RESOLVER

Section: C Library Functions (3)
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BSD mandoc
BSD 4  

NAME

res_ninit res_ourserver_p fp_resstat res_hostalias res_pquery res_nquery res_nsearch res_nquerydomain res_nmkquery res_nsend res_nupdate res_nmkupdate res_nclose res_nsendsigned res_findzonecut res_getservers res_setservers dn_comp dn_expand hstrerror res_init res_isourserver fp_nquery p_query hostalias res_query res_search res_querydomain res_mkquery res_send res_update res_close herror - resolver routines  

SYNOPSIS

Fd #include <sys/types.h> Fd #include <netinet/in.h> Fd #include <arpa/nameser.h> Fd #include <resolv.h> Fd #include <res_update.h> Vt typedef struct __res_state *res_state ;

Ft int Fn res_ninit res_state statp Ft int Fn res_ourserver_p const res_state statp const struct sockaddr_in *addr Ft void Fn fp_resstat const res_state statp FILE *fp Ft const char * Fn res_hostalias const res_state statp const char *name char *buf size_t buflen Ft int Fn res_pquery const res_state statp const u_char *msg int msglen FILE *fp Ft int Fn res_nquery res_state statp const char *dname int class int type u_char *answer int anslen Ft int Fn res_nsearch res_state statp const char *dname int class int type u_char * answer int anslen Ft int Fn res_nquerydomain res_state statp const char *name const char *domain int class int type u_char *answer int anslen Ft int Fo res_nmkquery Fa res_state statp Fa int op Fa const char *dname Fa int class Fa int type Fa const u_char *data Fa int datalen Fa const u_char *newrr Fa u_char *buf Fa int buflen Fc Ft int Fn res_nsend res_state statp const u_char *msg int msglen u_char *answer int anslen Ft int Fn res_nupdate res_state statp ns_updrec *rrecp_in Ft int Fn res_nmkupdate res_state statp ns_updrec *rrecp_in u_char *buf int buflen Ft void Fn res_nclose res_state statp Ft int Fn res_nsendsigned res_state statp const u_char *msg int msglen ns_tsig_key *key u_char *answer int anslen Ft int Fn res_findzonecut res_state statp const char *dname ns_class class int options char *zname size_t zsize struct in_addr *addrs int naddrs Ft int Fn res_getservers res_state statp union res_sockaddr_union *set int cnt Ft void Fn res_setservers res_state statp const union res_sockaddr_union *set int cnt Ft int Fn dn_comp const char *exp_dn u_char *comp_dn int length u_char **dnptrs u_char **lastdnptr Ft int Fn dn_expand const u_char *msg const u_char *eomorig const u_char *comp_dn char *exp_dn int length Ft const char * Fn hstrerror int err  

DEPRECATED

Fd #include <sys/types.h> Fd #include <netinet/in.h> Fd #include <arpa/nameser.h> Fd #include <resolv.h> Fd #include <res_update.h> Ft int Fn res_init void Ft int Fn res_isourserver const struct sockaddr_in *addr Ft int Fn fp_nquery const u_char *msg int msglen FILE *fp Ft void Fn p_query const u_char *msg FILE *fp Ft const char * Fn hostalias const char *name Ft int Fn res_query const char *dname int class int type u_char *answer int anslen Ft int Fn res_search const char *dname int class int type u_char *answer int anslen Ft int Fn res_querydomain const char *name const char *domain int class int type u_char *answer int anslen Ft int Fo res_mkquery Fa int op Fa const char *dname Fa int class Fa int type Fa const char *data Fa int datalen Fa struct rrec *newrr Fa u_char *buf Fa int buflen Fc Ft int Fn res_send const u_char *msg int msglen u_char *answer int anslen Ft int Fn res_update ns_updrec *rrecp_in Ft void Fn res_close void Ft void Fn 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 Fa statp and is used to control the behavior of these functions. Fa statp should be set to all zeros prior to the first call to any of these functions.

The functions Fn res_init , Fn res_isourserver , Fn fp_nquery , Fn p_query , Fn hostalias , Fn res_query , Fn res_search , Fn res_querydomain , Fn res_mkquery , Fn res_send , Fn res_update , Fn res_close and Fn herror are deprecated and are supplied for compatability with old source code. They use global configuration and state information that is kept in the structure Ft _res rather than that referenced through Ft statp .

Most of the values in Ft statp and Ft _res are initialized on the first call to Fn res_ninit / Fn res_init to reasonable defaults and can be ignored. Options stored in Ft statp->options / Ft _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., Fn res_ninit / Fn 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. (Fn res_nsend / Fn res_send does not do iterative queries and expects the name server to handle recursion.)
RES_DEFNAMES
If set, Fn res_nsearch / Fn res_search will append the default domain 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, Fn res_nsearch / Fn res_search will search for host names in the current domain and in parent domains; see hostname(7). This is used by the standard host lookup routine gethostbyname(3). 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(3) to look for AAAA records before looking for A records if none are found.
RES_ROTATE
This options causes the Fn res_nsend / Fn res_send to rotate the list of nameservers in Fa statp->nsaddr_list / Fa _res.nsaddr_list .
RES_KEEPTSIG
This option causes Fn res_nsendsigned to leave the message unchanged after TSIG verification; otherwise the TSIG record would be removed and the header updated.
RES_NOTLDQUERY
This option causes Fn res_nsearch to not attempt to resolve a unqualified name as if it were a top level domain (TLD). This option can cause problems if the site has "localhost" as a TLD rather than having localhost on one or more elements of the search list. This option has no effect if neither RES_DEFNAMES or RES_DNSRCH is set.

The Fn res_ninit / Fn res_init routine reads the configuration file (if any; see resolver(5)) to get the default domain name, search list and the Internet address of the local name server(s). If no server is configured, 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 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 environment variable (``RES_OPTIONS '' ) can be set to override certain internal resolver options which are otherwise set by changing fields in the Ft statp / Ft _res structure or are inherited from the configuration file's options command. The syntax of the ``RES_OPTIONS '' environment variable is explained in resolver(5). Initialization normally occurs on the first call to one of the other resolver routines.

The Fn res_nquery / Fn res_query functions provides interfaces to the server query mechanism. They 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 Fa type and Fa class for the specified fully-qualified domain name Fa dname . The reply message is left in the Fa answer buffer with length Fa anslen supplied by the caller. Fn res_nquery / Fn res_query return -1 on error or the length of the answer.

The Fn res_nsearch / Fn res_search routines make a query and awaits a response like Fn res_nquery / Fn 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 Ft answer or -1 on error.

The remaining routines are lower-level routines used by Fn res_nquery / Fn res_query . The Fn res_nmkquery / Fn res_mkquery functions constructs a standard query message and places it in Fa buf . It returns the size of the query, or -1 if the query is larger than Fa buflen . The query type Fa 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 Fa dname . Fa Newrr is currently unused but is intended for making update messages.

The Fn res_nsend / Fn res_send / Fn res_nsendsigned routines sends a pre-formatted query and returns an answer. It will call Fn res_ninit / Fn res_init if RES_INIT is not set, send the query to the local name server, and handle timeouts and retries. Additionally, Fn 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.

Fn res_nquery / Fn res_query , Fn res_nsearch / Fn res_search and Fn res_nsend / Fn res_send return a length that may be bigger than Fa 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.

Fa 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 function Fn res_ourserver_p returns true when Fa inp is one of the servers in Fa statp->nsaddr_list / Fa _res.nsaddr_list .

The functions Fn fp_nquery / Fn p_query print out the query and any answer in Fa msg on Fa fp . Fn p_query is equivalent to Fn fp_nquery with Fa msglen set to 512.

The function Fn fp_resstat prints out the active flag bits in Fa statp->options preceeded by the text ";; res options:" on Fa file .

The functions Fn res_hostalias / Fn 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. Fn res_hostalias uses Fa buf to store the result in, Fn hostalias uses a static buffer.

The functions Fn res_getservers and Fn res_setservers are used to get and set the list of server to be queried.

The functions Fn res_nupdate / Fn res_update take a list of ns_updrec Fa 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 Fn res_nupdate will perform TSIG authenticated dynamic update operations if the key is not NULL.

The function Fn 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 Fn res_nmkupdate / Fn res_mkupdate take a linked list of ns_updrec Fa rrecp_in and construct a UPDATE message in Fa buf . Fn res_nmkupdate / Fn res_mkupdate return the length of the constructed message on no error or one of the following error values.

-1
An error occurred parsing Fa rrecp_in .
-2
The buffer Fa 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 Fn res_nclose / Fn res_close close any open files referenced through Fa statp / Fa _res .

The Fn dn_comp function compresses the domain name Fa exp_dn and stores it in Fa comp_dn . The size of the compressed name is returned or -1 if there were errors. The size of the array pointed to by Fa comp_dn is given by Fa length . The compression uses an array of pointers Fa dnptrs to previously-compressed names in the current message. The first pointer points to to the beginning of the message and the list ends with NULL The limit to the array is specified by Fa lastdnptr . A side effect of Fn dn_comp is to update the list of pointers for labels inserted into the message as the name is compressed. If Fa dnptr is NULL , names are not compressed. If Fa lastdnptr is NULL , the list of labels is not updated.

The Fn dn_expand entry expands the compressed domain name Fa comp_dn to a full domain name. The compressed name is contained in a query or reply message; Fa msg is a pointer to the beginning of the message. Fa eomorig is a pointer to the first location after the message. The uncompressed name is placed in the buffer indicated by Fa exp_dn which is of size Fa length . The size of compressed name is returned or -1 if there was an error.

The variables Ft statp->res_h_errno / Ft _res.res_h_errno and external variable Ft 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 Fn herror function writes a message to the diagnostic output consisting of the string parameter Fa s , the constant string ": ", and a message corresponding to the value of Ft h_errno .

The Fn hstrerror function returns a string which is the message text corresponding to the value of the Fa err parameter.  

FILES

/etc/resolv.conf
See resolver(5).

 

SEE ALSO

gethostbyname(3), hostname(7), named(8), resolver(5); RFC1032, RFC1033, RFC1034, RFC1035, RFC974; SMM:11, ``Name Server Operations Guide for BIND''


 

Index

NAME
SYNOPSIS
DEPRECATED
DESCRIPTION
FILES
SEE ALSO

linux.jgfs.net manual pages