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cc...-lsocket#include <sys/types.h> #include <netinet/in.h> #include <arpa/nameser.h> #include <resolv.h>
typedef struct __res_state *res_state ;
res_ninit(res_state statp);
res_ourserver_p(const res_state statp, const struct sockaddr_in *addr);
fp_resstat(const res_state statp, FILE *fp);
res_hostalias(const res_state statp, const char *name, char *buf, size_t buflen);
res_pquery(const res_state statp, const u_char *msg, int msglen, FILE *fp);
res_nquery(res_state statp, const char *dname, int class, int type, u_char *answer, int anslen);
res_nsearch(res_state statp, const char *dname, int class, int type, u_char * answer, int anslen);
res_nquerydomain(res_state statp, const char *name, const char *domain, int class, int type, u_char *answer, int anslen);
res_nmkquery(res_state statp, int op, const char *dname, int class, int type, const u_char *data, int datalen, const u_char *newrr, u_char *buf, int buflen);
res_nsend(res_state statp, const u_char *msg, int msglen, u_char *answer, int anslen);
res_nupdate(res_state statp, ns_updrec *rrecp_in);
res_nmkupdate(res_state statp, ns_updrec *rrecp_in, u_char *buf, int buflen);
res_nclose(res_state statp);
res_nsendsigned(res_state statp, const u_char *msg, int msglen, ns_tsig_key *key, u_char *answer, int anslen);
res_findzonecut(res_state statp, const char *dname, ns_class class, int options, char *zname, size_t zsize, struct in_addr *addrs, int naddrs);
dn_comp(const char *exp_dn, u_char *comp_dn, int length, u_char **dnptrs, u_char **lastdnptr);
dn_expand(const u_char *msg, const u_char *eomorig, const u_char *comp_dn, char *exp_dn, int length);
hstrerror(int err);
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
res_init(void);
res_isourserver(const struct sockaddr_in *addr);
fp_nquery(const u_char *msg, int msglen, FILE *fp);
p_query(const u_char *msg, FILE *fp);
hostalias(const char *name);
res_query(const char *dname, int class, int type, u_char *answer,
int anslen);
res_search(const char *dname, int class, int type, u_char *answer,
int anslen);
res_querydomain(const char *name, const char *domain, int class,
int type, u_char *answer, int anslen);
res_mkquery(int op, const char *dname, int class, int type,
const char *data, int datalen, struct rrec *newrr, u_char *buf,
int buflen);
res_send(const u_char *msg, int msglen, u_char *answer, int anslen);
res_update(ns_updrec *rrecp_in);
res_close(void);
herror(const char *s);
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. statp should be set to all zeros prior to the first
call to any of these functions.
The functions res_init(), res_isourserver(), fp_nquery(), p_query(),
hostalias(), res_query(), res_search(), res_querydomain(), res_mkquery(),
res_send(), res_update(), res_close() and herror() are deprecated and are
supplied for compatability with old source code. They use global config-
uration and state information that is kept in the structure _res rather
than that referenced through statp .
Most of the values in statp and _res are initialized on the first call to
res_ninit() / res_init() to reasonable defaults and can be ignored. Op-
tions stored in statp->options / _res.options are defined in resolv.h and
are as follows. Options 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 (i.e., res_ninit() / res_init() has been
called).
RES_DEBUG
Print debugging messages.
RES_AAONLY
Accept authoritative answers only. should continue until it
finds an authoritative answer or finds an error. Currently this
is not implemented.
RES_USEVC
Use TCP connections for queries instead of UDP datagrams.
RES_STAYOPEN
Used with RES_USEVC to keep the TCP connection open between
queries. This is useful only in programs that regularly do many
queries. UDP should be the normal mode used.
RES_IGNTC
Ignore truncation errors, i.e., don't retry with TCP.
RES_RECURSE
Set the recursion-desired bit in queries. This is the default.
(res_nsend() / res_send() does not do iterative queries and ex-
pects the name server to handle recursion.)
RES_DEFNAMES
If set, res_nsearch() / res_search() will append the default do-
main name to single-component names (those that do not contain a
dot). This option is enabled by default.
RES_DNSRCH
If this option is set, res_nsearch() / res_search() will search
for host names in the current domain and in parent domains; see
hostname(ADMN). This is used by the standard host lookup routine
gethostbyname(SLIB). 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_USE_INET6
This option causes gethostbyname(SLIB) to look for AAAA records
before looking for A records if none are found.
RES_ROTATE
This options causes the res_nsend() / res_send() to rotate the
list of nameservers in statp->nsaddr_list / _res.nsaddr_list.
RES_KEEPTSIG
This option causes res_nsendsigned() to leave the message un-
changed after TSIG verification; otherwise the TSIG record would
be removed and the header updated.
The res_ninit() / res_init() routine reads the configuration file (if
any; see resolver(SLIB)) to get the default domain name, search list and
the Internet address of the local name server(s). If no server is con-
figured, the host running the resolver is tried. The current domain name
is defined by the hostname if not specified in the configuration file; it
can be overridden by the environment variable LOCALDOMAIN. This environ-
ment 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 environment vari-
able (``RES_OPTIONS'') can be set to override certain internal resolver
options which are otherwise set by changing fields in the statp / _res
structure or are inherited from the configuration file's options command.
The syntax of the ``RES_OPTIONS'' environment variable is explained in
resolver(SLIB). Initialization normally occurs on the first call to one of
the other resolver routines.
The res_nquery() / res_query() functions provides interfaces to the serv-
er query mechanism. They constructs a query, sends it to the local serv-
er, awaits a response, and makes preliminary checks on the reply. The
query requests information of the specified type and class for the speci-
fied fully-qualified domain name dname. The reply message is left in the
answer buffer with length anslen supplied by the caller. res_nquery() /
res_query() return -1 on error or the length of the answer.
The res_nsearch() / res_search() routines make a query and awaits a re-
sponse like res_nquery() / res_query(), but in addition, it implements
the default and search rules controlled by the RES_DEFNAMES and
RES_DNSRCH options. It returns the length of the first successful reply
which is stored in answer or -1 on error.
The remaining routines are lower-level routines used by res_nquery() /
res_query(). The res_nmkquery() / res_mkquery() functions constructs a
standard query message and places it in buf. It 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.
The res_nsend() / res_send() / res_nsendsigned() routines sends a pre-
formatted query and returns an answer. It will call res_ninit() /
res_init() if RES_INIT is not set, send the query to the local name serv-
er, and handle timeouts and retries. Additionally, res_nsendsigned()
will use TSIG signatures to add authentication to the query and verify
the response. In this case, only one nameserver will be contacted. The
length of the reply message is returned, or -1 if there were errors.
res_nquery() / res_query(), res_nsearch() / res_search() and res_nsend()
/ res_send() return a length that may be bigger than anslen. In that case
the query should be retried with a bigger buffer. NOTE the answer to the
second query may be larger still so supplying a buffer that bigger that
the answer returned by the previous query is recommended.
answer MUST be big 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.
The functions res_ourserver_p() returns true when inp is one of
the servers in statp-_->nsaddr_list / _res.nsaddr_list.
The functions fp_nquery() / p_query() print out the query and any
answer in msg on fp. p_query() is equivalent to fp_nquery() with
msglen set to 512.
The function fp_resstat() prints out the active flag bits in
statp-_->options preceeded by the text ";; res options:" on file.
The functions res_hostalias() / hostalias() lookup up name in the file
referred to by the HOSTALIASES files return a fully qualified hostname if
found or NULL if not found or an error occurred. res_hostalias() uses
buf to store the result in, hostalias() uses a static buffer.
The functions res_nupdate() / res_update() take a list of ns_updrec
rrecp_in. Identifies the containing zone for each record and groups the
records according to containing zone maintaining in zone order then sends
and update request to the servers for these zones. The number of zones
updated is returned or -1 on error. Note that res_nupdate() will
perform TSIG authenticated dynamic update operations if they
key is not NULL.
The function res_findzonecut() discovers the closest enclosing zone cut
for a specified domain name, and finds the IP addresses of the zone's
master servers.
The functions res_nmkupdate() / res_mkupdate() take a linked list of
ns_updrec rrecp_in and construct a UPDATE message in buf. res_nmkupdate()
/ res_mkupdate() return the length of the constructed message on no error
or one of the following error values.
-1 An error occurred parsing rrecp_in.
-2 The buffer buf was too small.
-3 The first record was not a zone section or there was a section order
problem. The section order is S_ZONE, S_PREREQ and S_UPDATE.
-4 A number overflow occurred.
-5 Unknown operation or no records.
The functions res_nclose() / res_close() close any open files referenced
through statp / _res.
The dn_comp() function 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 size of the array pointed to by comp_dn is given by length.
The compression uses an array of pointers dnptrs to previously-compressed
names in the current message. The first pointer points to to the begin-
ning of the message and the list ends with NULL. The limit to the array
is specified by lastdnptr. A side effect of dn_comp() is to update the
list of pointers for labels inserted into the message as the name is com-
pressed. If dnptr is NULL, names are not compressed. If lastdnptr is
NULL, the list of labels is not updated.
The dn_expand() entry 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 the message. The uncom-
pressed name is placed in the buffer indicated by exp_dn which is of size
length. The size of compressed name is returned or -1 if there was an er-
ror.
The variables statp->res_h_errno / _res.res_h_errno and external variable
h_errno is set whenever an error occurs during 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 consist-
ing of the string parameter s, the constant string ": ", and a message
corresponding to the value of h_errno .
The hstrerror() function returns a string which is the message text cor-
responding to the value of the err parameter.
/etc/resolv.conf See resolver(SLIB).