.\"	$NetBSD: getipnodebyname.3,v 1.1.1.2 2012/09/09 16:07:43 christos Exp $
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.\" Id: getipnodebyname.3,v 1.3 2009/01/22 23:49:23 tbox Exp 
.\"
.Dd September 17, 1999
.Dt GETIPNODEBYNAME @LIB_NETWORK_EXT_U@ 
.Os BSD 4
.Sh NAME
.Nm getipnodebyname ,
.Nm getipnodebyaddr
.Nd get network host entry
.br
.Nm freehostent 
.Nd free network host entry
.Sh SYNOPSIS
.Fd #include <netdb.h>
.Pp
.Ft struct hostent *
.Fn getipnodebyname "const char *name" "int af" "int flags" "int *error"
.Ft struct hostent *
.Fn getipnodebyaddr "const void *addr" "size_t len" "int af" "int *error"
.Ft void
.Fn freehostent "struct hostent *he"
.Sh DESCRIPTION
.Fn Getipnodebyname ,
and
.Fn getipnodebyaddr
each return a pointer to a
.Ft hostent
structure (see below) describing an internet host
referenced by name or by address, as the function names indicate.
This structure contains either the information obtained from the name server,
or broken-out fields from a line in 
.Pa /etc/hosts .
If the local name server is not running, these routines do a lookup in
.Pa /etc/hosts .
.Bd -literal -offset indent
struct	hostent {
	char	*h_name;	/* official 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 from name server */
};

#define	h_addr  h_addr_list[0]	/* address, for backward compatibility */
.Ed
.Pp
The members of this structure are:
.Bl -tag -width "h_addr_list" 
.It h_name
Official name of the host.
.It h_aliases
A zero-terminated array of alternate names for the host.
.It h_addrtype
The type of address being returned.
.It h_length
The length, in bytes, of the address.
.It h_addr_list
A zero-terminated array of network addresses for the host.
Host addresses are returned in network byte order.
.It h_addr
The first address in 
.Li h_addr_list ; 
this is for backward compatibility.
.El
.Pp
This structure should be freed after use by calling
.Fn freehostent .
.Pp
When using the nameserver,
.Fn getiphostbyaddr
will search for the named host in each parent domain given in the 
.Dq Li search
directive of
.Xr resolv.conf @FORMAT_EXT@
unless the name contains a dot
.Pq Dq \&. .
If the name contains no dot, and if the environment variable 
.Ev HOSTALIASES
contains the name of an alias file, the alias file will first be searched
for an alias matching the input name.
See
.Xr hostname @DESC_EXT@
for the domain search procedure and the alias file format.
.Pp
.Fn Getiphostbyaddr
can be told to look for IPv4 addresses, IPv6 addresses or both IPv4 and IPv6.
If IPv4 addresses only are to be looked up then
.Fa af
should be set to
.Dv AF_INET , 
otherwise it should be set to
.Dv AF_INET6 .  
.Pp
There are three flags that can be set
.Bl -tag -width "AI_ADDRCONFIG" 
.It Dv AI_V4MAPPED
Return IPv4 addresses if no IPv6 addresses are found.
This flag is ignored unless
.Fa af
is
.Dv AF_INET6 .
.It Dv AI_ALL
Return IPv4 addresses as well IPv6 addresses if 
.Dv AI_V4MAPPED
is set.
This flag is ignored unless
.Fa af
is
.Dv AF_INET6 .
.It Dv AI_ADDRCONFIG
Only return addresses of a given type if the system has an active interface
with that type.
.El
.Pp
Also
.Dv AI_DEFAULT
is defined to be
.Dv (AI_V4MAPPED|AI_ADDRCONFIG) .
.Pp
.Fn Getipnodebyaddr
will lookup IPv4 mapped and compatible addresses in the IPv4 name
space and IPv6 name space
.Pp
.Fn Freehostent
frees the hostent structure allocated be
.Fn getipnodebyname
and
.Fn getipnodebyaddr .
The structures returned by 
.Fn gethostbyname ,
.Fn gethostbyname2 ,
.Fn gethostbyaddr 
and
.Fn gethostent
should not be passed to
.Fn freehostent
as they are pointers to static areas.
.Sh ENVIRONMENT
.Bl -tag -width "HOSTALIASES  " -compact
.It Ev HOSTALIASES
Name of file containing 
.Pq Ar host alias , full hostname
pairs.
.El
.Sh FILES
.Bl -tag -width "HOSTALIASES  " -compact
.It Pa /etc/hosts
See
.Xr hosts @FORMAT_EXT@ .
.El
.Sh DIAGNOSTICS
.Pp
Error return status from 
.Fn getipnodebyname
and
.Fn getipnodebyaddr
is indicated by return of a null pointer.
In this case
.Ft error
may then be checked to see whether this is a temporary failure
or an invalid or unknown host.
.Ft errno
can have the following values:
.Bl -tag -width "HOST_NOT_FOUND  " -offset indent 
.It Dv NETDB_INTERNAL 
This indicates an internal error in the library, unrelated to the network
or name service.
.Ft errno
will be valid in this case; see
.Xr perror @SYSCALL_EXT@ .
.It Dv HOST_NOT_FOUND
No such host is known.
.It Dv TRY_AGAIN 
This is usually a temporary error
and means that the local server did not receive
a response from an authoritative server.
A retry at some later time may succeed.
.It Dv NO_RECOVERY 
Some unexpected server failure was encountered.
This is a non-recoverable error, as one might expect.
.It Dv NO_ADDRESS
The requested name is valid but does not have an IP address; 
this is not a temporary error.  
This means that the name is known to the name server but there is no address
associated with this name.
Another type of request to the name server using this domain name
will result in an answer;
for example, a mail-forwarder may be registered for this domain.
.El
.Sh SEE ALSO
.Xr hosts @FORMAT_EXT@ , 
.Xr hostname @DESC_EXT@ , 
.Xr resolver @LIB_NETWORK_EXT@ , 
.Xr resolver @FORMAT_EXT@ ,
.Xr gethostbyname @LIB_NETWORK_EXT@ ,
.Xr RFC2553 .