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.\" ========================================================================
.\"
.IX Title "IO::Async::Listener 3pm"
.TH IO::Async::Listener 3pm 2024-02-04 "perl v5.38.2" "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
"IO::Async::Listener" \- listen on network sockets for incoming connections
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\&   use Future::AsyncAwait;
\&   use IO::Async::Listener;
\&
\&   use IO::Async::Loop;
\&   my $loop = IO::Async::Loop\->new;
\&
\&   my $listener = IO::Async::Listener\->new(
\&      on_stream => sub {
\&         my ( undef, $stream ) = @_;
\&
\&         $stream\->configure(
\&            on_read => sub {
\&               my ( $self, $buffref, $eof ) = @_;
\&               $self\->write( $$buffref );
\&               $$buffref = "";
\&               return 0;
\&            },
\&         );
\&
\&         $loop\->add( $stream );
\&      },
\&   );
\&
\&   $loop\->add( $listener );
\&
\&   await $listener\->listen(
\&      service  => "echo",
\&      socktype => \*(Aqstream\*(Aq,
\&   );
\&
\&   $loop\->run;
.Ve
.PP
This object can also be used indirectly via an IO::Async::Loop:
.PP
.Vb 1
\&   use IO::Async::Stream;
\&
\&   use IO::Async::Loop;
\&   my $loop = IO::Async::Loop\->new;
\&
\&   await $loop\->listen(
\&      service  => "echo",
\&      socktype => \*(Aqstream\*(Aq,
\&
\&      on_stream => sub {
\&         ...
\&      },
\&   );
\&
\&   $loop\->run;
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
This subclass of IO::Async::Handle adds behaviour which watches a socket in
listening mode, to accept incoming connections on them.
.PP
A Listener can be constructed and given a existing socket in listening mode.
Alternatively, the Listener can construct a socket by calling the \f(CW\*(C`listen\*(C'\fR
method. Either a list of addresses can be provided, or a service name can be
looked up using the underlying loop's \f(CW\*(C`resolve\*(C'\fR method.
.SH EVENTS
.IX Header "EVENTS"
The following events are invoked, either using subclass methods or CODE
references in parameters:
.ie n .SS "on_accept $clientsocket | $handle"
.el .SS "on_accept \f(CW$clientsocket\fP | \f(CW$handle\fP"
.IX Subsection "on_accept $clientsocket | $handle"
Invoked whenever a new client connects to the socket.
.PP
If neither \f(CW\*(C`handle_constructor\*(C'\fR nor \f(CW\*(C`handle_class\*(C'\fR parameters are set, this
will be invoked with the new client socket directly. If a handle constructor
or class are set, this will be invoked with the newly-constructed handle,
having the new socket already configured onto it.
.ie n .SS "on_stream $stream"
.el .SS "on_stream \f(CW$stream\fP"
.IX Subsection "on_stream $stream"
An alternative to \f(CW\*(C`on_accept\*(C'\fR, this is passed an instance of
IO::Async::Stream when a new client connects. This is provided as a
convenience for the common case that a Stream object is required as the
transport for a Protocol object.
.PP
This is now vaguely deprecated in favour of using \f(CW\*(C`on_accept\*(C'\fR with a handle
constructor or class.
.ie n .SS "on_socket $socket"
.el .SS "on_socket \f(CW$socket\fP"
.IX Subsection "on_socket $socket"
Similar to \f(CW\*(C`on_stream\*(C'\fR, but constructs an instance of IO::Async::Socket.
This is most useful for \f(CW\*(C`SOCK_DGRAM\*(C'\fR or \f(CW\*(C`SOCK_RAW\*(C'\fR sockets.
.PP
This is now vaguely deprecated in favour of using \f(CW\*(C`on_accept\*(C'\fR with a handle
constructor or class.
.ie n .SS "on_accept_error $socket, $errno"
.el .SS "on_accept_error \f(CW$socket\fP, \f(CW$errno\fP"
.IX Subsection "on_accept_error $socket, $errno"
Optional. Invoked if the \f(CW\*(C`accept\*(C'\fR syscall indicates an error (other than
\&\f(CW\*(C`EAGAIN\*(C'\fR or \f(CW\*(C`EWOULDBLOCK\*(C'\fR). If not provided, failures of \f(CW\*(C`accept\*(C'\fR will
be passed to the main \f(CW\*(C`on_error\*(C'\fR handler.
.SH PARAMETERS
.IX Header "PARAMETERS"
The following named parameters may be passed to \f(CW\*(C`new\*(C'\fR or \f(CW\*(C`configure\*(C'\fR:
.SS "on_accept => CODE"
.IX Subsection "on_accept => CODE"
.SS "on_stream => CODE"
.IX Subsection "on_stream => CODE"
.SS "on_socket => CODE"
.IX Subsection "on_socket => CODE"
CODE reference for the event handlers. Because of the mutually-exclusive
nature of their behaviour, only one of these may be set at a time. Setting one
will remove the other two.
.SS "handle => IO"
.IX Subsection "handle => IO"
The IO handle containing an existing listen-mode socket.
.SS "handle_constructor => CODE"
.IX Subsection "handle_constructor => CODE"
Optional. If defined, gives a CODE reference to be invoked every time a new
client socket is accepted from the listening socket. It is passed the listener
object itself, and is expected to return a new instance of
IO::Async::Handle or a subclass, used to wrap the new client socket.
.PP
.Vb 1
\&   $handle = $handle_constructor\->( $listener );
.Ve
.PP
This can also be given as a subclass method
.PP
.Vb 1
\&   $handle = $listener\->handle_constructor();
.Ve
.SS "handle_class => STRING"
.IX Subsection "handle_class => STRING"
Optional. If defined and \f(CW\*(C`handle_constructor\*(C'\fR isn't, then new wrapper handles
are constructed by invoking the \f(CW\*(C`new\*(C'\fR method on the given class name, passing
in no additional parameters.
.PP
.Vb 1
\&   $handle = $handle_class\->new();
.Ve
.PP
This can also be given as a subclass method
.PP
.Vb 1
\&   $handle = $listener\->handle_class\->new;
.Ve
.SS "acceptor => STRING|CODE"
.IX Subsection "acceptor => STRING|CODE"
Optional. If defined, gives the name of a method or a CODE reference to use to
implement the actual accept behaviour. This will be invoked as:
.PP
.Vb 1
\&   ( $accepted ) = await $listener\->acceptor( $socket );
\&
\&   ( $handle ) = await $listener\->acceptor( $socket, handle => $handle );
.Ve
.PP
It is invoked with the listening socket as its its argument, and optionally
an IO::Async::Handle instance as a named parameter, and is expected to
return a \f(CW\*(C`Future\*(C'\fR that will eventually yield the newly-accepted socket or
handle instance, if such was provided.
.SH METHODS
.IX Header "METHODS"
The following methods documented in \f(CW\*(C`await\*(C'\fR expressions return Future
instances.
.SS acceptor
.IX Subsection "acceptor"
.Vb 1
\&   $acceptor = $listener\->acceptor;
.Ve
.PP
Returns the currently-set \f(CW\*(C`acceptor\*(C'\fR method name or code reference. This may
be of interest to Loop \f(CW\*(C`listen\*(C'\fR extension methods that wish to extend or wrap
it.
.SS sockname
.IX Subsection "sockname"
.Vb 1
\&   $name = $listener\->sockname;
.Ve
.PP
Returns the \f(CW\*(C`sockname\*(C'\fR of the underlying listening socket
.SS family
.IX Subsection "family"
.Vb 1
\&   $family = $listener\->family;
.Ve
.PP
Returns the socket address family of the underlying listening socket
.SS socktype
.IX Subsection "socktype"
.Vb 1
\&   $socktype = $listener\->socktype;
.Ve
.PP
Returns the socket type of the underlying listening socket
.SS listen
.IX Subsection "listen"
.Vb 1
\&   await $listener\->listen( %params );
.Ve
.PP
This method sets up a listening socket and arranges for the acceptor callback
to be invoked each time a new connection is accepted on the socket.
.PP
Most parameters given to this method are passed into the \f(CW\*(C`listen\*(C'\fR method of
the IO::Async::Loop object. In addition, the following arguments are also
recognised directly:
.IP "on_listen => CODE" 8
.IX Item "on_listen => CODE"
Optional. A callback that is invoked when the listening socket is ready.
Similar to that on the underlying loop method, except it is passed the
listener object itself.
.Sp
.Vb 1
\&   $on_listen\->( $listener );
.Ve
.SH EXAMPLES
.IX Header "EXAMPLES"
.SS "Listening on UNIX Sockets"
.IX Subsection "Listening on UNIX Sockets"
The \f(CW\*(C`handle\*(C'\fR argument can be passed an existing socket already in listening
mode, making it possible to listen on other types of socket such as UNIX
sockets.
.PP
.Vb 2
\&   use IO::Async::Listener;
\&   use IO::Socket::UNIX;
\&
\&   use IO::Async::Loop;
\&   my $loop = IO::Async::Loop\->new;
\&
\&   my $listener = IO::Async::Listener\->new(
\&      on_stream => sub {
\&         my ( undef, $stream ) = @_;
\&
\&         $stream\->configure(
\&            on_read => sub {
\&               my ( $self, $buffref, $eof ) = @_;
\&               $self\->write( $$buffref );
\&               $$buffref = "";
\&               return 0;
\&            },
\&         );
\&
\&         $loop\->add( $stream );
\&      },
\&   );
\&
\&   $loop\->add( $listener );
\&
\&   my $socket = IO::Socket::UNIX\->new(
\&      Local => "echo.sock",
\&      Listen => 1,
\&   ) or die "Cannot make UNIX socket \- $!\en";
\&
\&   $listener\->listen(
\&      handle => $socket,
\&   );
\&
\&   $loop\->run;
.Ve
.SS "Passing Plain Socket Addresses"
.IX Subsection "Passing Plain Socket Addresses"
The \f(CW\*(C`addr\*(C'\fR or \f(CW\*(C`addrs\*(C'\fR parameters should contain a definition of a plain
socket address in a form that the IO::Async::OS \f(CW\*(C`extract_addrinfo\*(C'\fR
method can use.
.PP
This example shows how to listen on TCP port 8001 on address 10.0.0.1:
.PP
.Vb 9
\&   $listener\->listen(
\&      addr => {
\&         family   => "inet",
\&         socktype => "stream",
\&         port     => 8001,
\&         ip       => "10.0.0.1",
\&      },
\&      ...
\&   );
.Ve
.PP
This example shows another way to listen on a UNIX socket, similar to the
earlier example:
.PP
.Vb 8
\&   $listener\->listen(
\&      addr => {
\&         family   => "unix",
\&         socktype => "stream",
\&         path     => "echo.sock",
\&      },
\&      ...
\&   );
.Ve
.SS "Using A Kernel-Assigned Port Number"
.IX Subsection "Using A Kernel-Assigned Port Number"
Rather than picking a specific port number, is it possible to ask the kernel
to assign one arbitrarily that is currently free. This can be done by
requesting port number 0 (which is actually the default if no port number is
otherwise specified). To determine which port number the kernel actually
picked, inspect the \f(CW\*(C`sockport\*(C'\fR accessor on the actual socket filehandle.
.PP
Either use the Future returned by the \f(CW\*(C`listen\*(C'\fR method:
.PP
.Vb 5
\&   $listener\->listen(
\&      addr => { family => "inet" },
\&   )\->on_done( sub {
\&      my ( $listener ) = @_;
\&      my $socket = $listener\->read_handle;
\&
\&      say "Now listening on port ", $socket\->sockport;
\&   });
.Ve
.PP
Or pass an \f(CW\*(C`on_listen\*(C'\fR continuation:
.PP
.Vb 2
\&   $listener\->listen(
\&      addr => { family => "inet" },
\&
\&      on_listen => sub {
\&         my ( $listener ) = @_;
\&         my $socket = $listener\->read_handle;
\&
\&         say "Now listening on port ", $socket\->sockport;
\&      },
\&   );
.Ve
.SH AUTHOR
.IX Header "AUTHOR"
Paul Evans <leonerd@leonerd.org.uk>