Партнёры:
Хостинг:
NAME
resolver, res_init, res_mkquery, res_mkupdate, res_mkupdrec,
res_query, res_search, res_send, res_update, dn_comp,
dn_expand - resolver routines
SYNOPSIS
cc [ flag ... ] file ... -lresolv -lsocket -lnsl [ library ... ]
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
int res_init(void);
int res_mkquery(int op, const char *dname, int class, int
type, const char *data, int datalen, struct rrec *newrr,
uchar_t *buf, int buflen);
int res_mkupdate(ns_updrec **rrecp_in, uchar *buf, int
length);
ns_updrec *res_mkupdrec(int section, const char *dname,
uint_t class, uint_t type, uint_t ttl);
int res_query(const char *dname, int class, int type,
uchar_t *answer, int anslen);
int res_search(const char *dname, int class, int type,
uchar_t *answer, int anslen);
int res_send(uchar_t *msg, int msglen, uchar_t *answer, int
anslen);
int res_update(ns_updrec *rrecp_in);
int dn_comp(const char *exp_dn, uchar_t *comp_dn, int
length, uchar_t **dnptrs, uchar_t **lastdnptr);
int dn_expand(const uchar_t *msg, const uchar_t *eomorig,
uchar_t *comp_dn, char exp_dn, int length);
DESCRIPTION
These routines are used for making, sending, and interpret-
ing query and reply messages passed to and from Internet
domain name servers. The res_update() and res_mkupdrec()
routines are used to dynamically update the name server with
resource records.
The global structure _res holds options and state informa-
tion. Option values can be set to affect the collective
behavior of groups of resolver library routines. However,
most resolver library routines use reasonable defaults so
that the explicit enabling of an option is rarely required.
The library manual page entry for the resolver library
includes public domain routines beyond those described here.
See libresolv(3LIB). Those function names that are exported
but are not explained here are lower-level routines called
by these routines. Their direct use is discouraged. If you
do make direct use of unsupported routines, you do so at
considerable added risk and with no expectation of documen-
tation or other support beyond that available publicly.
Options for the resolver library are stored as a single bit
mask containing the bitwise- OR sum of the options enabled.
The options stored in _res.options are those defined in
<resolv.h> and as follows. The field _res.options is a
member of the _res structure.
RES_INIT
True if the initial name server address and default
domain name are initialized, that is, res_init() 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 authorita-
tive answer or finds an error. Currently this option
is not implemented.
RES_USEVC
Use TCP connections for queries instead of UDP
datagrams.
RES_PRIMARY
Query primary server only. This option is not imple-
mented.
RES_IGNTC
Unused currently. 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() does not do iterative queries and
expects the name server to handle recursion.
RES_DEFNAMES
If set, res_search() appends the default domain name
to single-component names (names that do not contain a
dot). This is useful only in programs that regularly
do many queries. UDP should be the normal mode used.
RES_DNSRCH
Enables searching up through the current domain tree.
If this option is set, res_search() searches for host
names in the current domain and in parent domains.
This 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_init
If the system initialization file resolv.conf exists,
res_init() reads it to get the default domain name, the
search list, and the Internet address of the local name
server or servers. See resolv.conf(4). If no server is con-
figured by the local resolv.conf file, res_init tries to
obtain name resolution services from the host on which it is
running.
The res_init() function also sets the RES_INIT field of the
_res global structure so that other service routines
(res_search()) can determine for certain whether it needs to
be called first before other processing begins.
In the absence of a resolv.conf configuration file, the
current domain is either set to the value of the environ-
mental variable LOCALDOMAIN, derived from the domain name
or derived from the host name. See domainname(1M). The
current domain name as defined in the system initialization
file resolv.conf can be overridden by the environment vari-
able LOCALDOMAIN. 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. Another environ-
ment variable ( RES_OPTIONS) can be set to override certain
internal resolver options. Otherwise, these options are set
by changing fields in the global _res structure or they are
inherited from the configuration file's options command.
The syntax of the RES_OPTIONS environment variable is
explained in resolv.conf(4).
The initializations performed by res_init() can be invoked
explicitly with this function. However, they are normally
performed automatically as a result of a call to one of the
other resolver routines.
res_search
res_search() formulates and sends a normal query (QUERY)
message, and stores the response in a buffer supplied by
the caller.
The parameters class and type define the class and type of
query. See <arpa/nameser.h>. The response is returned in the
user-supplied buffer answer. res_search returns the length
of answer in anslen. Like the other resolver routines,
res_search() calls res_init() if the RES_INIT flag is not
enabled.
The res_search() function acts in a similar manner as
res_query(), except that it can implement the default and
search rules controlled by the RES_DEFNAMES and RES_DNSRCH
options.
The parameter dname is the domain name. However, if dname
consists of a single-component name and the RES_DEFNAMES
flag is enabled (the default), dname is appended with the
current domain name.
If the RES_DNSRCH flag is enabled, res_search() searches up
the current domain tree until an answer has been retrieved
or an unrecoverable error has been encountered. res_search()
returns the first successful reply.
res_mkquery
The res_mkquery() function constructs a standard query mes-
sage and places it in buf.
res_mkquery() returns the size of the query or -1 if the
query is larger than buflen. The op parameter is usually
QUERY, but can be any of the query types defined in
<arpa/nameser.h>.
The parameter dname is the domain name for the query.
The parameters class and type define the class and type of
query (see <arpa/nameser.h>). The parameter data is the
resource record; datalen is the length of the record.
newrr is unused and should be specified as a null pointer
(0).
res_query
The res_query function provides an interface to most of the
server query mechanism. It constructs a query, sends it to
the local server, awaits a response, and makes 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. The
res_mkquery and res_send routines described elsewhere in
this section are lower-level routines that res_query calls.
res_send
res_send() sends a pre-formatted query to name servers and
returns an answer. It calls res_init() if RES_INIT is not
set, send the query to the local name server, and handle
timeouts and retries. msg is the query sent; msglen is its
length. answer is the response returned. The length of the
response is stored in anslen. res_send() returns the length
of the response or -1 if there were errors.
dn_expand
dn_expand() expands the compressed domain name given by the
pointer comp_dn into a full domain name. Expanded names are
converted to upper case. The compressed name is contained in
a query or reply message; msg is a pointer to the beginning
of that message. Expanded names are stored in the buffer
referenced by the exp_dn buffer of size length, which should
be large enough to hold the expanded result.
dn_expand() returns the size of the compressed name, or -1
if there was an error.
dn_comp
dn_comp() compresses the domain name exp_dn and stores it in
comp_dn. dn_comp() 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. dnptrs 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 begin-
ning 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. However, if lastdnptr is NULL,
dn_comp() does not update the list of labels. If dnptrs is
NULL, names are not compressed.
res_mkupdrec
res_mkupdrec() takes the elements of a resource record as
its arguments, for instance, section, domainname, class,
type, and ttl, and returns a pointer to a linked list
ns_updrec. It returns NULL upon failure.
res_update
res_update() takes a linked list of resource records
ns_updrec as its only argument and separates the records
into groups such that all records in a group will belong to
a single name server. It creates a dynamic update packet
for each zone and sends it to the name server and awaits an
answer. Upon success, res_update() returns the number of
zones updated. It returns <0 upon error.
res_mkupdate
res_mkupdate() creates update packets by running through the
elements of the ns_updrec link list. It is called by
res_update() to create packets for res_send() to send to
the name server. res_mkupdate() returns the actual size of
the packet, or
-1 Error in reading a word or number in the rdata por-
tion for update packets.
-2 The length of the packet passed is insufficient.
-3 The zone section is not the first section in the
linked list, or the section order has a problem.
-4 A number overflow.
-5 Unknown operations or no records.
If an error occurs it could leave the zones being updated in
an inconsistent state. For example, a record might be suc-
cessfully added to the forward lookup zone but the
corresponding PTR record might have failed to update in the
reverse lookup tables.
FILES
/etc/resolv.conf
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| MT-Level | Unsafe |
|_____________________________|_____________________________|
SEE ALSO
domainname(1M), in.named(1M), nstest(1M),
gethostbyname(3NSL), libresolv(3LIB), resolv.conf(4), attri-
butes(5)
Lottor, M., Domain Administrators Operators Guide, RFC 1033,
SRI International, Menlo Park, Calif., November 1987.
Mockapetris, Paul, Domain Names - Concepts and Facilities,
RFC 1034, Network Information Center, SRI International,
Menlo Park, Calif., November 1987.
Mockapetris, Paul, Domain Names - Implementation and Specif-
ication, RFC 1035, Network Information Center, SRI Interna-
tional, Menlo Park, Calif., November 1987.
Partridge, Craig, Mail Routing and the Domain System, RFC
974, Network Information Center, SRI International, Menlo
Park, Calif., January 1986. Stahl, M., Domain Administrators
Guide, RFC 1032, SRI International, Menlo Park, Calif.,
November 1987.
Vixie, Paul;Dunlap, Keven J., Karels, Michael J., Name
Server Operations Guide for BIND (public domain), Internet
Software Consortium, 1996.
NOTES
These interfaces are unsafe in multithreaded applications.
Unsafe interfaces should be called only from the main
thread.
|
Закладки на сайте Проследить за страницей |
Created 1996-2024 by Maxim Chirkov Добавить, Поддержать, Вебмастеру |