path: root/newlib/libc/sys/linux/net/getipnodebyname.3

GETIPNODEBYNAME(3)                 BSD Library Functions Manual                GETIPNODEBYNAME(3)

NAME
     getipnodebyname, getipnodebyaddr, freehostent -- nodename-to-address and address-to-nodename
     translation

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>
     #include <netdb.h>

     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);

DESCRIPTION
     getipnodebyname() and getipnodebyaddr() functions are very similar to gethostbyname(3),
     gethostbyname2(3) and gethostbyaddr(3).  The functions cover all the functionalities pro-
     vided by the older ones, and provide better interface to programmers.  The functions require
     additional arguments, af, and flags, for specifying address family and operation mode.  The
     additional arguments allow programmer to get address for a nodename, for specific address
     family (such as AF_INET or AF_INET6).  The functions also require an additional pointer ar-
     gument, error_num to return the appropriate error code, to support thread safe error code
     returns.

     The type and usage of the return value, struct hostent is described in gethostbyname(3).

     For getipnodebyname(), the name argument can be either a node name or a numeric address
     string (i.e., a dotted-decimal IPv4 address or an IPv6 hex address).  The af argument speci-
     fies the address family, either AF_INET or AF_INET6.  The flags argument specifies the types
     of addresses that are searched for, and the types of addresses that are returned.  We note
     that a special flags value of AI_DEFAULT (defined below) should handle most applications.
     That is, porting simple applications to use IPv6 replaces the call

        hptr = gethostbyname(name);

     with

        hptr = getipnodebyname(name, AF_INET6, AI_DEFAULT, &error_num);

     Applications desiring finer control over the types of addresses searched for and returned,
     can specify other combinations of the flags argument.

     A flags of 0 implies a strict interpretation of the af argument:

     +o   If flags is 0 and af is AF_INET, then the caller wants only IPv4 addresses.  A query is
         made for A records.  If successful, the IPv4 addresses are returned and the h_length
         member of the hostent structure will be 4, else the function returns a NULL pointer.

     +o   If flags is 0 and if af is AF_INET6, then the caller wants only IPv6 addresses.  A query
         is made for AAAA records.  If successful, the IPv6 addresses are returned and the
         h_length member of the hostent structure will be 16, else the function returns a NULL
         pointer.

     Other constants can be logically-ORed into the flags argument, to modify the behavior of the
     function.

     +o   If the AI_V4MAPPED flag is specified along with an af of AF_INET6, then the caller will
         accept IPv4-mapped IPv6 addresses.  That is, if no AAAA records are found then a query
         is made for A records and any found are returned as IPv4-mapped IPv6 addresses (h_length
         will be 16).  The AI_V4MAPPED flag is ignored unless af equals AF_INET6.

     +o   The AI_V4MAPPED_CFG flag is exact same as the AI_V4MAPPED flag only if the kernel sup-
         ports IPv4-mapped IPv6 address.

     +o   If the AI_ALL flag is used in conjunction with the AI_V4MAPPED flag, and only used with
         the IPv6 address family.  When AI_ALL is logically or'd with AI_V4MAPPED flag then the
         caller wants all addresses: IPv6 and IPv4-mapped IPv6.  A query is first made for AAAA
         records and if successful, the IPv6 addresses are returned.  Another query is then made
         for A records and any found are returned as IPv4-mapped IPv6 addresses.  h_length will
         be 16.  Only if both queries fail does the function return a NULL pointer.  This flag is
         ignored unless af equals AF_INET6.  If both AI_ALL and AI_V4MAPPED are specified, AI_ALL
         takes precedence.

     +o   The AI_ADDRCONFIG flag specifies that a query for AAAA records should occur only if the
         node has at least one IPv6 source address configured and a query for A records should
         occur only if the node has at least one IPv4 source address configured.

         For example, if the node has no IPv6 source addresses configured, and af equals
         AF_INET6, and the node name being looked up has both AAAA and A records, then: (a) if
         only AI_ADDRCONFIG is specified, the function returns a NULL pointer; (b) if
         AI_ADDRCONFIG | AI_V4MAPPED is specified, the A records are returned as IPv4-mapped IPv6
         addresses;

     The special flags value of AI_DEFAULT is defined as

        #define  AI_DEFAULT  (AI_V4MAPPED_CFG | AI_ADDRCONFIG)

     We noted that the getipnodebyname() function must allow the name argument to be either a
     node name or a literal address string (i.e., a dotted-decimal IPv4 address or an IPv6 hex
     address).  This saves applications from having to call inet_pton(3) to handle literal ad-
     dress strings.  When the name argument is a literal address string, the flags argument is
     always ignored.

     There are four scenarios based on the type of literal address string and the value of the af
     argument.  The two simple cases are when name is a dotted-decimal IPv4 address and af equals
     AF_INET, or when name is an IPv6 hex address and af equals AF_INET6.  The members of the re-
     turned hostent structure are: h_name points to a copy of the name argument, h_aliases is a
     NULL pointer, h_addrtype is a copy of the af argument, h_length is either 4 (for AF_INET) or
     16 (for AF_INET6), h_addr_list[0] is a pointer to the 4-byte or 16-byte binary address, and
     h_addr_list[1] is a NULL pointer.

     When name is a dotted-decimal IPv4 address and af equals AF_INET6, and AI_V4MAPPED is speci-
     fied, an IPv4-mapped IPv6 address is returned: h_name points to an IPv6 hex address contain-
     ing the IPv4-mapped IPv6 address, h_aliases is a NULL pointer, h_addrtype is AF_INET6,
     h_length is 16, h_addr_list[0] is a pointer to the 16-byte binary address, and
     h_addr_list[1] is a NULL pointer.

     It is an error when name is an IPv6 hex address and af equals AF_INET.  The function's re-
     turn value is a NULL pointer and the value pointed to by error_num equals HOST_NOT_FOUND.

     getipnodebyaddr() takes almost the same argument as gethostbyaddr(3), but adds a pointer to
     return an error number.  Additionally it takes care of IPv4-mapped IPv6 addresses, and
     IPv4-compatible IPv6 addresses.

     getipnodebyname() and getipnodebyaddr() dynamically allocate the structure to be returned to
     the caller.  freehostent() reclaims memory region allocated and returned by
     getipnodebyname() or getipnodebyaddr().

FILES
     /etc/hosts
     /etc/nsswitch.conf
     /etc/resolv.conf

DIAGNOSTICS
     getipnodebyname() and getipnodebyaddr() returns NULL on errors.  The integer values pointed
     to by error_num may then be checked to see whether this is a temporary failure or an invalid
     or unknown host.  The meanings of each error code are described in gethostbyname(3).

SEE ALSO
     gethostbyaddr(3), gethostbyname(3), hosts(5), nsswitch.conf(5), services(5), hostname(7),
     named(8)

     R. Gilligan, S. Thomson, J. Bound, and W. Stevens, Basic Socket Interface Extensions for
     IPv6, RFC2553, March 1999.

HISTORY
     The implementation first appeared in KAME advanced networking kit.

STANDARDS
     getipnodebyname() and getipnodebyaddr() are documented in "Basic Socket Interface Extensions
     for IPv6" (RFC2553).

BUGS
     getipnodebyname() and getipnodebyaddr() do not handle scoped IPv6 address properly.  If you
     use these functions, your program will not be able to handle scoped IPv6 addresses.  For
     IPv6 address manipulation, getaddrinfo(3) and getnameinfo(3) are recommended.

     The current implementation is not thread-safe.

     The text was shamelessly copied from RFC2553.

BSD                                        May 25, 1995                                       BSD