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NAME="NET-COMMON-TCPIP-MANPAGES-RESOLVER">resolver</H1
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>RESOLVER(3) System Library Functions Manual RESOLVER(3)
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>RESOLVER(3) System Library Functions Manual RESOLVER(3)
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NAME
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NAME
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res_query, res_search, res_mkquery, res_send, res_init, dn_comp,
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res_query, res_search, res_mkquery, res_send, res_init, dn_comp,
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dn_expand - resolver routines
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dn_expand - resolver routines
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SYNOPSIS
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SYNOPSIS
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#include <sys/types.h>
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#include <sys/types.h>
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#include <netinet/in.h>
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#include <netinet/in.h>
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#include <arpa/nameser.h>
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#include <arpa/nameser.h>
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#include <resolv.h>
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#include <resolv.h>
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int
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int
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res_query(char *dname, int class, int type, u_char *answer, int anslen);
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res_query(char *dname, int class, int type, u_char *answer, int anslen);
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int
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int
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res_search(char *dname, int class, int type, u_char *answer, int anslen);
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res_search(char *dname, int class, int type, u_char *answer, int anslen);
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int
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int
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res_mkquery(int op, char *dname, int class, int type, char *data,
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res_mkquery(int op, char *dname, int class, int type, char *data,
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int datalen, struct rrec *newrr, char *buf, int buflen);
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int datalen, struct rrec *newrr, char *buf, int buflen);
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int
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int
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res_send(char *msg, int msglen, char *answer, int anslen);
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res_send(char *msg, int msglen, char *answer, int anslen);
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int
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int
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res_init(void);
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res_init(void);
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int
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int
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dn_comp(char *exp_dn, char *comp_dn, int length, char **dnptrs,
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dn_comp(char *exp_dn, char *comp_dn, int length, char **dnptrs,
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char **lastdnptr);
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char **lastdnptr);
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int
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int
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dn_expand(u_char *msg, u_char *eomorig, u_char *comp_dn, u_char *exp_dn,
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dn_expand(u_char *msg, u_char *eomorig, u_char *comp_dn, u_char *exp_dn,
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int length);
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int length);
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DESCRIPTION
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DESCRIPTION
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These routines are used for making, sending, and interpreting query and
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These routines are used for making, sending, and interpreting query and
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reply messages with Internet domain name servers.
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reply messages with Internet domain name servers.
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Global configuration and state information that is used by the resolver
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Global configuration and state information that is used by the resolver
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routines is kept in the structure _res. Most of the values have reason-
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routines is kept in the structure _res. Most of the values have reason-
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able defaults and can be ignored. Options stored in _res.options are
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able defaults and can be ignored. Options stored in _res.options are
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defined in <resolv.h> and are as follows. Options are stored as a simple
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defined in <resolv.h> and are as follows. Options are stored as a simple
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bit mask containing the bitwise OR of the options enabled.
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bit mask containing the bitwise OR of the options enabled.
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RES_INIT True if the initial name server address and default domain
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RES_INIT True if the initial name server address and default domain
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name are initialized (i.e., res_init() has been called).
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name are initialized (i.e., res_init() has been called).
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RES_DEBUG Print debugging messages.
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RES_DEBUG Print debugging messages.
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RES_AAONLY Accept authoritative answers only. With this option,
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RES_AAONLY Accept authoritative answers only. With this option,
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res_send() should continue until it finds an authoritative
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res_send() should continue until it finds an authoritative
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answer or finds an error. Currently this is not imple-
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answer or finds an error. Currently this is not imple-
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mented.
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mented.
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RES_USEVC Use TCP connections for queries instead of UDP datagrams.
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RES_USEVC Use TCP connections for queries instead of UDP datagrams.
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RES_STAYOPEN Used with RES_USEVC to keep the TCP connection open
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RES_STAYOPEN Used with RES_USEVC to keep the TCP connection open
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between queries. This is useful only in programs that
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between queries. This is useful only in programs that
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regularly do many queries. UDP should be the normal mode
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regularly do many queries. UDP should be the normal mode
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used.
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used.
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RES_IGNTC Unused currently (ignore truncation errors, i.e., don't
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RES_IGNTC Unused currently (ignore truncation errors, i.e., don't
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retry with TCP).
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retry with TCP).
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RES_RECURSE Set the recursion-desired bit in queries. This is the
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RES_RECURSE Set the recursion-desired bit in queries. This is the
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default. (res_send() does not do iterative queries and
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default. (res_send() does not do iterative queries and
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expects the name server to handle recursion.)
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expects the name server to handle recursion.)
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RES_DEFNAMES If set, res_search() will append the default domain name
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RES_DEFNAMES If set, res_search() will append the default domain name
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to single-component names (those that do not contain a
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to single-component names (those that do not contain a
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dot). This option is enabled by default.
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dot). This option is enabled by default.
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RES_DNSRCH If this option is set, res_search() will search for host
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RES_DNSRCH If this option is set, res_search() will search for host
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names in the current domain and in parent domains; see
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names in the current domain and in parent domains; see
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hostname(7). This is used by the standard host lookup
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hostname(7). This is used by the standard host lookup
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routine gethostbyname(3). This option is enabled by
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routine gethostbyname(3). This option is enabled by
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default.
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default.
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RES_USE_INET6 Enables support for IPv6-only applications. This causes
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RES_USE_INET6 Enables support for IPv6-only applications. This causes
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IPv4 addresses to be returned as an IPv4 mapped address.
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IPv4 addresses to be returned as an IPv4 mapped address.
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For example, 10.1.1.1 will be returned as ::ffff:10.1.1.1.
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For example, 10.1.1.1 will be returned as ::ffff:10.1.1.1.
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The option is not meaningful on OpenBSD.
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The option is not meaningful on OpenBSD.
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The res_init() routine reads the configuration file (if any; see
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The res_init() routine reads the configuration file (if any; see
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resolv.conf(5)) to get the default domain name, search list, and the
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resolv.conf(5)) to get the default domain name, search list, and the
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Internet address of the local name server(s). If no server is config-
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Internet address of the local name server(s). If no server is config-
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ured, the host running the resolver is tried. The current domain name is
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ured, the host running the resolver is tried. The current domain name is
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defined by the hostname if not specified in the configuration file; it
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defined by the hostname if not specified in the configuration file; it
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can be overridden by the environment variable LOCALDOMAIN. This environ-
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can be overridden by the environment variable LOCALDOMAIN. This environ-
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ment variable may contain several blank-separated tokens if you wish to
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ment variable may contain several blank-separated tokens if you wish to
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override the search list on a per-process basis. This is similar to the
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override the search list on a per-process basis. This is similar to the
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search command in the configuration file. Another environment variable
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search command in the configuration file. Another environment variable
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RES_OPTIONS can be set to override certain internal resolver options
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RES_OPTIONS can be set to override certain internal resolver options
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which are otherwise set by changing fields in the _res structure or are
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which are otherwise set by changing fields in the _res structure or are
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inherited from the configuration file's options command. The syntax of
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inherited from the configuration file's options command. The syntax of
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the RES_OPTIONS environment variable is explained in resolv.conf(5).
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the RES_OPTIONS environment variable is explained in resolv.conf(5).
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Initialization normally occurs on the first call to one of the following
|
Initialization normally occurs on the first call to one of the following
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routines.
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routines.
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|
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The res_query() function provides an interface to the server query mecha-
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The res_query() function provides an interface to the server query mecha-
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nism. It constructs a query, sends it to the local server, awaits a
|
nism. It constructs a query, sends it to the local server, awaits a
|
response, and makes preliminary checks on the reply. The query requests
|
response, and makes preliminary checks on the reply. The query requests
|
information of the specified type and class for the specified fully qual-
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information of the specified type and class for the specified fully qual-
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ified domain name dname. The reply message is left in the answer buffer
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ified domain name dname. The reply message is left in the answer buffer
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with length anslen supplied by the caller.
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with length anslen supplied by the caller.
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|
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The res_search() routine makes a query and awaits a response like
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The res_search() routine makes a query and awaits a response like
|
res_query(), but in addition, it implements the default and search rules
|
res_query(), but in addition, it implements the default and search rules
|
controlled by the RES_DEFNAMES and RES_DNSRCH options. It returns the
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controlled by the RES_DEFNAMES and RES_DNSRCH options. It returns the
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first successful reply.
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first successful reply.
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|
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The remaining routines are lower-level routines used by res_query(). The
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The remaining routines are lower-level routines used by res_query(). The
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res_mkquery() function constructs a standard query message and places it
|
res_mkquery() function constructs a standard query message and places it
|
in buf. It returns the size of the query, or -1 if the query is larger
|
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
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than buflen. The query type op is usually QUERY, but can be any of the
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query types defined in <arpa/nameser.h>. The domain name for the query
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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
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is given by dname. newrr is currently unused but is intended for making
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update messages.
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update messages.
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|
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The res_send() routine sends a pre-formatted query and returns an answer.
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The res_send() routine sends a pre-formatted query and returns an answer.
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It will call res_init() if RES_INIT is not set, send the query to the
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It will call res_init() if RES_INIT is not set, send the query to the
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local name server, and handle timeouts and retries. The length of the
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local name server, and handle timeouts and retries. The length of the
|
reply message is returned, or -1 if there were errors.
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reply message is returned, or -1 if there were errors.
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|
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The dn_comp() function compresses the domain name exp_dn and stores it in
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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
|
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.
|
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
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The compression uses an array of pointers dnptrs to previously compressed
|
names in the current message. The first pointer points to the beginning
|
names in the current message. The first pointer points to the beginning
|
of the message and the list ends with NULL. The limit to the array is
|
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
|
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-
|
of pointers for labels inserted into the message as the name is com-
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pressed. If dnptr is NULL, names are not compressed. If lastdnptr is
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pressed. If dnptr is NULL, names are not compressed. If lastdnptr is
|
NULL, the list of labels is not updated.
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NULL, the list of labels is not updated.
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|
|
The dn_expand() entry expands the compressed domain name comp_dn to a
|
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
|
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-
|
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
|
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
|
length. The size of compressed name is returned or -1 if there was an
|
error.
|
error.
|
|
|
FILES
|
FILES
|
/etc/resolv.conf configuration file see resolv.conf(5).
|
/etc/resolv.conf configuration file see resolv.conf(5).
|
|
|
SEE ALSO
|
SEE ALSO
|
gethostbyname(3), resolv.conf(5), hostname(7), named(8)
|
gethostbyname(3), resolv.conf(5), hostname(7), named(8)
|
|
|
RFC1032, RFC1033, RFC1034, RFC1035, RFC1535, RFC974
|
RFC1032, RFC1033, RFC1034, RFC1035, RFC1535, RFC974
|
|
|
Name Server Operations Guide for BIND.
|
Name Server Operations Guide for BIND.
|
|
|
HISTORY
|
HISTORY
|
The res_query function appeared in 4.3BSD.
|
The res_query function appeared in 4.3BSD.
|
|
|
BSD June 4, 1993 BSD
|
BSD June 4, 1993 BSD
|
</PRE
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