inet6_opt_init()--Initialize Buffer Data for IPv6 Extension Header

  #include <netinet/in.h>

  int inet6_opt_init(void *extension_buffer,
                     socklen_t extension_length)

The inet6_opt_init() function returns the number of bytes needed for an extension header without any options. If extension_buffer is not NULL, it will also initialize the extension header's length field based on the length provided in extension_length.

Parameters

extension_buffer

(Input) Pointer to a buffer that contains the extension header.

extension_length

(Input) Length of the extension header pointed to by extension_buffer. Must be a positive multiple of 8.
This value is the total number of bytes in the buffer pointed to by extension_buffer.

Authorities

No authorization is required.

Return Value

inet6_opt_init() returns an integer. Possible values are:

• -1 (unsuccessful)
  
  
• n (successful), where n is the number of bytes needed for an empty extension header (header with no options)

Error Conditions

When inet6_opt_init() fails, errno can be set to one of the following:

Usage Notes

1. When called with extension_buffer as a NULL pointer, inet6_opt_init() only returns the number of bytes in an extension header with no options.
2. When called with a valid pointer for extension_buffer, inet6_opt_init() will initialize the entire extension header. It will set the length field of the options header to the size of the extension header, specified in extension_length, in addition to returning the current number of bytes set in the extension header.
3. inet6_opt_init() is normally called twice when building an options header.

   The first call is used to begin calculating the size of the extension header as follows:

        int currentlen, extlen;
        void *extbuf;
        currentlen = inet6_opt_init(NULL, 0);
   

   This is followed by the desired number of inet6_opt_append() calls to increment the calculated length and by a call to inet6_opt_finish() to calculate the final length to be used when actually initializing the extension header as follows:

        extlen = currentlen;
        extbuf = malloc(extlen); 
        currentlen = inet6_opt_init(extbuf, extlen);
   

Related Information

• inet6_opt_append()--Append New Option to IPv6 Extension Header
• inet6_opt_find()--Extract Option of Specified Type from IPv6 Extension Header
• inet6_opt_finish()--Finish Adding Options to IPv6 Extension Header
• inet6_opt_get_val()--Retrieve Data Item from an IPv6 Option
• inet6_opt_next()--Extract the Next Option from the IPv6 Extension Header
• inet6_opt_set_val()--Insert Data Items into IPv6 Option

[ Back to top | UNIX-Type APIs | APIs by category ]