Provided by: libio-async-perl_0.61-1_all 
NAME
"IO::Async::Resolver" - performing name resolutions asynchronously
SYNOPSIS
This object is used indirectly via an "IO::Async::Loop":
use IO::Async::Loop;
my $loop = IO::Async::Loop->new;
$loop->resolver->getaddrinfo(
host => "www.example.com",
service => "http",
)->on_done( sub {
foreach my $addr ( @_ ) {
printf "http://www.example.com can be reached at " .
"socket(%d,%d,%d) + connect('%v02x')\n",
@{$addr}{qw( family socktype protocol addr )};
}
});
$loop->resolve( type => 'getpwuid', data => [ $< ] )
->on_done( sub {
print "My passwd ent: " . join( "|", @_ ) . "\n";
});
$loop->run;
DESCRIPTION
This module extends an "IO::Async::Loop" to use the system's name resolver functions
asynchronously. It provides a number of named resolvers, each one providing an
asynchronous wrapper around a single resolver function.
Because the system may not provide asynchronous versions of its resolver functions, this
class is implemented using a "IO::Async::Function" object that wraps the normal (blocking)
functions. In this case, name resolutions will be performed asynchronously from the rest
of the program, but will likely be done by a single background worker process, so will be
processed in the order they were requested; a single slow lookup will hold up the queue of
other requests behind it. To mitigate this, multiple worker processes can be used; see the
"workers" argument to the constructor.
The "idle_timeout" parameter for the underlying "IO::Async::Function" object is set to a
default of 30 seconds, and "min_workers" is set to 0. This ensures that there are no spare
processes sitting idle during the common case of no outstanding requests.
METHODS
$loop->resolve( %params ) ==> @result
Performs a single name resolution operation, as given by the keys in the hash.
The %params hash keys the following keys:
type => STRING
Name of the resolution operation to perform. See BUILT-IN RESOLVERS for the list
of available operations.
data => ARRAY
Arguments to pass to the resolver function. Exact meaning depends on the specific
function chosen by the "type"; see BUILT-IN RESOLVERS.
timeout => NUMBER
Optional. Timeout in seconds, after which the resolver operation will abort with a
timeout exception. If not supplied, a default of 10 seconds will apply.
$resolver->resolve( %params )
When not returning a future, additional parameters can be given containing the
continuations to invoke on success or failure:
on_resolved => CODE
A continuation that is invoked when the resolver function returns a successful
result. It will be passed the array returned by the resolver function.
$on_resolved->( @result )
on_error => CODE
A continuation that is invoked when the resolver function fails. It will be passed
the exception thrown by the function.
$resolver->getaddrinfo( %args ) ==> @addrs
A shortcut wrapper around the "getaddrinfo" resolver, taking its arguments in a more
convenient form.
host => STRING
service => STRING
The host and service names to look up. At least one must be provided.
family => INT or STRING
socktype => INT or STRING
protocol => INT
Hint values used to filter the results.
flags => INT
Flags to control the getaddrinfo(3) function. See the "AI_*" constants in Socket's
"getaddrinfo" function for more detail.
passive => BOOL
If true, sets the "AI_PASSIVE" flag. This is provided as a convenience to avoid
the caller from having to import the "AI_PASSIVE" constant from "Socket".
timeout => NUMBER
Time in seconds after which to abort the lookup with a "Timed out" exception
On success, the future will yield the result as a list of HASH references; each containing
one result. Each result will contain fields called "family", "socktype", "protocol" and
"addr". If requested by "AI_CANONNAME" then the "canonname" field will also be present.
As a specific optimisation, this method will try to perform a lookup of numeric values
synchronously, rather than asynchronously, if it looks likely to succeed.
Specifically, if the service name is entirely numeric, and the hostname looks like an IPv4
or IPv6 string, a synchronous lookup will first be performed using the "AI_NUMERICHOST"
flag. If this gives an "EAI_NONAME" error, then the lookup is performed asynchronously
instead.
$resolver->getaddrinfo( %args )
When not returning a future, additional parameters can be given containing the
continuations to invoke on success or failure:
on_resolved => CODE
Callback which is invoked after a successful lookup.
$on_resolved->( @addrs )
on_error => CODE
Callback which is invoked after a failed lookup, including for a timeout.
$on_error->( $exception )
$resolver->getnameinfo( %args ) ==> ( $host, $service )
A shortcut wrapper around the "getnameinfo" resolver, taking its arguments in a more
convenient form.
addr => STRING
The packed socket address to look up.
flags => INT
Flags to control the getnameinfo(3) function. See the "NI_*" constants in Socket's
"getnameinfo" for more detail.
numerichost => BOOL
numericserv => BOOL
dgram => BOOL
If true, set the "NI_NUMERICHOST", "NI_NUMERICSERV" or "NI_DGRAM" flags.
numeric => BOOL
If true, sets both "NI_NUMERICHOST" and "NI_NUMERICSERV" flags.
timeout => NUMBER
Time in seconds after which to abort the lookup with a "Timed out" exception
As a specific optimisation, this method will try to perform a lookup of numeric values
synchronously, rather than asynchronously, if both the "NI_NUMERICHOST" and
"NI_NUMERICSERV" flags are given.
$future = $resolver->getnameinfo( %args )
When not returning a future, additional parameters can be given containing the
continuations to invoke on success or failure:
on_resolved => CODE
Callback which is invoked after a successful lookup.
$on_resolved->( $host, $service )
on_error => CODE
Callback which is invoked after a failed lookup, including for a timeout.
$on_error->( $exception )
FUNCTIONS
register_resolver( $name, $code )
Registers a new named resolver function that can be called by the "resolve" method. All
named resolvers must be registered before the object is constructed.
$name The name of the resolver function; must be a plain string. This name will be used
by the "type" argument to the "resolve" method, to identify it.
$code A CODE reference to the resolver function body. It will be called in list context,
being passed the list of arguments given in the "data" argument to the "resolve"
method. The returned list will be passed to the "on_resolved" callback. If the
code throws an exception at call time, it will be passed to the "on_error"
continuation. If it returns normally, the list of values it returns will be passed
to "on_resolved".
BUILT-IN RESOLVERS
The following resolver names are implemented by the same-named perl function, taking and
returning a list of values exactly as the perl function does:
getpwnam getpwuid
getgrnam getgrgid
getservbyname getservbyport
gethostbyname gethostbyaddr
getnetbyname getnetbyaddr
getprotobyname getprotobynumber
The following three resolver names are implemented using the Socket module.
getaddrinfo_hash
getaddrinfo_array
getnameinfo
The "getaddrinfo_hash" resolver takes arguments in a hash of name/value pairs and returns
a list of hash structures, as the "Socket::getaddrinfo" function does. For neatness it
takes all its arguments as named values; taking the host and service names from arguments
called "host" and "service" respectively; all the remaining arguments are passed into the
hints hash.
The "getaddrinfo_array" resolver behaves more like the "Socket6" version of the function.
It takes hints in a flat list, and mangles the result of the function, so that the
returned value is more useful to the caller. It splits up the list of 5-tuples into a list
of ARRAY refs, where each referenced array contains one of the tuples of 5 values.
As an extra convenience to the caller, both resolvers will also accept plain string names
for the "family" argument, converting "inet" and possibly "inet6" into the appropriate
"AF_*" value, and for the "socktype" argument, converting "stream", "dgram" or "raw" into
the appropriate "SOCK_*" value.
For backward-compatibility with older code, the resolver name "getaddrinfo" is currently
aliased to "getaddrinfo_array"; but any code that wishes to rely on the array-like nature
of its arguments and return values, should request it specifically by name, as this alias
will be changed in a later version of "IO::Async".
The "getnameinfo" resolver returns its result in the same form as "Socket".
Because this module simply uses the system's "getaddrinfo" resolver, it will be fully
IPv6-aware if the underlying platform's resolver is. This allows programs to be fully
IPv6-capable.
EXAMPLES
The following somewhat contrieved example shows how to implement a new resolver function.
This example just uses in-memory data, but a real function would likely make calls to OS
functions to provide an answer. In traditional Unix style, a pair of functions are
provided that each look up the entity by either type of key, where both functions return
the same type of list. This is purely a convention, and is in no way required or enforced
by the "IO::Async::Resolver" itself.
@numbers = qw( zero one two three four
five six seven eight nine );
register_resolver getnumberbyindex => sub {
my ( $index ) = @_;
die "Bad index $index" unless $index >= 0 and $index < @numbers;
return ( $index, $numbers[$index] );
};
register_resolver getnumberbyname => sub {
my ( $name ) = @_;
foreach my $index ( 0 .. $#numbers ) {
return ( $index, $name ) if $numbers[$index] eq $name;
}
die "Bad name $name";
};
TODO
• Look into (system-specific) ways of accessing asynchronous resolvers directly
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>