res_mkquery()--Place Domain Query in Buffer

 #include <sys/types.h>
 #include <netinet/in.h>
 #include <arpa/nameser.h>
 #include <resolv.h>

 int res_mkquery(int  operation,
                 char *domain_name,
                 int  class,
                 int  type,
                 char *search_data,
                 int  search_data_length,
                 struct rrec *reserved,
                 char *query_buffer,
                 int  query_buffer_length)

The res_mkquery() function is used to make standard query messages (DNS packets) for name servers.

Parameters

operation

(Input) The query operation desired. This gets put into OPCODE in the header of the packet. Common values are listed below (see <arpa/nameser.h> for all possible values):

ns_o_query or QUERY

Standard query request. (This value is almost always used.)

domain_name

(Input) The pointer to the name of the domain.

class

(Input) The class of data being looked for. Common values are listed below (see <arpa/nameser.h> for all possible values):

ns_c_in or C_IN	Specifies the ARPA Internet.
ns_c_any or C_ANY	This is the wildcard match.

type

(Input) The type of request being made. Common values are listed below (see <arpa/nameser.h> for all possible values):

ns_t_a or T_A	Host address.
ns_t_aaaa	IPv6 address.
ns_t_ns or T_NS	Authoritative server.
ns_t_cname or T_CNAME	Canonical name.
ns_t_soa or T_SOA	Start of authority zone.
ns_t_wks or T_WKS	Well-known service.
ns_t_ptr or T_PTR	Domain name pointer.
ns_t_hinfo or T_HINFO	Host information.
ns_t_mx or T_MX	Mail routing information.
ns_t_txt or T_TXT	Text strings.
ns_t_any or T_ANY	Wildcard match.

search_data

(Input) A buffer containing the data for inverse queries. It is NULL for types other than IQUERY.

search_data_length

(Input) The length of search_data. It is NULL for types other than IQUERY.

reserved

(Input) A reserved and currently unused parameter. It is always a NULL pointer (defined for compatibility).

query_buffer

(Output) A pointer to a user-supplied location containing the query message.

query_buffer_length

(Input) The length of query_buffer.

Authorities:

No authorization is required.

Return Value

res_mkquery() returns an integer. Possible values are:

• -1 (unsuccessful)
  
  
• n (successful), where n is the size of the query.

Error Conditions

When the res_mkquery() function fails, errno can be set to one of the following:

[EFAULT]

The system detected a pointer that was invalid while attempting to access an input pointer.

[EINVAL]

The _res appears to be initialized but the reserved field is not set to zeros.

[EMSGSIZE]

The message buffer was too small. The query was larger than the value of query_buffer_length

Usage Notes

1. res_mkquery() creates a standard query message (DNS packet). It fills in the header fields, compresses the domain name into the question section, and fills in the other question fields. This query message is placed in query_buffer.
   
   
2. res_mkquery() calls res_init() if the _res structure has not been initialized.
   
   
3. res_mkquery() expects EBCDIC data as input. The output from res_mkquery() is also EBCDIC.
   
   
4. In a thread-enabled environment, the _res structure is shared among all threads within a process.

Related Information

• res_nmkquery()--Place Domain Query in Buffer
  
  
• res_hostalias()--Retrieve the host alias
  
  
• res_init()--Initialize _res Structure
  
  
• res_close()--Close Socket and Reset _res Structure
  
  
• res_query()--Send Domain Query
  
  
• res_search()--Search for Domain Name
  
  
• res_send()--Send Buffered Domain Query
  
  
• res_xlate()--Translate DNS Packets

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