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

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  21 <!-- $Id$ -->
  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       <year>2012</year>
  40       <holder>Internet Systems Consortium, Inc. ("ISC")</holder>
  41     </copyright>
  42     <copyright>
  43       <year>2001</year>
  44       <holder>Internet Software Consortium.</holder>
  45     </copyright>
  46   </docinfo>
  47
  48   <refnamediv>
  49     <refname>lwres_gethostbyname</refname>
  50     <refname>lwres_gethostbyname2</refname>
  51     <refname>lwres_gethostbyaddr</refname>
  52     <refname>lwres_gethostent</refname>
  53     <refname>lwres_sethostent</refname>
  54     <refname>lwres_endhostent</refname>
  55     <refname>lwres_gethostbyname_r</refname>
  56     <refname>lwres_gethostbyaddr_r</refname>
  57     <refname>lwres_gethostent_r</refname>
  58     <refname>lwres_sethostent_r</refname>
  59     <refname>lwres_endhostent_r</refname>
  60     <refpurpose>lightweight resolver get network host entry</refpurpose>
  61   </refnamediv>
  62   <refsynopsisdiv>
  63     <funcsynopsis>
  64 <funcsynopsisinfo>#include &lt;lwres/netdb.h&gt;</funcsynopsisinfo>
  65 <funcprototype>
  66         <funcdef>
  67 struct hostent *
  68 <function>lwres_gethostbyname</function></funcdef>
  69         <paramdef>const char *<parameter>name</parameter></paramdef>
  70         </funcprototype>
  71 <funcprototype>
  72         <funcdef>
  73 struct hostent *
  74 <function>lwres_gethostbyname2</function></funcdef>
  75         <paramdef>const char *<parameter>name</parameter></paramdef>
  76         <paramdef>int <parameter>af</parameter></paramdef>
  77         </funcprototype>
  78 <funcprototype>
  79         <funcdef>
  80 struct hostent *
  81 <function>lwres_gethostbyaddr</function></funcdef>
  82         <paramdef>const char *<parameter>addr</parameter></paramdef>
  83         <paramdef>int <parameter>len</parameter></paramdef>
  84         <paramdef>int <parameter>type</parameter></paramdef>
  85         </funcprototype>
  86 <funcprototype>
  87         <funcdef>
  88 struct hostent *
  89 <function>lwres_gethostent</function></funcdef>
  90         <paramdef>void</paramdef>
  91         </funcprototype>
  92 <funcprototype>
  93         <funcdef>
  94 void
  95 <function>lwres_sethostent</function></funcdef>
  96         <paramdef>int <parameter>stayopen</parameter></paramdef>
  97         </funcprototype>
  98 <funcprototype>
  99         <funcdef>
 100 void
 101 <function>lwres_endhostent</function></funcdef>
 102         <paramdef>void</paramdef>
 103         </funcprototype>
 104 <funcprototype>
 105         <funcdef>
 106 struct hostent *
 107 <function>lwres_gethostbyname_r</function></funcdef>
 108         <paramdef>const char *<parameter>name</parameter></paramdef>
 109         <paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>
 110         <paramdef>char *<parameter>buf</parameter></paramdef>
 111         <paramdef>int <parameter>buflen</parameter></paramdef>
 112         <paramdef>int *<parameter>error</parameter></paramdef>
 113         </funcprototype>
 114 <funcprototype>
 115         <funcdef>
 116 struct hostent  *
 117 <function>lwres_gethostbyaddr_r</function></funcdef>
 118         <paramdef>const char *<parameter>addr</parameter></paramdef>
 119         <paramdef>int <parameter>len</parameter></paramdef>
 120         <paramdef>int <parameter>type</parameter></paramdef>
 121         <paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>
 122         <paramdef>char *<parameter>buf</parameter></paramdef>
 123         <paramdef>int <parameter>buflen</parameter></paramdef>
 124         <paramdef>int *<parameter>error</parameter></paramdef>
 125         </funcprototype>
 126 <funcprototype>
 127         <funcdef>
 128 struct hostent  *
 129 <function>lwres_gethostent_r</function></funcdef>
 130         <paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>
 131         <paramdef>char *<parameter>buf</parameter></paramdef>
 132         <paramdef>int <parameter>buflen</parameter></paramdef>
 133         <paramdef>int *<parameter>error</parameter></paramdef>
 134         </funcprototype>
 135 <funcprototype>
 136         <funcdef>
 137 void
 138 <function>lwres_sethostent_r</function></funcdef>
 139         <paramdef>int <parameter>stayopen</parameter></paramdef>
 140         </funcprototype>
 141 <funcprototype>
 142         <funcdef>
 143 void
 144 <function>lwres_endhostent_r</function></funcdef>
 145         <paramdef>void</paramdef>
 146       </funcprototype>
 147 </funcsynopsis>
 148   </refsynopsisdiv>
 149
 150   <refsect1>
 151     <title>DESCRIPTION</title>
 152     <para>
 153       These functions provide hostname-to-address and
 154       address-to-hostname lookups by means of the lightweight resolver.
 155       They are similar to the standard
 156       <citerefentry>
 157         <refentrytitle>gethostent</refentrytitle><manvolnum>3</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     </para>
 165     <para><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>
 180           <term><constant>h_name</constant></term>
 181           <listitem>
 182             <para>
 183               The official (canonical) name of the host.
 184             </para>
 185           </listitem>
 186         </varlistentry>
 187         <varlistentry>
 188           <term><constant>h_aliases</constant></term>
 189           <listitem>
 190             <para>
 191               A NULL-terminated array of alternate names (nicknames) for the
 192               host.
 193             </para>
 194           </listitem>
 195         </varlistentry>
 196         <varlistentry>
 197           <term><constant>h_addrtype</constant></term>
 198           <listitem>
 199             <para>
 200               The type of address being returned &mdash;
 201               <type>PF_INET</type>
 202               or
 203               <type>PF_INET6</type>.
 204             </para>
 205           </listitem>
 206         </varlistentry>
 207         <varlistentry>
 208           <term><constant>h_length</constant></term>
 209           <listitem>
 210             <para>
 211               The length of the address in bytes.
 212             </para>
 213           </listitem>
 214         </varlistentry>
 215         <varlistentry>
 216           <term><constant>h_addr_list</constant></term>
 217           <listitem>
 218             <para>
 219               A <type>NULL</type>
 220               terminated array of network addresses for the host.
 221               Host addresses are returned in network byte order.
 222             </para>
 223           </listitem>
 224         </varlistentry>
 225       </variablelist>
 226     </para>
 227     <para>
 228       For backward compatibility with very old software,
 229       <constant>h_addr</constant>
 230       is the first address in
 231       <constant>h_addr_list.</constant>
 232     </para>
 233     <para><function>lwres_gethostent()</function>,
 234       <function>lwres_sethostent()</function>,
 235       <function>lwres_endhostent()</function>,
 236       <function>lwres_gethostent_r()</function>,
 237       <function>lwres_sethostent_r()</function>
 238       and
 239       <function>lwres_endhostent_r()</function>
 240       provide iteration over the known host entries on systems that
 241       provide such functionality through facilities like
 242       <filename>/etc/hosts</filename>
 243       or NIS.  The lightweight resolver does not currently implement
 244       these functions; it only provides them as stub functions that always
 245       return failure.
 246     </para>
 247
 248     <para><function>lwres_gethostbyname()</function>
 249       and <function>lwres_gethostbyname2()</function> look up the
 250       hostname <parameter>name</parameter>.
 251       <function>lwres_gethostbyname()</function> always looks for an
 252       IPv4 address while <function>lwres_gethostbyname2()</function>
 253       looks for an address of protocol family
 254       <parameter>af</parameter>: either <type>PF_INET</type> or
 255       <type>PF_INET6</type> &mdash; IPv4 or IPV6 addresses
 256       respectively.  Successful calls of the functions return a
 257       <type>struct hostent</type>for the name that was looked up.
 258       <type>NULL</type> is returned if the lookups by
 259       <function>lwres_gethostbyname()</function> or
 260       <function>lwres_gethostbyname2()</function> fail.
 261     </para>
 262
 263     <para>
 264       Reverse lookups of addresses are performed by
 265       <function>lwres_gethostbyaddr()</function>.
 266       <parameter>addr</parameter> is an address of length
 267       <parameter>len</parameter> bytes and protocol family
 268       <parameter>type</parameter> &mdash; <type>PF_INET</type> or
 269       <type>PF_INET6</type>.
 270       <function>lwres_gethostbyname_r()</function> is a
 271       thread-safe function
 272       for forward lookups.  If an error occurs, an error code is returned in
 273       <parameter>*error</parameter>.
 274       <parameter>resbuf</parameter> is a pointer to a
 275       <type>struct hostent</type> which is initialised by a successful call to
 276       <function>lwres_gethostbyname_r()</function>.
 277       <parameter>buf</parameter> is a buffer of length
 278       <parameter>len</parameter> bytes which is used to store the
 279       <constant>h_name</constant>, <constant>h_aliases</constant>, and
 280       <constant>h_addr_list</constant> elements of the
 281       <type>struct hostent</type> returned in <parameter>resbuf</parameter>.
 282       Successful calls to <function>lwres_gethostbyname_r()</function>
 283       return <parameter>resbuf</parameter>,
 284       which is a pointer to the <type>struct hostent</type> it created.
 285     </para>
 286
 287     <para><function>lwres_gethostbyaddr_r()</function>
 288       is a thread-safe function
 289       that performs a reverse lookup of address <parameter>addr</parameter>
 290       which is <parameter>len</parameter> bytes long and is of
 291       protocol
 292       family <parameter>type</parameter> &mdash; <type>PF_INET</type> or
 293       <type>PF_INET6</type>.  If an error occurs, the error code is returned
 294       in <parameter>*error</parameter>.  The other function
 295       parameters are
 296       identical to those in <function>lwres_gethostbyname_r()</function>.
 297       <parameter>resbuf</parameter> is a pointer to a
 298       <type>struct hostent</type> which is initialised by a successful call to
 299       <function>lwres_gethostbyaddr_r()</function>.
 300       <parameter>buf</parameter> is a buffer of length
 301       <parameter>len</parameter> bytes which is used to store the
 302       <constant>h_name</constant>, <constant>h_aliases</constant>, and
 303       <constant>h_addr_list</constant> elements of the
 304       <type>struct hostent</type> returned in <parameter>resbuf</parameter>.
 305       Successful calls to <function>lwres_gethostbyaddr_r()</function> return
 306       <parameter>resbuf</parameter>, which is a pointer to the
 307       <function>struct hostent()</function> it created.
 308     </para>
 309
 310   </refsect1>
 311
 312   <refsect1>
 313     <title>RETURN VALUES</title>
 314     <para>
 315       The functions
 316       <function>lwres_gethostbyname()</function>,
 317       <function>lwres_gethostbyname2()</function>,
 318       <function>lwres_gethostbyaddr()</function>,
 319       and
 320       <function>lwres_gethostent()</function>
 321       return NULL to indicate an error.  In this case the global variable
 322       <type>lwres_h_errno</type>
 323       will contain one of the following error codes defined in
 324       <filename>&lt;lwres/netdb.h&gt;</filename>:
 325
 326       <variablelist>
 327         <varlistentry>
 328           <term><constant>HOST_NOT_FOUND</constant></term>
 329           <listitem>
 330             <para>
 331               The host or address was not found.
 332             </para>
 333           </listitem>
 334         </varlistentry>
 335         <varlistentry>
 336           <term><constant>TRY_AGAIN</constant></term>
 337           <listitem>
 338             <para>
 339               A recoverable error occurred, e.g., a timeout.
 340               Retrying the lookup may succeed.
 341             </para>
 342           </listitem>
 343         </varlistentry>
 344         <varlistentry>
 345           <term><constant>NO_RECOVERY</constant></term>
 346           <listitem>
 347             <para>
 348               A non-recoverable error occurred.
 349             </para>
 350           </listitem>
 351         </varlistentry>
 352         <varlistentry>
 353           <term><constant>NO_DATA</constant></term>
 354           <listitem>
 355             <para>
 356               The name exists, but has no address information
 357               associated with it (or vice versa in the case
 358               of a reverse lookup).  The code NO_ADDRESS
 359               is accepted as a synonym for NO_DATA for backwards
 360               compatibility.
 361             </para>
 362           </listitem>
 363         </varlistentry>
 364       </variablelist>
 365     </para>
 366
 367     <para><citerefentry>
 368         <refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3</manvolnum>
 369       </citerefentry>
 370       translates these error codes to suitable error messages.
 371     </para>
 372
 373     <para><function>lwres_gethostent()</function>
 374       and <function>lwres_gethostent_r()</function>
 375       always return <type>NULL</type>.
 376     </para>
 377
 378     <para>
 379       Successful calls to <function>lwres_gethostbyname_r()</function> and
 380       <function>lwres_gethostbyaddr_r()</function> return
 381       <parameter>resbuf</parameter>, a pointer to the
 382       <type>struct hostent</type> that was initialised by these functions.  They return
 383       <type>NULL</type> if the lookups fail or if <parameter>buf</parameter>
 384       was too small to hold the list of addresses and names referenced by
 385       the <constant>h_name</constant>, <constant>h_aliases</constant>, and
 386       <constant>h_addr_list</constant> elements of the
 387       <type>struct hostent</type>.
 388       If <parameter>buf</parameter> was too small, both
 389       <function>lwres_gethostbyname_r()</function> and
 390       <function>lwres_gethostbyaddr_r()</function> set the global
 391       variable
 392       <type>errno</type> to <errorcode>ERANGE</errorcode>.
 393     </para>
 394
 395   </refsect1>
 396   <refsect1>
 397     <title>SEE ALSO</title>
 398     <para><citerefentry>
 399         <refentrytitle>gethostent</refentrytitle><manvolnum>3</manvolnum>
 400       </citerefentry>,
 401
 402       <citerefentry>
 403         <refentrytitle>lwres_getipnode</refentrytitle><manvolnum>3</manvolnum>
 404       </citerefentry>,
 405
 406       <citerefentry>
 407         <refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3</manvolnum>
 408       </citerefentry>
 409     </para>
 410   </refsect1>
 411
 412   <refsect1>
 413     <title>BUGS</title>
 414     <para><function>lwres_gethostbyname()</function>,
 415       <function>lwres_gethostbyname2()</function>,
 416       <function>lwres_gethostbyaddr()</function>
 417       and
 418       <function>lwres_endhostent()</function>
 419       are not thread safe; they return pointers to static data and
 420       provide error codes through a global variable.
 421       Thread-safe versions for name and address lookup are provided by
 422       <function>lwres_gethostbyname_r()</function>,
 423       and
 424       <function>lwres_gethostbyaddr_r()</function>
 425       respectively.
 426     </para>
 427     <para>
 428       The resolver daemon does not currently support any non-DNS
 429       name services such as
 430       <filename>/etc/hosts</filename>
 431       or
 432       <type>NIS</type>,
 433       consequently the above functions don't, either.
 434     </para>
 435   </refsect1>
 436 </refentry><!--
 437  - Local variables:
 438  - mode: sgml
 439  - End:
 440 -->