contrib/bind9/lib/lwres/man/lwres_gethostent.docbook

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  22
  23 <refentry>
  24
  25 <refentryinfo>
  26 <date>Jun 30, 2000</date>
  27 </refentryinfo>
  28
  29 <refmeta>
  30 <refentrytitle>lwres_gethostent</refentrytitle>
  31 <manvolnum>3</manvolnum>
  32 <refmiscinfo>BIND9</refmiscinfo>
  33 </refmeta>
  34
  35   <docinfo>
  36     <copyright>
  37       <year>2004</year>
  38       <year>2005</year>
  39       <holder>Internet Systems Consortium, Inc. ("ISC")</holder>
  40     </copyright>
  41     <copyright>
  42       <year>2001</year>
  43       <holder>Internet Software Consortium.</holder>
  44     </copyright>
  45   </docinfo>
  46
  47 <refnamediv>
  48 <refname>lwres_gethostbyname</refname>
  49 <refname>lwres_gethostbyname2</refname>
  50 <refname>lwres_gethostbyaddr</refname>
  51 <refname>lwres_gethostent</refname>
  52 <refname>lwres_sethostent</refname>
  53 <refname>lwres_endhostent</refname>
  54 <refname>lwres_gethostbyname_r</refname>
  55 <refname>lwres_gethostbyaddr_r</refname>
  56 <refname>lwres_gethostent_r</refname>
  57 <refname>lwres_sethostent_r</refname>
  58 <refname>lwres_endhostent_r</refname>
  59 <refpurpose>lightweight resolver get network host entry</refpurpose>
  60 </refnamediv>
  61 <refsynopsisdiv>
  62 <funcsynopsis>
  63 <funcsynopsisinfo>#include &lt;lwres/netdb.h&gt;</funcsynopsisinfo>
  64 <funcprototype>
  65 <funcdef>
  66 struct hostent *
  67 <function>lwres_gethostbyname</function></funcdef>
  68 <paramdef>const char *name</paramdef>
  69 </funcprototype>
  70 <funcprototype>
  71 <funcdef>
  72 struct hostent *
  73 <function>lwres_gethostbyname2</function></funcdef>
  74 <paramdef>const char *name</paramdef>
  75 <paramdef>int af</paramdef>
  76 </funcprototype>
  77 <funcprototype>
  78 <funcdef>
  79 struct hostent *
  80 <function>lwres_gethostbyaddr</function></funcdef>
  81 <paramdef>const char *addr</paramdef>
  82 <paramdef>int len</paramdef>
  83 <paramdef>int type</paramdef>
  84 </funcprototype>
  85 <funcprototype>
  86 <funcdef>
  87 struct hostent *
  88 <function>lwres_gethostent</function></funcdef>
  89 <paramdef>void</paramdef>
  90 </funcprototype>
  91 <funcprototype>
  92 <funcdef>
  93 void
  94 <function>lwres_sethostent</function></funcdef>
  95 <paramdef>int stayopen</paramdef>
  96 </funcprototype>
  97 <funcprototype>
  98 <funcdef>
  99 void
 100 <function>lwres_endhostent</function></funcdef>
 101 <paramdef>void</paramdef>
 102 </funcprototype>
 103 <funcprototype>
 104 <funcdef>
 105 struct hostent *
 106 <function>lwres_gethostbyname_r</function></funcdef>
 107 <paramdef>const char *name</paramdef>
 108 <paramdef>struct hostent *resbuf</paramdef>
 109 <paramdef>char *buf</paramdef>
 110 <paramdef>int buflen</paramdef>
 111 <paramdef>int *error</paramdef>
 112 </funcprototype>
 113 <funcprototype>
 114 <funcdef>
 115 struct hostent  *
 116 <function>lwres_gethostbyaddr_r</function></funcdef>
 117 <paramdef>const char *addr</paramdef>
 118 <paramdef>int len</paramdef>
 119 <paramdef>int type</paramdef>
 120 <paramdef>struct hostent *resbuf</paramdef>
 121 <paramdef>char *buf</paramdef>
 122 <paramdef>int buflen</paramdef>
 123 <paramdef>int *error</paramdef>
 124 </funcprototype>
 125 <funcprototype>
 126 <funcdef>
 127 struct hostent  *
 128 <function>lwres_gethostent_r</function></funcdef>
 129 <paramdef>struct hostent *resbuf</paramdef>
 130 <paramdef>char *buf</paramdef>
 131 <paramdef>int buflen</paramdef>
 132 <paramdef>int *error</paramdef>
 133 </funcprototype>
 134 <funcprototype>
 135 <funcdef>
 136 void
 137 <function>lwres_sethostent_r</function></funcdef>
 138 <paramdef>int stayopen</paramdef>
 139 </funcprototype>
 140 <funcprototype>
 141 <funcdef>
 142 void
 143 <function>lwres_endhostent_r</function></funcdef>
 144 <paramdef>void</paramdef>
 145 </funcprototype>
 146 </funcsynopsis>
 147 </refsynopsisdiv>
 148
 149 <refsect1>
 150 <title>DESCRIPTION</title>
 151 <para>
 152 These functions provide hostname-to-address and
 153 address-to-hostname lookups by means of the lightweight resolver.
 154 They are similar to the standard
 155 <citerefentry>
 156 <refentrytitle>gethostent</refentrytitle><manvolnum>3
 157 </manvolnum>
 158 </citerefentry>
 159 functions provided by most operating systems.
 160 They use a
 161 <type>struct hostent</type>
 162 which is usually defined in
 163 <filename>&lt;namedb.h&gt;</filename>.
 164
 165 <programlisting>
 166 struct  hostent {
 167         char    *h_name;        /* official name of host */
 168         char    **h_aliases;    /* alias list */
 169         int     h_addrtype;     /* host address type */
 170         int     h_length;       /* length of address */
 171         char    **h_addr_list;  /* list of addresses from name server */
 172 };
 173 #define h_addr  h_addr_list[0]  /* address, for backward compatibility */
 174 </programlisting>
 175 </para>
 176 <para>
 177 The members of this structure are:
 178 <variablelist>
 179 <varlistentry><term><constant>h_name</constant></term>
 180 <listitem>
 181 <para>
 182 The official (canonical) name of the host.
 183 </para>
 184 </listitem></varlistentry>
 185 <varlistentry><term><constant>h_aliases</constant></term>
 186 <listitem>
 187 <para>
 188 A NULL-terminated array of alternate names (nicknames) for the host.
 189 </para>
 190 </listitem></varlistentry>
 191 <varlistentry><term><constant>h_addrtype</constant></term>
 192 <listitem>
 193 <para>
 194 The type of address being returned &mdash;
 195 <type>PF_INET</type>
 196 or
 197 <type>PF_INET6</type>.
 198 </para>
 199 </listitem></varlistentry>
 200 <varlistentry><term><constant>h_length</constant></term>
 201 <listitem>
 202 <para>
 203 The length of the address in bytes.
 204 </para>
 205 </listitem></varlistentry>
 206 <varlistentry><term><constant>h_addr_list</constant></term>
 207 <listitem>
 208 <para>
 209 A <type>NULL</type>
 210 terminated array of network addresses for the host.
 211 Host addresses are returned in network byte order.
 212 </para>
 213 </listitem></varlistentry>
 214 </variablelist>
 215 </para>
 216 <para>
 217 For backward compatibility with very old software,
 218 <constant>h_addr</constant>
 219 is the first address in
 220 <constant>h_addr_list.</constant>
 221 </para>
 222 <para>
 223 <function>lwres_gethostent()</function>,
 224 <function>lwres_sethostent()</function>,
 225 <function>lwres_endhostent()</function>,
 226 <function>lwres_gethostent_r()</function>,
 227 <function>lwres_sethostent_r()</function>
 228 and
 229 <function>lwres_endhostent_r()</function>
 230 provide iteration over the known host entries on systems that
 231 provide such functionality through facilities like
 232 <filename>/etc/hosts</filename>
 233 or NIS.  The lightweight resolver does not currently implement
 234 these functions; it only provides them as stub functions that always
 235 return failure.
 236 </para>
 237
 238 <para>
 239 <function>lwres_gethostbyname()</function> and
 240 <function>lwres_gethostbyname2()</function> look up the hostname
 241 <parameter>name</parameter>.
 242 <function>lwres_gethostbyname()</function> always looks for an IPv4
 243 address while <function>lwres_gethostbyname2()</function> looks for an
 244 address of protocol family <parameter>af</parameter>: either
 245 <type>PF_INET</type> or <type>PF_INET6</type> &mdash; IPv4 or IPV6
 246 addresses respectively.  Successful calls of the functions return a
 247 <type>struct hostent</type>for the name that was looked up.
 248 <type>NULL</type> is returned if the lookups by
 249 <function>lwres_gethostbyname()</function> or
 250 <function>lwres_gethostbyname2()</function> fail.
 251 </para>
 252
 253 <para>
 254 Reverse lookups of addresses are performed by
 255 <function>lwres_gethostbyaddr()</function>.
 256 <parameter>addr</parameter> is an address of length
 257 <parameter>len</parameter> bytes and protocol family
 258 <parameter>type</parameter> &mdash; <type>PF_INET</type> or
 259 <type>PF_INET6</type>.
 260 <function>lwres_gethostbyname_r()</function> is a thread-safe function
 261 for forward lookups.  If an error occurs, an error code is returned in
 262 <parameter>*error</parameter>.
 263 <parameter>resbuf</parameter> is a pointer to a <type>struct
 264 hostent</type> which is initialised by a successful call to
 265 <function>lwres_gethostbyname_r()</function> .
 266 <parameter>buf</parameter> is a buffer of length
 267 <parameter>len</parameter> bytes which is used to store the
 268 <constant>h_name</constant>, <constant>h_aliases</constant>, and
 269 <constant>h_addr_list</constant> elements of the <type>struct
 270 hostent</type> returned in <parameter>resbuf</parameter>.
 271 Successful calls to <function>lwres_gethostbyname_r()</function>
 272 return <parameter>resbuf</parameter>,
 273 which is a pointer to the <type>struct hostent</type> it created.
 274 </para>
 275
 276 <para>
 277 <function>lwres_gethostbyaddr_r()</function> is a thread-safe function
 278 that performs a reverse lookup of address <parameter>addr</parameter>
 279 which is <parameter>len</parameter> bytes long and is of protocol
 280 family <parameter>type</parameter> &mdash; <type>PF_INET</type> or
 281 <type>PF_INET6</type>.  If an error occurs, the error code is returned
 282 in <parameter>*error</parameter>.  The other function parameters are
 283 identical to those in <function>lwres_gethostbyname_r()</function>.
 284 <parameter>resbuf</parameter> is a pointer to a <type>struct
 285 hostent</type> which is initialised by a successful call to
 286 <function>lwres_gethostbyaddr_r()</function>.
 287 <parameter>buf</parameter> is a buffer of length
 288 <parameter>len</parameter> bytes which is used to store the
 289 <constant>h_name</constant>, <constant>h_aliases</constant>, and
 290 <constant>h_addr_list</constant> elements of the <type>struct
 291 hostent</type> returned in <parameter>resbuf</parameter>.  Successful
 292 calls to <function>lwres_gethostbyaddr_r()</function> return
 293 <parameter>resbuf</parameter>, which is a pointer to the
 294 <function>struct hostent()</function> it created.
 295 </para>
 296
 297 </refsect1>
 298
 299 <refsect1>
 300 <title>RETURN VALUES</title>
 301 <para>
 302 The functions
 303 <function>lwres_gethostbyname()</function>,
 304 <function>lwres_gethostbyname2()</function>,
 305 <function>lwres_gethostbyaddr()</function>,
 306 and
 307 <function>lwres_gethostent()</function>
 308 return NULL to indicate an error.  In this case the global variable
 309 <type>lwres_h_errno</type>
 310 will contain one of the following error codes defined in
 311 <filename>&lt;lwres/netdb.h&gt;</filename>:
 312
 313 <variablelist>
 314 <varlistentry><term><constant>HOST_NOT_FOUND</constant></term>
 315 <listitem>
 316 <para>
 317 The host or address was not found.
 318 </para>
 319 </listitem></varlistentry>
 320 <varlistentry><term><constant>TRY_AGAIN</constant></term>
 321 <listitem>
 322 <para>
 323 A recoverable error occurred, e.g., a timeout.
 324 Retrying the lookup may succeed.
 325 </para>
 326 </listitem></varlistentry>
 327 <varlistentry><term><constant>NO_RECOVERY</constant></term>
 328 <listitem>
 329 <para>
 330 A non-recoverable error occurred.
 331 </para>
 332 </listitem></varlistentry>
 333 <varlistentry><term><constant>NO_DATA</constant></term>
 334 <listitem>
 335 <para>
 336 The name exists, but has no address information
 337 associated with it (or vice versa in the case
 338 of a reverse lookup).  The code NO_ADDRESS
 339 is accepted as a synonym for NO_DATA for backwards
 340 compatibility.
 341 </para>
 342 </listitem></varlistentry>
 343 </variablelist>
 344 </para>
 345
 346 <para>
 347 <citerefentry>
 348 <refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3
 349 </manvolnum>
 350 </citerefentry>
 351 translates these error codes to suitable error messages.
 352 </para>
 353
 354 <para>
 355 <function>lwres_gethostent()</function>
 356 and
 357 <function>lwres_gethostent_r()</function>
 358 always return
 359 <type>NULL</type>.
 360 </para>
 361
 362 <para>
 363 Successful calls to <function>lwres_gethostbyname_r()</function> and
 364 <function>lwres_gethostbyaddr_r()</function> return
 365 <parameter>resbuf</parameter>, a pointer to the <type>struct
 366 hostent</type> that was initialised by these functions.  They return
 367 <type>NULL</type> if the lookups fail or if <parameter>buf</parameter>
 368 was too small to hold the list of addresses and names referenced by
 369 the <constant>h_name</constant>, <constant>h_aliases</constant>, and
 370 <constant>h_addr_list</constant> elements of the <type>struct
 371 hostent</type>.  If <parameter>buf</parameter> was too small, both
 372 <function>lwres_gethostbyname_r()</function> and
 373 <function>lwres_gethostbyaddr_r()</function> set the global variable
 374 <type>errno</type> to <errorcode>ERANGE</errorcode>.
 375 </para>
 376
 377 </refsect1>
 378 <refsect1>
 379 <title>SEE ALSO</title>
 380 <para>
 381 <citerefentry>
 382 <refentrytitle>gethostent</refentrytitle><manvolnum>3</manvolnum>
 383 </citerefentry>,
 384
 385 <citerefentry>
 386 <refentrytitle>lwres_getipnode</refentrytitle><manvolnum>3</manvolnum>
 387 </citerefentry>,
 388
 389 <citerefentry>
 390 <refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3
 391 </manvolnum>
 392 </citerefentry>
 393 </para>
 394 </refsect1>
 395
 396 <refsect1>
 397 <title>BUGS</title>
 398 <para>
 399 <function>lwres_gethostbyname()</function>,
 400 <function>lwres_gethostbyname2()</function>,
 401 <function>lwres_gethostbyaddr()</function>
 402 and
 403 <function>lwres_endhostent()</function>
 404 are not thread safe; they return pointers to static data and
 405 provide error codes through a global variable.
 406 Thread-safe versions for name and address lookup are provided by
 407 <function>lwres_gethostbyname_r()</function>,
 408 and
 409 <function>lwres_gethostbyaddr_r()</function>
 410 respectively.
 411 </para>
 412 <para>
 413 The resolver daemon does not currently support any non-DNS
 414 name services such as
 415 <filename>/etc/hosts</filename>
 416 or
 417 <type>NIS</type>,
 418 consequently the above functions don't, either.
 419 </para>
 420 </refsect1>
 421 </refentry>