path: root/lib/liblwres/man/lwres_gethostent.3

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.TH "LWRES_GETHOSTENT" "3" "Jun 30, 2000" "BIND9" ""
.SH NAME
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
.SH SYNOPSIS
\fB#include <lwres/netdb.h>
.sp
.na
struct hostent *
lwres_gethostbyname(const char *name);
.ad
.sp
.na
struct hostent *
lwres_gethostbyname2(const char *name, int af);
.ad
.sp
.na
struct hostent *
lwres_gethostbyaddr(const char *addr, int len, int type);
.ad
.sp
.na
struct hostent *
lwres_gethostent(void);
.ad
.sp
.na
void
lwres_sethostent(int stayopen);
.ad
.sp
.na
void
lwres_endhostent(void);
.ad
.sp
.na
struct hostent *
lwres_gethostbyname_r(const char *name, struct hostent *resbuf, char *buf, int buflen, int *error);
.ad
.sp
.na
struct hostent *
lwres_gethostbyaddr_r(const char *addr, int len, int type, struct hostent *resbuf, char *buf, int buflen, int *error);
.ad
.sp
.na
struct hostent *
lwres_gethostent_r(struct hostent *resbuf, char *buf, int buflen, int *error);
.ad
.sp
.na
void
lwres_sethostent_r(int stayopen);
.ad
.sp
.na
void
lwres_endhostent_r(void);
.ad
\fR.SH "DESCRIPTION"
.PP
These functions provide hostname-to-address and
address-to-hostname lookups by means of the lightweight resolver.
They are similar to the standard
\fBgethostent\fR(3)
functions provided by most operating systems.
They use a
\fBstruct hostent\fR
which is usually defined in
\fI<namedb.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 */
.sp
.fi
.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 \(em
\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
For backward compatibility with very old software,
h_addr
is the first address in
h_addr_list.
.PP
\fBlwres_gethostent()\fR,
\fBlwres_sethostent()\fR,
\fBlwres_endhostent()\fR,
\fBlwres_gethostent_r()\fR,
\fBlwres_sethostent_r()\fR
and
\fBlwres_endhostent_r()\fR
provide iteration over the known host entries on systems that
provide such functionality through facilities like
\fI/etc/hosts\fR
or NIS. The lightweight resolver does not currently implement
these functions; it only provides them as stub functions that always
return failure.
.PP
\fBlwres_gethostbyname()\fR and
\fBlwres_gethostbyname2()\fR look up the hostname
\fIname\fR.
\fBlwres_gethostbyname()\fR always looks for an IPv4
address while \fBlwres_gethostbyname2()\fR looks for an
address of protocol family \fIaf\fR: either
\fBPF_INET\fR or \fBPF_INET6\fR \(em IPv4 or IPV6
addresses respectively. Successful calls of the functions return a
\fBstruct hostent\fRfor the name that was looked up.
\fBNULL\fR is returned if the lookups by
\fBlwres_gethostbyname()\fR or
\fBlwres_gethostbyname2()\fR fail.
.PP
Reverse lookups of addresses are performed by
\fBlwres_gethostbyaddr()\fR.
\fIaddr\fR is an address of length
\fIlen\fR bytes and protocol family
\fItype\fR \(em \fBPF_INET\fR or
\fBPF_INET6\fR.
\fBlwres_gethostbyname_r()\fR is a thread-safe function
for forward lookups. If an error occurs, an error code is returned in
\fI*error\fR.
\fIresbuf\fR is a pointer to a \fBstruct
hostent\fR which is initialised by a successful call to
\fBlwres_gethostbyname_r()\fR .
\fIbuf\fR is a buffer of length
\fIlen\fR bytes which is used to store the
h_name, h_aliases, and
h_addr_list elements of the \fBstruct
hostent\fR returned in \fIresbuf\fR.
Successful calls to \fBlwres_gethostbyname_r()\fR
return \fIresbuf\fR,
which is a pointer to the \fBstruct hostent\fR it created.
.PP
\fBlwres_gethostbyaddr_r()\fR is a thread-safe function
that performs a reverse lookup of address \fIaddr\fR
which is \fIlen\fR bytes long and is of protocol
family \fItype\fR \(em \fBPF_INET\fR or
\fBPF_INET6\fR. If an error occurs, the error code is returned
in \fI*error\fR. The other function parameters are
identical to those in \fBlwres_gethostbyname_r()\fR.
\fIresbuf\fR is a pointer to a \fBstruct
hostent\fR which is initialised by a successful call to
\fBlwres_gethostbyaddr_r()\fR.
\fIbuf\fR is a buffer of length
\fIlen\fR bytes which is used to store the
h_name, h_aliases, and
h_addr_list elements of the \fBstruct
hostent\fR returned in \fIresbuf\fR. Successful
calls to \fBlwres_gethostbyaddr_r()\fR return
\fIresbuf\fR, which is a pointer to the
\fBstruct hostent()\fR it created.
.SH "RETURN VALUES"
.PP
The functions
\fBlwres_gethostbyname()\fR,
\fBlwres_gethostbyname2()\fR,
\fBlwres_gethostbyaddr()\fR,
and
\fBlwres_gethostent()\fR
return NULL to indicate an error. In this case the global variable
\fBlwres_h_errno\fR
will contain one of the following error codes defined in
\fI<lwres/netdb.h>\fR:
.TP
\fBHOST_NOT_FOUND\fR
The host or address was not found.
.TP
\fBTRY_AGAIN\fR
A recoverable error occurred, e.g., a timeout.
Retrying the lookup may succeed.
.TP
\fBNO_RECOVERY\fR
A non-recoverable error occurred.
.TP
\fBNO_DATA\fR
The name exists, but has no address information
associated with it (or vice versa in the case
of a reverse lookup). The code NO_ADDRESS
is accepted as a synonym for NO_DATA for backwards
compatibility.
.PP
\fBlwres_hstrerror\fR(3)
translates these error codes to suitable error messages.
.PP
\fBlwres_gethostent()\fR
and
\fBlwres_gethostent_r()\fR
always return
\fBNULL\fR.
.PP
Successful calls to \fBlwres_gethostbyname_r()\fR and
\fBlwres_gethostbyaddr_r()\fR return
\fIresbuf\fR, a pointer to the \fBstruct
hostent\fR that was initialised by these functions. They return
\fBNULL\fR if the lookups fail or if \fIbuf\fR
was too small to hold the list of addresses and names referenced by
the h_name, h_aliases, and
h_addr_list elements of the \fBstruct
hostent\fR. If \fIbuf\fR was too small, both
\fBlwres_gethostbyname_r()\fR and
\fBlwres_gethostbyaddr_r()\fR set the global variable
\fBerrno\fR to ERANGE.
.SH "SEE ALSO"
.PP
\fBgethostent\fR(3),
\fBlwres_getipnode\fR(3),
\fBlwres_hstrerror\fR(3)
.SH "BUGS"
.PP
\fBlwres_gethostbyname()\fR,
\fBlwres_gethostbyname2()\fR,
\fBlwres_gethostbyaddr()\fR
and
\fBlwres_endhostent()\fR
are not thread safe; they return pointers to static data and 
provide error codes through a global variable.
Thread-safe versions for name and address lookup are provided by
\fBlwres_gethostbyname_r()\fR,
and
\fBlwres_gethostbyaddr_r()\fR
respectively.
.PP
The resolver daemon does not currently support any non-DNS
name services such as 
\fI/etc/hosts\fR
or
\fBNIS\fR,
consequently the above functions don't, either.