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 rea‐
sonable 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
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
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 recur‐
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 con‐
sists 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 han‐
dle timeouts and retries. The length of the message is
returned or -1 if there were errors.
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 previ‐
ously 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 com‐
pressed. If dnptr is NULL, the names are not
compressed. If lastdnptr is NULL, the list is
dn_expand This routine expands the compressed domain name to a
full BIND domain name. Expanded names are converted to
msg This variable is a pointer to the beginning of
exp_dn This variable is a pointer to a buffer of size
length for the result. The size of the com‐
pressed name is returned or -1 if there was an
FilesSee Alsonamed(8), resolv.conf(5)
Guide to the BIND/Hesiod Service