1GETNAMEINFO(3P) POSIX Programmer's Manual GETNAMEINFO(3P)
2
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.
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13 getnameinfo — get name information
14
16 #include <sys/socket.h>
17 #include <netdb.h>
18 int getnameinfo(const struct sockaddr *restrict sa, socklen_t salen,
20 char *restrict node, socklen_t nodelen, char *restrict service,
21 socklen_t servicelen, int flags);
22
24 The getnameinfo() function shall translate a socket address to a node
25 name and service location, all of which are defined as in freead‐
26 drinfo().
27 The sa argument points to a socket address structure to be translated.
29 The salen argument contains the length of the address pointed to by sa.
30 If the socket address structure contains an IPv4-mapped IPv6 address or
32 an IPv4-compatible IPv6 address, the implementation shall extract the
33 embedded IPv4 address and lookup the node name for that IPv4 address.
34 If the address is the IPv6 unspecified address ("::"), a lookup shall
36 not be performed and the behavior shall be the same as when the node's
37 name cannot be located.
38 If the node argument is non-NULL and the nodelen argument is non-zero,
40 then the node argument points to a buffer able to contain up to nodelen
41 bytes that receives the node name as a null-terminated string. If the
42 node argument is NULL or the nodelen argument is zero, the node name
43 shall not be returned. If the node's name cannot be located, the
44 numeric form of the address contained in the socket address structure
45 pointed to by the sa argument is returned instead of its name.
46 If the service argument is non-NULL and the servicelen argument is non-
48 zero, then the service argument points to a buffer able to contain up
49 to servicelen bytes that receives the service name as a null-terminated
50 string. If the service argument is NULL or the servicelen argument is
51 zero, the service name shall not be returned. If the service's name
52 cannot be located, the numeric form of the service address (for exam‐
53 ple, its port number) shall be returned instead of its name.
54 The flags argument is a flag that changes the default actions of the
56 function. By default the fully-qualified domain name (FQDN) for the
57 host shall be returned, but:
58 * If the flag bit NI_NOFQDN is set, only the node name portion of the
60 FQDN shall be returned for local hosts.
61 * If the flag bit NI_NUMERICHOST is set, the numeric form of the
63 address contained in the socket address structure pointed to by the
64 sa argument shall be returned instead of its name.
65 * If the flag bit NI_NAMEREQD is set, an error shall be returned if
67 the host's name cannot be located.
68 * If the flag bit NI_NUMERICSERV is set, the numeric form of the ser‐
70 vice address shall be returned (for example, its port number)
71 instead of its name.
72 * If the flag bit NI_NUMERICSCOPE is set, the numeric form of the
74 scope identifier shall be returned (for example, interface index)
75 instead of its name. This flag shall be ignored if the sa argument
76 is not an IPv6 address.
77 * If the flag bit NI_DGRAM is set, this indicates that the service is
79 a datagram service (SOCK_DGRAM). The default behavior shall assume
80 that the service is a stream service (SOCK_STREAM).
81 Notes:
83 1. The two NI_NUMERICxxx flags are required to support the
85 −n flag that many commands provide.
86 2. The NI_DGRAM flag is required for the few AF_INET and
88 AF_INET6 port numbers (for example, [512,514]) that rep‐
89 resent different services for UDP and TCP.
90 The getnameinfo() function shall be thread-safe.
92
94 A zero return value for getnameinfo() indicates successful completion;
95 a non-zero return value indicates failure. The possible values for the
96 failures are listed in the ERRORS section.
97 Upon successful completion, getnameinfo() shall return the node and
99 service names, if requested, in the buffers provided. The returned
100 names are always null-terminated strings.
101
103 The getnameinfo() function shall fail and return the corresponding
104 value if:
105 [EAI_AGAIN] The name could not be resolved at this time. Future
107 attempts may succeed.
108 [EAI_BADFLAGS]
110 The flags had an invalid value.
111 [EAI_FAIL] A non-recoverable error occurred.
113 [EAI_FAMILY]
115 The address family was not recognized or the address length
116 was invalid for the specified family.
117 [EAI_MEMORY]
119 There was a memory allocation failure.
120 [EAI_NONAME]
122 The name does not resolve for the supplied parameters.
123 NI_NAMEREQD is set and the host's name cannot be located,
125 or both nodename and servname were null.
126 [EAI_OVERFLOW]
128 An argument buffer overflowed. The buffer pointed to by the
129 node argument or the service argument was too small.
130 [EAI_SYSTEM]
132 A system error occurred. The error code can be found in
133 errno.
134 The following sections are informative.
136
138 None.
139
141 If the returned values are to be used as part of any further name reso‐
142 lution (for example, passed to getaddrinfo()), applications should pro‐
143 vide buffers large enough to store any result possible on the system.
144 Given the IPv4-mapped IPv6 address "::ffff:1.2.3.4", the implementation
146 performs a lookup as if the socket address structure contains the IPv4
147 address "1.2.3.4".
148 The IPv6 unspecified address ("::") and the IPv6 loopback address
150 ("::1") are not IPv4-compatible addresses.
151
153 None.
154
156 None.
157
159 endservent(), freeaddrinfo(), gai_strerror(), inet_ntop(), socket()
160 The Base Definitions volume of POSIX.1‐2008, <netdb.h>, <sys_socket.h>
162
164 Portions of this text are reprinted and reproduced in electronic form
165 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
166 -- Portable Operating System Interface (POSIX), The Open Group Base
167 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
168 cal and Electronics Engineers, Inc and The Open Group. (This is
169 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
170 event of any discrepancy between this version and the original IEEE and
171 The Open Group Standard, the original IEEE and The Open Group Standard
172 is the referee document. The original Standard can be obtained online
173 at http://www.unix.org/online.html .
174 Any typographical or formatting errors that appear in this page are
176 most likely to have been introduced during the conversion of the source
177 files to man page format. To report such errors, see https://www.ker‐
178 nel.org/doc/man-pages/reporting_bugs.html .
179IEEE/The Open Group 2013 GETNAMEINFO(3P)