272 lines
7.8 KiB
Groff
272 lines
7.8 KiB
Groff
.\"
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.\" Copyright (C) 2000, 2001 Internet Software Consortium.
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM
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.\" DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
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.\" INTERNET SOFTWARE CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
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.\" INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
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.\" FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
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.\" NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
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.\" WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.TH "LWRES_GETHOSTENT" "3" "Jun 30, 2000" "BIND9" ""
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.SH NAME
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lwres_gethostbyname, lwres_gethostbyname2, lwres_gethostbyaddr, lwres_gethostent, lwres_sethostent, lwres_endhostent, lwres_gethostbyname_r, lwres_gethostbyaddr_r, lwres_gethostent_r, lwres_sethostent_r, lwres_endhostent_r \- lightweight resolver get network host entry
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.SH SYNOPSIS
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\fB#include <lwres/netdb.h>
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.sp
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.na
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struct hostent *
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lwres_gethostbyname(const char *name);
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.ad
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.sp
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.na
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struct hostent *
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lwres_gethostbyname2(const char *name, int af);
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.ad
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.sp
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.na
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struct hostent *
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lwres_gethostbyaddr(const char *addr, int len, int type);
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.ad
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.sp
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.na
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struct hostent *
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lwres_gethostent(void);
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.ad
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.sp
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.na
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void
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lwres_sethostent(int stayopen);
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.ad
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.sp
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.na
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void
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lwres_endhostent(void);
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.ad
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.sp
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.na
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struct hostent *
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lwres_gethostbyname_r(const char *name, struct hostent *resbuf, char *buf, int buflen, int *error);
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.ad
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.sp
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.na
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struct hostent *
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lwres_gethostbyaddr_r(const char *addr, int len, int type, struct hostent *resbuf, char *buf, int buflen, int *error);
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.ad
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.sp
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.na
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struct hostent *
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lwres_gethostent_r(struct hostent *resbuf, char *buf, int buflen, int *error);
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.ad
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.sp
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.na
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void
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lwres_sethostent_r(int stayopen);
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.ad
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.sp
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.na
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void
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lwres_endhostent_r(void);
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.ad
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\fR
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.SH "DESCRIPTION"
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.PP
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These functions provide hostname-to-address and
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address-to-hostname lookups by means of the lightweight resolver.
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They are similar to the standard
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\fBgethostent\fR(3)
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functions provided by most operating systems.
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They use a
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\fBstruct hostent\fR
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which is usually defined in
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\fI<namedb.h>\fR.
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.sp
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.nf
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struct hostent {
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char *h_name; /* official name of host */
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char **h_aliases; /* alias list */
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int h_addrtype; /* host address type */
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int h_length; /* length of address */
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char **h_addr_list; /* list of addresses from name server */
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};
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#define h_addr h_addr_list[0] /* address, for backward compatibility */
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.sp
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.fi
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.PP
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The members of this structure are:
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.TP
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\fBh_name\fR
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The official (canonical) name of the host.
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.TP
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\fBh_aliases\fR
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A NULL-terminated array of alternate names (nicknames) for the host.
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.TP
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\fBh_addrtype\fR
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The type of address being returned \(em
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\fBPF_INET\fR
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or
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\fBPF_INET6\fR.
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.TP
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\fBh_length\fR
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The length of the address in bytes.
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.TP
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\fBh_addr_list\fR
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A \fBNULL\fR
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terminated array of network addresses for the host.
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Host addresses are returned in network byte order.
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.PP
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For backward compatibility with very old software,
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h_addr
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is the first address in
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h_addr_list.
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.PP
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\fBlwres_gethostent()\fR,
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\fBlwres_sethostent()\fR,
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\fBlwres_endhostent()\fR,
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\fBlwres_gethostent_r()\fR,
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\fBlwres_sethostent_r()\fR
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and
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\fBlwres_endhostent_r()\fR
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provide iteration over the known host entries on systems that
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provide such functionality through facilities like
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\fI/etc/hosts\fR
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or NIS. The lightweight resolver does not currently implement
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these functions; it only provides them as stub functions that always
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return failure.
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.PP
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\fBlwres_gethostbyname()\fR and
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\fBlwres_gethostbyname2()\fR look up the hostname
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\fIname\fR.
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\fBlwres_gethostbyname()\fR always looks for an IPv4
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address while \fBlwres_gethostbyname2()\fR looks for an
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address of protocol family \fIaf\fR: either
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\fBPF_INET\fR or \fBPF_INET6\fR \(em IPv4 or IPV6
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addresses respectively. Successful calls of the functions return a
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\fBstruct hostent\fRfor the name that was looked up.
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\fBNULL\fR is returned if the lookups by
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\fBlwres_gethostbyname()\fR or
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\fBlwres_gethostbyname2()\fR fail.
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.PP
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Reverse lookups of addresses are performed by
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\fBlwres_gethostbyaddr()\fR.
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\fIaddr\fR is an address of length
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\fIlen\fR bytes and protocol family
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\fItype\fR \(em \fBPF_INET\fR or
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\fBPF_INET6\fR.
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\fBlwres_gethostbyname_r()\fR is a thread-safe function
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for forward lookups. If an error occurs, an error code is returned in
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\fI*error\fR.
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\fIresbuf\fR is a pointer to a \fBstruct
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hostent\fR which is initialised by a successful call to
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\fBlwres_gethostbyname_r()\fR .
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\fIbuf\fR is a buffer of length
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\fIlen\fR bytes which is used to store the
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h_name, h_aliases, and
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h_addr_list elements of the \fBstruct
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hostent\fR returned in \fIresbuf\fR.
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Successful calls to \fBlwres_gethostbyname_r()\fR
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return \fIresbuf\fR,
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which is a pointer to the \fBstruct hostent\fR it created.
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.PP
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\fBlwres_gethostbyaddr_r()\fR is a thread-safe function
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that performs a reverse lookup of address \fIaddr\fR
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which is \fIlen\fR bytes long and is of protocol
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family \fItype\fR \(em \fBPF_INET\fR or
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\fBPF_INET6\fR. If an error occurs, the error code is returned
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in \fI*error\fR. The other function parameters are
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identical to those in \fBlwres_gethostbyname_r()\fR.
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\fIresbuf\fR is a pointer to a \fBstruct
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hostent\fR which is initialised by a successful call to
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\fBlwres_gethostbyaddr_r()\fR.
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\fIbuf\fR is a buffer of length
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\fIlen\fR bytes which is used to store the
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h_name, h_aliases, and
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h_addr_list elements of the \fBstruct
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hostent\fR returned in \fIresbuf\fR. Successful
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calls to \fBlwres_gethostbyaddr_r()\fR return
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\fIresbuf\fR, which is a pointer to the
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\fBstruct hostent()\fR it created.
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.SH "RETURN VALUES"
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.PP
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The functions
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\fBlwres_gethostbyname()\fR,
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\fBlwres_gethostbyname2()\fR,
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\fBlwres_gethostbyaddr()\fR,
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and
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\fBlwres_gethostent()\fR
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return NULL to indicate an error. In this case the global variable
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\fBlwres_h_errno\fR
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will contain one of the following error codes defined in
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\fI<lwres/netdb.h>\fR:
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.TP
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\fBHOST_NOT_FOUND\fR
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The host or address was not found.
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.TP
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\fBTRY_AGAIN\fR
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A recoverable error occurred, e.g., a timeout.
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Retrying the lookup may succeed.
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.TP
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\fBNO_RECOVERY\fR
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A non-recoverable error occurred.
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.TP
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\fBNO_DATA\fR
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The name exists, but has no address information
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associated with it (or vice versa in the case
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of a reverse lookup). The code NO_ADDRESS
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is accepted as a synonym for NO_DATA for backwards
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compatibility.
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.PP
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\fBlwres_hstrerror\fR(3)
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translates these error codes to suitable error messages.
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.PP
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\fBlwres_gethostent()\fR
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and
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\fBlwres_gethostent_r()\fR
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always return
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\fBNULL\fR.
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.PP
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Successful calls to \fBlwres_gethostbyname_r()\fR and
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\fBlwres_gethostbyaddr_r()\fR return
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\fIresbuf\fR, a pointer to the \fBstruct
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hostent\fR that was initialised by these functions. They return
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\fBNULL\fR if the lookups fail or if \fIbuf\fR
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was too small to hold the list of addresses and names referenced by
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the h_name, h_aliases, and
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h_addr_list elements of the \fBstruct
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hostent\fR. If \fIbuf\fR was too small, both
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\fBlwres_gethostbyname_r()\fR and
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\fBlwres_gethostbyaddr_r()\fR set the global variable
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\fBerrno\fR to ERANGE.
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.SH "SEE ALSO"
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.PP
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\fBgethostent\fR(3),
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\fBlwres_getipnode\fR(3),
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\fBlwres_hstrerror\fR(3)
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.SH "BUGS"
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.PP
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\fBlwres_gethostbyname()\fR,
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\fBlwres_gethostbyname2()\fR,
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\fBlwres_gethostbyaddr()\fR
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and
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\fBlwres_endhostent()\fR
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are not thread safe; they return pointers to static data and
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provide error codes through a global variable.
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Thread-safe versions for name and address lookup are provided by
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\fBlwres_gethostbyname_r()\fR,
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and
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\fBlwres_gethostbyaddr_r()\fR
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respectively.
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.PP
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The resolver daemon does not currently support any non-DNS
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name services such as
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\fI/etc/hosts\fR
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or
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\fBNIS\fR,
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consequently the above functions don't, either.
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