| 1 |
28 |
unneback |
<!-- Copyright (C) 2003 Red Hat, Inc. -->
|
| 2 |
|
|
<!-- This material may be distributed only subject to the terms -->
|
| 3 |
|
|
<!-- and conditions set forth in the Open Publication License, v1.0 -->
|
| 4 |
|
|
<!-- or later (the latest version is presently available at -->
|
| 5 |
|
|
<!-- http://www.opencontent.org/openpub/). -->
|
| 6 |
|
|
<!-- Distribution of the work or derivative of the work in any -->
|
| 7 |
|
|
<!-- standard (paper) book form is prohibited unless prior -->
|
| 8 |
|
|
<!-- permission is obtained from the copyright holder. -->
|
| 9 |
|
|
<HTML
|
| 10 |
|
|
><HEAD
|
| 11 |
|
|
><TITLE
|
| 12 |
|
|
>resolver</TITLE
|
| 13 |
|
|
><meta name="MSSmartTagsPreventParsing" content="TRUE">
|
| 14 |
|
|
<META
|
| 15 |
|
|
NAME="GENERATOR"
|
| 16 |
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
|
| 17 |
|
|
"><LINK
|
| 18 |
|
|
REL="HOME"
|
| 19 |
|
|
TITLE="eCos Reference Manual"
|
| 20 |
|
|
HREF="ecos-ref.html"><LINK
|
| 21 |
|
|
REL="UP"
|
| 22 |
|
|
TITLE="TCP/IP Library Reference"
|
| 23 |
|
|
HREF="tcpip-library-reference.html"><LINK
|
| 24 |
|
|
REL="PREVIOUS"
|
| 25 |
|
|
TITLE="ns"
|
| 26 |
|
|
HREF="net-common-tcpip-manpages-ns.html"><LINK
|
| 27 |
|
|
REL="NEXT"
|
| 28 |
|
|
TITLE="accept"
|
| 29 |
|
|
HREF="net-common-tcpip-manpages-accept.html"></HEAD
|
| 30 |
|
|
><BODY
|
| 31 |
|
|
CLASS="SECT1"
|
| 32 |
|
|
BGCOLOR="#FFFFFF"
|
| 33 |
|
|
TEXT="#000000"
|
| 34 |
|
|
LINK="#0000FF"
|
| 35 |
|
|
VLINK="#840084"
|
| 36 |
|
|
ALINK="#0000FF"
|
| 37 |
|
|
><DIV
|
| 38 |
|
|
CLASS="NAVHEADER"
|
| 39 |
|
|
><TABLE
|
| 40 |
|
|
SUMMARY="Header navigation table"
|
| 41 |
|
|
WIDTH="100%"
|
| 42 |
|
|
BORDER="0"
|
| 43 |
|
|
CELLPADDING="0"
|
| 44 |
|
|
CELLSPACING="0"
|
| 45 |
|
|
><TR
|
| 46 |
|
|
><TH
|
| 47 |
|
|
COLSPAN="3"
|
| 48 |
|
|
ALIGN="center"
|
| 49 |
|
|
>eCos Reference Manual</TH
|
| 50 |
|
|
></TR
|
| 51 |
|
|
><TR
|
| 52 |
|
|
><TD
|
| 53 |
|
|
WIDTH="10%"
|
| 54 |
|
|
ALIGN="left"
|
| 55 |
|
|
VALIGN="bottom"
|
| 56 |
|
|
><A
|
| 57 |
|
|
HREF="net-common-tcpip-manpages-ns.html"
|
| 58 |
|
|
ACCESSKEY="P"
|
| 59 |
|
|
>Prev</A
|
| 60 |
|
|
></TD
|
| 61 |
|
|
><TD
|
| 62 |
|
|
WIDTH="80%"
|
| 63 |
|
|
ALIGN="center"
|
| 64 |
|
|
VALIGN="bottom"
|
| 65 |
|
|
>Chapter 38. TCP/IP Library Reference</TD
|
| 66 |
|
|
><TD
|
| 67 |
|
|
WIDTH="10%"
|
| 68 |
|
|
ALIGN="right"
|
| 69 |
|
|
VALIGN="bottom"
|
| 70 |
|
|
><A
|
| 71 |
|
|
HREF="net-common-tcpip-manpages-accept.html"
|
| 72 |
|
|
ACCESSKEY="N"
|
| 73 |
|
|
>Next</A
|
| 74 |
|
|
></TD
|
| 75 |
|
|
></TR
|
| 76 |
|
|
></TABLE
|
| 77 |
|
|
><HR
|
| 78 |
|
|
ALIGN="LEFT"
|
| 79 |
|
|
WIDTH="100%"></DIV
|
| 80 |
|
|
><DIV
|
| 81 |
|
|
CLASS="SECT1"
|
| 82 |
|
|
><H1
|
| 83 |
|
|
CLASS="SECT1"
|
| 84 |
|
|
><A
|
| 85 |
|
|
NAME="NET-COMMON-TCPIP-MANPAGES-RESOLVER">resolver</H1
|
| 86 |
|
|
><TABLE
|
| 87 |
|
|
BORDER="5"
|
| 88 |
|
|
BGCOLOR="#E0E0F0"
|
| 89 |
|
|
WIDTH="70%"
|
| 90 |
|
|
><TR
|
| 91 |
|
|
><TD
|
| 92 |
|
|
><PRE
|
| 93 |
|
|
CLASS="SCREEN"
|
| 94 |
|
|
>RESOLVER(3) System Library Functions Manual RESOLVER(3)
|
| 95 |
|
|
|
| 96 |
|
|
NAME
|
| 97 |
|
|
res_query, res_search, res_mkquery, res_send, res_init, dn_comp,
|
| 98 |
|
|
dn_expand - resolver routines
|
| 99 |
|
|
|
| 100 |
|
|
SYNOPSIS
|
| 101 |
|
|
#include <sys/types.h>
|
| 102 |
|
|
#include <netinet/in.h>
|
| 103 |
|
|
#include <arpa/nameser.h>
|
| 104 |
|
|
#include <resolv.h>
|
| 105 |
|
|
|
| 106 |
|
|
int
|
| 107 |
|
|
res_query(char *dname, int class, int type, u_char *answer, int anslen);
|
| 108 |
|
|
|
| 109 |
|
|
int
|
| 110 |
|
|
res_search(char *dname, int class, int type, u_char *answer, int anslen);
|
| 111 |
|
|
|
| 112 |
|
|
int
|
| 113 |
|
|
res_mkquery(int op, char *dname, int class, int type, char *data,
|
| 114 |
|
|
int datalen, struct rrec *newrr, char *buf, int buflen);
|
| 115 |
|
|
|
| 116 |
|
|
int
|
| 117 |
|
|
res_send(char *msg, int msglen, char *answer, int anslen);
|
| 118 |
|
|
|
| 119 |
|
|
int
|
| 120 |
|
|
res_init(void);
|
| 121 |
|
|
|
| 122 |
|
|
int
|
| 123 |
|
|
dn_comp(char *exp_dn, char *comp_dn, int length, char **dnptrs,
|
| 124 |
|
|
char **lastdnptr);
|
| 125 |
|
|
|
| 126 |
|
|
int
|
| 127 |
|
|
dn_expand(u_char *msg, u_char *eomorig, u_char *comp_dn, u_char *exp_dn,
|
| 128 |
|
|
int length);
|
| 129 |
|
|
|
| 130 |
|
|
DESCRIPTION
|
| 131 |
|
|
These routines are used for making, sending, and interpreting query and
|
| 132 |
|
|
reply messages with Internet domain name servers.
|
| 133 |
|
|
|
| 134 |
|
|
Global configuration and state information that is used by the resolver
|
| 135 |
|
|
routines is kept in the structure _res. Most of the values have reason-
|
| 136 |
|
|
able defaults and can be ignored. Options stored in _res.options are
|
| 137 |
|
|
defined in <resolv.h> and are as follows. Options are stored as a simple
|
| 138 |
|
|
bit mask containing the bitwise OR of the options enabled.
|
| 139 |
|
|
|
| 140 |
|
|
RES_INIT True if the initial name server address and default domain
|
| 141 |
|
|
name are initialized (i.e., res_init() has been called).
|
| 142 |
|
|
|
| 143 |
|
|
RES_DEBUG Print debugging messages.
|
| 144 |
|
|
|
| 145 |
|
|
RES_AAONLY Accept authoritative answers only. With this option,
|
| 146 |
|
|
res_send() should continue until it finds an authoritative
|
| 147 |
|
|
answer or finds an error. Currently this is not imple-
|
| 148 |
|
|
mented.
|
| 149 |
|
|
|
| 150 |
|
|
RES_USEVC Use TCP connections for queries instead of UDP datagrams.
|
| 151 |
|
|
|
| 152 |
|
|
RES_STAYOPEN Used with RES_USEVC to keep the TCP connection open
|
| 153 |
|
|
between queries. This is useful only in programs that
|
| 154 |
|
|
regularly do many queries. UDP should be the normal mode
|
| 155 |
|
|
used.
|
| 156 |
|
|
|
| 157 |
|
|
RES_IGNTC Unused currently (ignore truncation errors, i.e., don't
|
| 158 |
|
|
retry with TCP).
|
| 159 |
|
|
|
| 160 |
|
|
RES_RECURSE Set the recursion-desired bit in queries. This is the
|
| 161 |
|
|
default. (res_send() does not do iterative queries and
|
| 162 |
|
|
expects the name server to handle recursion.)
|
| 163 |
|
|
|
| 164 |
|
|
RES_DEFNAMES If set, res_search() will append the default domain name
|
| 165 |
|
|
to single-component names (those that do not contain a
|
| 166 |
|
|
dot). This option is enabled by default.
|
| 167 |
|
|
|
| 168 |
|
|
RES_DNSRCH If this option is set, res_search() will search for host
|
| 169 |
|
|
names in the current domain and in parent domains; see
|
| 170 |
|
|
hostname(7). This is used by the standard host lookup
|
| 171 |
|
|
routine gethostbyname(3). This option is enabled by
|
| 172 |
|
|
default.
|
| 173 |
|
|
|
| 174 |
|
|
RES_USE_INET6 Enables support for IPv6-only applications. This causes
|
| 175 |
|
|
IPv4 addresses to be returned as an IPv4 mapped address.
|
| 176 |
|
|
For example, 10.1.1.1 will be returned as ::ffff:10.1.1.1.
|
| 177 |
|
|
The option is not meaningful on OpenBSD.
|
| 178 |
|
|
|
| 179 |
|
|
The res_init() routine reads the configuration file (if any; see
|
| 180 |
|
|
resolv.conf(5)) to get the default domain name, search list, and the
|
| 181 |
|
|
Internet address of the local name server(s). If no server is config-
|
| 182 |
|
|
ured, the host running the resolver is tried. The current domain name is
|
| 183 |
|
|
defined by the hostname if not specified in the configuration file; it
|
| 184 |
|
|
can be overridden by the environment variable LOCALDOMAIN. This environ-
|
| 185 |
|
|
ment variable may contain several blank-separated tokens if you wish to
|
| 186 |
|
|
override the search list on a per-process basis. This is similar to the
|
| 187 |
|
|
search command in the configuration file. Another environment variable
|
| 188 |
|
|
RES_OPTIONS can be set to override certain internal resolver options
|
| 189 |
|
|
which are otherwise set by changing fields in the _res structure or are
|
| 190 |
|
|
inherited from the configuration file's options command. The syntax of
|
| 191 |
|
|
the RES_OPTIONS environment variable is explained in resolv.conf(5).
|
| 192 |
|
|
Initialization normally occurs on the first call to one of the following
|
| 193 |
|
|
routines.
|
| 194 |
|
|
|
| 195 |
|
|
The res_query() function provides an interface to the server query mecha-
|
| 196 |
|
|
nism. It constructs a query, sends it to the local server, awaits a
|
| 197 |
|
|
response, and makes preliminary checks on the reply. The query requests
|
| 198 |
|
|
information of the specified type and class for the specified fully qual-
|
| 199 |
|
|
ified domain name dname. The reply message is left in the answer buffer
|
| 200 |
|
|
with length anslen supplied by the caller.
|
| 201 |
|
|
|
| 202 |
|
|
The res_search() routine makes a query and awaits a response like
|
| 203 |
|
|
res_query(), but in addition, it implements the default and search rules
|
| 204 |
|
|
controlled by the RES_DEFNAMES and RES_DNSRCH options. It returns the
|
| 205 |
|
|
first successful reply.
|
| 206 |
|
|
|
| 207 |
|
|
The remaining routines are lower-level routines used by res_query(). The
|
| 208 |
|
|
res_mkquery() function constructs a standard query message and places it
|
| 209 |
|
|
in buf. It returns the size of the query, or -1 if the query is larger
|
| 210 |
|
|
than buflen. The query type op is usually QUERY, but can be any of the
|
| 211 |
|
|
query types defined in <arpa/nameser.h>. The domain name for the query
|
| 212 |
|
|
is given by dname. newrr is currently unused but is intended for making
|
| 213 |
|
|
update messages.
|
| 214 |
|
|
|
| 215 |
|
|
The res_send() routine sends a pre-formatted query and returns an answer.
|
| 216 |
|
|
It will call res_init() if RES_INIT is not set, send the query to the
|
| 217 |
|
|
local name server, and handle timeouts and retries. The length of the
|
| 218 |
|
|
reply message is returned, or -1 if there were errors.
|
| 219 |
|
|
|
| 220 |
|
|
The dn_comp() function compresses the domain name exp_dn and stores it in
|
| 221 |
|
|
comp_dn. The size of the compressed name is returned or -1 if there were
|
| 222 |
|
|
errors. The size of the array pointed to by comp_dn is given by length.
|
| 223 |
|
|
The compression uses an array of pointers dnptrs to previously compressed
|
| 224 |
|
|
names in the current message. The first pointer points to the beginning
|
| 225 |
|
|
of the message and the list ends with NULL. The limit to the array is
|
| 226 |
|
|
specified by lastdnptr. A side effect of dn_comp() is to update the list
|
| 227 |
|
|
of pointers for labels inserted into the message as the name is com-
|
| 228 |
|
|
pressed. If dnptr is NULL, names are not compressed. If lastdnptr is
|
| 229 |
|
|
NULL, the list of labels is not updated.
|
| 230 |
|
|
|
| 231 |
|
|
The dn_expand() entry expands the compressed domain name comp_dn to a
|
| 232 |
|
|
full domain name The compressed name is contained in a query or reply
|
| 233 |
|
|
message; msg is a pointer to the beginning of the message. The uncom-
|
| 234 |
|
|
pressed name is placed in the buffer indicated by exp_dn which is of size
|
| 235 |
|
|
length. The size of compressed name is returned or -1 if there was an
|
| 236 |
|
|
error.
|
| 237 |
|
|
|
| 238 |
|
|
FILES
|
| 239 |
|
|
/etc/resolv.conf configuration file see resolv.conf(5).
|
| 240 |
|
|
|
| 241 |
|
|
SEE ALSO
|
| 242 |
|
|
gethostbyname(3), resolv.conf(5), hostname(7), named(8)
|
| 243 |
|
|
|
| 244 |
|
|
RFC1032, RFC1033, RFC1034, RFC1035, RFC1535, RFC974
|
| 245 |
|
|
|
| 246 |
|
|
Name Server Operations Guide for BIND.
|
| 247 |
|
|
|
| 248 |
|
|
HISTORY
|
| 249 |
|
|
The res_query function appeared in 4.3BSD.
|
| 250 |
|
|
|
| 251 |
|
|
BSD June 4, 1993 BSD
|
| 252 |
|
|
</PRE
|
| 253 |
|
|
></TD
|
| 254 |
|
|
></TR
|
| 255 |
|
|
></TABLE
|
| 256 |
|
|
></DIV
|
| 257 |
|
|
><DIV
|
| 258 |
|
|
CLASS="NAVFOOTER"
|
| 259 |
|
|
><HR
|
| 260 |
|
|
ALIGN="LEFT"
|
| 261 |
|
|
WIDTH="100%"><TABLE
|
| 262 |
|
|
SUMMARY="Footer navigation table"
|
| 263 |
|
|
WIDTH="100%"
|
| 264 |
|
|
BORDER="0"
|
| 265 |
|
|
CELLPADDING="0"
|
| 266 |
|
|
CELLSPACING="0"
|
| 267 |
|
|
><TR
|
| 268 |
|
|
><TD
|
| 269 |
|
|
WIDTH="33%"
|
| 270 |
|
|
ALIGN="left"
|
| 271 |
|
|
VALIGN="top"
|
| 272 |
|
|
><A
|
| 273 |
|
|
HREF="net-common-tcpip-manpages-ns.html"
|
| 274 |
|
|
ACCESSKEY="P"
|
| 275 |
|
|
>Prev</A
|
| 276 |
|
|
></TD
|
| 277 |
|
|
><TD
|
| 278 |
|
|
WIDTH="34%"
|
| 279 |
|
|
ALIGN="center"
|
| 280 |
|
|
VALIGN="top"
|
| 281 |
|
|
><A
|
| 282 |
|
|
HREF="ecos-ref.html"
|
| 283 |
|
|
ACCESSKEY="H"
|
| 284 |
|
|
>Home</A
|
| 285 |
|
|
></TD
|
| 286 |
|
|
><TD
|
| 287 |
|
|
WIDTH="33%"
|
| 288 |
|
|
ALIGN="right"
|
| 289 |
|
|
VALIGN="top"
|
| 290 |
|
|
><A
|
| 291 |
|
|
HREF="net-common-tcpip-manpages-accept.html"
|
| 292 |
|
|
ACCESSKEY="N"
|
| 293 |
|
|
>Next</A
|
| 294 |
|
|
></TD
|
| 295 |
|
|
></TR
|
| 296 |
|
|
><TR
|
| 297 |
|
|
><TD
|
| 298 |
|
|
WIDTH="33%"
|
| 299 |
|
|
ALIGN="left"
|
| 300 |
|
|
VALIGN="top"
|
| 301 |
|
|
>ns</TD
|
| 302 |
|
|
><TD
|
| 303 |
|
|
WIDTH="34%"
|
| 304 |
|
|
ALIGN="center"
|
| 305 |
|
|
VALIGN="top"
|
| 306 |
|
|
><A
|
| 307 |
|
|
HREF="tcpip-library-reference.html"
|
| 308 |
|
|
ACCESSKEY="U"
|
| 309 |
|
|
>Up</A
|
| 310 |
|
|
></TD
|
| 311 |
|
|
><TD
|
| 312 |
|
|
WIDTH="33%"
|
| 313 |
|
|
ALIGN="right"
|
| 314 |
|
|
VALIGN="top"
|
| 315 |
|
|
>accept</TD
|
| 316 |
|
|
></TR
|
| 317 |
|
|
></TABLE
|
| 318 |
|
|
></DIV
|
| 319 |
|
|
></BODY
|
| 320 |
|
|
></HTML
|
| 321 |
|
|
>
|
