NAME "Socket::GetAddrInfo" - RFC 2553's "getaddrinfo" and "getnameinfo" functions. SYNOPSIS use Socket qw( SOCK_STREAM ); use Socket::GetAddrInfo qw( :newapi getaddrinfo getnameinfo ); use IO::Socket; my $sock; my %hints = ( socktype => SOCK_STREAM ); my ( $err, @res ) = getaddrinfo( "www.google.com", "www", \%hints ); 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". If neither style is selected, then this module will provide a Socket6-like API to be compatible with earlier versions of "Socket::GetAddrInfo". This behaviour will change in a later version of the module - make sure to always specify the required API type. ( $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". BUGS * At the time of writing, there are no test reports from the "MSWin32" platform either PASS or FAIL. I suspect the code will not currently work as it stands on that platform, but it should be fairly easy to fix, as "Socket6" is known to work there. Patches welcomed. :) SEE ALSO * - Basic Socket Interface Extensions for IPv6 ACKNOWLEDGEMENTS With thanks to Zefram for help with fixing some bugs in the XS code. AUTHOR Paul Evans