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.
10
12 getnameinfo - get name information
13
15 #include <sys/socket.h>
16 #include <netdb.h>
17 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
24 The getnameinfo() function shall translate a socket address to a node
25 name and service location, all of which are defined as in getad‐
26 drinfo().
27 The sa argument points to a socket address structure to be translated.
29 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 Note: The IPv6 unspecified address ( "::" ) and the IPv6 loopback
35 address ( "::1" ) are not IPv4-compatible addresses. If the
36 address is the IPv6 unspecified address ( "::" ), a lookup is
37 not performed, and the [EAI_NONAME] error is returned.
38 If the node argument is non-NULL and the nodelen argument is non-zero,
41 then the node argument points to a buffer able to contain up to nodelen
42 characters that receives the node name as a null-terminated string. If
43 the node argument is NULL or the nodelen argument is zero, the node
44 name shall not be returned. If the node's name cannot be located, the
45 numeric form of the address contained in the socket address structure
46 pointed to by the sa argument is returned instead of its name.
47 If the service argument is non-NULL and the servicelen argument is non-
49 zero, then the service argument points to a buffer able to contain up
50 to servicelen bytes that receives the service name as a null-terminated
51 string. If the service argument is NULL or the servicelen argument is
52 zero, the service name shall not be returned. If the service's name
53 cannot be located, the numeric form of the service address (for exam‐
54 ple, its port number) shall be returned instead of its name.
55 The flags argument is a flag that changes the default actions of the
57 function. By default the fully-qualified domain name (FQDN) for the
58 host shall be returned, but:
59 * If the flag bit NI_NOFQDN is set, only the node name portion of the
61 FQDN shall be returned for local hosts.
62 * If the flag bit NI_NUMERICHOST is set, the numeric form of the
64 address contained in the socket address structure pointed to by the
65 sa argument shall be returned instead of its name, under all circum‐
66 stances.
67 * If the flag bit NI_NAMEREQD is set, an error shall be returned if
69 the host's name cannot be located.
70 * If the flag bit NI_NUMERICSERV is set, the numeric form of the ser‐
72 vice address shall be returned (for example, its port number)
73 instead of its name, under all circumstances.
74 * If the flag bit NI_NUMERICSCOPE is set, the numeric form of the
76 scope identifier shall be returned (for example, interface index)
77 instead of its name. This flag shall be ignored if the sa argument
78 is not an IPv6 address.
79 * If the flag bit NI_DGRAM is set, this indicates that the service is
81 a datagram service (SOCK_DGRAM). The default behavior shall assume
82 that the service is a stream service (SOCK_STREAM).
83 Notes:
85 1. The two NI_NUMERICxxx flags are required to support the -n
87 flag that many commands provide.
88 2. The NI_DGRAM flag is required for the few AF_INET and
90 AF_INET6 port numbers (for example, [512,514]) that repre‐
91 sent different services for UDP and TCP.
92 The getnameinfo() function shall be thread-safe.
94
96 A zero return value for getnameinfo() indicates successful completion;
97 a non-zero return value indicates failure. The possible values for the
98 failures are listed in the ERRORS section.
99 Upon successful completion, getnameinfo() shall return the node and
101 service names, if requested, in the buffers provided. The returned
102 names are always null-terminated strings.
103
105 The getnameinfo() function shall fail and return the corresponding
106 value if:
107 EAI_AGAIN
109 The name could not be resolved at this time. Future attempts may
110 succeed.
111 EAI_BADFLAGS
113 The flags had an invalid value.
115 EAI_FAIL
117 A non-recoverable error occurred.
118 EAI_FAMILY
120 The address family was not recognized or the address length was
121 invalid for the specified family.
122 EAI_MEMORY
124 There was a memory allocation failure.
125 EAI_NONAME
127 The name does not resolve for the supplied parameters.
128 NI_NAMEREQD is set and the host's name cannot be located, or both node‐
130 name and servname were null.
131 EAI_OVERFLOW
133 An argument buffer overflowed. The buffer pointed to by the node
135 argument or the service argument was too small.
136 EAI_SYSTEM
138 A system error occurred. The error code can be found in errno.
139 The following sections are informative.
142
144 None.
145
147 If the returned values are to be used as part of any further name reso‐
148 lution (for example, passed to getaddrinfo()), applications should pro‐
149 vide buffers large enough to store any result possible on the system.
150 Given the IPv4-mapped IPv6 address "::ffff:1.2.3.4", the implementation
152 performs a lookup as if the socket address structure contains the IPv4
153 address "1.2.3.4" .
154
156 None.
157
159 None.
160
162 gai_strerror(), getaddrinfo(), getservbyname(), inet_ntop(), socket(),
163 the Base Definitions volume of IEEE Std 1003.1-2001, <netdb.h>,
164 <sys/socket.h>
165
167 Portions of this text are reprinted and reproduced in electronic form
168 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
169 -- Portable Operating System Interface (POSIX), The Open Group Base
170 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
171 Electrical and Electronics Engineers, Inc and The Open Group. In the
172 event of any discrepancy between this version and the original IEEE and
173 The Open Group Standard, the original IEEE and The Open Group Standard
174 is the referee document. The original Standard can be obtained online
175 at http://www.opengroup.org/unix/online.html .
176IEEE/The Open Group 2003 GETNAMEINFO(3P)