Sockets Library Functions getipnodebyname(3SOCKET)
NAME
getipnodebyname, getipnodebyaddr, freehostent - get IP node
entrySYNOPSIS
cc [ flag... ] file... -lsocket -lnsl [ library... ]
#include
#include
struct hostent *getipnodebyname(const char *name, int af,int flags, int *error_num);
struct hostent *getipnodebyaddr(const void *src, size_t len,
int af, int *error_num);
void freehostent(struct hostent *ptr);
PARAMETERS
af Address family flags Various flags name Name of hosterror_num Error storage
src Address for lookup len Length of address ptr Pointer to hostent structureDESCRIPTION
The getipnodebyname() function searches the ipnodes databasefrom the beginning. The function finds the first h_name
member that matches the hostname specified by name. The function takes an af argument that specifies the addressfamily. The address family can be AF_INET for IPv4 addresses
or AF_INET6 for IPv6 addresses. The flags argument deter-
mines what results are returned based on the value of flags.If the flags argument is set to 0 (zero), the default opera-
tion of the function is specified as follows:SunOS 5.11 Last change: 22 Aug 2007 1
Sockets Library Functions getipnodebyname(3SOCKET)o If the af argument is AF_INET, a query is made for
an IPv4 address. If successful, IPv4 addresses arereturned and the h_length member of the hostent
structure is 4. Otherwise, the function returns a NULL pointer.o If the af argument is AF_INET6, a query is made for
an IPv6 address. If successful, IPv6 addresses arereturned and the h_length member of the hostent
structure is 16. Otherwise, the function returns a NULL pointer.The flags argument changes the default actions of the func-
tion. Set the flags argument with a logical OR operation on any of combination of the following values:o AI_V4MAPPED
o AI_ALL
o AI_ADDRCONFIG
The special flags value, AI_DEFAULT, should handle most
applications. Porting simple applications to use IPv6 replaces the call hptr = gethostbyname(name); withhptr = getipnodebyname(name, AF_INET6, AI_DEFAULT, &error_num);
The flags value 0 (zero) implies a strict interpretation of the af argument:o If flags is 0 and af is AF_INET, the caller wants
only IPv4 addresses. A query is made for A records. If successful, IPv4 addresses are returned and theh_length member of the hostent structure is 4. Oth-
erwise, the function returns a NULL pointer.o If flags is 0 and af is AF_INET6, the caller wants
only IPv6 addresses. A query is made for AAAA records. If successful, IPv6 addresses are returnedand the h_length member of the hostent structure is
16. Otherwise, the function returns a NULL pointer.SunOS 5.11 Last change: 22 Aug 2007 2
Sockets Library Functions getipnodebyname(3SOCKET) Logically OR other constants into the flags argument to modify the behavior of the getipnodebyname() function.o If the AI_V4MAPPED flag is specified with af set to
AF_INET6, the caller can accept IPv4-mapped IPv6
addresses. If no AAAA records are found, a query is made for A records. Any A records found arereturned as IPv4-mapped IPv6 addresses and the
h_length is 16. The AI_V4MAPPED flag is ignored
unless af equals AF_INET6.
o The AI_ALL flag is used in conjunction with the
AI_V4MAPPED flag, exclusively with the IPv6 address
family. When AI_ALL is logically ORed with
AI_V4MAPPED flag, the caller wants all addresses:
IPv6 and IPv4-mapped IPv6 addresses. A query is
first made for AAAA records and, if successful, IPv6 addresses are returned. Another query is then made for A records. Any A records found arereturned as IPv4-mapped IPv6 addresses and the
h_length is 16. Only when both queries fail does
the function return a NULL pointer. The AI_ALL flag
is ignored unless af is set to AF_INET6.
o The AI_ADDRCONFIG flag specifies that a query for
AAAA records should occur only when the node is configured with at least one IPv6 source address. A query for A records should occur only when the node is configured with at least one IPv4 source address. For example, if a node is configured withno IPv6 source addresses, af equals AF_INET6, and
the node name queried has both AAAA and A records, then: o A NULL pointer is returned when only theAI_ADDRCONFIG value is specified.
o The A records are returned as IPv4-mapped IPv6
addresses when the AI_ADDRCONFIG and
AI_V4MAPPED values are specified.
The special flags value, AI_DEFAULT, is defined as
#define AI_DEFAULT (AI_V4MAPPED | AI_ADDRCONFIG)
The getipnodebyname() function allows the name argument tobe a node name or a literal address string: a dotted-decimal
IPv4 address or an IPv6 hex address. Applications do nothave to call inet_pton(3SOCKET) to handle literal address
SunOS 5.11 Last change: 22 Aug 2007 3
Sockets Library Functions getipnodebyname(3SOCKET) strings. Four scenarios arise based on the type of literal address string and the value of the af argument. The two simplecases occur when name is a dotted-decimal IPv4 address and
af equals AF_INET and when name is an IPv6 hex address and
af equals AF_INET6. The members of the returned hostent
structure are:h_name Pointer to a copy of the name argument
h_aliases NULL pointer.
h_addrtype Copy of the af argument.
h_length 4 for AF_INET or 16 for AF_INET6.
h_addr_list Array of pointers to 4-byte or 16-byte binary
addresses. The array is terminated by a NULL pointer.RETURN VALUES
Upon successful completion, getipnodebyname() and getipnode-
byaddr() return a hostent structure. Otherwise they return NULL. The hostent structure does not change from the existing definition when used with gethostbyname(3NSL). For example, host entries are represented by the struct hostent structure defined in: struct hostent { char *h_name; /* canonical name of host */
char **h_aliases; /* alias list */
int h_addrtype; /* host address type */
int h_length; /* length of address */
char **h_addr_list; /* list of addresses */
}; An error occurs when name is an IPv6 hex address and afequals AF_INET. The return value of the function is a NULL
pointer and error_num equals HOST_NOT_FOUND.
SunOS 5.11 Last change: 22 Aug 2007 4
Sockets Library Functions getipnodebyname(3SOCKET) The getipnodebyaddr() function has the same arguments as the existing gethostbyaddr(3NSL) function, but adds an error number. As with getipnodebyname(), getipnodebyaddr() isthread-safe. The error_num value is returned to the caller
with the appropriate error code to support thread-safe error
code returns. The following error conditions can be returnedfor error_num:
HOST_NOT_FOUND Host is unknown.
NO_DATA No address is available for the name
specified in the server request. This error is not a soft error. Another type of name server request might be successful.NO_RECOVERY An unexpected server failure occurred,
which is a non-recoverable error.
TRY_AGAIN This error is a soft error that indicates
that the local server did not receive a response from an authoritative server. Aretry at some later time might be success-
ful.One possible source of confusion is the handling of IPv4-
mapped IPv6 addresses and IPv4-compatible IPv6 addresses,
but the following logic should apply:1. If af is AF_INET6, and if len equals 16, and if the
IPv6 address is an IPv4-mapped IPv6 address or an
IPv4-compatible IPv6 address, then skip over the
first 12 bytes of the IPv6 address, set af toAF_INET, and set len to 4.
2. If af is AF_INET, lookup the name for the given
IPv4 address.3. If af is AF_INET6, lookup the name for the given
IPv6 address.4. If the function is returning success, then the sin-
gle address that is returned in the hostent struc-
ture is a copy of the first argument to the func-
tion with the same address family that was passed as an argument to this function.SunOS 5.11 Last change: 22 Aug 2007 5
Sockets Library Functions getipnodebyname(3SOCKET) All four steps listed are performed in order. This structure, and the information pointed to by this structure, are dynamically allocated by getipnodebyname()and getipnodebyaddr(). The freehostent() function frees this
memory.EXAMPLES
Example 1 Getting the Canonical Name, Aliases, and Internet IP Addresses for a Given HostnameThe following is a sample program that retrieves the canoni-
cal name, aliases, and all Internet IP addresses, both ver-
sion 6 and version 4, for a given hostname.#include
#include
#include
#include
#include
#include
#include
main(int argc, const char **argv) {char abuf[INET6_ADDRSTRLEN];
int error_num;
struct hostent *hp; char **p; if (argc != 2) {(void) printf("usage: %s hostname0, argv[0]);
exit (1); } /* argv[1] can be a pointer to a hostname or literal IP address */hp = getipnodebyname(argv[1], AF_INET6, AI_ALL | AI_ADDRCONFIG |
AI_V4MAPPED, &error_num);
if (hp == NULL) {if (error_num == TRY_AGAIN) {
printf("%s: unknown host or invalid literal address "
"(try again later)0, argv[1]); } else {printf("%s: unknown host or invalid literal address0,
argv[1]); } exit (1); }for (p = hp->h_addr_list; *p != 0; p++) {
SunOS 5.11 Last change: 22 Aug 2007 6
Sockets Library Functions getipnodebyname(3SOCKET)struct in6_addr in6;
char **q;bcopy(*p, (caddr_t)&in6, hp->h_length);
(void) printf("%s%s", inet_ntop(AF_INET6, (void *)&in6,
abuf, sizeof(abuf)), hp->h_name);
for (q = hp->h_aliases; *q != 0; q++)
(void) printf(" %s", *q);
(void) putchar('0); }freehostent(hp);
exit (0); }ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | Safe |
|_____________________________|_____________________________|
SEE ALSO
getaddrinfo(3SOCKET), gethostbyname(3NSL), htonl(3SOCKET), inet(3SOCKET), netdb.h(3HEAD), hosts(4), nsswitch.conf(4), attributes(5) NOTES No enumeration functions are provided for IPv6. Existing enumeration functions such as sethostent(3NSL) do not workin combination with the getipnodebyname() and getipnode-
byaddr() functions. All the functions that return a struct hostent must alwaysreturn the canonical in the h_name field. This name, by
definition, is the well-known and official hostname shared
between all aliases and all addresses. The underlying source that satisfies the request determines the mapping of the input name or address into the set of names and addresses in hostent. Different sources might make such as determination in different ways. If more than one alias and more than one address in hostent exist, no pairing is implied between the alias and address.SunOS 5.11 Last change: 22 Aug 2007 7
Sockets Library Functions getipnodebyname(3SOCKET) The current implementations of these functions return or accept only addresses for the Internet address family (typeAF_INET) or the Internet address family Version 6 (type
AF_INET6).
IPv4-mapped addresses are not recommended. The
getaddrinfo(3SOCKET) function is preferred over getipnode-
byaddr() because it allows applications to lookup IPv4 andIPv6 addresses without relying on IPv4-mapped addresses.
The form for an address of type AF_INET is a struct in_addr
defined in. The form for an address of type AF_INET6 is a struct in6_addr, also defined in
. The functions described in inet_ntop(3SOCKET) and inet_pton(3SOCKET) that are illus-
trated in the EXAMPLES section are helpful in constructing
and manipulating addresses in either of these forms.SunOS 5.11 Last change: 22 Aug 2007 8