Wireshark · Wireshark-dev: Re: [Wireshark-dev] Protocol Col / Info col error

[Guy Harris <guy@xxxxxxxxxxxx>]

On Mar 31, 2009, at 10:45 AM, vinayak kamath wrote:

>   iDataLen = tvb_length(tvb); /* get length of packet */

That's the amount of captured packet data in the packet, which could  
be smaller than the length of the packet, as the capture might have  
been done with a "snapshot length" or "slice length" that caused a  
maximum of N bytes of packet data to be captured, discarding all the  
data following it.

You want tvb_reported_length().

>   if ( IsABCMessage(tvb, iDataLen)) /* check if it is a ABC  message  
> */
> {
>  if (check_col(pinfo->cinfo,COL_PROTOCOL))  // #######This is NULL,  
> asa a result it doesn't enter the if condition

What is the "This" in "This is NULL"?  check_col() returns a Boolean  
value, not a pointer, so it's true or false, not null or non-null.

Note also that check_col() will not always return true - it should do  
so the first time the dissector is called, but won't necessarily be  
true on times it's called after that.  (And it's possible that, in the  
future, it won't return true the first time the dissector is called.)