1RESOLVER(3) Library Functions Manual RESOLVER(3)
2
6 res_mkquery, res_send, res_init, dn_comp, dn_expand - resolver routines
7
9 #include <sys/types.h>
10 #include <netinet/in.h>
11 #include <arpa/nameser.h>
12 #include <resolv.h>
13 res_mkquery(op, dname, class, type, data, datalen, newrr, buf, buflen)
15 int op;
16 char *dname;
17 int class, type;
18 char *data;
19 int datalen;
20 struct rrec *newrr;
21 char *buf;
22 int buflen;
23 res_send(msg, msglen, answer, anslen)
25 char *msg;
26 int msglen;
27 char *answer;
28 int anslen;
29 res_init()
31 dn_comp(exp_dn, comp_dn, length, dnptrs, lastdnptr)
33 char *exp_dn, *comp_dn;
34 int length;
35 char **dnptrs, **lastdnptr;
36 dn_expand(msg, eomorig, comp_dn, exp_dn, length)
38 char *msg, *eomorig, *comp_dn, exp_dn;
39 int length;
40
42 These routines are used for making, sending and interpreting packets
43 for use with Internet domain name servers. Global information that is
44 used by the resolver routines is kept in the variable _res. Most of
45 the values have reasonable defaults and can be ignored. Options stored
46 in _res.options are defined in resolv.h and are as follows. Options
47 are stored a simple bit mask containing the bitwise ``or'' of the
48 options enabled.
49 RES_INIT
51 True if the initial name server address and default domain name
52 are initialized (i.e., res_init has been called).
53 RES_DEBUG
55 Print debugging messages.
56 RES_AAONLY
58 Accept authoritative answers only. With this option, res_send
59 should continue until it finds an authoritative answer or finds
60 an error. Currently this is not implemented.
61 RES_USEVC
63 Use TCP connections for queries instead of UDP datagrams.
64 RES_STAYOPEN
66 Used with RES_USEVC to keep the TCP connection open between
67 queries. This is useful only in programs that regularly do many
68 queries. UDP should be the normal mode used.
69 RES_IGNTC
71 Unused currently (ignore truncation errors, i.e., don't retry
72 with TCP).
73 RES_RECURSE
75 Set the recursion-desired bit in queries. This is the default.
76 ( res_send does not do iterative queries and expects the name
77 server to handle recursion.)
78 RES_DEFNAMES
80 If set, res_mkquery will append the default domain name to sin‐
81 gle-component names (those that do not contain a dot). This is
82 the default.
83 RES_DNSRCH
85 If this option is set, the standard host lookup routine gethost‐
86 byname(3) will search for host names in the current domain and
87 in parent domains; see hostname(7).
88 Res_init
90 reads the initialization file to get the default domain name and the
92 Internet address of the initial hosts running the name server. If this
93 line does not exist, the host running the resolver is tried.
94 Res_mkquery makes a standard query message and places it in buf.
95 Res_mkquery will return the size of the query or -1 if the query is
96 larger than buflen. Op is usually QUERY but can be any of the query
97 types defined in nameser.h. Dname is the domain name. If dname con‐
98 sists of a single label and the RES_DEFNAMES flag is enabled (the
99 default), the current domain name will be appended to dname. The cur‐
100 rent domain name is defined by the hostname or is specified in a system
101 file; it can be overridden by the environment variable LOCALDOMAIN.
102 Newrr is currently unused but is intended for making update messages.
103 Res_send sends a query to name servers and returns an answer. It will
105 call res_init if RES_INIT is not set, send the query to the local name
106 server, and handle timeouts and retries. The length of the message is
107 returned, or -1 if there were errors.
108 Dn_expand expands the compressed domain name comp_dn to a full domain
110 name. Expanded names are converted to upper case. Msg is a pointer to
111 the beginning of the message, exp_dn is a pointer to a buffer of size
112 length for the result. The size of compressed name is returned or -1
113 if there was an error.
114 Dn_comp compresses the domain name exp_dn and stores it in comp_dn.
116 The size of the compressed name is returned or -1 if there were errors.
117 length is the size of the array pointed to by comp_dn. Dnptrs is a
118 list of pointers to previously compressed names in the current message.
119 The first pointer points to to the beginning of the message and the
120 list ends with NULL. lastdnptr is a pointer to the end of the array
121 pointed to dnptrs. A side effect is to update the list of pointers for
122 labels inserted into the message by dn_comp as the name is compressed.
123 If dnptr is NULL, names are not compressed. If lastdnptr is NULL, the
124 list of labels is not updated.
125
127 /etc/resolv.conf see resolver(5)
128
130 gethostbyname(3), named(8), resolver(5), hostname(7),
131 RFC882, RFC883, RFC973, RFC974,
132 SMM:11 Name Server Operations Guide for BIND
1334th Berkeley Distribution November 21, 1987 RESOLVER(3)