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1 .\" $NetBSD: lwres_gethostent.3,v 1.5 2014/12/10 04:38:02 christos Exp $
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3 .\" Copyright (C) 2004, 2005, 2007, 2014 Internet Systems Consortium, Inc. ("ISC")
4 .\" Copyright (C) 2001 Internet Software Consortium.
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18 .\" Id
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20 .hy 0
21 .ad l
22 .\" Title: lwres_gethostent
23 .\" Author:
24 .\" Generator: DocBook XSL Stylesheets v1.71.1 <http://docbook.sf.net/>
25 .\" Date: June 18, 2007
26 .\" Manual: BIND9
27 .\" Source: BIND9
28 .\"
29 .TH "LWRES_GETHOSTENT" "3" "June 18, 2007" "BIND9" "BIND9"
30 .\" disable hyphenation
31 .nh
32 .\" disable justification (adjust text to left margin only)
33 .ad l
34 .SH "NAME"
35 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
36 .SH "SYNOPSIS"
37 .nf
38 #include <lwres/netdb.h>
39 .fi
40 .HP 37
41 .BI "struct hostent * lwres_gethostbyname(const\ char\ *" "name" ");"
42 .HP 38
43 .BI "struct hostent * lwres_gethostbyname2(const\ char\ *" "name" ", int\ " "af" ");"
44 .HP 37
45 .BI "struct hostent * lwres_gethostbyaddr(const\ char\ *" "addr" ", int\ " "len" ", int\ " "type" ");"
46 .HP 34
47 .BI "struct hostent * lwres_gethostent(void);"
48 .HP 22
49 .BI "void lwres_sethostent(int\ " "stayopen" ");"
50 .HP 22
51 .BI "void lwres_endhostent(void);"
52 .HP 39
53 .BI "struct hostent * lwres_gethostbyname_r(const\ char\ *" "name" ", struct\ hostent\ *" "resbuf" ", char\ *" "buf" ", int\ " "buflen" ", int\ *" "error" ");"
54 .HP 39
55 .BI "struct hostent * lwres_gethostbyaddr_r(const\ char\ *" "addr" ", int\ " "len" ", int\ " "type" ", struct\ hostent\ *" "resbuf" ", char\ *" "buf" ", int\ " "buflen" ", int\ *" "error" ");"
56 .HP 36
57 .BI "struct hostent * lwres_gethostent_r(struct\ hostent\ *" "resbuf" ", char\ *" "buf" ", int\ " "buflen" ", int\ *" "error" ");"
58 .HP 24
59 .BI "void lwres_sethostent_r(int\ " "stayopen" ");"
60 .HP 24
61 .BI "void lwres_endhostent_r(void);"
62 .SH "DESCRIPTION"
63 .PP
64 These functions provide hostname\-to\-address and address\-to\-hostname lookups by means of the lightweight resolver. They are similar to the standard
65 \fBgethostent\fR(3)
66 functions provided by most operating systems. They use a
67 \fBstruct hostent\fR
68 which is usually defined in
69 \fI<namedb.h>\fR.
70 .PP
71 .RS 4
72 .nf
73 struct hostent {
74 char *h_name; /* official name of host */
75 char **h_aliases; /* alias list */
76 int h_addrtype; /* host address type */
77 int h_length; /* length of address */
78 char **h_addr_list; /* list of addresses from name server */
79 };
80 #define h_addr h_addr_list[0] /* address, for backward compatibility */
81 .fi
82 .RE
83 .sp
84 .PP
85 The members of this structure are:
86 .PP
87 \fBh_name\fR
88 .RS 4
89 The official (canonical) name of the host.
90 .RE
91 .PP
92 \fBh_aliases\fR
93 .RS 4
94 A NULL\-terminated array of alternate names (nicknames) for the host.
95 .RE
96 .PP
97 \fBh_addrtype\fR
98 .RS 4
99 The type of address being returned \(em
100 \fBPF_INET\fR
101 or
102 \fBPF_INET6\fR.
103 .RE
104 .PP
105 \fBh_length\fR
106 .RS 4
107 The length of the address in bytes.
108 .RE
109 .PP
110 \fBh_addr_list\fR
111 .RS 4
112 A
113 \fBNULL\fR
114 terminated array of network addresses for the host. Host addresses are returned in network byte order.
115 .RE
116 .PP
117 For backward compatibility with very old software,
118 \fBh_addr\fR
119 is the first address in
120 \fBh_addr_list.\fR
121 .PP
122 \fBlwres_gethostent()\fR,
123 \fBlwres_sethostent()\fR,
124 \fBlwres_endhostent()\fR,
125 \fBlwres_gethostent_r()\fR,
126 \fBlwres_sethostent_r()\fR
127 and
128 \fBlwres_endhostent_r()\fR
129 provide iteration over the known host entries on systems that provide such functionality through facilities like
130 \fI/etc/hosts\fR
131 or NIS. The lightweight resolver does not currently implement these functions; it only provides them as stub functions that always return failure.
132 .PP
133 \fBlwres_gethostbyname()\fR
134 and
135 \fBlwres_gethostbyname2()\fR
136 look up the hostname
137 \fIname\fR.
138 \fBlwres_gethostbyname()\fR
139 always looks for an IPv4 address while
140 \fBlwres_gethostbyname2()\fR
141 looks for an address of protocol family
142 \fIaf\fR: either
143 \fBPF_INET\fR
144 or
145 \fBPF_INET6\fR
146 \(em IPv4 or IPV6 addresses respectively. Successful calls of the functions return a
147 \fBstruct hostent\fRfor the name that was looked up.
148 \fBNULL\fR
149 is returned if the lookups by
150 \fBlwres_gethostbyname()\fR
151 or
152 \fBlwres_gethostbyname2()\fR
153 fail.
154 .PP
155 Reverse lookups of addresses are performed by
156 \fBlwres_gethostbyaddr()\fR.
157 \fIaddr\fR
158 is an address of length
159 \fIlen\fR
160 bytes and protocol family
161 \fItype\fR
162 \(em
163 \fBPF_INET\fR
164 or
165 \fBPF_INET6\fR.
166 \fBlwres_gethostbyname_r()\fR
167 is a thread\-safe function for forward lookups. If an error occurs, an error code is returned in
168 \fI*error\fR.
169 \fIresbuf\fR
170 is a pointer to a
171 \fBstruct hostent\fR
172 which is initialised by a successful call to
173 \fBlwres_gethostbyname_r()\fR.
174 \fIbuf\fR
175 is a buffer of length
176 \fIlen\fR
177 bytes which is used to store the
178 \fBh_name\fR,
179 \fBh_aliases\fR, and
180 \fBh_addr_list\fR
181 elements of the
182 \fBstruct hostent\fR
183 returned in
184 \fIresbuf\fR. Successful calls to
185 \fBlwres_gethostbyname_r()\fR
186 return
187 \fIresbuf\fR, which is a pointer to the
188 \fBstruct hostent\fR
189 it created.
190 .PP
191 \fBlwres_gethostbyaddr_r()\fR
192 is a thread\-safe function that performs a reverse lookup of address
193 \fIaddr\fR
194 which is
195 \fIlen\fR
196 bytes long and is of protocol family
197 \fItype\fR
198 \(em
199 \fBPF_INET\fR
200 or
201 \fBPF_INET6\fR. If an error occurs, the error code is returned in
202 \fI*error\fR. The other function parameters are identical to those in
203 \fBlwres_gethostbyname_r()\fR.
204 \fIresbuf\fR
205 is a pointer to a
206 \fBstruct hostent\fR
207 which is initialised by a successful call to
208 \fBlwres_gethostbyaddr_r()\fR.
209 \fIbuf\fR
210 is a buffer of length
211 \fIlen\fR
212 bytes which is used to store the
213 \fBh_name\fR,
214 \fBh_aliases\fR, and
215 \fBh_addr_list\fR
216 elements of the
217 \fBstruct hostent\fR
218 returned in
219 \fIresbuf\fR. Successful calls to
220 \fBlwres_gethostbyaddr_r()\fR
221 return
222 \fIresbuf\fR, which is a pointer to the
223 \fBstruct hostent()\fR
224 it created.
225 .SH "RETURN VALUES"
226 .PP
227 The functions
228 \fBlwres_gethostbyname()\fR,
229 \fBlwres_gethostbyname2()\fR,
230 \fBlwres_gethostbyaddr()\fR, and
231 \fBlwres_gethostent()\fR
232 return NULL to indicate an error. In this case the global variable
233 \fBlwres_h_errno\fR
234 will contain one of the following error codes defined in
235 \fI<lwres/netdb.h>\fR:
236 .PP
237 \fBHOST_NOT_FOUND\fR
238 .RS 4
239 The host or address was not found.
240 .RE
241 .PP
242 \fBTRY_AGAIN\fR
243 .RS 4
244 A recoverable error occurred, e.g., a timeout. Retrying the lookup may succeed.
245 .RE
246 .PP
247 \fBNO_RECOVERY\fR
248 .RS 4
249 A non\-recoverable error occurred.
250 .RE
251 .PP
252 \fBNO_DATA\fR
253 .RS 4
254 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.
255 .RE
256 .PP
257 \fBlwres_hstrerror\fR(3)
258 translates these error codes to suitable error messages.
259 .PP
260 \fBlwres_gethostent()\fR
261 and
262 \fBlwres_gethostent_r()\fR
263 always return
264 \fBNULL\fR.
265 .PP
266 Successful calls to
267 \fBlwres_gethostbyname_r()\fR
268 and
269 \fBlwres_gethostbyaddr_r()\fR
270 return
271 \fIresbuf\fR, a pointer to the
272 \fBstruct hostent\fR
273 that was initialised by these functions. They return
274 \fBNULL\fR
275 if the lookups fail or if
276 \fIbuf\fR
277 was too small to hold the list of addresses and names referenced by the
278 \fBh_name\fR,
279 \fBh_aliases\fR, and
280 \fBh_addr_list\fR
281 elements of the
282 \fBstruct hostent\fR. If
283 \fIbuf\fR
284 was too small, both
285 \fBlwres_gethostbyname_r()\fR
286 and
287 \fBlwres_gethostbyaddr_r()\fR
288 set the global variable
289 \fBerrno\fR
290 to
291 \fBERANGE\fR.
292 .SH "SEE ALSO"
293 .PP
294 \fBgethostent\fR(3),
295 \fBlwres_getipnode\fR(3),
296 \fBlwres_hstrerror\fR(3)
297 .SH "BUGS"
298 .PP
299 \fBlwres_gethostbyname()\fR,
300 \fBlwres_gethostbyname2()\fR,
301 \fBlwres_gethostbyaddr()\fR
302 and
303 \fBlwres_endhostent()\fR
304 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
305 \fBlwres_gethostbyname_r()\fR, and
306 \fBlwres_gethostbyaddr_r()\fR
307 respectively.
308 .PP
309 The resolver daemon does not currently support any non\-DNS name services such as
310 \fI/etc/hosts\fR
311 or
312 \fBNIS\fR, consequently the above functions don't, either.
313 .SH "COPYRIGHT"
314 Copyright \(co 2004, 2005, 2007, 2014 Internet Systems Consortium, Inc. ("ISC")
315 .br
316 Copyright \(co 2001 Internet Software Consortium.
317 .br