man-pages/man3p/getnameinfo.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "GETNAMEINFO" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" getnameinfo 
.SH NAME
getnameinfo \- get name information
.SH SYNOPSIS
.LP
\fB#include <sys/socket.h>
.br
#include <netdb.h>
.br
.sp
int getnameinfo(const struct sockaddr *restrict\fP \fIsa\fP\fB, socklen_t\fP
\fIsalen\fP\fB,
.br
\ \ \ \ \ \  char *restrict\fP \fInode\fP\fB, socklen_t\fP \fInodelen\fP\fB,
char *restrict\fP
\fIservice\fP\fB,
.br
\ \ \ \ \ \  socklen_t\fP \fIservicelen\fP\fB, int\fP \fIflags\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fIgetnameinfo\fP() function shall translate a socket address
to a node name and service location, all of which are defined
as in \fIgetaddrinfo\fP() .
.LP
The \fIsa\fP argument points to a socket address structure to be translated.
.LP
If the socket address structure contains an IPv4-mapped IPv6 address
or an IPv4-compatible IPv6 address, the implementation shall
extract the embedded IPv4 address and lookup the node name for that
IPv4 address.  
.TP 7
\fBNote:\fP
The IPv6 unspecified address ( \fB"::"\fP ) and the IPv6 loopback
address ( \fB"::1"\fP ) are not IPv4-compatible
addresses. If the address is the IPv6 unspecified address ( \fB"::"\fP
), a lookup is not performed, and the [EAI_NONAME] error
is returned.
.sp
.LP
If the \fInode\fP argument is non-NULL and the \fInodelen\fP argument
is non-zero, then the \fInode\fP argument points to a
buffer able to contain up to \fInodelen\fP characters that receives
the node name as a null-terminated string. If the \fInode\fP
argument is NULL or the \fInodelen\fP argument is zero, the node name
shall not be returned. If the node's name cannot be located,
the numeric form of the address contained in the socket address structure
pointed to by the \fIsa\fP argument is returned instead
of its name.
.LP
If the \fIservice\fP argument is non-NULL and the \fIservicelen\fP
argument is non-zero, then the \fIservice\fP argument
points to a buffer able to contain up to \fIservicelen\fP bytes that
receives the service name as a null-terminated string. If the
\fIservice\fP argument is NULL or the \fIservicelen\fP argument is
zero, the service name shall not be returned. If the service's
name cannot be located, the numeric form of the service address (for
example, its port number) shall be returned instead of its
name.
.LP
The \fIflags\fP argument is a flag that changes the default actions
of the function. By default the fully-qualified domain name
(FQDN) for the host shall be returned, but:
.IP " *" 3
If the flag bit NI_NOFQDN is set, only the node name portion of the
FQDN shall be returned for local hosts.
.LP
.IP " *" 3
If the flag bit NI_NUMERICHOST is set, the numeric form of the address
contained in the socket address structure pointed to by
the \fIsa\fP argument shall be returned instead of its name, under
all circumstances.
.LP
.IP " *" 3
If the flag bit NI_NAMEREQD is set, an error shall be returned if
the host's name cannot be located.
.LP
.IP " *" 3
If the flag bit NI_NUMERICSERV is set, the numeric form of the service
address shall be returned (for example, its port number)
instead of its name, under all circumstances.
.LP
.IP " *" 3
If the flag bit NI_NUMERICSCOPE is set, the numeric form of the scope
identifier shall be returned (for example, interface
index) instead of its name. This flag shall be ignored if the \fIsa\fP
argument is not an IPv6 address.
.LP
.IP " *" 3
If the flag bit NI_DGRAM is set, this indicates that the service is
a datagram service (SOCK_DGRAM). The default behavior shall
assume that the service is a stream service (SOCK_STREAM).
.LP
.TP 7
\fBNotes:\fP
.RS
.IP " 1." 4
The two NI_NUMERICxxx flags are required to support the \fB-n\fP flag
that many commands provide.
.LP
.IP " 2." 4
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.
.LP
.RE
.sp
.LP
The \fIgetnameinfo\fP() function shall be thread-safe.
.SH RETURN VALUE
.LP
A zero return value for \fIgetnameinfo\fP() indicates successful completion;
a non-zero return value indicates failure. The
possible values for the failures are listed in the ERRORS section.
.LP
Upon successful completion, \fIgetnameinfo\fP() shall return the \fInode\fP
and \fIservice\fP names, if requested, in the
buffers provided. The returned names are always null-terminated strings.
.SH ERRORS
.LP
The \fIgetnameinfo\fP() function shall fail and return the corresponding
value if:
.TP 7
.B EAI_AGAIN
The name could not be resolved at this time. Future attempts may succeed.
.TP 7
.B EAI_BADFLAGS
.sp
The \fIflags\fP had an invalid value.
.TP 7
.B EAI_FAIL
A non-recoverable error occurred.
.TP 7
.B EAI_FAMILY
The address family was not recognized or the address length was invalid
for the specified family.
.TP 7
.B EAI_MEMORY
There was a memory allocation failure.
.TP 7
.B EAI_NONAME
The name does not resolve for the supplied parameters. 
.LP
NI_NAMEREQD is set and the host's name cannot be located, or both
\fInodename\fP and \fIservname\fP were null.
.TP 7
.B EAI_OVERFLOW
.sp
An argument buffer overflowed. The buffer pointed to by the \fInode\fP
argument or the \fIservice\fP argument was too small.
.TP 7
.B EAI_SYSTEM
A system error occurred. The error code can be found in \fIerrno\fP.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
If the returned values are to be used as part of any further name
resolution (for example, passed to \fIgetaddrinfo\fP()), applications
should provide buffers large enough to store any result
possible on the system.
.LP
Given the IPv4-mapped IPv6 address \fB"::ffff:1.2.3.4"\fP , the implementation
performs a lookup as if the socket address
structure contains the IPv4 address \fB"1.2.3.4"\fP .
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIgai_strerror\fP() , \fIgetaddrinfo\fP() , \fIgetservbyname\fP()
, \fIinet_ntop\fP() , \fIsocket\fP() , the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, \fI<netdb.h>\fP, \fI<sys/socket.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .