lwres_getipnode.3

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.\" $Id: lwres_getipnode.3,v 1.13.2.2.4.6 2005/10/13 02:33:53 marka Exp $
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.TH "LWRES_GETIPNODE" "3" "Jun 30, 2000" "BIND9" "BIND9"
.\" disable hyphenation
.nh
.\" disable justification (adjust text to left margin only)
.ad l
.SH "NAME"
lwres_getipnodebyname, lwres_getipnodebyaddr, lwres_freehostent \- lightweight resolver nodename / address translation API
.SH "SYNOPSIS"
.nf
#include <lwres/netdb.h>
.fi
.HP 39
\fBstruct\ hostent\ *\ \fBlwres_getipnodebyname\fR\fR\fB(\fR\fBconst\ char\ *name\fR\fB, \fR\fBint\ af\fR\fB, \fR\fBint\ flags\fR\fB, \fR\fBint\ *error_num\fR\fB);\fR
.HP 39
\fBstruct\ hostent\ *\ \fBlwres_getipnodebyaddr\fR\fR\fB(\fR\fBconst\ void\ *src\fR\fB, \fR\fBsize_t\ len\fR\fB, \fR\fBint\ af\fR\fB, \fR\fBint\ *error_num\fR\fB);\fR
.HP 23
\fBvoid\ \fBlwres_freehostent\fR\fR\fB(\fR\fBstruct\ hostent\ *he\fR\fB);\fR
.SH "DESCRIPTION"
.PP
These functions perform thread safe, protocol independent nodename\-to\-address and address\-to\-nodename translation as defined in RFC2553.
.PP
They use a
\fBstruct hostent\fR
which is defined in
\fInamedb.h\fR:
.sp
.nf
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 */
.fi
.sp
.PP
The members of this structure are:
.TP
\fBh_name\fR
The official (canonical) name of the host.
.TP
\fBh_aliases\fR
A NULL\-terminated array of alternate names (nicknames) for the host.
.TP
\fBh_addrtype\fR
The type of address being returned \- usually
\fBPF_INET\fR
or
\fBPF_INET6\fR.
.TP
\fBh_length\fR
The length of the address in bytes.
.TP
\fBh_addr_list\fR
A
\fBNULL\fR
terminated array of network addresses for the host. Host addresses are returned in network byte order.
.PP
\fBlwres_getipnodebyname()\fR
looks up addresses of protocol family
\fIaf\fR
for the hostname
\fIname\fR. The
\fIflags\fR
parameter contains ORed flag bits to specify the types of addresses that are searched for, and the types of addresses that are returned. The flag bits are:
.TP
\fBAI_V4MAPPED\fR
This is used with an
\fIaf\fR
of AF_INET6, and causes IPv4 addresses to be returned as IPv4\-mapped IPv6 addresses.
.TP
\fBAI_ALL\fR
This is used with an
\fIaf\fR
of AF_INET6, and causes all known addresses (IPv6 and IPv4) to be returned. If AI_V4MAPPED is also set, the IPv4 addresses are return as mapped IPv6 addresses.
.TP
\fBAI_ADDRCONFIG\fR
Only return an IPv6 or IPv4 address if here is an active network interface of that type. This is not currently implemented in the BIND 9 lightweight resolver, and the flag is ignored.
.TP
\fBAI_DEFAULT\fR
This default sets the
\fBAI_V4MAPPED\fR
and
\fBAI_ADDRCONFIG\fR
flag bits.
.PP
\fBlwres_getipnodebyaddr()\fR
performs a reverse lookup of address
\fIsrc\fR
which is
\fIlen\fR
bytes long.
\fIaf\fR
denotes the protocol family, typically
\fBPF_INET\fR
or
\fBPF_INET6\fR.
.PP
\fBlwres_freehostent()\fR
releases all the memory associated with the
\fBstruct hostent\fR
pointer
\fIhe\fR. Any memory allocated for the
\fBh_name\fR,
\fBh_addr_list\fR
and
\fBh_aliases\fR
is freed, as is the memory for the
\fBhostent\fR
structure itself.
.SH "RETURN VALUES"
.PP
If an error occurs,
\fBlwres_getipnodebyname()\fR
and
\fBlwres_getipnodebyaddr()\fR
set
\fI*error_num\fR
to an appropriate error code and the function returns a
\fBNULL\fR
pointer. The error codes and their meanings are defined in
\fI<lwres/netdb.h>\fR:
.TP
\fBHOST_NOT_FOUND\fR
No such host is known.
.TP
\fBNO_ADDRESS\fR
The server recognised the request and the name but no address is available. Another type of request to the name server for the domain might return an answer.
.TP
\fBTRY_AGAIN\fR
A temporary and possibly transient error occurred, such as a failure of a server to respond. The request may succeed if retried.
.TP
\fBNO_RECOVERY\fR
An unexpected failure occurred, and retrying the request is pointless.
.PP
\fBlwres_hstrerror\fR(3 )
translates these error codes to suitable error messages.
.SH "SEE ALSO"
.PP
\fBRFC2553\fR(),
\fBlwres\fR(3),
\fBlwres_gethostent\fR(3),
\fBlwres_getaddrinfo\fR(3),
\fBlwres_getnameinfo\fR(3),
\fBlwres_hstrerror\fR(3).