1GETNAMEINFO(P) POSIX Programmer's Manual GETNAMEINFO(P)
2
6 getnameinfo - get name information
7
9 #include <sys/socket.h>
10 #include <netdb.h>
11 int getnameinfo(const struct sockaddr *restrict sa, socklen_t salen,
13 char *restrict node, socklen_t nodelen, char *restrict service,
14 socklen_t servicelen, int flags);
15
18 The getnameinfo() function shall translate a socket address to a node
19 name and service location, all of which are defined as in getaddrinfo()
20 .
21 The sa argument points to a socket address structure to be translated.
23 If the socket address structure contains an IPv4-mapped IPv6 address or
25 an IPv4-compatible IPv6 address, the implementation shall extract the
26 embedded IPv4 address and lookup the node name for that IPv4 address.
27 Note: The IPv6 unspecified address ( "::" ) and the IPv6 loopback
29 address ( "::1" ) are not IPv4-compatible addresses. If the
30 address is the IPv6 unspecified address ( "::" ), a lookup is
31 not performed, and the [EAI_NONAME] error is returned.
32 If the node argument is non-NULL and the nodelen argument is non-zero,
35 then the node argument points to a buffer able to contain up to nodelen
36 characters that receives the node name as a null-terminated string. If
37 the node argument is NULL or the nodelen argument is zero, the node
38 name shall not be returned. If the node's name cannot be located, the
39 numeric form of the address contained in the socket address structure
40 pointed to by the sa argument is returned instead of its name.
41 If the service argument is non-NULL and the servicelen argument is non-
43 zero, then the service argument points to a buffer able to contain up
44 to servicelen bytes that receives the service name as a null-terminated
45 string. If the service argument is NULL or the servicelen argument is
46 zero, the service name shall not be returned. If the service's name
47 cannot be located, the numeric form of the service address (for exam‐
48 ple, its port number) shall be returned instead of its name.
49 The flags argument is a flag that changes the default actions of the
51 function. By default the fully-qualified domain name (FQDN) for the
52 host shall be returned, but:
53 * If the flag bit NI_NOFQDN is set, only the node name portion of the
55 FQDN shall be returned for local hosts.
56 * If the flag bit NI_NUMERICHOST is set, the numeric form of the
58 address contained in the socket address structure pointed to by the
59 sa argument shall be returned instead of its name, under all circum‐
60 stances.
61 * If the flag bit NI_NAMEREQD is set, an error shall be returned if
63 the host's name cannot be located.
64 * If the flag bit NI_NUMERICSERV is set, the numeric form of the ser‐
66 vice address shall be returned (for example, its port number)
67 instead of its name, under all circumstances.
68 * If the flag bit NI_NUMERICSCOPE is set, the numeric form of the
70 scope identifier shall be returned (for example, interface index)
71 instead of its name. This flag shall be ignored if the sa argument
72 is not an IPv6 address.
73 * If the flag bit NI_DGRAM is set, this indicates that the service is
75 a datagram service (SOCK_DGRAM). The default behavior shall assume
76 that the service is a stream service (SOCK_STREAM).
77 Notes:
79 1. The two NI_NUMERICxxx flags are required to support the -n
81 flag that many commands provide.
82 2. The NI_DGRAM flag is required for the few AF_INET and
84 AF_INET6 port numbers (for example, [512,514]) that repre‐
85 sent different services for UDP and TCP.
86 The getnameinfo() function shall be thread-safe.
88
90 A zero return value for getnameinfo() indicates successful completion;
91 a non-zero return value indicates failure. The possible values for the
92 failures are listed in the ERRORS section.
93 Upon successful completion, getnameinfo() shall return the node and
95 service names, if requested, in the buffers provided. The returned
96 names are always null-terminated strings.
97
99 The getnameinfo() function shall fail and return the corresponding
100 value if:
101 EAI_AGAIN
103 The name could not be resolved at this time. Future attempts may
104 succeed.
105 EAI_BADFLAGS
107 The flags had an invalid value.
109 EAI_FAIL
111 A non-recoverable error occurred.
112 EAI_FAMILY
114 The address family was not recognized or the address length was
115 invalid for the specified family.
116 EAI_MEMORY
118 There was a memory allocation failure.
119 EAI_NONAME
121 The name does not resolve for the supplied parameters.
122 NI_NAMEREQD is set and the host's name cannot be located, or both node‐
124 name and servname were null.
125 EAI_OVERFLOW
127 An argument buffer overflowed. The buffer pointed to by the node
129 argument or the service argument was too small.
130 EAI_SYSTEM
132 A system error occurred. The error code can be found in errno.
133 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 implementa‐
146 tion performs a lookup as if the socket address structure contains the
147 IPv4 address "1.2.3.4" .
148
150 None.
151
153 None.
154
156 gai_strerror() , getaddrinfo() , getservbyname() , inet_ntop() ,
157 socket() , the Base Definitions volume of IEEE Std 1003.1-2001,
158 <netdb.h>, <sys/socket.h>
159
161 Portions of this text are reprinted and reproduced in electronic form
162 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
163 -- Portable Operating System Interface (POSIX), The Open Group Base
164 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
165 Electrical and Electronics Engineers, Inc and The Open Group. In the
166 event of any discrepancy between this version and the original IEEE and
167 The Open Group Standard, the original IEEE and The Open Group Standard
168 is the referee document. The original Standard can be obtained online
169 at http://www.opengroup.org/unix/online.html .
170IEEE/The Open Group 2003 GETNAMEINFO(P)