getnameinfo

Turn a packed sockaddr into a host name and service name, with optional flags to force numeric output or demand a successful DNS lookup.

Synopsis

my ($err, $host, $service) = getnameinfo($sockaddr);
my ($err, $host, $service) = getnameinfo($sockaddr, $flags);
my ($err, $host, $service) = getnameinfo($sockaddr, $flags, $xflags);

What you get back

($err, $host, $service); on error, $err alone. $err is the same dualvar getaddrinfo returns. $xflags takes NIx_NOHOST and NIx_NOSERV, which skip that half of the lookup and return it as undef.

Useful flag bits:

• NI_NUMERICHOST - skip DNS, return a printable address.

• NI_NUMERICSERV - return the port number as a decimal string.

• NI_NAMEREQD - fail instead of falling back to numeric host.

• NI_NOFQDN - local hosts keep their short name.

• NI_DGRAM - look up the service as UDP rather than TCP.

Examples

my ($err, $host, $svc) = getnameinfo(getpeername($sock));
die "reverse lookup: $err\n" if $err;
print "peer: $host:$svc\n";

# Numeric formatting only - no DNS, no /etc/services.
my ($err, $host, $svc) = getnameinfo($sockaddr,
    NI_NUMERICHOST | NI_NUMERICSERV);

Edge cases

• A sockaddr that is not a string croaks “addr is not a string”.

• A malformed sockaddr is reported through $err (EAI_FAMILY).

See also

• getaddrinfo - reverse direction, name to sockaddr.

• inet_ntop - format a raw address without a resolver.

• unpack_sockaddr_in, unpack_sockaddr_in6 - when you need the numeric port and address without any lookup.