.\" $KAME: getipnodebyname.3,v 1.6 2000/08/09 21:16:17 itojun Exp $ .\" .\" Copyright (c) 1983, 1987, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" From: @(#)gethostbyname.3 8.4 (Berkeley) 5/25/95 .\" $FreeBSD: src/lib/libc/net/getipnodebyname.3,v 1.18 2007/01/09 00:28:02 imp Exp $ .\" .Dd August 6, 2004 .Dt GETIPNODEBYNAME 3 .Os .\" .Sh NAME .Nm getipnodebyname , .Nm getipnodebyaddr , .Nm freehostent .Nd nodename-to-address and address-to-nodename translation .\" .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In sys/types.h .In sys/socket.h .In netdb.h .Ft "struct hostent *" .Fn getipnodebyname "const char *name" "int af" "int flags" "int *error_num" .Ft "struct hostent *" .Fn getipnodebyaddr "const void *src" "size_t len" "int af" "int *error_num" .Ft void .Fn freehostent "struct hostent *ptr" .\" .Sh DESCRIPTION The .Fn getipnodebyname and .Fn getipnodebyaddr functions are very similar to .Xr gethostbyname 3 , .Xr gethostbyname2 3 and .Xr gethostbyaddr 3 . The functions cover all the functionalities provided by the older ones, and provide better interface to programmers. The functions require additional arguments, .Fa af , and .Fa 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 .Dv AF_INET or .Dv AF_INET6 ) . The functions also require an additional pointer argument, .Fa error_num to return the appropriate error code, to support thread safe error code returns. .Pp The type and usage of the return value, .Li "struct hostent" is described in .Xr gethostbyname 3 . .Pp For .Fn getipnodebyname , the .Fa 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 .Fa af argument specifies the address family, either .Dv AF_INET or .Dv AF_INET6 . The .Fa 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 .Dv AI_DEFAULT (defined below) should handle most applications. That is, porting simple applications to use IPv6 replaces the call .Bd -literal -offset hptr = gethostbyname(name); .Ed .Pp with .Bd -literal -offset hptr = getipnodebyname(name, AF_INET6, AI_DEFAULT, &error_num); .Ed .Pp Applications desiring finer control over the types of addresses searched for and returned, can specify other combinations of the .Fa flags argument. .Pp A .Fa flags of .Li 0 implies a strict interpretation of the .Fa af argument: .Bl -bullet .It If .Fa flags is 0 and .Fa af is .Dv AF_INET , then the caller wants only IPv4 addresses. A query is made for .Li A records. If successful, the IPv4 addresses are returned and the .Li h_length member of the .Li hostent structure will be 4, else the function returns a .Dv NULL pointer. .It If .Fa flags is 0 and if .Fa af is .Li AF_INET6 , then the caller wants only IPv6 addresses. A query is made for .Li AAAA records. If successful, the IPv6 addresses are returned and the .Li h_length member of the .Li hostent structure will be 16, else the function returns a .Dv NULL pointer. .El .Pp Other constants can be logically-ORed into the .Fa flags argument, to modify the behavior of the function. .Bl -bullet .It If the .Dv AI_V4MAPPED flag is specified along with an .Fa af of .Dv AF_INET6 , then the caller will accept IPv4-mapped IPv6 addresses. That is, if no .Li AAAA records are found then a query is made for .Li A records and any found are returned as IPv4-mapped IPv6 addresses .Li ( h_length will be 16). The .Dv AI_V4MAPPED flag is ignored unless .Fa af equals .Dv AF_INET6 . .It The .Dv AI_V4MAPPED_CFG flag is exact same as the .Dv AI_V4MAPPED flag only if the kernel supports IPv4-mapped IPv6 address. .It If the .Dv AI_ALL flag is used in conjunction with the .Dv AI_V4MAPPED flag, and only used with the IPv6 address family. When .Dv AI_ALL is logically or'd with .Dv AI_V4MAPPED flag then the caller wants all addresses: IPv6 and IPv4-mapped IPv6. A query is first made for .Li AAAA records and if successful, the IPv6 addresses are returned. Another query is then made for .Li A records and any found are returned as IPv4-mapped IPv6 addresses. .Li h_length will be 16. Only if both queries fail does the function return a .Dv NULL pointer. This flag is ignored unless af equals AF_INET6. If both .Dv AI_ALL and .Dv AI_V4MAPPED are specified, .Dv AI_ALL takes precedence. .It The .Dv AI_ADDRCONFIG flag specifies that a query for .Li AAAA records should occur only if the node has at least one IPv6 source address configured and a query for .Li A records should occur only if the node has at least one IPv4 source address configured. .Pp For example, if the node has no IPv6 source addresses configured, and .Fa af equals AF_INET6, and the node name being looked up has both .Li AAAA and .Li A records, then: (a) if only .Dv AI_ADDRCONFIG is specified, the function returns a .Dv NULL pointer; (b) if .Dv AI_ADDRCONFIG | .Dv AI_V4MAPPED is specified, the .Li A records are returned as IPv4-mapped IPv6 addresses; .El .Pp The special flags value of .Dv AI_DEFAULT is defined as .Bd -literal -offset #define AI_DEFAULT (AI_V4MAPPED_CFG | AI_ADDRCONFIG) .Ed .Pp We noted that the .Fn getipnodebyname function must allow the .Fa 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 .Xr inet_pton 3 to handle literal address strings. When the .Fa name argument is a literal address string, the .Fa flags argument is always ignored. .Pp There are four scenarios based on the type of literal address string and the value of the .Fa af argument. The two simple cases are when .Fa name is a dotted-decimal IPv4 address and .Fa af equals .Dv AF_INET , or when .Fa name is an IPv6 hex address and .Fa af equals .Dv AF_INET6 . The members of the returned hostent structure are: .Li h_name points to a copy of the .Fa name argument, .Li h_aliases is a .Dv NULL pointer, .Li h_addrtype is a copy of the .Fa af argument, .Li h_length is either 4 (for .Dv AF_INET ) or 16 (for .Dv AF_INET6 ) , .Li h_addr_list is a pointer to the 4-byte or 16-byte binary address, and .Li h_addr_list is a .Dv NULL pointer. .Pp When .Fa name is a dotted-decimal IPv4 address and .Fa af equals .Dv AF_INET6 , and .Dv AI_V4MAPPED is specified, an IPv4-mapped IPv6 address is returned: .Li h_name points to an IPv6 hex address containing the IPv4-mapped IPv6 address, .Li h_aliases is a .Dv NULL pointer, .Li h_addrtype is .Dv AF_INET6 , .Li h_length is 16, .Li h_addr_list is a pointer to the 16-byte binary address, and .Li h_addr_list is a .Dv NULL pointer. .Pp It is an error when .Fa name is an IPv6 hex address and .Fa af equals .Dv AF_INET . The function's return value is a .Dv NULL pointer and the value pointed to by .Fa error_num equals .Dv HOST_NOT_FOUND . .Pp The .Fn getipnodebyaddr function takes almost the same argument as .Xr 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. .Pp The .Fn getipnodebyname and .Fn getipnodebyaddr functions dynamically allocate the structure to be returned to the caller. The .Fn freehostent function reclaims memory region allocated and returned by .Fn getipnodebyname or .Fn getipnodebyaddr . .\" .Sh FILES .Bl -tag -width /etc/nsswitch.conf -compact .It Pa /etc/hosts .\".It Pa /etc/nsswitch.conf .It Pa /etc/resolv.conf .El .\" .Sh DIAGNOSTICS The .Fn getipnodebyname and .Fn getipnodebyaddr functions returns .Dv NULL on errors. The integer values pointed to by .Fa 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 .Xr gethostbyname 3 . .\" .Sh SEE ALSO .Xr getaddrinfo 3 , .Xr gethostbyaddr 3 , .Xr gethostbyname 3 , .Xr getnameinfo 3 , .Xr hosts 5 , .Xr nsswitch.conf 5 , .Xr services 5 , .Xr hostname 7 , .Xr named 8 .Pp .Rs .%A R. Gilligan .%A S. Thomson .%A J. Bound .%A W. Stevens .%T Basic Socket Interface Extensions for IPv6 .%R RFC2553 .%D March 1999 .Re .\" .Sh STANDARDS The .Fn getipnodebyname and .Fn getipnodebyaddr functions are documented in .Dq Basic Socket Interface Extensions for IPv6 (RFC2553). .\" .Sh HISTORY The implementation first appeared in KAME advanced networking kit. .\" .Sh BUGS The .Fn getipnodebyname and .Fn getipnodebyaddr functions 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, .Fn getaddrinfo 3 and .Fn getnameinfo 3 are recommended. .Pp The text was shamelessly copied from RFC2553.