Re: [core] question on draft-softgear-core-coapa-00 (CoAP/A)

[Carsten Bormann <[e-mail]>]

On Aug 5, 2013, at 13:25, Olaf Bergmann <[e-mail]> wrote:

> Given I want to contact an ASCII-only
> node (e.g. a sensor listed in my home's RD), where do I know that I need
> to encode the request in CoAP/A? (Or, when using transcoding proxies,
> where does the proxy know that it has to encode/decode the message?)

If you are a client, that information should come out of the transport selection information in the URI (which we haven't completed discussing).

If you are a server that speaks a protocol like TCP that would be useful for carrying ASCII streams but also for a "native" CoAP version, there probably should be some detection mechanism.
In draft-bormann-core-coap-tcp-00, there are signatures (not in the crypto sense) that could be used for that detection.

The signature that I proposed happens to be valid base64url (except for whitespace (\r\n), which probably should be ignored by a CoAP/A implementation), so it would need to be changed to work as a differentiator.

To make CoAP/A a bit more robust, I also would propose
-- allowing # at the start of a message (effectively, reliably discarding zero-length messages), so implementations can make a habit of start- and end-delimiting messages.
-- considering adding a checksum (Hmm.)

Grüße, Carsten