IO::Async::Connector - perform non-blocking socket connections


This object is used indirectly via an IO::Async::Loop:

 use IO::Async::Loop;
 my $loop = IO::Async::Loop->new;

    host     => "",
    service  => "http",
    socktype => 'stream',

    on_connected => sub {
       my ( $sock ) = @_;
       print "Now connected via $sock\n";

    on_resolve_error => sub { die "Cannot resolve - $_[-1]\n"; },
    on_connect_error => sub { die "Cannot connect - $_[0] failed $_[-1]\n"; },


This module extends an IO::Async::Loop to give it the ability to create socket connections in a non-blocking manner.

There are two modes of operation. Firstly, a list of addresses can be provided which will be tried in turn. Alternatively as a convenience, if a host and service name are provided instead of a list of addresses, these will be resolved using the underlying loop's resolve method into the list of addresses.

When attempting to connect to any among a list of addresses, there may be failures among the first attempts, before a valid connection is made. For example, the resolver may have returned some IPv6 addresses, but only IPv4 routes are valid on the system. In this case, the first connect(2) syscall will fail. This isn't yet a fatal error, if there are more addresses to try, perhaps some IPv4 ones.

For this reason, it is possible that the operation eventually succeeds even though some system calls initially fail. To be aware of individual failures, the optional on_fail callback can be used. This will be invoked on each individual socket(2) or connect(2) failure, which may be useful for debugging or logging.

Because this module simply uses the getaddrinfo resolver, it will be fully IPv6-aware if the underlying platform's resolver is. This allows programs to be fully IPv6-capable.


$loop->connect( %params )

This method performs a non-blocking connection to a given address or set of addresses, and invokes a continuation when the socket is connected.

In plain address mode, the %params hash takes the following keys:

addrs => ARRAY

Reference to an array of (possibly-multiple) address structures to attempt to connect to. Each should be in the layout described for addr. Such a layout is returned by the getaddrinfo named resolver.

addr => HASH or ARRAY

Shortcut for passing a single address to connect to; it may be passed directly with this key, instead of in another array on its own. This should be in a format recognised by IO::Async::OS's extract_addrinfo method. See also the EXAMPLES section.

local_addrs => ARRAY
local_addr => HASH or ARRAY

Optional. Similar to the addrs or addr parameters, these specify a local address or set of addresses to bind(2) the socket to before connect(2)ing it.

on_connected => CODE

A continuation that is invoked on a successful connect(22) call to a valid socket. It will be passed the connected socket handle, as an IO::Socket object.

 $on_connected->( $handle )
on_stream => CODE

An alternative to on_connected, a continuation that is passed an instance of IO::Async::Stream when the socket is connected. This is provided as a convenience for the common case that a Stream object is required as the transport for a Protocol object.

 $on_stream->( $stream )
on_socket => CODE

Similar to on_stream, but constructs an instance of IO::Async::Socket. This is most useful for SOCK_DGRAM or SOCK_RAW sockets.

 $on_socket->( $socket )
on_connect_error => CODE

A continuation that is invoked after all of the addresses have been tried, and none of them succeeded. It will be passed the most significant error that occurred, and the name of the operation it occurred in. Errors from the connect(2) syscall are considered most significant, then bind(2), then finally socket(2).

 $on_connect_error->( $syscall, $! )
on_fail => CODE

Optional. After an individual socket(2) or connect(2) syscall has failed, this callback is invoked to inform of the error. It is passed the name of the syscall that failed, the arguments that were passed to it, and the error it generated. I.e.

 $on_fail->( "socket", $family, $socktype, $protocol, $! );

 $on_fail->( "bind", $sock, $address, $! );

 $on_fail->( "connect", $sock, $address, $! );

Because of the "try all" nature when given a list of multiple addresses, this callback may be invoked multiple times, even before an eventual success.

When performing the resolution step too, the addrs or addr keys are ignored, and instead the following keys are taken:

host => STRING
service => STRING

The hostname and service name to connect to.

local_host => STRING
local_service => STRING

Optional. The hostname and/or service name to bind(2) the socket to locally before connecting to the peer.

family => INT
socktype => INT
protocol => INT
flags => INT

Optional. Other arguments to pass along with host and service to the getaddrinfo call.

socktype => STRING

Optionally may instead be one of the values 'stream', 'dgram' or 'raw' to stand for SOCK_STREAM, SOCK_DGRAM or SOCK_RAW. This utility is provided to allow the caller to avoid a separate use Socket only for importing these constants.

on_resolve_error => CODE

A continuation that is invoked when the name resolution attempt fails. This is invoked in the same way as the on_error continuation for the resolve method.

It is necessary to pass the socktype hint to the resolver when resolving the host/service names into an address, as some OS's getaddrinfo functions require this hint. A warning is emitted if neither socktype nor protocol hint is defined when performing a getaddrinfo lookup. To avoid this warning while still specifying no particular socktype hint (perhaps to invoke some OS-specific behaviour), pass 0 as the socktype value.

$future = $loop->connect( %params )

When returning a future, the on_connected, on_stream, on_socket and various on_*_error continuations are optional. When the socket is connected, the future will be given the connected socket handle. No direct support for automatically constructing a IO::Async::Stream or IO::Async::Socket object is provided.


Passing Plain Socket Addresses

The addr or addrs parameters should contain a definition of a plain socket address in a form that the IO::Async::OS extract_addrinfo method can use.

This example shows how to use the Socket functions to construct one for TCP port 8001 on address

    addr => {
       family   => "inet",
       socktype => "stream",
       port     => 8001,
       ip       => "",

This example shows another way to connect to a UNIX socket at echo.sock.

    addr => {
       family   => "unix",
       socktype => "stream",
       path     => "echo.sock",


Paul Evans <>