NAME

Socket::GetAddrInfo - RFC 2553's getaddrinfo and getnameinfo functions.

SYNOPSIS

 use Socket::GetAddrInfo qw( :newapi getaddrinfo getnameinfo );
 use IO::Socket;

 my $sock;

 my ( $err, @res ) = getaddrinfo( "www.google.com", "www" );

 die "Cannot resolve name - $err" if $err;

 while( my $ai = shift @res ) {

    $sock = IO::Socket->new();
    $sock->socket( $ai->{family}, $ai->{socktype}, $ai->{protocol} ) or
       undef $sock, next;

    $sock->connect( $ai->{addr} ) or undef $sock, next;

    last;
 }

 if( $sock ) {
    my ( $err, $host, $service ) = getnameinfo( $sock->peername );
    print "Connected to $host:$service\n" if !$err;
 }

DESCRIPTION

The RFC 2553 functions getaddrinfo and getnameinfo provide an abstracted way to convert between a pair of host name/service name and socket addresses, or vice versa. getaddrinfo converts names into a set of arguments to pass to the socket() and connect() syscalls, and getnameinfo converts a socket address back into its host name/service name pair.

These functions provide a useful interface for performing either of these name resolution operation, without having to deal with IPv4/IPv6 transparency, or whether the underlying host can support IPv6 at all, or other such issues. However, not all platforms can support the underlying calls at the C layer, which means a dilema for authors wishing to write forward-compatible code. Either to support these functions, and cause the code not to work on older platforms, or stick to the older "legacy" resolvers such as gethostbyname(), which means the code becomes more portable.

This module attempts to solve this problem, by detecting at compiletime whether the underlying OS will support these functions, and only compiling the XS code if it can. At runtime, when the module is loaded, if the XS implementation is not available, emulations of the functions using the legacy resolver functions instead. The emulations support the same interface as the real functions, and behave as close as is resonably possible to emulate using the legacy resolvers. See below for details on the limits of this emulation.

FUNCTIONS

The functions in this module are provided in one of two API styles, selectable at the time they are imported into the caller, by the use of the following tags:

 use Socket::GetAddrInfo qw( :newapi getaddrinfo );

 use Socket::GetAddrInfo qw( :Socket6api getaddrinfo );

The choice is implemented by importing different functions into the caller, which means different importing packages may choose different API styles. It is recommended that new code import the :newapi style to take advantage of neater argument / return results, and error reporting. The :Socket6api style is provided as backward-compatibility for code that wants to use Socket6.

( $err, @res ) = getaddrinfo( $host, $service, $hints )

When given both host and service, this function attempts to resolve the host name to a set of network addresses, and the service name into a protocol and port number, and then returns a list of address structures suitable to connect() to it.

When given just a host name, this function attempts to resolve it to a set of network addresses, and then returns a list of these addresses in the returned structures.

When given just a service name, this function attempts to resolve it to a protocol and port number, and then returns a list of address structures that represent it suitable to bind() to.

When given neither name, it generates an error.

The optional $hints parameter can be passed a HASH reference to indicate how the results are generated. It may contain any of the following four fields:

flags => INT

A bitfield containing AI_* constants

family => INT

Restrict to only generating addresses in this address family

socktype => INT

Restrict to only generating addresses of this socket type

protocol => INT

Restrict to only generating addresses for this protocol

Errors are indicated by the $err value returned; which will be non-zero in numeric context, and contain a string error message as a string. The value can be compared against any of the EAI_* constants to determine what the error is.

If no error occurs, @res will contain HASH references, each representing one address. It will contain the following five fields:

family => INT

The address family (e.g. AF_INET)

socktype => INT

The socket type (e.g. SOCK_STREAM)

protocol => INT

The protocol (e.g. IPPROTO_TCP)

addr => STRING

The address in a packed string (such as would be returned by pack_sockaddr_in)

canonname => STRING

The canonical name for the host if the AI_CANONNAME flag was provided, or undef otherwise.

( $err, $host, $service ) = getnameinfo( $addr, $flags )

This function attempts to resolve the given socket address into a pair of host and service names.

The optional $flags parameter is a bitfield containing NI_* constants.

Errors are indicated by the $err value returned; which will be non-zero in numeric context, and contain a string error message as a string. The value can be compared against any of the EAI_* constants to determine what the error is.

SOCKET6 COMPATIBILITY FUNCTIONS

@res = getaddrinfo( $host, $service, $family, $socktype, $protocol, $flags )

This version of the API takes the hints values as separate ordered parameters. Unspecified parameters should be passed as 0.

If successful, this function returns a flat list of values, five for each returned address structure. Each group of five elements will contain, in order, the family, socktype, protocol, addr and canonname values of the address structure.

If unsuccessful, it will return a single value, containing the string error message. To remain compatible with the Socket6 interface, this value does not have the error integer part.

( $host, $service ) = getnameinfo( $addr, $flags )

This version of the API returns only the host name and service name, if successfully resolved. On error, it will return an empty list. To remain compatible with the Socket6 interface, no error information will be supplied.

LIMITS OF EMULATION

These emulations are not a complete replacement of the real functions, because they only support IPv4 (the AF_INET socket family).

getaddrinfo

• If $family is supplied, it must be AF_INET. Any other value will result in an error thrown by croak.

• The only supported $flags values are AI_PASSIVE, AI_CANONNAME, and AI_NUMERICHOST.

getnameinfo

• If the sockaddr family of $addr is anything other than AF_INET, an error will be thrown with croak.

• The only supported $flags values are NI_NUMERICHOST, NI_NUMERICSERV, NI_NAMEREQD and NI_DGRAM.

SEE ALSO

• RFC 2553 - Basic Socket Interface Extensions for IPv6

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>

cpanm Socket::GetAddrInfo

perl -MCPAN -e shell
install Socket::GetAddrInfo