res_query res_search res_mkquery res_send res_init dn_comp dn_expand dn_skipname ns_get16 ns_get32 ns_put16 ns_put32 - resolver routines
Global configuration and state information that is used by the
resolver routines is kept in the structure
Most of the values have reasonable defaults and can be ignored.
are defined in
and are as follows. Options are stored as a simple bit mask containing the bitwise ``or'' of the options enabled.
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 _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 following routines.
function provides an interface to 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 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.
routine makes a query and awaits a response like res_query (,);
but in addition, it implements the default and search rules controlled by the RES_DEFNAMES and RES_DNSRCH options. It returns the first successful reply.
The remaining routines are lower-level routines used by
The res_mkquery ();
function 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 In arpa/nameser.h . The domain name for the query is given by Fa dname . The Fa newrr_in argument is currently unused but is intended for making update messages.
routine sends a pre-formatted query and returns an answer. It will call res_init ();
if RES_INIT is not set, send the query to the local name server, and handle timeouts and retries. The length of the reply message is returned, or -1 if there were errors.
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 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 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.
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. 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.
function skips over a compressed domain name, which starts at a location pointed to by Fa comp_dn . The compressed name is contained in a query or reply message; Fa eom is a pointer to the end of the message. The size of compressed name is returned or -1 if there was an error.
function gets a 16-bit quantity from a buffer pointed to by Fa src .
function gets a 32-bit quantity from a buffer pointed to by Fa src .
function puts a 16-bit quantity Fa src to a buffer pointed to by Fa dst .
function puts a 32-bit quantity Fa src to a buffer pointed to by Fa dst .
and res_query ();
functions return the size of the response on success, or -1 if an error occurs. The integer Vt h_errno may be checked to determine the reason for error. See gethostbyname(3) for more information.
RFC1032 , RFC1033 , RFC1034 , RFC1035 , RFC974
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Created 1996-2021 by Maxim Chirkov
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