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);

What you get back#

A three-element list: error string (empty on success), host, and service. On error, host and service come back 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#

  • Input shorter than 2 bytes returns the error string "Invalid sockaddr" and two undefs.

  • Internally the packed sockaddr is capped at 128 bytes; this is enough for every standard family.

Differences from upstream#

Fully compatible with upstream Socket.

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.