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

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  21 <!-- $Id: lwres_gethostent.docbook,v 1.11 2007/06/18 23:47:51 tbox Exp $ -->
  22 <refentry>
  23
  24   <refentryinfo>
  25     <date>Jun 30, 2000</date>
  26   </refentryinfo>
  27
  28   <refmeta>
  29     <refentrytitle>lwres_gethostent</refentrytitle>
  30     <manvolnum>3</manvolnum>
  31     <refmiscinfo>BIND9</refmiscinfo>
  32   </refmeta>
  33
  34   <docinfo>
  35     <copyright>
  36       <year>2004</year>
  37       <year>2005</year>
  38       <year>2007</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 *<parameter>name</parameter></paramdef>
  69         </funcprototype>
  70 <funcprototype>
  71         <funcdef>
  72 struct hostent *
  73 <function>lwres_gethostbyname2</function></funcdef>
  74         <paramdef>const char *<parameter>name</parameter></paramdef>
  75         <paramdef>int <parameter>af</parameter></paramdef>
  76         </funcprototype>
  77 <funcprototype>
  78         <funcdef>
  79 struct hostent *
  80 <function>lwres_gethostbyaddr</function></funcdef>
  81         <paramdef>const char *<parameter>addr</parameter></paramdef>
  82         <paramdef>int <parameter>len</parameter></paramdef>
  83         <paramdef>int <parameter>type</parameter></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 <parameter>stayopen</parameter></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 *<parameter>name</parameter></paramdef>
 108         <paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>
 109         <paramdef>char *<parameter>buf</parameter></paramdef>
 110         <paramdef>int <parameter>buflen</parameter></paramdef>
 111         <paramdef>int *<parameter>error</parameter></paramdef>
 112         </funcprototype>
 113 <funcprototype>
 114         <funcdef>
 115 struct hostent  *
 116 <function>lwres_gethostbyaddr_r</function></funcdef>
 117         <paramdef>const char *<parameter>addr</parameter></paramdef>
 118         <paramdef>int <parameter>len</parameter></paramdef>
 119         <paramdef>int <parameter>type</parameter></paramdef>
 120         <paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>
 121         <paramdef>char *<parameter>buf</parameter></paramdef>
 122         <paramdef>int <parameter>buflen</parameter></paramdef>
 123         <paramdef>int *<parameter>error</parameter></paramdef>
 124         </funcprototype>
 125 <funcprototype>
 126         <funcdef>
 127 struct hostent  *
 128 <function>lwres_gethostent_r</function></funcdef>
 129         <paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>
 130         <paramdef>char *<parameter>buf</parameter></paramdef>
 131         <paramdef>int <parameter>buflen</parameter></paramdef>
 132         <paramdef>int *<parameter>error</parameter></paramdef>
 133         </funcprototype>
 134 <funcprototype>
 135         <funcdef>
 136 void
 137 <function>lwres_sethostent_r</function></funcdef>
 138         <paramdef>int <parameter>stayopen</parameter></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</manvolnum>
 157       </citerefentry>
 158       functions provided by most operating systems.
 159       They use a
 160       <type>struct hostent</type>
 161       which is usually defined in
 162       <filename>&lt;namedb.h&gt;</filename>.
 163     </para>
 164     <para><programlisting>
 165 struct  hostent {
 166         char    *h_name;        /* official name of host */
 167         char    **h_aliases;    /* alias list */
 168         int     h_addrtype;     /* host address type */
 169         int     h_length;       /* length of address */
 170         char    **h_addr_list;  /* list of addresses from name server */
 171 };
 172 #define h_addr  h_addr_list[0]  /* address, for backward compatibility */
 173 </programlisting>
 174     </para>
 175     <para>
 176       The members of this structure are:
 177       <variablelist>
 178         <varlistentry>
 179           <term><constant>h_name</constant></term>
 180           <listitem>
 181             <para>
 182               The official (canonical) name of the host.
 183             </para>
 184           </listitem>
 185         </varlistentry>
 186         <varlistentry>
 187           <term><constant>h_aliases</constant></term>
 188           <listitem>
 189             <para>
 190               A NULL-terminated array of alternate names (nicknames) for the
 191               host.
 192             </para>
 193           </listitem>
 194         </varlistentry>
 195         <varlistentry>
 196           <term><constant>h_addrtype</constant></term>
 197           <listitem>
 198             <para>
 199               The type of address being returned &mdash;
 200               <type>PF_INET</type>
 201               or
 202               <type>PF_INET6</type>.
 203             </para>
 204           </listitem>
 205         </varlistentry>
 206         <varlistentry>
 207           <term><constant>h_length</constant></term>
 208           <listitem>
 209             <para>
 210               The length of the address in bytes.
 211             </para>
 212           </listitem>
 213         </varlistentry>
 214         <varlistentry>
 215           <term><constant>h_addr_list</constant></term>
 216           <listitem>
 217             <para>
 218               A <type>NULL</type>
 219               terminated array of network addresses for the host.
 220               Host addresses are returned in network byte order.
 221             </para>
 222           </listitem>
 223         </varlistentry>
 224       </variablelist>
 225     </para>
 226     <para>
 227       For backward compatibility with very old software,
 228       <constant>h_addr</constant>
 229       is the first address in
 230       <constant>h_addr_list.</constant>
 231     </para>
 232     <para><function>lwres_gethostent()</function>,
 233       <function>lwres_sethostent()</function>,
 234       <function>lwres_endhostent()</function>,
 235       <function>lwres_gethostent_r()</function>,
 236       <function>lwres_sethostent_r()</function>
 237       and
 238       <function>lwres_endhostent_r()</function>
 239       provide iteration over the known host entries on systems that
 240       provide such functionality through facilities like
 241       <filename>/etc/hosts</filename>
 242       or NIS.  The lightweight resolver does not currently implement
 243       these functions; it only provides them as stub functions that always
 244       return failure.
 245     </para>
 246
 247     <para><function>lwres_gethostbyname()</function>
 248       and <function>lwres_gethostbyname2()</function> look up the
 249       hostname <parameter>name</parameter>.
 250       <function>lwres_gethostbyname()</function> always looks for an
 251       IPv4 address while <function>lwres_gethostbyname2()</function>
 252       looks for an address of protocol family
 253       <parameter>af</parameter>: either <type>PF_INET</type> or
 254       <type>PF_INET6</type> &mdash; IPv4 or IPV6 addresses
 255       respectively.  Successful calls of the functions return a
 256       <type>struct hostent</type>for the name that was looked up.
 257       <type>NULL</type> is returned if the lookups by
 258       <function>lwres_gethostbyname()</function> or
 259       <function>lwres_gethostbyname2()</function> fail.
 260     </para>
 261
 262     <para>
 263       Reverse lookups of addresses are performed by
 264       <function>lwres_gethostbyaddr()</function>.
 265       <parameter>addr</parameter> is an address of length
 266       <parameter>len</parameter> bytes and protocol family
 267       <parameter>type</parameter> &mdash; <type>PF_INET</type> or
 268       <type>PF_INET6</type>.
 269       <function>lwres_gethostbyname_r()</function> is a
 270       thread-safe function
 271       for forward lookups.  If an error occurs, an error code is returned in
 272       <parameter>*error</parameter>.
 273       <parameter>resbuf</parameter> is a pointer to a
 274       <type>struct hostent</type> which is initialised by a successful call to
 275       <function>lwres_gethostbyname_r()</function>.
 276       <parameter>buf</parameter> is a buffer of length
 277       <parameter>len</parameter> bytes which is used to store the
 278       <constant>h_name</constant>, <constant>h_aliases</constant>, and
 279       <constant>h_addr_list</constant> elements of the
 280       <type>struct hostent</type> returned in <parameter>resbuf</parameter>.
 281       Successful calls to <function>lwres_gethostbyname_r()</function>
 282       return <parameter>resbuf</parameter>,
 283       which is a pointer to the <type>struct hostent</type> it created.
 284     </para>
 285
 286     <para><function>lwres_gethostbyaddr_r()</function>
 287       is a thread-safe function
 288       that performs a reverse lookup of address <parameter>addr</parameter>
 289       which is <parameter>len</parameter> bytes long and is of
 290       protocol
 291       family <parameter>type</parameter> &mdash; <type>PF_INET</type> or
 292       <type>PF_INET6</type>.  If an error occurs, the error code is returned
 293       in <parameter>*error</parameter>.  The other function
 294       parameters are
 295       identical to those in <function>lwres_gethostbyname_r()</function>.
 296       <parameter>resbuf</parameter> is a pointer to a
 297       <type>struct hostent</type> which is initialised by a successful call to
 298       <function>lwres_gethostbyaddr_r()</function>.
 299       <parameter>buf</parameter> is a buffer of length
 300       <parameter>len</parameter> bytes which is used to store the
 301       <constant>h_name</constant>, <constant>h_aliases</constant>, and
 302       <constant>h_addr_list</constant> elements of the
 303       <type>struct hostent</type> returned in <parameter>resbuf</parameter>.
 304       Successful calls to <function>lwres_gethostbyaddr_r()</function> return
 305       <parameter>resbuf</parameter>, which is a pointer to the
 306       <function>struct hostent()</function> it created.
 307     </para>
 308
 309   </refsect1>
 310
 311   <refsect1>
 312     <title>RETURN VALUES</title>
 313     <para>
 314       The functions
 315       <function>lwres_gethostbyname()</function>,
 316       <function>lwres_gethostbyname2()</function>,
 317       <function>lwres_gethostbyaddr()</function>,
 318       and
 319       <function>lwres_gethostent()</function>
 320       return NULL to indicate an error.  In this case the global variable
 321       <type>lwres_h_errno</type>
 322       will contain one of the following error codes defined in
 323       <filename>&lt;lwres/netdb.h&gt;</filename>:
 324
 325       <variablelist>
 326         <varlistentry>
 327           <term><constant>HOST_NOT_FOUND</constant></term>
 328           <listitem>
 329             <para>
 330               The host or address was not found.
 331             </para>
 332           </listitem>
 333         </varlistentry>
 334         <varlistentry>
 335           <term><constant>TRY_AGAIN</constant></term>
 336           <listitem>
 337             <para>
 338               A recoverable error occurred, e.g., a timeout.
 339               Retrying the lookup may succeed.
 340             </para>
 341           </listitem>
 342         </varlistentry>
 343         <varlistentry>
 344           <term><constant>NO_RECOVERY</constant></term>
 345           <listitem>
 346             <para>
 347               A non-recoverable error occurred.
 348             </para>
 349           </listitem>
 350         </varlistentry>
 351         <varlistentry>
 352           <term><constant>NO_DATA</constant></term>
 353           <listitem>
 354             <para>
 355               The name exists, but has no address information
 356               associated with it (or vice versa in the case
 357               of a reverse lookup).  The code NO_ADDRESS
 358               is accepted as a synonym for NO_DATA for backwards
 359               compatibility.
 360             </para>
 361           </listitem>
 362         </varlistentry>
 363       </variablelist>
 364     </para>
 365
 366     <para><citerefentry>
 367         <refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3</manvolnum>
 368       </citerefentry>
 369       translates these error codes to suitable error messages.
 370     </para>
 371
 372     <para><function>lwres_gethostent()</function>
 373       and <function>lwres_gethostent_r()</function>
 374       always return <type>NULL</type>.
 375     </para>
 376
 377     <para>
 378       Successful calls to <function>lwres_gethostbyname_r()</function> and
 379       <function>lwres_gethostbyaddr_r()</function> return
 380       <parameter>resbuf</parameter>, a pointer to the
 381       <type>struct hostent</type> that was initialised by these functions.  They return
 382       <type>NULL</type> if the lookups fail or if <parameter>buf</parameter>
 383       was too small to hold the list of addresses and names referenced by
 384       the <constant>h_name</constant>, <constant>h_aliases</constant>, and
 385       <constant>h_addr_list</constant> elements of the
 386       <type>struct hostent</type>.
 387       If <parameter>buf</parameter> was too small, both
 388       <function>lwres_gethostbyname_r()</function> and
 389       <function>lwres_gethostbyaddr_r()</function> set the global
 390       variable
 391       <type>errno</type> to <errorcode>ERANGE</errorcode>.
 392     </para>
 393
 394   </refsect1>
 395   <refsect1>
 396     <title>SEE ALSO</title>
 397     <para><citerefentry>
 398         <refentrytitle>gethostent</refentrytitle><manvolnum>3</manvolnum>
 399       </citerefentry>,
 400
 401       <citerefentry>
 402         <refentrytitle>lwres_getipnode</refentrytitle><manvolnum>3</manvolnum>
 403       </citerefentry>,
 404
 405       <citerefentry>
 406         <refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3</manvolnum>
 407       </citerefentry>
 408     </para>
 409   </refsect1>
 410
 411   <refsect1>
 412     <title>BUGS</title>
 413     <para><function>lwres_gethostbyname()</function>,
 414       <function>lwres_gethostbyname2()</function>,
 415       <function>lwres_gethostbyaddr()</function>
 416       and
 417       <function>lwres_endhostent()</function>
 418       are not thread safe; they return pointers to static data and
 419       provide error codes through a global variable.
 420       Thread-safe versions for name and address lookup are provided by
 421       <function>lwres_gethostbyname_r()</function>,
 422       and
 423       <function>lwres_gethostbyaddr_r()</function>
 424       respectively.
 425     </para>
 426     <para>
 427       The resolver daemon does not currently support any non-DNS
 428       name services such as
 429       <filename>/etc/hosts</filename>
 430       or
 431       <type>NIS</type>,
 432       consequently the above functions don't, either.
 433     </para>
 434   </refsect1>
 435 </refentry><!--
 436  - Local variables:
 437  - mode: sgml
 438  - End:
 439 -->