Re: [lwip-devel] Extended udp_recv callback

[Jakob Stoklund Olesen]

Kieran Mansley wrote:
> On Tue, 2009-01-13 at 15:59 +0100, Jakob Stoklund Olesen wrote:
>> I would like to add two arguments to the udp_recv() callback function. I
>> am receiving multicast and unicast UDP packets, and I would like to know
>> the destination IP address and receiving interface.
> 
> Can you explain more about why you need this?  It's quite unusual for an
> application-visible interface to include these sorts of details.

I am integrating Apple's mDNSResponder code with lwIP. The multicast DNS
daemon needs to know if a DNS query was sent to a multicast or unicast
address. It also needs to know the receiving interface, so it can reply
with udp_sendto_if() on the same network.

Since multicast DNS is link local, replies should not be sent on all
networks. Sometimes replies are sent as multicast, so you cannot trust
udp_sendto() and ip_route() to pick the correct interface.

I see what you mean: Most applications don't need the information, so we
don't want to pollute the API. Is there perhaps a better way of making
this information available?

Regards,
/stoklund