Re: [netmod] [Technical Errata Reported] RFC6020 (4911)

[Martin Bjorklund <[e-mail]>]

Ladislav Lhotka <[e-mail]> wrote:
> 
> > On 18 Jan 2017, at 14:55, Martin Bjorklund <[e-mail]> wrote:
> > 
> > RFC Errata System <[e-mail]> wrote:
> >> The following errata report has been submitted for RFC6020,
> >> "YANG - A Data Modeling Language for the Network Configuration
> >> Protocol (NETCONF)".
> >> 
> >> --------------------------------------
> >> You may review the report below and at:
> >> http://www.rfc-editor.org/errata_search.php?rfc=6020&eid=4911
> >> 
> >> --------------------------------------
> >> Type: Technical
> >> Reported by: Ladislav Lhotka <[e-mail]>
> >> 
> >> Section: 6.1.3
> >> 
> >> Original Text
> >> -------------
> >> Within a double-quoted string (enclosed within " "), a backslash
> >> character introduces a special character, which depends on the
> >> character that immediately follows the backslash:
> >> 
> >> \n      new line
> >> \t      a tab character
> >> \"      a double quote
> >> \      a single backslash
> >> 
> >> 
> >> Corrected Text
> >> --------------
> >> Within a double-quoted string (enclosed within " "), a backslash
> >> character introduces a special character, which depends on the
> >> character that immediately follows the backslash:
> >> 
> >> \n      new line
> >> \t      a tab character
> >> \"      a double quote
> >> \      a single backslash
> >> 
> >> The backslash MUST NOT be followed by any other character.
> >> 
> >> Notes
> >> -----
> >> The text doesn't state whether other characters may follow the
> >> backslash, and if yes, what it means. Existing implementations have
> >> used three approaches:
> >> 
> >> 1. report an error if another character follows the backslash
> >> 2. keep only the character following the backslash, i.e., for example,
> >> "\x" is the same as "x".
> >> 3. keep both the backslash and the character following it.
> >> 
> >> This ambiguity is undesirable and YANG 1.1 [RFC 7950] explicitly
> >> adopted option #1. However, many modules are still being written using
> >> YANG version 1.0, so it is important to clarify this issue in RFC 6020
> >> as well.
> > 
> > I don't think this errata should be accepted.  As stated, the spec is
> > unclear, and YANG 1.1 has fixed this problem.  But it is not clear
> > that the original intention when RFC 6020 was written was #1.
> > Accepting this errata now would make existing implementations and
> > modules invalid.
> 
> The problem is that the spec is clearly ambiguous

Agreed.

> and it is
> impossible to decide whether such a module is valid or not and, if
> it is, what the other backslash-escaped characters mean. Existing
> implementations can already reject such modules - the fact that
> pyang (and probably other tail-f tools) adopted one interpretation
> doesn't mean that everybody does the same. 

This is exactly my point.

> > The solution moving forward is to use YANG 1.1.
> > 
> 
> YANG 1.0 modules continue to be written, and I think it is important
> to stop this problem from spreading further. I think tools should
> at least issue a warning because otherwise future upgrades to YANG
> 1.1 may become a nightmare - modules will suddenly break in
> unexpected places.

Sure, but that's a different story (I already added a warning for this
in pyang).

> If this erratum is rejected, what is the basis for accepting erratum
> #4909 that started this discussion?

That module relied on one interpretation, but as you write, the spec
is unclear and toold behave differently.  Thus, modules should avoid
this pattern.


/martin