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Man Pages


Manual Reference Pages  -  IO::ASYNC::RESOLVER (3)

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NAME

"IO::Async::Resolver" - performing name resolutions asynchronously

CONTENTS

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

The following methods documented with a trailing call to ->get return Future instances.

    resolve



   @result = $loop->resolve( %params )->get



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.
On failure, the fail category name is resolve; the details give the individual resolver function name (e.g. getaddrinfo), followed by other error details specific to the resolver in question.



 ->fail( $message, resolve => $type => @details )



    resolve (void)



   $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.

    getaddrinfo



   @addrs = $resolver->getaddrinfo( %args )->get



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.

On failure, the detail field will give the error number, which should match one of the Socket::EAI_* constants.



 ->fail( $message, resolve => getaddrinfo => $eai_errno )



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.

    getaddrinfo (void)



   $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 )



    getnameinfo



   ( $host, $service ) = $resolver->getnameinfo( %args )->get



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
On failure, the detail field will give the error number, which should match one of the Socket::EAI_* constants.



 ->fail( $message, resolve => getnameinfo => $eai_errno )



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.

    getnameinfo (void)



   $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( CW$name, CW$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
 getaddrinfo_array
 getnameinfo



The getaddrinfo 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. This name is also aliased as simply getaddrinfo.

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.

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";
 };



AUTHOR

Paul Evans <leonerd@leonerd.org.uk>
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perl v5.20.3 IO::ASYNC::RESOLVER (3) 2015-12-15

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