NAME
`Socket::GetAddrInfo' - address-family independent name resolving
functions
SYNOPSIS
use Socket qw( SOCK_STREAM );
use Socket::GetAddrInfo qw( getaddrinfo getnameinfo );
use IO::Socket;
my %hints = ( socktype => SOCK_STREAM );
my ( $err, @res ) = getaddrinfo( "www.google.com", "www", \%hints );
die "Cannot resolve name - $err" if $err;
my $sock;
foreach my $ai ( @res ) {
my $candidate = IO::Socket->new();
$candidate->socket( $ai->{family}, $ai->{socktype}, $ai->{protocol} )
or next;
$candidate->connect( $ai->{addr} )
or next;
$sock = $candidate;
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. If it does not,
the module will use pure-perl 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
Socket::GetAddrInfo::Emul for details on the limits of this emulation.
As of Perl version 5.14.0, Perl already supports `getaddrinfo' in core.
On such a system, this module simply uses the functions provided by
`Socket', and does not need to use its own compiled XS, or pure-perl
legacy emulation.
As `Socket' in core now provides all the functions also provided by this
module, it is likely this may be the last released version of this
module. And code currently using this module would be advised to switch
to using core `Socket' instead.
EXPORT TAGS
The following tags may be imported by `use Socket::GetAddrInfo qw( :tag
)':
AI Imports all of the `AI_*' constants for `getaddrinfo' flags
NI Imports all of the `NI_*' constants for `getnameinfo' flags
EAI Imports all of the `EAI_*' for error values
constants
Imports all of the above constants
FUNCTIONS
( $err, @res ) = getaddrinfo( $host, $service, $hints )
`getaddrinfo' turns human-readable text strings (containing hostnames,
numeric addresses, service names, or port numbers) into sets of binary
values containing socket-level representations of these addresses.
When given both host and service, this function attempts to resolve the
host name to a set of network addresses, and the service name into a
protocol and port number, and then returns a list of address structures
suitable to connect() to it.
When given just a host name, this function attempts to resolve it to a
set of network addresses, and then returns a list of these addresses in
the returned structures.
When given just a service name, this function attempts to resolve it to
a protocol and port number, and then returns a list of address
structures that represent it suitable to bind() to.
When given neither name, it generates an error.
The optional `$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. At least the following
flags will be available:
* `AI_PASSIVE'
Indicates that this resolution is for a local `bind()' for a
passive (i.e. listening) socket, rather than an active (i.e.
connecting) socket.
* `AI_CANONNAME'
Indicates that the caller wishes the canonical hostname
(`canonname') field of the result to be filled in.
* `AI_NUMERICHOST'
Indicates that the caller will pass a numeric address, rather
than a hostname, and that `getaddrinfo' must not perform a
resolve operation on this name. This flag will prevent a
possibly-slow network lookup operation, and instead return an
error, if a hostname is passed.
Other flags may be provided by the OS.
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. Rather than explicitly checking, see
also Socket::GetAddrInfo::Strict which provides functions that throw
exceptions on errors.
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. This field will only be present
on the first returned address.
( $err, $host, $service ) = getnameinfo( $addr, $flags, $xflags )
`getnameinfo' turns a binary socket address into a pair of
human-readable strings, containing the host name, numeric address,
service name, or port number.
The optional `$flags' parameter is a bitfield containing `NI_*'
constants. At least the following flags will be available:
* `NI_NUMERICHOST'
Requests that a human-readable string representation of the numeric
address is returned directly, rather than performing a name resolve
operation that may convert it into a hostname.
* `NI_NUMERICSERV'
Requests that the port number be returned directly as a number
representation rather than performing a name resolve operation that
may convert it into a service name.
* `NI_NAMEREQD'
If a name resolve operation fails to provide a name, then this flag
will cause `getnameinfo' to indicate an error, rather than returning
the numeric representation as a human-readable string.
* `NI_DGRAM'
Indicates that the socket address relates to a `SOCK_DGRAM' socket,
for the services whose name differs between `TCP' and `UDP' protocols.
Other flags may be provided by the OS.
The optional `$xflags' parameter is a bitfield containing `NIx_*'
constants. These are a Perl-level extension to the API, to indicate
extra information.
* `NIx_NOHOST'
Indicates that the caller is not interested in the hostname of the
result, so it does not have to be converted; `undef' will be returned
as the hostname.
* `NIx_NOSERV'
Indicates that the caller is not interested in the service name of the
result, so it does not have to be converted; `undef' will be returned
as the service name.
Errors are indicated by the `$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. Rather than explicitly checking, see
also Socket::GetAddrInfo::Strict which provides functions that throw
exceptions on errors.
EXAMPLES
Lookup for `connect'
The `getaddrinfo' function converts a hostname and a service name into a
list of structures, each containing a potential way to `connect()' to
the named service on the named host.
my %hints = ( socktype => SOCK_STREAM );
my ( $err, @res ) = getaddrinfo( $hostname, $servicename, \%hints );
die "Cannot getaddrinfo - $err" if $err;
my $sock;
foreach my $ai ( @res ) {
my $candidate = IO::Socket->new();
$candidate->socket( $ai->{family}, $ai->{socktype}, $ai->{protocol} )
or next;
$candidate->connect( $ai->{addr} )
or next;
$sock = $candidate;
last;
}
Because a list of potential candidates is returned, the `while' loop
tries each in turn until it it finds one that succeeds both the
`socket()' and `connect()' calls.
This function performs the work of the legacy functions `gethostbyname',
`getservbyname', `inet_aton' and `pack_sockaddr_in'.
Making a human-readable string out of an address
The `getnameinfo' function converts a socket address, such as returned
by `getsockname' or `getpeername', into a pair of human-readable strings
representing the address and service name.
my ( $err, $hostname, $servicename ) = getnameinfo( $socket->peername );
die "Cannot getnameinfo - $err" if $err;
print "The peer is connected from $hostname\n";
Since in this example only the hostname was used, the redundant
conversion of the port number into a service name may be omitted by
passing the `NIx_NOSERV' flag.
my ( $err, $hostname ) = getnameinfo( $socket->peername, 0, NIx_NOSERV );
This function performs the work of the legacy functions
`unpack_sockaddr_in', `inet_ntoa', `gethostbyaddr' and `getservbyport'.
Resolving hostnames into IP addresses
To turn a hostname into a human-readable plain IP address use
`getaddrinfo' to turn the hostname into a list of socket structures,
then `getnameinfo' on each one to make it a readable IP address again.
my ( $err, @res ) = getaddrinfo( $hostname, "", { socktype => SOCK_RAW } );
die "Cannot getaddrinfo - $err" if $err;
while( my $ai = shift @res ) {
my ( $err, $ipaddr ) = getnameinfo( $ai->{addr}, NI_NUMERICHOST, NIx_NOSERV );
die "Cannot getnameinfo - $err" if $err;
print "$ipaddr\n";
}
The `socktype' hint to `getaddrinfo' filters the results to only include
one socket type and protocol. Without this most OSes return three
combinations, for `SOCK_STREAM', `SOCK_DGRAM' and `SOCK_RAW', resulting
in triplicate output of addresses. The `NI_NUMERICHOST' flag to
`getnameinfo' causes it to return a string-formatted plain IP address,
rather than reverse resolving it back into a hostname.
This combination performs the work of the legacy functions
`gethostbyname' and `inet_ntoa'.
BUILDING WITHOUT XS CODE
In some environments it may be preferred not to build the XS
implementation, leaving a choice only of the core or pure-perl emulation
implementations.
$ perl Build.PL --pp
or
$ PERL_SOCKET_GETADDRINFO_NO_BUILD_XS=1 perl Build.PL
BUGS
* Appears to FAIL on older Darwin machines (e.g. `osvers=8.11.1'). The
failure mode occurs in t/02getnameinfo.t and appears to relate to an
endian bug; expecting to receive `80' and instead receiving `20480'
(which is a 16-bit `80' byte-swapped).
SEE ALSO
*
http://tools.ietf.org/html/rfc2553 - Basic Socket Interface
Extensions for IPv6
ACKNOWLEDGEMENTS
Christian Hansen <
[email protected]> - for help with some XS features and
Win32 build fixes.
Zefram <
[email protected]> - for help with fixing some bugs in the XS
code.
Reini Urban <
[email protected]> - for help with older perls and more Win32
build fixes.
AUTHOR
Paul Evans <
[email protected]>
