1GETADDRINFO(3)           BSD Library Functions Manual           GETADDRINFO(3)
2

NAME

4     getaddrinfo freeaddrinfo, gai_strerror — nodename-to-address translation
5     in protocol-independent manner
6

SYNOPSIS

8     #include <sys/socket.h>
9     #include <netdb.h>
10
11     int
12     getaddrinfo(const char *nodename, const char *servname,
13         const struct addrinfo *hints, struct addrinfo **res);
14
15     void
16     freeaddrinfo(struct addrinfo *ai);
17
18     char *
19     gai_strerror(int ecode);
20

DESCRIPTION

22     The getaddrinfo() function is defined for protocol-independent nodename-
23     to-address translation.  It performs functionality of gethostbyname(3)
24     and getservbyname(3), in more sophisticated manner.
25
26     The addrinfo structure is defined as a result of including the <netdb.h>
27     header:
28
29     struct addrinfo {                                                  *
30          int     ai_flags;     /* AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST */
31          int     ai_family;    /* PF_xxx */
32          int     ai_socktype;  /* SOCK_xxx */
33          int     ai_protocol;  /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
34          size_t  ai_addrlen;   /* length of ai_addr */
35          char   *ai_canonname; /* canonical name for nodename */
36          struct sockaddr  *ai_addr; /* binary address */
37          struct addrinfo  *ai_next; /* next structure in linked list */
38     };
39
40     The nodename and servname arguments are pointers to null-terminated
41     strings or NULL.  One or both of these two arguments must be a non-NULL
42     pointer.  In the normal client scenario, both the nodename and servname
43     are specified.  In the normal server scenario, only the servname is spec‐
44     ified.  A non-NULL nodename string can be either a node name or a numeric
45     host address string (i.e., a dotted-decimal IPv4 address or an IPv6 hex
46     address).  A non-NULL servname string can be either a service name or a
47     decimal port number.
48
49     The caller can optionally pass an addrinfo structure, pointed to by the
50     third argument, to provide hints concerning the type of socket that the
51     caller supports.  In this hints structure all members other than
52     ai_flags, ai_family, ai_socktype, and ai_protocol must be zero or a NULL
53     pointer.  A value of PF_UNSPEC for ai_family means the caller will accept
54     any protocol family.  A value of 0 for ai_socktype means the caller will
55     accept any socket type.  A value of 0 for ai_protocol means the caller
56     will accept any protocol.  For example, if the caller handles only TCP
57     and not UDP, then the ai_socktype member of the hints structure should be
58     set to SOCK_STREAM when getaddrinfo() is called.  If the caller handles
59     only IPv4 and not IPv6, then the ai_family member of the hints structure
60     should be set to PF_INET when getaddrinfo() is called.  If the third
61     argument to getaddrinfo() is a NULL pointer, this is the same as if the
62     caller had filled in an addrinfo structure initialized to zero with
63     ai_family set to PF_UNSPEC.
64
65     Upon successful return a pointer to a linked list of one or more addrinfo
66     structures is returned through the final argument.  The caller can
67     process each addrinfo structure in this list by following the ai_next
68     pointer, until a NULL pointer is encountered.  In each returned addrinfo
69     structure the three members ai_family, ai_socktype, and ai_protocol are
70     the corresponding arguments for a call to the socket() function.  In each
71     addrinfo structure the ai_addr member points to a filled-in socket
72     address structure whose length is specified by the ai_addrlen member.
73
74     If the AI_PASSIVE bit is set in the ai_flags member of the hints struc‐
75     ture, then the caller plans to use the returned socket address structure
76     in a call to bind().  In this case, if the nodename argument is a NULL
77     pointer, then the IP address portion of the socket address structure will
78     be set to INADDR_ANY for an IPv4 address or IN6ADDR_ANY_INIT for an IPv6
79     address.
80
81     If the AI_PASSIVE bit is not set in the ai_flags member of the hints
82     structure, then the returned socket address structure will be ready for a
83     call to connect() (for a connection-oriented protocol) or either
84     connect(), sendto(), or sendmsg() (for a connectionless protocol).  In
85     this case, if the nodename argument is a NULL pointer, then the IP
86     address portion of the socket address structure will be set to the loop‐
87     back address.
88
89     If the AI_CANONNAME bit is set in the ai_flags member of the hints struc‐
90     ture, then upon successful return the ai_canonname member of the first
91     addrinfo structure in the linked list will point to a null-terminated
92     string containing the canonical name of the specified nodename.
93
94     If the AI_NUMERICHOST bit is set in the ai_flags member of the hints
95     structure, then a non-NULL nodename string must be a numeric host address
96     string.  Otherwise an error of EAI_NONAME is returned.  This flag pre‐
97     vents any type of name resolution service (e.g., the DNS) from being
98     called.
99
100     All of the information returned by getaddrinfo() is dynamically allo‐
101     cated: the addrinfo structures, and the socket address structures and
102     canonical node name strings pointed to by the addrinfo structures.  To
103     return this information to the system the function Fn freeaddrinfo is
104     called.  The addrinfo structure pointed to by the ai argument is freed,
105     along with any dynamic storage pointed to by the structure.  This opera‐
106     tion is repeated until a NULL ai_next pointer is encountered.
107
108     To aid applications in printing error messages based on the EAI_xxx codes
109     returned by getaddrinfo(), gai_strerror() is defined.  The argument is
110     one of the EAI_xxx values defined earlier and the return value points to
111     a string describing the error.  If the argument is not one of the EAI_xxx
112     values, the function still returns a pointer to a string whose contents
113     indicate an unknown error.
114

FILES

116     /etc/hosts
117     /etc/host.conf
118     /etc/resolv.conf
119

DIAGNOSTICS

121     Error return status from getaddrinfo() is zero on success and non-zero on
122     errors.  Non-zero error codes are defined in <netdb.h>, and as follows:
123
124     EAI_ADDRFAMILY  address family for nodename not supported
125     EAI_AGAIN       temporary failure in name resolution
126     EAI_BADFLAGS    invalid value for ai_flags
127     EAI_FAIL        non-recoverable failure in name resolution
128     EAI_FAMILY      ai_family not supported
129     EAI_MEMORY      memory allocation failure
130     EAI_NODATA      no address associated with nodename
131     EAI_NONAME      nodename nor servname provided, or not known
132     EAI_SERVICE     servname not supported for ai_socktype
133     EAI_SOCKTYPE    ai_socktype not supported
134     EAI_SYSTEM      system error returned in errno
135
136     If called with proper argument, gai_strerror() returns a pointer to a
137     string describing the given error code.  If the argument is not one of
138     the EAI_xxx values, the function still returns a pointer to a string
139     whose contents indicate an unknown error.
140

SEE ALSO

142     getnameinfo(3), gethostbyname(3), getservbyname(3), hosts(5),
143     services(5), hostname(7), named(8)
144
145     R. Gilligan, S.  Thomson, J. Bound, and W. Stevens, ``Basic Socket Inter‐
146     face Extensions for IPv6,'' RFC2133, April 1997.
147

HISTORY

149     The implementation first appeared in WIDE Hydrangea IPv6 protocol stack
150     kit.
151

STANDARDS

153     The getaddrinfo() function is defined IEEE POSIX 1003.1g draft specifica‐
154     tion, and documented in ``Basic Socket Interface Extensions for IPv6''
155     (RFC2133).
156

BUGS

158     The text was shamelessly copied from RFC2133.
159
160KAME                             May 25, 1995                             KAME
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