Accepting Connections Yourself

POE::Component::Server::TCP has a default mode where it accepts new connections and creates the sessions to handle them. Programs can do this themselves by providing their own "Acceptor" callbacks. See "Acceptor" for details.

Master Listener Session

At creation time, POE::Component::Server::TCP starts one POE::Session to listen for new connections. The component's "Alias" refers to this master session.

If "Acceptor" is specified, then it's up to that callback to deal with newly accepted sockets. Its parameters are that of POE::Wheel::SocketFactory's "SuccessEvent".

Otherwise, the default "Acceptor" callback will start a new session to handle each connection. These child sessions do not have their own aliases, but their "ClientConnected" and "ClientDisconnected" callbacks may be used to register and unregister the sessions with a shared namespace, such as a hash keyed on session IDs, or an object that manages such a hash.

  my %client_namespace;
  sub handle_client_connected {
    my $client_session_id = $_[SESSION]->ID;
    $client_namespace{$client_session_id} = \%anything;
  }
  sub handle_client_disconnected {
    my $client_session_id = $_[SESSION]->ID;
    $client_namespace{$client_session_id} = \%anything;
  }

The component's "Started" callback is invoked at the end of the master session's start-up routine. The @_[ARG0..$#_] parameters are set to a copy of the values in the server's "ListenerArgs" constructor parameter. The other parameters are standard for POE::Session's _start handlers.

The component's "Stopped" callback is invoked at the beginning of the master session's _stop routine. The parameters are standard for POE::Session's _stop handlers.

The component's "Error" callback is invoked when the server has a problem listening for connections. "Error" may also be called if the component's default acceptor has trouble accepting a connection. "Error" receives the usual ones for "FailureEvent" in POE::Wheel::SocketFactory and "ErrorEvent" in POE::Wheel::ReadWrite.

Default Child Connection Sessions

If "Acceptor" isn't specified, POE::Component::Server::TCP's default handler will start a new session for each new client connection. As mentioned above, these child sessions have no aliases of their own, but they may set aliases or register themselves another way during their "ClientConnected" and "ClientDisconnected" callbacks.

It can't be stressed enough that the following callbacks are executed within the context of dynamic child sessions---one per client connection---and not in the master listening session. This has been a major point of confusion. We welcome suggestions for making this clearer.

The component's "ClientInput" callback defines how child sessions will handle input from their clients. Its parameters are that of POE::Wheel::ReadWrite's "InputEvent".

As mentioned "ClientConnected" is called at the end of the child session's "_start" routine. The "ClientConneted" callback receives the same parameters as the client session's _start does. The arrayref passed to the constructor's "Args" parameter is flattened and included in "ClientConnected"'s parameters as @_[ARG0..$#_].

  sub handle_client_connected {
    my @constructor_args = @_[ARG0..$#_];
    ...
  }

"ClientPreConnect" is called before "ClientConnected", and its purpose is to allow programs to reject connections or condition sockets before they're given to POE::Wheel::ReadWrite for management.

The "ClientPreConnect" handler is called with the client socket in $_[ARG0], and its return value is significant. It must return a valid client socket if the connection is acceptable. It must return undef to reject the connection.

Most $_[HEAP] values are valid in the "ClientPreConnect" handler. Obviously, $_[HEAP]{client} is not because that wheel hasn't been created yet.

In the following example, the "ClientPreConnect" handler returns the client socket after it has been upgraded to an SSL connection.

  sub handle_client_pre_connect {
    # Make sure the remote address and port are valid.
    return undef unless validate(
      $_[HEAP]{remote_ip}, $_[HEAP]{remote_port}
    );
    # SSLify the socket, which is in $_[ARG0].
    my $socket = eval { Server_SSLify($_[ARG0]) };
    return undef if $@;
    # Return the SSL-ified socket.
    return $socket;
  }

"ClientDisconnected" is called when the client has disconnected, either because the remote socket endpoint has closed or the local endpoint has been closed by the server. This doesn't mean the client's session has ended, but the session most likely will very shortly. "ClientDisconnected" is called from a couple disparate places within the component, so its parameters are neither consistent nor generally useful.

"ClientError" is called when an error has occurred on the socket. Its parameters are those of POE::Wheel::ReadWrite's "ErrorEvent".

"ClientFlushed" is called when all pending output has been flushed to the client socket. Its parameters come from POE::Wheel::ReadWrite's "ErrorEvent".

Performance Considerations

This ease of use comes at a price: POE::Component::Server::TCP often performs significantly slower than a comparable server written with POE::Wheel::SocketFactory and POE::Wheel::ReadWrite.

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.

Special Needs Considerations

POE::Component::Server::TCP is written to be easy for the most common use cases. Programs with more special needs should consider using POE::Wheel::SocketFactory and POE::Wheel::ReadWrite instead. These are lower-level modules, and using them requires more effort. They are more flexible and customizable, however.

new

new() starts a server based on POE::Component::Server::TCP and returns a session ID for the master listening session. All error handling is done within the server, via the "Error" and "ClientError" callbacks.

The server may be shut down by posting a "shutdown" event to the master session, either by its ID or the name given to it by the "Alias" parameter.

POE::Component::Server::TCP does a lot of work in its constructor. The design goal is to push as much overhead into one-time construction so that ongoing run-time has less overhead. Because of this, the server's constructor can take quite a daunting number of parameters.

POE::Component::Server::TCP always returns a POE::Session ID for the session that will be listening for new connections.

Many of the constructor parameters have been previously described. They are covered briefly again below.

Server Session Configuration

These constructor parameters affect POE::Component::Server::TCP's main listening session.

Acceptor

"Acceptor" defines a CODE reference that POE::Wheel::SocketFactory's "SuccessEvent" will trigger to handle new connections. Therefore the parameters passed to "Acceptor" are identical to those given to "SuccessEvent".

"Acceptor" is optional; the default handler will create a new session for each connection. All the "Client" constructor parameters are used to customize this session. In other words, "ClientInput" and such are not used when "Acceptor" is set.

The default "Acceptor" adds significant convenience and flexibility to POE::Component::Server::TCP, but it's not always a good fit for every application. In some cases, a custom "Acceptor" or even rolling one's own server with POE::Wheel::SocketFactory and POE::Wheel::ReadWrite may be better and/or faster.

  Acceptor => sub {
    my ($socket, $remote_address, $remote_port) = @_[ARG0..ARG2];
    # Set up something to interact with the client.
  }

Address

"Address" defines a single interface address the server will bind to. It defaults to INADDR_ANY or INADDR6_ANY, when using IPv4 or IPv6, respectively. It is often used with "Port".

The value in "Address" is passed to POE::Wheel::SocketFactory's "BindAddress" parameter, so it may be in whatever form that module supports. At the time of this writing, that may be a dotted IPv4 quad, an IPv6 address, a host name, or a packed Internet address. See also "Hostname".

  Address => '127.0.0.1'   # Localhost IPv4
  Address => "::1"         # Localhost IPv6

Alias

"Alias" is an optional name that will be given to the server's master listening session. Events sent to this name will not be delivered to individual connections.

The server's "Alias" may be important if it's necessary to shut a server down.

  sub sigusr1_handler {
    $_[KERNEL]->post(chargen_server => 'shutdown');
    $_[KERNEL]->sig_handled();
  }

Concurrency

"Concurrency" controls how many connections may be active at the same time. It defaults to -1, which allows POE::Component::Server::TCP to accept concurrent connections until the process runs out of resources.

Setting "Concurrency" to 0 prevents the server from accepting new connections. This may be useful if a server must perform lengthy initialization before allowing connections. When the initialization finishes, it can yield(set_concurrency => -1) to enable connections. Likewise, a running server may yield(set_concurrency => 0) or any other number to dynamically tune its concurrency. See "EVENTS" for more about the set_concurrency event.

Note: For "Concurrency" to work with a custom "Acceptor", the server's listening session must receive a "disconnected" event whenever clients disconnect. Otherwise the listener cannot mediate between its connections.

Example:

  Acceptor => sub {
    # ....
    POE::Session->create(
      # ....
      inline_states => {
        _start => sub {
          # ....
          # remember who our parent is
          $_[HEAP]->{server_tcp} = $_[SENDER]->ID;
          # ....
        },
        got_client_disconnect => sub {
          # ....
          $_[KERNEL]->post( $_[HEAP]->{server_tcp} => 'disconnected' );
          # ....
        }
      }
    );
  }

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 or Socket6, depending on your version of Perl. Also be sure to have Socket::GetAddrInfo installed, which is required by POE::Wheel::SocketFactory for IPv6 support.

Error

"Error" is the callback that will be invoked when the server socket reports an error. The Error callback will be used to handle POE::Wheel::SocketFactory's FailureEvent, so it will receive the same parameters as discussed there.

A default error handler will be provided if Error is omitted. The default handler will log the error to STDERR and shut down the server. Active connections will be permitted to complete their transactions.

  Error => sub {
    my ($syscall_name, $err_num, $err_str) = @_[ARG0..ARG2];
    # Handle the error.
  }

Hostname

"Hostname" is the optional non-packed name of the interface the TCP server will bind to. The hostname will always be resolved via inet_aton() and so can either be a dotted quad or a name. Name resolution is a one-time start-up action; there are no ongoing run-time penalties for using it.

"Hostname" guarantees name resolution, where "Address" does not. It's therefore preferred to use "Hostname" in cases where resolution must always be done.

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.

Remember: These InlineStates handlers will be added to the client sessions, not to the main listening session. A yield() in the listener will not reach these handlers.

If POE::Kernel::ASSERT_USAGE is enabled, the constructor will croak() if it detects a state that it uses internally. For example, please use the "Started" and "Stopped" callbacks if you want to specify your own "_start" and "_stop" events respectively.

ObjectStates

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

Remember: These ObjectStates handlers will be added to the client sessions, not to the main listening session. A yield() in the listener will not reach these handlers.

If POE::Kernel::ASSERT_USAGE is enabled, the constructor will croak() if it detects a state that it uses internally. For example, please use the "Started" and "Stopped" callbacks if you want to specify your own "_start" and "_stop" events respectively.

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.

Remember: These PackageStates handlers will be added to the client sessions, not to the main listening session. A yield() in the listener will not reach these handlers.

If POE::Kernel::ASSERT_USAGE is enabled, the constructor will croak() if it detects a state that it uses internally. For example, please use the "Started" and "Stopped" callbacks if you want to specify your own "_start" and "_stop" events respectively.

Port

"Port" contains the port the listening socket will be bound to. It defaults to 0, which usually lets the operating system pick a port at random.

  Port => 30023

It is often used with "Address".

Started

"Started" sets an optional callback that will be invoked within the main server session's context. It notifies the server that it has fully started. The callback's parameters are the usual for a session's _start handler.

Stopped

"Stopped" sets an optional callback that will be invoked within the main server session's context. It notifies the server that it has fully stopped. The callback's parameters are the usual for a session's _stop handler.

ListenerArgs

"ListenerArgs" is passed to the listener session as the "args" parameter. In other words, it must be an arrayref, and the values are passed into the "Started" handler as ARG0, ARG1, etc.

Connection Session Configuration

These constructor parameters affect the individual sessions that interact with established connections.

ClientArgs

"ClientArgs" is optional. When specified, it holds an ARRAYREF that will be expanded one level and passed to the "ClientConnected" callback in @_[ARG0..$#_].

ClientConnected

Each new client connection is handled by a new POE::Session instance. "ClientConnected" is a callback that notifies the application when a client's session is started and ready for operation. Banners are often sent to the remote client from this callback.

The @_[ARG0..$#_] parameters to "ClientConnected" are a copy of the values in the "ClientArgs" constructor parameter's array reference. The other @_ members are standard for a POE::Session _start handler.

"ClientConnected" is called once per session start-up. It will never be called twice for the same connection.

  ClientConnected => sub {
    $_[HEAP]{client}->put("Hello, client!");
    # Other client initialization here.
  },

ClientDisconnected

"ClientDisconnected" is a callback that will be invoked when the client disconnects or has been disconnected by the server. It's useful for cleaning up global client information, such as chat room structures. "ClientDisconnected" callbacks receive the usual POE parameters, but nothing special is included.

  ClientDisconnected => sub {
    warn "Client disconnected"; # log it
  }

ClientError

The "ClientError" callback is invoked when a client socket reports an error. "ClientError" is called with POE's usual parameters, plus the common error parameters: $_[ARG0] describes what was happening at the time of failure. $_[ARG1] and $_[ARG2] contain the numeric and string versions of $!, respectively.

"ClientError" is optional. If omitted, POE::Component::Server::TCP will provide a default callback that logs most errors to STDERR.

If "ClientShutdownOnError" is set, the connection will be shut down after "ClientError" returns. If "ClientDisconnected" is specified, it will be called as the client session is cleaned up.

"ClientError" is triggered by POE::Wheel::ReadWrite's ErrorEvent, so it follows that event's form. Please see the ErrorEvent documentation in POE::Wheel::ReadWrite for more details.

  ClientError => sub {
    my ($syscall_name, $error_num, $error_str) = @_[ARG0..ARG2];
    # Handle the client error here.
  }

ClientFilter

"ClientFilter" specifies the POE::Filter object or class that will parse input from each client and serialize output before it's sent to each client.

"ClientFilter" may be a SCALAR, in which case it should name the POE::Filter class to use. Each new connection will be given a freshly instantiated filter of that class. No constructor parameters will be passed.

  ClientFilter => "POE::Filter::Stream",

Some filters require constructor parameters. These may be specified by an ARRAYREF. The first element is the POE::Filter class name, and subsequent elements are passed to the class' constructor.

  ClientFilter => [ "POE::Filter::Line", Literal => "\n" ],

"ClientFilter" may also be given an archetypical POE::Filter OBJECT. In this case, each new client session will receive a clone() of the given object.

  ClientFilter => POE::Filter::Line->new(Literal => "\n"),

"ClientFilter" is optional. The component will use "POE::Filter::Line" if it is omitted. There is "ClientInputFilter" and "ClientOutputFilter" if you want to specify a different filter for both directions.

Filter modules are not automatically loaded. Be sure that the program loads the class before using it.

ClientFlushed

"ClientFlushed" exposes POE::Wheel::ReadWrite's "FlushedEvent" as a callback. It is called whenever the client's output buffer has been fully flushed to the client socket. At this point it's safe to shut down the socket without losing data.

"ClientFlushed" is useful for streaming servers, where a "flushed" event signals the need to send more data.

  ClientFlushed => sub {
    my $data_source = $_[HEAP]{file_handle};
    my $read_count = sysread($data_source, my $buffer = "", 65536);
    if ($read_count) {
      $_[HEAP]{client}->put($buffer);
    }
    else {
      $_[KERNEL]->yield("shutdown");
    }
  },

POE::Component::Server::TCP's default "Acceptor" ensures that data is flushed before finishing a client shutdown.

ClientInput

"ClientInput" defines a per-connection callback to handle client input. This callback receives its parameters directly from POE::Wheel::ReadWrite's "InputEvent". ARG0 contains the input record, the format of which is defined by "ClientFilter" or "ClientInputFilter". ARG1 has the wheel's unique ID, and so on. Please see POE:Wheel::ReadWrite for an in-depth description of "InputEvent".

"ClientInput" and "Acceptor" are mutually exclusive. Enabling one prohibits the other.

  ClientInput => sub {
    my $input = $_[ARG0];
    $_[HEAP]{wheel}->put("You said: $input");
  },

ClientInputFilter

"ClientInputFilter" is used with "ClientOutputFilter" to specify different protocols for input and output. Both must be used together. Both follow the same usage as "ClientFilter". Overrides the filter set by "ClientFilter".

  ClientInputFilter  => [ "POE::Filter::Line", Literal => "\n" ],
  ClientOutputFilter => 'POE::Filter::Stream',

ClientOutputFilter

"ClientOutputFilter" is used with "ClientInputFilter" to specify different protocols for input and output. Both must be used together. Both follow the same usage as "ClientFilter". Overrides the filter set by "ClientFilter".

  ClientInputFilter  => POE::Filter::Line->new(Literal => "\n"),
  ClientOutputFilter => 'POE::Filter::Stream',

ClientShutdownOnError

"ClientShutdownOnError" tells the component whether client connections should be shut down automatically if an error is detected. It defaults to "true". Setting it to false (0, undef, "") turns off this feature.

The application is responsible for dealing with client errors if this feature is disabled. Not doing so may cause the component to emit a constant stream of errors, eventually bogging down the application with dead connections that spin out of control.

Yes, this is terrible. You have been warned.

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::Server::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.

SessionType

"SessionType" specifies the POE::Session subclass that will be created for each new client connection. "POE::Session" is the default.

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

Main Server Commands

These events must be sent to the main server, usually by the alias set in its Alias parameter.

disconnected

The "disconnected" event informs the TCP server that a connection was closed. It is needed when using "Concurrency" with an "Acceptor" callback. The custom Acceptor must provide its own disconnect notification so that the server's connection counting logic works.

Otherwise Concurrency clients will be accepted, and then no more. The server will never know when clients have disconnected.

set_concurrency

"set_concurrency" set the number of simultaneous connections the server will be willing to accept. See "Concurrency" for more details. "set_concurrency" must have one parameter: the new maximum connection count.

  $kernel->call("my_server_alias", "set_concurrency", $max_count);

shutdown

The "shutdown" event starts a graceful server shutdown. No new connections will be accepted. Existing connections will be allowed to finish. The server will be destroyed after the last connection ends.

Per-Connection Commands

These commands affect each client connection session.

shutdown

Sending "shutdown" to an individual client session instructs the server to gracefully shut down that connection. No new input will be received, and any buffered output will be sent before the session ends.

Client sessions usually yield("shutdown") when they wish to disconnect the client.

  ClientInput => sub {
    if ($_[ARG0] eq "quit") {
      $_[HEAP]{client}->put("B'bye!");
      $_[KERNEL]->yield("shutdown");
      return;
    }
    # Handle other input here.
  },

HEAP Members for Master Listening Sessions

The master listening session holds different data than client connections.

alias

$_[HEAP]{alias} contains the server's Alias.

concurrency

$_[HEAP]{concurrency} remembers the server's "Concurrency" parameter.

connections

$_[HEAP]{connections} is used to track the current number of concurrent client connections. It's incremented whenever a new connection is accepted, and it's decremented whenever a client disconnects.

listener

$_[HEAP]{listener} contains the POE::Wheel::SocketFactory object used to listen for connections and accept them.

HEAP Members for Connection Sessions

These data members exist within the individual connections' sessions.

client

$_[HEAP]{client} contains a POE::Wheel::ReadWrite object used to interact with the client. All POE::Wheel::ReadWrite methods work.

got_an_error

$_[HEAP]{got_an_error} remembers whether the client connection has already encountered an error. It is part of the shutdown-on-error procedure.

remote_ip

$_[HEAP]{remote_ip} contains the remote client's numeric address in human-readable form.

remote_port

$_[HEAP]{remote_port} contains the remote client's numeric socket port in human-readable form.

remote_addr

$_[HEAP]{remote_addr} contains the remote client's packed socket address in computer-readable form.

shutdown

$_[HEAP]{shutdown} is true if the client is in the process of shutting down. The component uses it to ignore client input during shutdown, and to close the connection after pending output has been flushed.

shutdown_on_error

$_[HEAP]{shutdown_on_error} remembers whether the client connection should automatically shut down if an error occurs.