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getnameinfo(3c)
Standard C Library Functions getnameinfo(3C)
NAME
getnameinfo - get name information
SYNOPSIS
#include <sys/socket.h>
#include <netdb.h>
int getnameinfo(const struct sockaddr *restrict sa, socklen_t salen,
char *restrict node, socklen_t nodelen,
char *restrict service, socklen_t servicelen,
int flags);
DESCRIPTION
The getnameinfo() function translates a socket address to a node name
and service location, all of which are defined as in getaddrinfo(3C).
The sa argument points to a socket address structure to be translated.
If the socket address structure contains an IPv4-mapped IPv6 address or
an IPv4-compatible IPv6 address, the implementation extracts the embed‐
ded IPv4 address and lookup the node name for that IPv4 address.
If the node argument is non-NULL and the nodelen argument is non-zero,
then the node argument points to a buffer able to contain up to nodelen
characters that receives the node name as a null-terminated string. If
the node argument is NULL or the nodelen argument is zero, the node
name is not returned. If the node's name cannot be located, the numeric
form of the node's address is returned instead of its name.
If the service argument is non-NULL and the servicelen argument is non-
zero, then the service argument points to a buffer able to contain up
to servicelen bytes that receives the service name as a null-terminated
string. If the service argument is NULL or the servicelen argument is
zero, the service name is not returned. If the service's name cannot be
located, the numeric form of the service address (for example, its port
number) is returned instead of its name. The function can also return
the IPv6 zone-id in the form:
<address>%<zone-id>
as described in getaddrinfo(3C).
The flags argument is a flag that changes the default actions of the
function. By default the fully-qualified domain name (FQDN) for the
host is returned, but:
o If the flag bit NI_NOFQDN is set, only the node name portion
of the FQDN is returned for local hosts.
o If the flag bit NI_NUMERICHOST is set, the numeric form of
the host's address is returned instead of its name, under
all circumstances.
o If the flag bit NI_NAMEREQD is set, an error is returned if
the host's name cannot be located.
o If the flag bit NI_NUMERICSERV is set, the numeric form of
the service address is returned (for example, its port num‐
ber) instead of its name, under all circumstances.
o If the flag bit NI_DGRAM is set, this indicates that the
service is a datagram service (SOCK_DGRAM). The default
behavior assumes that the service is a stream service
(SOCK_STREAM).
These NI_* flags are defined in <netdb.h>.
RETURN VALUES
A 0 return value for getnameinfo() indicates successful completion; a
non-zero return value indicates failure. The possible values for the
failures are listed in the ERRORS section.
Upon successful completion, getnameinfo() returns the node and service
names, if requested, in the buffers provided. The returned names are
always null-terminated strings.
ERRORS
The getnameinfo() function will fail if:
EAI_AGAIN The name could not be resolved at this time. Future
attempts might succeed.
EAI_BADFLAGS The flags argument had an invalid value.
EAI_FAIL A non-recoverable error occurred.
EAI_FAMILY The address family was not recognized or the address
length was invalid for the specified family.
EAI_MEMORY There was a memory allocation failure.
EAI_NONAME The name does not resolve for the supplied parameters.
NI_NAMEREQD is set and the host's name cannot be
located, or both nodename and servname were NULL.
EAI_SYSTEM A system error occurred. The error code can be found in
errno.
USAGE
If the returned values are to be used as part of any further name reso‐
lution (for example, passed to getaddrinfo()), applications should pro‐
vide buffers large enough to store any result possible on the system.
Given the IPv4-mapped IPv6 address "::ffff:1.2.3.4", the implementation
performs a lookup as if the socket address structure contains the IPv4
address "1.2.3.4".
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelMT-Safe _ Stan‐
dardSee standards(7).
SEE ALSO
gai_strerror(3C), getaddrinfo(3C), getservbyname(3C), socket(3C),
attributes(7), standards(7)
Gilligan, R. RFC 3493, Basic Socket Interface Extensions for IPv6. Net‐
work Working Group. February 2003. https://tools.ietf.org/html/rfc3493
NOTES
The IPv6 unspecified address ("::") and the IPv6 loopback address
("::1") are not IPv4-compatible addresses. If the address is the IPv6
unspecified address ("::"), a lookup is not performed, and the EAI_NO‐
NAME error is returned.
The two NI_NUMERICxxx flags are required to support the -n flag that
many commands provide.
The NI_DGRAM flag is required for the few AF_INET and AF_INET6 port
numbers (for example, [512,514]) that represent different services for
UDP and TCP.
HISTORY
The getnameinfo() function was added to Oracle Solaris in the Solaris 8
release.
Oracle Solaris 11.4 20 Jan 2021 getnameinfo(3C)