Tribblix: manual page: resolver.3resolv

RESOLVER(3RESOLV) Resolver Library Functions RESOLVER(3RESOLV)

NAME

resolver, res_ninit, fp_resstat, res_hostalias, res_nquery,
res_nsearch, res_nquerydomain, res_nmkquery, res_nsend, res_nclose,
res_nsendsigned, dn_comp, dn_expand, hstrerror, res_init, res_query,
res_search, res_mkquery, res_send, herror, res_getservers,
res_setservers, res_ndestroy - resolver routines

SYNOPSIS

BIND 8.2.2 Interfaces

cc [ flag ... ] file ... -lresolv -lsocket -lnsl [ library ... ]
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include <netdb.h>

int res_ninit(res_state statp);

void res_ndestroy(res_state statp);

void fp_resstat(const res_state statp, FILE *fp);

const char *res_hostalias(const res_state statp, const char *name,
char * name, char *buf, size_tbuflen);

int res_nquery(res_state statp, const char *dname, int class, int type,
u_char *answer, int datalen, int anslen);

int res_nsearch(res_state statp, const char *dname, int class, int type,
u_char *answer, int anslen);

int res_nquerydomain(res_state statp, const char *name,
const char *domain, int class, int type,
u_char *answer, int anslen);

int res_nmkquery(res_state statp, int op, const char *dname, int class,
int type, u_char *answer, int datalen,
int anslen);

int res_nsend(res_state statp, const u_char *msg, int msglen,
u_char *answer, int anslen);

void res_nclose(res_state statp);

int res_snendsigned(res_state statp, const u_char *msg,
int msglen, ns_tsig_key *key, u_char *answer, int anslen);

int dn_comp(const char *exp_dn, u_char *comp_dn, int length,
u_char **dnptrs, **lastdnptr);

int dn_expand(const u_char *msg, *eomorig, *comp_dn, char *exp_dn,
int length);

const char *hstrerror(int err);

void res_setservers(res_state statp, const union res_sockaddr_union *set,
int cnt);

int res_getservers(res_state statp, union res_sockaddr_union *set,
int cnt);

Deprecated Interfaces

cc [ flag ... ] file ... -lresolv -lsocket -lnsl [ library ... ]
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include <netdb.h>

int res_init(void)

int res_query(const char *dname, int class,
int type, u_char *answer,
int anslen);

int res_search(const char *dname, int class,
int type, u_char *answer, int anslen);

int res_mkquery(int op, const char *dname, int class,
int type, const char *data,int datalen,
struct rrec *newrr, u_char *buf, int buflen);

int res_send(const u_char *msg, int msglen, u_char *answer,
int anslen);

void herror(const char *s);

DESCRIPTION

These routines are used for making, sending, and interpreting query
and reply messages with Internet domain name servers.

State information is kept in statp and is used to control the
behavior of these functions. Set statp to all zeros prior to making
the first call to any of these functions.

The res_ndestroy() function should be called to free memory allocated
by res_ninit() after the last use of statp.

The functions res_init(), res_query(), res_search(), res_mkquery(),
res_send(), and herror() are deprecated. They are supplied for
backwards compatibility. They use global configuration and state
information that is kept in the structure _res rather than state
information referenced through statp.

Most of the values in statp and _res are initialized to reasonable
defaults on the first call to res_ninit() or res_init() and can be
ignored. Options stored in statp->options or _res.options are defined
in <resolv.h>. They are stored as a simple bit mask containing the
bitwise OR of the options enabled.

RES_INIT
True if the initial name server address and default
domain name are initialized, that is, res_init() or
res_ninit() has been called.

RES_DEBUG
Print debugging messages.

RES_AAONLY
Accept authoritative answers only. With this option,
res_send() will continue until it finds an
authoritative answer or finds an error. Currently
this option is not implemented.

RES_USEVC
Use TCP connections for queries instead of UDP
datagrams.

RES_STAYOPEN
Use with RES_USEVC to keep the TCP connection open
between queries. This is a useful option for
programs that regularly do many queries. The normal
mode used should be UDP.

RES_IGNTC
Ignore truncation errors; that is, do not retry with
TCP.

RES_RECURSE
Set the recursion-desired bit in queries. This is
the default. res_send() and res_nsend() do not do
iterative queries and expect the name server to
handle recursion.

RES_DEFNAMES
If set, res_search() and res_nsearch() append the
default domain name to single-component names, that
is, names that do not contain a dot. This option is
enabled by default.

RES_DNSRCH
If this option is set, res_search() and
res_nsearch() search for host names in the current
domain and in parent domains. See hostname(1). This
option is used by the standard host lookup routine
gethostbyname(3NSL). This option is enabled by
default.

RES_NOALIASES
This option turns off the user level aliasing
feature controlled by the HOSTALIASES environment
variable. Network daemons should set this option.

RES_BLAST
If the RES_BLAST option is defined, resolver()
queries will be sent to all servers. If the
RES_BLAST option is not defined, but RES_ROTATE is ,
the list of nameservers are rotated according to a
round-robin scheme. RES_BLAST overrides RES_ROTATE.

RES_ROTATE
This option causes res_nsend() and res_send() to
rotate the list of nameservers in statp->nsaddr_list
or _res.nsaddr_list.

RES_KEEPTSIG
This option causes res_nsendsigned() to leave the
message unchanged after TSIG verification. Otherwise
the TSIG record would be removed and the header
would be updated.

res_ninit(), res_init()
The res_ninit() and res_init() routines read the configuration file,
if any is present, to get the default domain name, search list and
the Internet address of the local name server(s). See resolv.conf(5).
If no server is configured, res_init() or res_ninit() will try to
obtain name resolution services from the host on which it is running.
The current domain name is defined by domainname(8), or by the
hostname if it is not specified in the configuration file. Use the
environment variable LOCALDOMAIN to override the domain name. This
environment variable may contain several blank-separated tokens if
you wish to override the search list on a per-process basis. This is
similar to the search command in the configuration file. You can set
the RES_OPTIONS environment variable to override certain internal
resolver options. You can otherwise set them by changing fields in
the statp /_res structure. Alternatively, they are inherited from the
configuration file's options command. See resolv.conf(5) for
information regarding the syntax of the RES_OPTIONS environment
variable. Initialization normally occurs on the first call to one of
the other resolver routines.

res_nquery(), res_query()
The res_nquery() and res_query() functions provide interfaces to the
server query mechanism. They construct a query, send it to the local
server, await a response, and make preliminary checks on the reply.
The query requests information of the specified type and class for
the specified fully-qualified domain name dname. The reply message is
left in the answer buffer with length anslen supplied by the caller.
res_nquery() and res_query() return the length of the answer, or -1
upon error.

The res_nquery() and res_query() routines return a length that may be
bigger than anslen. In that case, retry the query with a larger buf.
The answer to the second query may be larger still], so it is
recommended that you supply a buf larger than the answer returned by
the previous query. answer must be large enough to receive a maximum
UDP response from the server or parts of the answer will be silently
discarded. The default maximum UDP response size is 512 bytes.

res_nsearch(), res_search()
The res_nsearch() and res_search() routines make a query and await a
response, just like like res_nquery() and res_query(). In addition,
they implement the default and search rules controlled by the
RES_DEFNAMES and RES_DNSRCH options. They return the length of the
first successful reply which is stored in answer. On error, they
return -1.

The res_nsearch() and res_search() routines return a length that may
be bigger than anslen. In that case, retry the query with a larger
buf. The answer to the second query may be larger still], so it is
recommended that you supply a buf larger than the answer returned by
the previous query. answer must be large enough to receive a maximum
UDP response from the server or parts of the answer will be silently
discarded. The default maximum UDP response size is 512 bytes.

res_nquerydomain()
The res_nquerydomain() function calls res_query() on the
concatenation of name and domain, removing a trailing dot from name
if domain is NULL.

res_nmkquery(), res_mkquery()
These routines are used by res_nquery() and res_query(). The
res_nmkquery() and res_mkquery() functions construct a standard query
message and place it in buf. The routine returns the size of the
query, or -1 if the query is larger than buflen. The query type op is
usually QUERY, but can be any of the query types defined in
<arpa/nameser.h>. The domain name for the query is given by dname.
newrr is currently unused but is intended for making update messages.

res_nsend(), res_send(), res_nsendsigned()
The res_nsend(), res_send(), and res_nsendsigned() routines send a
pre-formatted query that returns an answer. The routine calls
res_ninit() or res_init(). If RES_INIT is not set, the routine sends
the query to the local name server and handles timeouts and retries.
Additionally, the res_nsendsigned() uses TSIG signatures to add
authentication to the query and verify the response. In this case,
only one name server will be contacted. The routines return the
length of the reply message, or -1 if there are errors.

The res_nsend() and res_send() routines return a length that may be
bigger than anslen. In that case, retry the query with a larger buf.
The answer to the second query may be larger still], so it is
recommended that you supply a buf larger than the answer returned by
the previous query. answer must be large enough to receive a maximum
UDP response from the server or parts of the answer will be silently
discarded. The default maximum UDP response size is 512 bytes.

fp_resstat()
The function fp_resstat() prints out the active flag bits in
statp->options preceded by the text ";; res options:" on file.

res_hostalias()
The function res_hostalias() looks up name in the file referred to by
the HOSTALIASES environment variable and returns the fully qualified
host name. If name is not found or an error occurs, NULL is returned.
res_hostalias() stores the result in buf.

res_nclose()
The res_nclose() function closes any open files referenced through
statp.

res_ndestroy()
The res_ndestroy() function calls res_nclose(), then frees any memory
allocated by res_ninit() referenced through statp.

dn_comp()
The dn_comp() function compresses the domain name exp_dn and stores
it in comp_dn. The dn_comp() function returns the size of the
compressed name, or -1 if there were errors. length is the size of
the array pointed to by comp_dn.

The dnptrs parameter is a pointer to the head of the list of pointers
to previously compressed names in the current message. The first
pointer must point to the beginning of the message. The list ends
with NULL. The limit to the array is specified by lastdnptr.

A side effect of calling dn_comp() is to update the list of pointers
for labels inserted into the message by dn_comp() as the name is
compressed. If dnptrs is NULL, names are not compressed. If
lastdnptr is NULL, dn_comp() does not update the list of labels.

dn_expand()
The dn_expand() function expands the compressed domain name comp_dn
to a full domain name. The compressed name is contained in a query or
reply message. msg is a pointer to the beginning of that message. The
uncompressed name is placed in the buffer indicated by exp_dn, which
is of size length. The dn_expand() function returns the size of the
compressed name, or -1 if there was an error.

hstrerror(), herror()
The variables statp->res_h_errno and _res.res_h_errno and external
variable h_errno are set whenever an error occurs during a resolver
operation. The following definitions are given in <netdb.h>:

#define NETDB_INTERNAL -1 /* see errno */
#define NETDB_SUCCESS 0 /* no problem */
#define HOST_NOT_FOUND 1 /* Authoritative Answer Host not found */
#define TRY_AGAIN 2 /* Non-Authoritative not found, or SERVFAIL */
#define NO_RECOVERY 3 /* Non-Recoverable: FORMERR, REFUSED, NOTIMP*/
#define NO_DATA 4 /* Valid name, no data for requested type */

The herror() function writes a message to the diagnostic output
consisting of the string parameters, the constant string ":", and a
message corresponding to the value of h_errno.

The hstrerror() function returns a string, which is the message text
that corresponds to the value of the err parameter.

res_setservers(), res_getservers()
The functions res_getservers() and res_setservers() are used to get
and set the list of servers to be queried.

FILES

/etc/resolv.conf
resolver configuration file

ATTRIBUTES

NOTES