dn_expand()--Expand Domain Name

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

 int dn_expand(unsigned char *message_pointer,
               unsigned char *end_of_message,
               unsigned char *compressed_domain_name,
               unsigned char *expanded_domain_name,
               int  answer_buffer_length)

The dn_expand() function is used to expand a compressed domain name.

Authorities and Locks

None.

Parameters

message_pointer

(Input) The pointer to the beginning of a DNS packet.

end_of_message

(Input) The pointer to the end of the DNS packet.

compressed_domain_name

(Input) The pointer to the compressed domain name within the DNS packet.

expanded_domain_name

(Output) The pointer to the expanded domain name.

answer_buffer_length

(Input) The size of the expanded_domain_name buffer.

Return Value

dn_expand() returns an integer. Possible values are:

• -1 (unsuccessful)
  
  
• n (successful), where n is the size of the compressed domain name.

  The dn_expand() routine expands the domain name pointed to by compressed_domain_name. The result is placed in expanded_domain_name.

Error Conditions

When the dn_expand() function fails, it does not set specific errno or h_errno values. An error occurs under the following conditions:

• NULL pointer(s) passed to the function.
  
  
• Invalid pointer(s) passed to the function.
  
  
• expanded_domain_name too small for the expanded domain name.
  
  
• end_of_message reached before the domain name could be expanded.

Usage Notes

1. The compressed domain name size is returned rather than the expanded domain name size because it is used to parse through the DNS packet.
   
   
2. dn_expand() uses end_of_message to insure that it doesn't run past the end of the DNS packet.
   
   
3. dn_expand() expects EBCDIC data as input. The output from dn_expand() is also EBCDIC.

Related Information

• dn_comp()--Compress Domain Name
  
  
• dn_find()--Search for Compressed Domain Name
  
  
• dn_skipname()--Skip over Compressed Domain Name

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