[bind10-dev] DNS message API: how to handle to-be-truncated case

[JINMEI Tatuya / 神明達哉]

At Wed, 30 Sep 2009 00:31:24 +0000,
Evan Hunt <each at isc.org> wrote:

> > A performance-sensitive client code that must expect truncation should
> > still be pretty simple:
> >   message.allow_truncation();
> >   message.to_wire();  // always succeed.  it may be an incomplete msg with TC
> >   message.sendto(somewhere);
> 
> This seems reasonable to me.  How does the caller find out the message was
> incomplete, though?

In this context, the caller doesn't bother to know that:-).  But when
a caller explicitly needs to do something based on whether the message
is complete or not, it would be able to possible by checking the TC
flag:

   if (message.get_tc()) { // returns true if TC is set
     // message is truncated.  do something special.
   }

> (Side note:  Doesn't "message.sendto()" kind of imply that the message has
> to be converted to wire format first?  I'm not sure why it has to be two
> steps.  Could the sendto() routine simply call to_wire() when it was
> needed?)

Hmm, I see the point, we may want to allow that shortcut.  Although
the above example is only for highlighting the point and the "message"
object I'm current thinking won't actually have a "sendto" method,
I'll keep this point in my mind.

Thanks,

---
JINMEI, Tatuya