Re: [core] Benjamin Kaduk's Discuss on draft-ietf-core-senml-data-ct-05: (with DISCUSS and COMMENT)
Carsten Bormann <cabo@tzi.org> Tue, 12 October 2021 13:37 UTC
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From: Carsten Bormann <cabo@tzi.org>
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Date: Tue, 12 Oct 2021 15:37:16 +0200
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To: Benjamin Kaduk <kaduk@mit.edu>
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Subject: Re: [core] Benjamin Kaduk's Discuss on draft-ietf-core-senml-data-ct-05: (with DISCUSS and COMMENT)
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Hi Ben, thank you for bringing up a number of important issues. > ---------------------------------------------------------------------- > DISCUSS: > ---------------------------------------------------------------------- > > I have a couple points for discussion, essentially relating to how much > we're diverging from HTTP and to what extent the specifics of the > divergence should be specifically mentioned in the document. > > (1) I'd like to dig a little more into the analogy with HTTP and > whether we are artificially limiting ourselves: currently we only allow > 0 or 1 content-codings to be specified, but per > https://www.ietf.org/archive/id/draft-ietf-httpbis-semantics-19.html#name-content-encoding > the HTTP ecosystem permits multiple codings to be applied in turn to the > same representation. While the sensor data values are likely to be > relatively small and applying multiple content-codings is not likely to > be useful in such a scenario, this seems like something where we should > only consciously diverge from HTTP, rather than inadvertently doing so. I agree that this should be handled (if only for application/json@deflate@aes128gcm and similar cases). We discussed this in the previous interim and it seems we like the syntax I proposed in the previous sentence. Combining the numerous changes needed with addressing Christer’s comments on the Abstract: https://github.com/core-wg/senml-data-ct/pull/8 > (2) Let's also discuss whether we want to reuse ABNF rule names from > HTTP while having the rule content diverge, without specific enumeration > of the divergence. So far I found instances where this document does > not allow HTAB or obs-text in places that draft-ietf-httpbis-semantics > does, which may well be the right way to spell the rule, but seems to > merit a little discussion. Very good point. I’m not sure the ABNF behind “ABNF rule names from HTTP” is stable enough that we need to stick with it in all cases. I was certainly surprised by the recent change to parameters = *( OWS ";" OWS [ parameter ] ) (which makes sequences of ";" legal; see also section B.2 in -semantics.) and wonder whether we should follow this change (and why!?). Httpbis-semantics uses modified ABNF anyway; so there is no way to have exactly the same ABNF. But it is worthwhile pointing out that legacy 8-bit text and HTAB have no place in the strings used in this protocol and therefore are not allowed. I added a comment: -; Cleaned up from RFC 7231: +; Cleaned up from RFC 7231, only leaving SP as blank space, and +; removing legacy 8-bit characters: The other difference from RFC 2616 and its descendants is the absence of “quoted-pair” from the “quoted-string” production, which indeed can be discussed. (May need to discuss this in the interim tomorrow for final resolution.) > ---------------------------------------------------------------------- > COMMENT: > ---------------------------------------------------------------------- > > Do we want to comment anywhere about the situation where an > implementation receives a message using an IANA-registered numeric > content-format that is "too new" for that implementation to know about? (Should have a discussion about error handling in the interim tomorrow. But generally, the important thing is that the implementation *know* that it needs to be updated to understand.) > It also feels a little weird that we have to end up using the > text-string encoding of a decimal number for the Content-Format, even > for the CBOR representation of SenML structures, but I guess that's what > RFC 8428 intended and not worth trying to change. We started out with a numeric encoding, but then noticed that SenML is usually very specific about only allowing a single data type per field. > Abstract > > I'm somewhat sympathetic to the gen-art reviewer's contention that the > new field is not indicating the "Content-Format" of the binary data > values (since Content-Format is a defined term in CoAP and SenML is > claimed to not be limited to CoAP usage). Perhaps we could switch > around the order of description, i.e., "for indicating the Internet > media type (including parameters) of these binary data values (i.e., the > CoAP Content-Format that would apply when CoAp is used), as well as any > content-coding that is applied"? This is addressed in https://github.com/core-wg/senml-data-ct/pull/8, but not exactly following your blueprint. The term “content format” is still used both for a “Content-Format number” and a “Content-Format-String”. > > Section 3 > > * a CoAP Content-Format identifier in decimal form with no leading > zeros (except for the value "0" itself). This value represents an > unsigned integer in the range of 0-65535, similar to the CoRE Link > Format [RFC6690] "ct" attribute). > > Should we also reference > https://datatracker.ietf.org/doc/html/rfc7252#section-7.2.1 which is > where the "ct" link attribute is actually defined? I spent a bit of > time looking for it in 6690 itself only to discover that it was removed > in draft-ietf-core-link-format-07 with remark "Moved [...] to the base > CoAP specification". Good point. YYY > > The CoAP Content-Format number provides a simple and efficient way to > indicate the type of the data. [...] > > If we're limited to string representation, is it really "efficient" in a > CBOR context? That’s not what the sentence is about :-), but “11050” is still more efficient than "application/json@deflate”. > Section 6 > > ; Cleaned up from RFC 7231: > > (per the DISCUSS,) I'm a bit anti-enthused about saying "cleaned up" without saying what > changed (i.e., whether it's just refactoring, or actual changes to the > rule like requiring specifically *SP instead of OWS that allows HTAB as > well). See above. > Section 7 > > These security considerations are well-thought-out and nicely written. > Thank you! > > I think there are some (rare) situations where individual media-type > (specifications) have their own security considerations, but I'm not > really convinced that we need to mention that/incorporate them by > reference, here. > > NITS > > Section 1 > > The receiver is expected to know how to interpret the data in the > "vd" field based on the context, e.g., name of the data source and > out-of-band knowledge of the application. However, this context may > not always be easily available to entities processing the SenML pack. > > I'd consider adding ", especially if the pack is propagated to multiple > entities". That is a bit implied in the context of SenML, but it doesn’t hurt to say it again. field based on the context, e.g., name of the data source and out-of-band knowledge of the application. However, this context may not always be -easily available to entities processing the SenML pack. To facilitate +easily available to entities processing the SenML pack, especially if +the pack is propagated over time and via multiple entities. To facilitate automatic interpretation it is useful to be able to indicate an Internet > Section 2 > > Content-Coding: A name registered in the HTTP Content Coding > registry [IANA.http-parameters] as specified by Section 8.5 of > [RFC7230], indicating an encoding transformation with semantics > further specified in Section 3.1.2.1 of [RFC7231]. [...] > > (I expect that the RFC Editor will be able to replace the references to > point to draft-ietf-httpb-semantics if it has been published before this > document.) (With the actual changes in this document, I’m not sure that is a mechanical operation. But let’s wait for httpbis-semantics to emerge from EDIT.) > Section 4 > > up to the end of the pack otherwise. Resolution (Section 4.6 of > [RFC8428]) of this base field is performed by adding its value with > the label "ct" to all Records in this range that carry a "vd" field > but do not already contain a Content-Format ("ct") field. > > The conjugation "resolution" does not actually appear in RFC 8428 > itself, just discussion of "resolved records" and "to resolve the > records". It might be helpful to tweak things so that we don't rely on > the reader knowing the irregular conjugation (but I don't have any good > ideas off the top of my head)... -pack otherwise. Resolution ({{Section 4.6 of -senml}}) of this base +pack otherwise. The process of resolving ({{Section 4.6 of -senml}}) this base The changes that are not already accepted in PR 8 are in https://github.com/core-wg/senml-data-ct/pull/9 Grüße, Carsten
- [core] Benjamin Kaduk's Discuss on draft-ietf-cor… Benjamin Kaduk via Datatracker
- Re: [core] Benjamin Kaduk's Discuss on draft-ietf… Carsten Bormann
- Re: [core] Benjamin Kaduk's Discuss on draft-ietf… Benjamin Kaduk
- Re: [core] Benjamin Kaduk's Discuss on draft-ietf… Carsten Bormann