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, her-
ror, res_getservers, res_setservers, res_ndestroy - resolver
routinesSYNOPSIS
BIND 8.2.2 Interfacescc [ flag ... ] file ... -lresolv -lsocket -lnsl [ library ... ]
#include
#include
#include
#include
#include
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);
SunOS 5.11 Last change: 26 Dec 2006 1
Resolver Library Functions resolver(3RESOLV)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 Interfacescc [ flag ... ] file ... -lresolv -lsocket -lnsl [ library ... ]
#include
#include
#include
#include
#include
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);
SunOS 5.11 Last change: 26 Dec 2006 2
Resolver Library Functions resolver(3RESOLV)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 interpret-
ing 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 compatability. They use global configuration and state information that is kept in thestructure _res rather than state information referenced
through statp.Most of the values in statp and _res are initialized to rea-
sonable 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
stored as a simple bit mask containing the bitwise OR of the options enabled.. They are RES_INIT True if the initial name server address and
default domain name are initialized, thatis, 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.SunOS 5.11 Last change: 26 Dec 2006 3
Resolver Library Functions resolver(3RESOLV)RES_USEVC Use TCP connections for queries instead of
UDP datagrams.RES_STAYOPEN Use with RES_USEVC to keep the TCP connec-
tion 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 alias-
ing 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 allservers. If the RES_BLAST option is not
defined, but RES_ROTATE is , the list of
nameservers are rotated according to around-robin scheme. RES_BLAST overrides
RES_ROTATE.
SunOS 5.11 Last change: 26 Dec 2006 4
Resolver Library Functions resolver(3RESOLV)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 configura-
tion 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(4). 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(1M), or by the hostname if it is not specified in the configuration file. Use the environment variable LOCALDOMAIN to override the domainname. This environment variable may contain several blank-
separated tokens if you wish to override the search list ona 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 inthe statp /_res structure. Alternatively, they are inherited
from the configuration file's options command. See resolv.conf(4) for information regarding the syntax of theRES_OPTIONS environment variable. Initialization normally
occurs on the first call to one of the other resolver rou-
tines.res_nquery(), res_query()
The res_nquery() and res_query() functions provide inter-
faces to the server query mechanism. They construct a query, send it to the local server, await a response, and makepreliminary checks on the reply. The query requests informa-
tion of the specified type and class for the specifiedfully-qualified domain name dname. The reply message is left
in the answer buffer with length anslen supplied by thecaller. 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 bufSunOS 5.11 Last change: 26 Dec 2006 5
Resolver Library Functions resolver(3RESOLV) 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 successfulreply which is stored in answer. On error, they reurn -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 stan-
dard query message and place it in buf. The routine returnsthe 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. 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 rou-
tine 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, theres_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 thelength of the reply message, or -1 if there are errors.
SunOS 5.11 Last change: 26 Dec 2006 6
Resolver Library Functions resolver(3RESOLV)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 foundor 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 ofpointers to previously compressed names in the current mes-
sage. 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 notcompressed. If lastdnptr is NULL, dn_comp() does not update
the list of labels.SunOS 5.11 Last change: 26 Dec 2006 7
Resolver Library Functions resolver(3RESOLV)dn_expand()
The dn_expand() function expands the compressed domain name
comp_dn to a full domain name. The compressed name is con-
tained in a query or reply message. msg is a pointer to the beginning of that message. The uncompressed name is placedin 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: #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 ofh_errno.
The hstrerror() function returns a string, which is the mes-
sage text that corresponds to the value of the err parame-
ter.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 fileATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:SunOS 5.11 Last change: 26 Dec 2006 8
Resolver Library Functions resolver(3RESOLV)____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| ____________________________|_____________________________|_
| Availability | system/library (32-bit) |
| | SUNWcslx (64-bit) |
| ____________________________|_____________________________|_
| Interface Stability | Committed || ____________________________|_____________________________|_
| MT-Level | Unsafe for deprecated|
| | interfaces; MT-Safe for all|
| | others. ||_____________________________|_____________________________|
SEE ALSO
domainname(1M), gethostbyname(3NSL), libresolv(3LIB), resolv.conf(4), attributes(5) Lottor, M. RFC 1033, Domain Administrators Operations Guide. Network Working Group. November 1987.Mockapetris, Paul. RFC 1034, Domain Names - Concepts and
Facilities. Network Working Group. November 1987.Mockapetris, Paul. RFC 1035, Domain Names - Implementation
and Specification. Network Working Group. November 1987.Partridge, Craig. RFC 974, Mail Routing and the Domain Sys-
tem. Network Working Group. January 1986. Stahl, M. RFC 1032, Domain Administrators Guide. Network Working Group. November 1987. Vixie, Paul, Dunlap, Kevin J., Karels, Michael J. NameServer Operations Guide for BIND. Internet Software Consor-
tium, 1996. NOTES When the caller supplies a work buffer, for example theanswer buffer argument to res_nsend() or res_send(), the
buffer should be aligned on an eight byte boundary. Other-
wise, an error such as a SIGBUS may result.SunOS 5.11 Last change: 26 Dec 2006 9