Using libbgpdump - obtain aspath?

Hi Rob,

In the entry data structure, there is a field called 'attr'. This 
contains various attributes, including the AS PATH:

see bgpdump_attr.h:
struct attr
{
   <snip>
   struct aspath         *aspath;
}

struct aspath
{
   u_int8_t              asn_len;
   int                   length;
   int                   count;
   caddr_t               data;
   char                  *str;
};

The 'data' is the raw attribute, but libbgpdump also helpfully fills in 
'str' as a decoded string representation of the AS Path (using function 
process_attr_aspath_string).

So to access it, quoting from what bgpdump.c and example.c does:

if (entry->attr && entry->attr->len) {
     if( (entry->attr->flag & ATTR_FLAG_BIT(BGP_ATTR_AS_PATH) ) !=0) {
         printf("ASPATH: %s\n",entry->attr->aspath->str);
     }
}

Hope this helps, if you need some more help with it, just let me know.

Colin

(bgpdump maintainer)


On 06-11-2023 19:59, Rob Ballantyne wrote:
> Hello All,
> 
>    I’ve just started looking at libbgpdump for a project where I will be 
> parsing MRT/BGP data.
> 
>    I’ve managed, following the example/advice I’ve seen, to get a basic 
> loop running through an update file from the repository working.
> 
>    However, I don’t seem to be able to find the ASPATH component in the 
> parsed data structure.
> 
>    I can see the type/subtype of the data block is 
> BGPDUMP_TYPE_ZEBRA_BGP/BGPDUMP_SUBTYPE_ZEBRA_BGP_MESSAGE.I can also see 
> that the BGPDUMP_BODY is a discriminated union based on these values.  I 
> can see that BGPDUMP_ENTRY.attr should probably contain an ASPATH but it 
> doesn’t seem to be set ever.
> 
>    Should I be expecting the ASPATH to be set in this case?  Should I be 
> doing something different (calling some init function after discovering 
> the BGPDUMP_BODY is of the right type?).
> 
>    Thanks!
> 
> Rob
>