Subversion Repositories openrisc_me

.\"     $OpenBSD: gethostbyname.3,v 1.16 2000/12/24 00:30:56 aaron 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.

.\" 3. All advertising materials mentioning features or use of this software

.\"    must display the following acknowledgement:

.\"     This product includes software developed by the University of

.\"     California, Berkeley and its contributors.

.\" 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.

.\"

.Dd March 13, 1997

.Dt GETHOSTBYNAME 3

.Os

.Sh NAME

.Nm gethostbyname ,

.Nm gethostbyname2 ,

.Nm gethostbyaddr ,

.Nm gethostent ,

.Nm sethostent ,

.Nm endhostent ,

.Nm hstrerror ,

.Nm herror

.Nd get network host entry

.Sh SYNOPSIS

.Fd #include 

.Fd extern int h_errno;

.Ft struct hostent *

.Fn gethostbyname "const char *name"

.Ft struct hostent *

.Fn gethostbyname2 "const char *name" "int af"

.Ft struct hostent *

.Fn gethostbyaddr "const char *addr" "int len" "int af"

.Ft struct hostent *

.Fn gethostent void

.Ft void

.Fn sethostent "int stayopen"

.Ft void

.Fn endhostent void

.Ft void

.Fn herror "const char *string"

.Ft const char *

.Fn hstrerror "int err"

.Sh DESCRIPTION

The

.Fn gethostbyname

and

.Fn gethostbyaddr

functions each return a pointer to an object with the following structure

describing an internet host referenced by name or by address, respectively.

This structure contains either information obtained from the name server (i.e.,

.Xr resolver 3

and

.Xr named 8 ) ,

broken-out fields from a line in

.Pa /etc/hosts ,

or database entries supplied by the

.Xr yp 8

system.

.Xr resolv.conf 5

describes how the particular database is chosen.

.Bd -literal

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 Fa h_name

Official name of the host.

.It Fa h_aliases

A zero-terminated array of alternate names for the host.

.It Fa h_addrtype

The type of address being returned.

.It Fa h_length

The length, in bytes, of the address.

.It Fa h_addr_list

A zero-terminated array of network addresses for the host.

Host addresses are returned in network byte order.

.It Fa h_addr

The first address in

.Fa h_addr_list ;

this is for backward compatibility.

.El

.Pp

The function

.Fn gethostbyname

will search for the named host in the current domain and its parents

using the search lookup semantics detailed in

.Xr resolv.conf 5

and

.Xr hostname 7 .

.Pp

.Fn gethostbyname2

is an advanced form of

.Fn gethostbyname

which allows lookups in address families other than

.Dv AF_INET ,

for example

.Dv AF_INET6 .

.Pp

The

.Fn gethostbyaddr

function will search for the specified address of length

.Fa len

in the address family

.Fa af .

The only address family currently supported is

.Dv AF_INET .

.Pp

The

.Fn sethostent

function may be used to request the use of a connected

.Tn TCP

socket for queries.

If the

.Fa stayopen

flag is non-zero,

this sets the option to send all queries to the name server using

.Tn TCP

and to retain the connection after each call to

.Fn gethostbyname

or

.Fn gethostbyaddr .

Otherwise, queries are performed using

.Tn UDP

datagrams.

.Pp

The

.Fn endhostent

function closes the

.Tn TCP

connection.

.Pp

The

.Fn herror

function prints an error message describing the failure.

If its argument

.Fa string

is non-null,

it is prepended to the message string and separated from it by a colon

.Pq Ql \&:

and a space.

The error message is printed with a trailing newline.

The contents of the error message is the same as that returned by

.Fn hstrerror

with argument

.Fa h_errno .

.Sh FILES

.Bl -tag -width /etc/resolv.conf -compact

.It Pa /etc/hosts

.It Pa /etc/resolv.conf

.El

.Sh DIAGNOSTICS

Error return status from

.Fn gethostbyname ,

.Fn gethostbyname2 ,

and

.Fn gethostbyaddr

is indicated by return of a null pointer.

The external integer

.Va h_errno

may then be checked to see whether this is a temporary failure

or an invalid or unknown host.

.Pp

The variable

.Va h_errno

can have the following values:

.Bl -tag -width HOST_NOT_FOUND

.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.

.It Dv NO_DATA

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 resolver 3 ,

.Xr getaddrinfo 3 ,

.Xr getnameinfo 3 ,

.Xr hosts 5 ,

.Xr resolv.conf 5 ,

.Xr hostname 7 ,

.Xr named 8

.Sh CAVEAT

If the search routines in

.Xr resolv.conf 5

decide to read the

.Pa /etc/hosts

file,

.Fn gethostent

and other functions will

read the next line of the file,

re-opening the file if necessary.

.Pp

The

.Fn sethostent

function opens and/or rewinds the file

.Pa /etc/hosts .

If the

.Fa stayopen

argument is non-zero, the file will not be closed after each call to

.Fn gethostbyname ,

.Fn gethostbyname2 ,

or

.Fn gethostbyaddr .

.Pp

The

.Fn endhostent

function closes the file.

.Sh HISTORY

The

.Fn herror

function appeared in

.Bx 4.3 .

The

.Fn endhostent ,

.Fn gethostbyaddr ,

.Fn gethostbyname ,

.Fn gethostent ,

and

.Fn sethostent

functions appeared in

.Bx 4.2 .

.Sh BUGS

These functions use static data storage;

if the data is needed for future use, it should be

copied before any subsequent calls overwrite it.

Only the Internet

address formats are currently understood.

.Pp

YP does not support any address families other than

.Dv AF_INET

and uses

the traditional database format.