1GETNAMEINFO(3P)            POSIX Programmer's Manual           GETNAMEINFO(3P)
2
3
4

PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
10

NAME

12       getnameinfo — get name information
13

SYNOPSIS

15       #include <sys/socket.h>
16       #include <netdb.h>
17
18       int getnameinfo(const struct sockaddr *restrict sa, socklen_t salen,
19           char *restrict node, socklen_t nodelen, char *restrict service,
20           socklen_t servicelen, int flags);
21

DESCRIPTION

23       The getnameinfo() function shall translate a socket address to  a  node
24       name  and  service  location,  all  of  which are defined as in freead‐
25       drinfo().
26
27       The sa argument points to a socket address structure to be  translated.
28       The salen argument contains the length of the address pointed to by sa.
29
30       If the socket address structure contains an IPv4-mapped IPv6 address or
31       an IPv4-compatible IPv6 address, the implementation shall  extract  the
32       embedded IPv4 address and lookup the node name for that IPv4 address.
33
34       If  the  address is the IPv6 unspecified address ("::"), a lookup shall
35       not be performed and the behavior shall be the same as when the  node's
36       name cannot be located.
37
38       If  the node argument is non-NULL and the nodelen argument is non-zero,
39       then the node argument points to a buffer able to contain up to nodelen
40       bytes  that  receives the node name as a null-terminated string. If the
41       node argument is NULL or the nodelen argument is zero,  the  node  name
42       shall  not  be  returned.  If  the  node's  name cannot be located, the
43       numeric form of the address contained in the socket  address  structure
44       pointed to by the sa argument is returned instead of its name.
45
46       If the service argument is non-NULL and the servicelen argument is non-
47       zero, then the service argument points to a buffer able to  contain  up
48       to servicelen bytes that receives the service name as a null-terminated
49       string.  If the service argument is NULL or the servicelen argument  is
50       zero,  the  service  name  shall not be returned. If the service's name
51       cannot be located, the numeric form of the service address  (for  exam‐
52       ple, its port number) shall be returned instead of its name.
53
54       The  flags  argument  is a flag that changes the default actions of the
55       function. By default the fully-qualified domain  name  (FQDN)  for  the
56       host shall be returned, but:
57
58        *  If the flag bit NI_NOFQDN is set, only the node name portion of the
59           FQDN shall be returned for local hosts.
60
61        *  If the flag bit NI_NUMERICHOST is set,  the  numeric  form  of  the
62           address contained in the socket address structure pointed to by the
63           sa argument shall be returned instead of its name.
64
65        *  If the flag bit NI_NAMEREQD is set, an error shall be  returned  if
66           the host's name cannot be located.
67
68        *  If the flag bit NI_NUMERICSERV is set, the numeric form of the ser‐
69           vice address shall be  returned  (for  example,  its  port  number)
70           instead of its name.
71
72        *  If  the  flag  bit  NI_NUMERICSCOPE is set, the numeric form of the
73           scope identifier shall be returned (for example,  interface  index)
74           instead  of its name. This flag shall be ignored if the sa argument
75           is not an IPv6 address.
76
77        *  If the flag bit NI_DGRAM is set, this indicates that the service is
78           a  datagram service (SOCK_DGRAM). The default behavior shall assume
79           that the service is a stream service (SOCK_STREAM).
80
81       Notes:
82
83                  1. The two NI_NUMERICxxx flags are required to  support  the
84                     -n flag that many commands provide.
85
86                  2. The  NI_DGRAM  flag  is  required for the few AF_INET and
87                     AF_INET6 port numbers (for example, [512,514]) that  rep‐
88                     resent different services for UDP and TCP.
89
90       The getnameinfo() function shall be thread-safe.
91

RETURN VALUE

93       A  zero return value for getnameinfo() indicates successful completion;
94       a non-zero return value indicates failure. The possible values for  the
95       failures are listed in the ERRORS section.
96
97       Upon  successful  completion,  getnameinfo()  shall return the node and
98       service names, if requested, in  the  buffers  provided.  The  returned
99       names are always null-terminated strings.
100

ERRORS

102       The  getnameinfo()  function  shall  fail  and return the corresponding
103       value if:
104
105       [EAI_AGAIN] The name  could  not  be  resolved  at  this  time.  Future
106                   attempts may succeed.
107
108       [EAI_BADFLAGS]
109                   The flags had an invalid value.
110
111       [EAI_FAIL]  A non-recoverable error occurred.
112
113       [EAI_FAMILY]
114                   The address family was not recognized or the address length
115                   was invalid for the specified family.
116
117       [EAI_MEMORY]
118                   There was a memory allocation failure.
119
120       [EAI_NONAME]
121                   The name does not resolve for the supplied parameters.
122
123                   NI_NAMEREQD is set and the host's name cannot  be  located,
124                   or both nodename and servname were null.
125
126       [EAI_OVERFLOW]
127                   An argument buffer overflowed. The buffer pointed to by the
128                   node argument or the service argument was too small.
129
130       [EAI_SYSTEM]
131                   A system error occurred. The error code  can  be  found  in
132                   errno.
133
134       The following sections are informative.
135

EXAMPLES

137       None.
138

APPLICATION USAGE

140       If the returned values are to be used as part of any further name reso‐
141       lution (for example, passed to getaddrinfo()), applications should pro‐
142       vide buffers large enough to store any result possible on the system.
143
144       Given the IPv4-mapped IPv6 address "::ffff:1.2.3.4", the implementation
145       performs a lookup as if the socket address structure contains the  IPv4
146       address "1.2.3.4".
147
148       The  IPv6  unspecified  address  ("::")  and  the IPv6 loopback address
149       ("::1") are not IPv4-compatible addresses.
150

RATIONALE

152       None.
153

FUTURE DIRECTIONS

155       None.
156

SEE ALSO

158       endservent(), freeaddrinfo(), gai_strerror(), inet_ntop(), socket()
159
160       The Base Definitions volume of POSIX.1‐2017, <netdb.h>, <sys_socket.h>
161
163       Portions of this text are reprinted and reproduced in  electronic  form
164       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
165       table Operating System Interface (POSIX), The Open Group Base  Specifi‐
166       cations  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of
167       Electrical and Electronics Engineers, Inc and The Open Group.   In  the
168       event of any discrepancy between this version and the original IEEE and
169       The Open Group Standard, the original IEEE and The Open Group  Standard
170       is  the  referee document. The original Standard can be obtained online
171       at http://www.opengroup.org/unix/online.html .
172
173       Any typographical or formatting errors that appear  in  this  page  are
174       most likely to have been introduced during the conversion of the source
175       files to man page format. To report such errors,  see  https://www.ker
176       nel.org/doc/man-pages/reporting_bugs.html .
177
178
179
180IEEE/The Open Group                  2017                      GETNAMEINFO(3P)
Impressum