Re: [Spud] discovery

[Brian Trammell <[e-mail]>]

hi Aaron,

> On 19 Mar 2015, at 11:48, Aaron Falk <[e-mail]> wrote:
> 
> The draft

... where "the draft" is draft-hildebrand-spud-prototype ...

> doesn't say much about how one efficiently determines whether the other end is SPUD-capable so that an application can know whether it can use it.

No, it doesn't.

> Has anyone given thought to this?

Yes, I have...

I think for the most part that this question is (1) very important but (2) mostly orthogonal to that we're trying to answer in spud-prototype.

Initially, I would expect that discovery works the same way that it does for any other user of the transport layer: you either have a URL, or a name and a port, or some information from your application-layer protocol's discovery service, which includes "uses x-over-SPUD" in its semantics.

Dynamically discovering a SPUD endpoint might make sense if a server port / URL schema is assigned to a service over X or a service over x-over-SPUD. In this case, the magic number we've selected makes SPUD server probing by the client possible: a SPUD packet is neither valid UTF-8, UTF-16, UTF-32, ASN.1 BER or DER, DTLS, NTP, DNS, DHCP, TFTP, or Bittorrent. This is not an exhaustive list, but we haven't found a protocol over UDP that is likely to consider d8 00 00 d8 as the first four bytes anything other than an error.

Maybe we should mention this in the draft, but I think it's the *next* problem to solve.

Cheers,

Brian