resolver(3) Library Functions Manual resolver(3)
res_mkquery, res_send, res_init, dn_comp, dn_expand - resolver routines
res_mkquery(op, dname, class, type, data, datalen, newrr, buf, buflen)
int class, type;
struct rrec *newrr;
res_send(msg, msglen, answer, anslen)
dn_comp(exp_dn, comp_dn, length, dnptrs, lastdnptr)
char *exp_dn, *comp_dn;
char **dnptrs, **lastdnptr;
dn_expand(msg, eomorig, comp_dn, exp_dn, length)
char *msg, *eomorig, *comp_dn, exp_dn;
The resolver routines are used for making, sending, and interpreting packets to BIND servers. Global information that is used by the
resolver routines is kept in the variable Most of the values have reasonable defaults and you need not be concerned with them. The options
are a simple bit mask and are or'ed in to enable. The options stored in are defined in and are as follows:
RES_INIT True if the initial name server address and default domain name are initialized, for example if has been called.
RES_DEBUG Print debugging messages.
RES_AAONLY Accept authoritative answers only.
RES_USEVC Use TCP connections for queries instead of UDP.
RES_STAYOPEN This is used with to keep the TCP connection open between queries. This is useful only in programs that regularly do
many queries. You should normally use UDP.
RES_RECURSE Set the recursion desired bit in queries. This is the default. The routine does not do iterative queries and expects
the BIND server to handle recursion.
RES_DEFNAMES Append the default domain name to single label queries. This is the default.
The following lists the routines found in
res_init This routine reads the initialization file to get the default domain name and the Internet address of the initial hosts
running the name server. If this line does not exist, the host running the resolver is tried.
res_mkquery This routine makes a standard query message and places it in buf. The res_mkquery routine returns the size of the query or
-1 if the query is larger than buflen.
op The opcode is usually but can be any of the query types defined in nameser.h.
Dname This variable is the domain name. If dname consists of a single label and the flag is enabled, which is the
default, dname is appended with the current domain name. The current domain name is defined in a system file, but
you can override it by using the environment variable
res_send This routine sends a query to the BIND servers and returns an answer. It calls the routine. If is not set, sends the
query to the local name server, and handle timeouts and retries. The length of the message is returned or -1 if there were
dn_comp This routine compresses the domain name exp_dn and stores it in comp_dn. The size of the compressed name is returned or -1
if there were errors. The length is the size of the array pointed to by comp_dn.
dnptrs This variable is a list of pointers to previously compressed names in the current message. The first pointer points
to the beginning of the message and the list ends with
This is a pointer to the end of the array pointed to by dnptrs. A side effect is to update the list of pointers for
labels inserted into the message by dn_comp as the name is compressed. If dnptr is NULL, the names are not com-
pressed. If lastdnptr is NULL, the list is not updated.
dn_expand This routine expands the compressed domain name to a full BIND domain name. Expanded names are converted to upper case.
msg This variable is a pointer to the beginning of the message.
exp_dn This variable is a pointer to a buffer of size length for the result. The size of the compressed name is returned
or -1 if there was an error.
Guide to the BIND/Hesiod Service