customized by providing callbacks for common operations. Most operations have sensible default callbacks, so clients may be created with as little work as possible.

  Performance Considerations
POE::Component::Client::TCP's ease of use comes at a price. The component is generic, so it's not tuned to perform well for any particular application.

If performance is your primary goal, POE::Kernel's select_read() and select_write() perform about the same as IO::Select, but your code will be portable across every event loop POE supports.

PUBLIC METHODS

  new
new() starts a client based on POE::Component::Client::TCP and returns the ID of the session that will handle server interaction.

new() returns immediately, which may be before the client has established its connection. It is always reliable to wait for the "Connected" callback to fire before transmitting data to the server.

The client's constructor may seem to take a daunting number of parameters. As with most POE modules, POE::Component::Client::TCP tries to do as much work in its constructor so that the run-time code path is relatively light.

Constructor Parameters Affecting the Session

The parameters in this section affect how the client's POE::Session object will be created.

Alias

"Alias" is an optional symbolic name for the client's Session. It allows other sessions to post events to the client, such as "shutdown" and "reconnect". The client itself may yield() these events, so an alias isn't usually needed.

  Alias => "client",

Args

"Args" is optional. When specified, it holds an ARRAYREF that will be passed to the "Started" callback via @_[ARG0..$#_]. This allows a program to pass extra information into the client session.

InlineStates

"InlineStates" is optional. If specified, it must hold a hashref of named callbacks. Its syntax is that of POE:Session->create()'s inline_states parameter.

ObjectStates

If "ObjectStates" is specified, it must hold an arrayref of objects and the events they will handle. The arrayref must follow the syntax for POE::Session->create()'s object_states parameter.

PackageStates

When the optional "PackageStates" is set, it must hold an arrayref of package names and the events they will handle The arrayref must follow the syntax for POE::Session->create()'s package_states parameter.

PreConnect

"PreConnect" is called before "Connected", and it has different parameters: $_[ARG0] contains a copy of the socket before it's given to POE::Wheel::ReadWrite for management. Most HEAP members are set, except of course $_[HEAP]{server}, because the POE::Wheel::ReadWrite object has not been created yet. "PreConnect" may enable SSL on the socket using POE::Component::SSLify. "PreConnect" must return a valid socket to complete the connection; the client will disconnect if anything else is returned.

  PreConnect => {
    # Convert the socket into an SSL socket.
    my $socket = eval { Client_SSLify($_[ARG0]) };

    # Disconnect if SSL failed.
    return if $@;

    # Return the SSL-ified socket.
    return $socket;
  }

SessionType

Each client is created within its own Session. "SessionType" names the class that will be used to create the session.

  SessionType => "POE::Session::MultiDispatch",

"SessionType" is optional. The component will use "POE::Session" by default.

SessionParams

"SessionParams" specifies additional parameters that will be passed to the "SessionType" constructor at creation time. It must be an array reference.

  SessionParams => [ options => { debug => 1, trace => 1 } ],

Note: POE::Component::Client::TCP supplies its own POE::Session constructor parameters. Conflicts between them and "SessionParams" may cause the component to behave erratically. To avoid such problems, please limit SessionParams to the "options" hash. See POE::Session for an known options.

We may enable other options later. Please let us know if you need something.

Started

"Started" sets an optional callback that will be invoked within the client session has been started. The callback's parameters are the usual for the session's _start handler.

"Args" may be used to pass additional parameters to "Started". This can be used to bypass issues introduced by closures. The values from "Args" will be included in the @_[ARG0..$#_] parameters.

  sub handle_started {
    my @args = @_[ARG0..$#_];
    # ...
  }

POE::Wheel::SocketFactory Constructor Parameters

The constructor parameters in this section affect how the client's POE::Wheel::SocketFactory object will be created.

BindAddress

"BindAddress" specifies the local interface address to bind to before starting to connect. This allows the client to connect from a specific address when multiple interfaces are available.

"BindAddress" is optional. If specified, its value will be passed directly to POE::Wheel::SocketFactory's BindAddress constructor parameter.

BindPort

"BindPort" sets the local socket port that the client will be bound to before starting to connect. This allows the client to connect from a specific port.

It's not usually necessary to bind to a particular port, so "BindPort" is optional and disabled by default.

If specified, the value in "BindPort" is passed directly to POE::Wheel::SocketFactory's own BindPort constructor parameter.

ConnectError

"ConnectError" is an optional callback to handle errors from POE::Wheel::SocketFactory. These errors happen when a socket can't be created or has trouble connecting to the remote host.

The following parameters will be passed to the callback along with the usual POE event parameters: $_[ARG0] will describe what was happening at the time of failure. $_[ARG1] and $_[ARG2] will contain the numeric and string versions of $!, respectively.

Depending on the nature of the error and the type of client, it may be useful to reconnect from the ConnectError callback.

  ConnectError => sub {
    my ($operation, $error_number, $error_string) = @_[ARG0..ARG2];
    warn "$operation error $error_number occurred: $error_string";
    if (error_is_recoverable($error_number)) {
      $_[KERNEL]->delay( reconnect => 60 );
    }
    else {
      $_[KERNEL]->yield("shutdown");
    }
  },

POE::Component::Client::TCP will shut down after ConnectError if a reconnect isn't requested.

Connected

Connections are asynchronously set up and may take some time to complete. "Connected" is an optional callback that notifies a program when the connection has finally been made.

This is an advisory callback that occurs after a POE::Wheel::ReadWrite object has already been created. Programs should not need to create their own.

"Connected" is called in response to POE::Wheel::SocketFactory's SuccessEvent. In addition to the usual POE event parameters, it includes a copy of the established socket handle in $_[ARG0]. POE::Component::Client::TCP will manage the socket, so an application should rarely need to save a copy of it. $_[ARG1] and $_[ARG2] contain the remote address and port as returned from getpeername().

  Connected => {
    my ($socket, $peer_addr, $peer_port) = @_[ARG0, ARG1, ARG2];
    # ...
  }

See "PreConnect" to modify the socket before it's given to POE::Wheel::ReadWrite.

ConnectTimeout

"ConnectTimeout" is the maximum number of seconds to wait for a connection to be established. If it is omitted, Client::TCP relies on the operating system to abort stalled connect() calls.

The application will be notified of a timeout via the ConnectError callback. In the case of a timeout, $_[ARG0] will contain "connect", and $_[ARG1] and $_[ARG2] will contain the numeric and string representations of the ETIMEDOUT error.

Domain

"Domain" sets the address or protocol family within which to operate. The "Domain" may be any value that POE::Wheel::SocketFactory supports. AF_INET (Internet address space) is used by default.

Use AF_INET6 for IPv6 support. This constant is exported by Socket. Also be sure to have Socket::GetAddrInfo installed, which is required by POE::Wheel::SocketFactory for IPv6 support.

RemoteAddress

"RemoteAddress" contains the address of the server to connect to. It is required and may contain a host name ("poe.perl.org"), a dot- or colon-separated numeric address (depending on the Domain), or a packed socket address. Pretty much anything POE::Wheel::SocketFactory's RemoteAddress parameter does.

RemotePort

"RemotePort" contains the port of the server to connect to. It is required and may be a service name ("echo") or number (7).

POE::Wheel::ReadWrite Constructor Parameters

Parameters in this section control configuration of the client's POE::Wheel::ReadWrite object.

Disconnected

"Disconnected" is an optional callback to notify a program that an established socket has been disconnected. It includes no special parameters.

It may be useful to reconnect from the Disconnected callback, in the case of MUD bots or long-running services. For example:

  Disconnected => sub {
    $_[KERNEL]->delay( reconnect => 60 );
  },

The component will shut down if the connection ceases without being reconnected.

Filter

"Filter" specifies the type of POE::Filter object that will parse input from and serialize output to a server. It may either be a scalar, an array reference, or a POE::Filter object.

If "Filter" is a scalar, it will be expected to contain a POE::Filter class name:

  Filter => "POE::Filter::Line",

"Filter" is optional. In most cases, the default "POE::Filter::Line" is fine.

If "Filter" is an array reference, the first item in the array will be treated as a POE::Filter class name. The remaining items will be passed to the filter's constructor. In this example, the vertical bar will be used as POE::Filter::Line's record terminator:

  Filter => [ "POE::Filter::Line", Literal => "|" ],

If it is an object, it will be cloned every time the client connects:

  Filter => POE::Filter::Line->new(Literal => "|"),

Be sure to "use" the appropriate POE::Filter subclass when specifying a "Filter" other than the default.

ServerError

"ServerError" is an optional callback that will be invoked when an established server connection has encountered some kind of error. It is triggered by POE::Wheel::ReadWrite's ErrorEvent. By default, the component will log any errors to STDERR. This may be suppressed by defining a quieter ServerError callback.

As with "ConnectError", it is invoked with the customary error parameters: $_[ARG0] will contain the name of the operation that failed. $_[ARG1] and $_[ARG2] will hold the numeric and string forms of $!, respectively.

Components usually disconnect on error. POE::Component::Client::TCP will shut down if the socket disconnects without being reconnected.

ServerFlushed

"ServerFlushed" is an optional callback to notify a program that ReadWrite's output buffers have completely flushed. It has no special parameters.

The component will shut down after a server flush if $heap->{shutdown} is set.

ServerInput

"ServerInput" is a required callback. It is called for each fully parsed input record received by POE::Wheel::ReadWrite. $_[ARG0] contains the input record, the format of which is determined by the "Filter" constructor parameter.

"SeverInput" will stop being called when $_[HEAP]{shutdown} is true. The most reliable way to set the "shutdown" member is to call $_[KERNEL]->yield("shutdown").

Public Events
POE::Component::Client::TCP handles a small number of public "command" messages. These may be posted into the client from an external session, or yielded from within the client.

  connect
The "connect" event causes POE::Component::Client::TCP to begin connecting to a server. It optionally includes a new RemoteHost and RemotePort, both of which will be used for subsequent reconnections.

  $_[KERNEL]->post(alias => connect => "127.0.0.1", 80);

If the client is already connected to a server, it will disconnect immediately before beginning the new connection procedure. Buffered input and output will be lost.

  reconnect
The "reconnect" command causes POE::Component::Client::TCP to immediately disconnect its current connection and begin reconnecting to its most recently set RemoteHost and RemotePort. Any buffered input and output will be lost.

  shutdown
The "shutdown" command tells POE::Component::Client::TCP to flush its buffers, disconnect, and begin DESTROY procedures.

All input will be discarded after receipt of "shutdown". All pending output will be written to the server socket before disconnecting and destructing.

Reserved Heap Members
POE::Component::Client::TCP requires some heap space for its own bookkeeping. The following members are used and should be used as directed, or with care.

This sample input handler is an example of most reserved heap members:

  sub handle_input {
    # Pending input from when we were connected.
    return unless $_[HEAP]{connected};

    # We've been shut down.
    return if $_[HEAP]{shutdown};

    my $input = $_[ARG0];
    $_[HEAP]{server}->put("you sent: $input");
  }

  server
The read-only "server" heap member contains the POE::Wheel object used to connect to or talk with the server. While the component is connecting, "server" will be a POE::Wheel::SocketFactory object. After the connection has been made, "server" is replaced with a POE::Wheel::ReadWrite object.

The most reliable way to avoid prematurely using "server" is to first check the "connected" reserved heap member. See the example above.

  shutdown
"shutdown" is a read-only flag that tells the component it's shutting down. It should only be by the "shutdown" event, which does other cleanup.

"shutdown" may be checked to avoid starting new work during a client's shutting-down procedure. See the example above.

  connected
"connected" is a read-only flag that indicates whether the component is currently connected.

  shutdown_on_error
"shutdown_on_error" is a read-only flag that governs the component's shutdown-on-error behavior. When true, POE::Component::Client::TCP will automatically shutdown when it encounters an error.

SEE ALSO
The SEE ALSO section in POE contains a table of contents covering the entire POE distribution.

POE::Component::Server::TCP is the server-side counterpart to this module.

This component uses and exposes features from POE::Filter, POE::Wheel::SocketFactory, and POE::Wheel::ReadWrite.

See "SYNOPSIS" in POE::Wheel::SocketFactory for a more efficient but lower-level way to create clients and servers.

CAVEATS
This looks nothing like what Ann envisioned.

POE::Component::Client::TCP is a generic client. As such, it's not tuned for any particular task. While it handles the common cases well and with a minimum of code, it may not be suitable for everything.

AUTHORS & COPYRIGHTS
POE::Component::Client::TCP is Copyright 2001-2013 by Rocco Caputo. All rights are reserved. POE::Component::Client::TCP is free software, and it may be redistributed and/or modified under the same terms as Perl itself.

POE::Component::Client::TCP is based on code, used with permission, from Ann Barcomb <kudra@domaintje.com>.

POE::Component::Client::TCP is based on code, used with permission, from Jos Boumans <kane@cpan.org>.