Re: [netmod] escapes - WAS: [Netconf] [Technical Errata Reported] RFC6536 (3862)

[Ladislav Lhotka <[e-mail]>]

Jernej Tuljak <[e-mail]> writes:

> I've read that section a couple of times now and I now agree with Martin 
> that "\*" is currently equivalent to '\*'. My reading would probably be 
> correct if there was no second comma in the text I quoted. Oh, well...
>
>     Within a double-quoted string (enclosed within " "), a backslash
>     character may introduce a special character, which depends on the
>     character that immediately follows the backslash:
>
> would be better, no?

IMO, current wording permits three defensible interpretations:

1. "\*" == '\*'
2. "\*" == '*'
3. "\*' is an error

So this should be clarified.

As I wrote, I'd prefer #3 because it would be the same as the behaviour of "\" in regex patterns.

Lada

>
> Jernej
>
> Dne 10.1.2014 15:31, piše Ladislav Lhotka:
>> On 10 Jan 2014, at 14:58, Jernej Tuljak <[e-mail]> wrote:
>>
>>> If this is true, then it is RFC6020 that needs a clarification on this. Namely, that the "special character" which follows a backslash need not be special and that it does not represent an escape sequence in such a case.
>>>
>>>    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
>>>
>>> My reading is that a backslash starts a YANG escape sequence and may therefore be removed during string dequoting. A "\*" ends up as *, which is not equivalent to '\*’.
>> In XSD regular expressions, which are also used by YANG, it is an error if a backslash plus something is not defined as an escape sequence. So I think YANG should behave the same for double-quoted string, i.e. a backslash followed by something else than the four characters listed above should be flagged as an error (“illegal escape”).
>>
>> Lada
>>
>>> Please move this discussion over to NETMOD it that's the case.
>>>
>>> Jernej
>>>
>>> Dne 10.1.2014 14:40, piše Martin Bjorklund:
>>>> Hi,
>>>>
>>>> This errata should be rejected.  "\*" is equvalent to '\*'.  \* in a
>>>> double quoted string is not an escape sequence, which means that the
>>>> characters are interpreted literally, i.e. the two characters \
>>>> followed by *.
>>>>
>>>> The same goes for errata 3863.
>>>>
>>>> /martin
>>>>
>>>> RFC Errata System <[e-mail]> wrote:
>>>>> The following errata report has been submitted for RFC6536,
>>>>> "Network Configuration Protocol (NETCONF) Access Control Model".
>>>>>
>>>>> --------------------------------------
>>>>> You may review the report below and at:
>>>>> http://www.rfc-editor.org/errata_search.php?rfc=6536&eid=3862
>>>>>
>>>>> --------------------------------------
>>>>> Type: Technical
>>>>> Reported by: Jernej Tuljak <[e-mail]>
>>>>>
>>>>> Section: 3.5.2.
>>>>>
>>>>> Original Text
>>>>> -------------
>>>>>       typedef matchall-string-type {
>>>>>         type string {
>>>>>           pattern "\*";
>>>>>         }
>>>>>         description
>>>>>           "The string containing a single asterisk '*' is used
>>>>>            to conceptually represent all possible values
>>>>>            for the particular leaf using this data type.";
>>>>>       }
>>>>>
>>>>> Corrected Text
>>>>> --------------
>>>>>       typedef matchall-string-type {
>>>>>         type string {
>>>>>           pattern '\*';
>>>>>         }
>>>>>         description
>>>>>           "The string containing a single asterisk '*' is used
>>>>>            to conceptually represent all possible values
>>>>>            for the particular leaf using this data type.";
>>>>>       }
>>>>>
>>>>> Notes
>>>>> -----
>>>>> As per RFC6020, Section 6.1.3., a backslash within a double-quoted
>>>>> string introduces a special character. The only valid escape sequences
>>>>> inside a double-quoted YANG string are: \n, \t, \" and \. As \* is not
>>>>> a valid escape sequence, a single quoted string should be used to
>>>>> specify the offending pattern statement's argument. The quotes could
>>>>> also be omitted.
>>>>>
>>>>> Instructions:
>>>>> -------------
>>>>> This errata is currently posted as "Reported". If necessary, please
>>>>> use "Reply All" to discuss whether it should be verified or
>>>>> rejected. When a decision is reached, the verifying party (IESG)
>>>>> can log in to change the status and edit the report, if necessary.
>>>>>
>>>>> --------------------------------------
>>>>> RFC6536 (draft-ietf-netconf-access-control-07)
>>>>> --------------------------------------
>>>>> Title : Network Configuration Protocol (NETCONF) Access Control Model
>>>>> Publication Date    : March 2012
>>>>> Author(s)           : A. Bierman, M. Bjorklund
>>>>> Category            : PROPOSED STANDARD
>>>>> Source              : Network Configuration
>>>>> Area                : Operations and Management
>>>>> Stream              : IETF
>>>>> Verifying Party     : IESG
>>>>>
>>> _______________________________________________
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>>> https://www.ietf.org/mailman/listinfo/netconf
>> --
>> Ladislav Lhotka, CZ.NIC Labs
>> PGP Key ID: E74E8C0C
>>
>>
>>
>>
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>

-- 
Ladislav Lhotka, CZ.NIC Labs
PGP Key ID: E74E8C0C