Re: [netmod] [Technical Errata Reported] RFC7950 (5157)

[Vladimir Vassilev <[e-mail]>]

On 10/24/2017 07:06 PM, Andy Bierman wrote:

>
>
> On Tue, Oct 24, 2017 at 5:27 AM, Vladimir Vassilev 
> <[e-mail] <mailto:[e-mail]>> wrote:
>
>     On 10/24/2017 03:42 AM, Andy Bierman wrote:
>
>
>
>         On Mon, Oct 23, 2017 at 4:57 AM, Vladimir Vassilev
>         <[e-mail] <mailto:[e-mail]>
>         <mailto:[e-mail]
>         <mailto:[e-mail]>>> wrote:
>
>             On 10/23/2017 01:35 PM, Martin Bjorklund wrote:
>
>                 Vladimir Vassilev <[e-mail]
>         <mailto:[e-mail]>
>                 <mailto:[e-mail]
>         <mailto:[e-mail]>>> wrote:
>
>                     Hello,
>
>                     I would like to use the occasion of this Errata
>         report to
>                     point out
>                     some additional issues with the
>         instance-identifier type
>                     definition.
>
>                     IMO the instance-identifier built-in type has 2
>         additional
>                     problems
>                     that can be addressed with alternative and
>         significantly
>                     more radical
>                     errata or fixed in a new version of YANG.:
>
>                     Problem 1: The obvious limitation inherited from
>         Xpath 1.0
>                     - inability
>                     to escape single or double quote characters. In Xpath
>                     world this
>                     limitation is worked around by use of concat()
>         which is
>                     not available
>                     in the YANG 1.1 instance-identifier definition. 2
>         examples
>                     of this
>                     limitation:
>
>                     1. It is impossible to create value of type
>                     instance-identifier
>                     referencing nodes in lists with key string values
>                     containing both a
>                     single and a double quote characters e.g.
>                     ...<interface><name>"It's
>                     valid string!"</name></interface>.
>
>                     2. Another example of the same problem would be a
>         leaf of type
>                     instance-identifier referencing another leaf of type
>                     instance-identifier. With 2 references it works
>         provided
>                     one is
>                     encoded with single quotes and the other with
>         double but it is
>                     impossible to create third e.g.
>
>                     YANG:
>
>                          list id-list {
>                            key "id";
>
>                            leaf id {
>                                type instance-identifier;
>                            }
>                          }
>
>
>
>
>         Although the instance-identifier is problematic, it is rarely
>         used at all,
>         let alone using it as a list key.
>
>     It is used as a key in ietf-alarms /alarms/alarm-list/alarm.
>
>
>         The XPath mixed-quotes problem is well-known, and the suggested
>         solution seems to be use the "concat" function
>
>            /foo/bar[name=concat("It's a", ' "valiid" string')]
>
>         Not very user friendly, is it?
>
>     I think people naming their interfaces "It's a valid string!" can
>     take it. Prettier escaping solutions are available e.g. C string
>     but it will require more work then a line in the next YANG version
>     RFC. IMO solution is needed either concat or an alternative one.
>
>     Practical reason: YANG 1.1 can not create instance-identifier to
>     the alarm /alarms/alarm-list/alarm[...
>     resource="/interfaces/interface[name='eth0']"]. And this is not
>     the "That's a valid string!" named interface. The "That's a valid
>     string!" interface alarms can not be reported as a valid
>     ietf-alarms instance-identifier based resource alarm at all.
>
>
>
>
> Actually the XPath designers made a reasonable trade-off by using 
> concat as the solution to
> a problem that rarely happens.   It is up to the IETF to define YANG 
> in a way that does
> not ignore the XPath solutions.
Yes. How about some proper rules mandating th use of quotes and concat 
like: 1. Only allow use of double quotes when there is single quote 
present. 2. Only use concat when there is both single and double quotes 
present to split the string into 1 char single quote strings and the rest.

Then  /foo/bar[name=concat('It',"'",'s a valid string!"')] is the only 
possible canonic representation for all implementations and the solution 
is solving the rare problem without reinventing the wheel.

Vladimir
>
>
> Andy
>
>
>
>
>
>                     Data:
>
>                     * /top/id-list[id="/top/list[idx='4']"]
>
>                     *
>         /top/id-list[id="/top/id-list[idx='/top/list[idx=4]'"]
>                     <assuming the
>                     * proposed errata is also in effect>
>
>                     * <next reference not possible with YANG 1.1>
>
>                     Problem 2: The instance-identifier type lacks
>         canonical
>                     form (which
>                     makes it the only data type with implementation
>         dependent
>                     representation at the data level ... think of the
>         integer
>                     types
>                     allowing optional spaces between the digits). This
>         is in
>                     fact the only
>                     built-in data type that allows the server
>         implementation
>                     to change the
>                     configuration data replacing double quotes with
>         single or
>                     the other
>                     way around. Inserting white spaces where you did
>         not have
>                     them when
>                     the configuration was submitted. You can not
>         simply read a
>                     configuration and use fast data comparison without
>         schema
>                     support just
>                     because of this type. This is useless flexibility for
>                     simple data
>                     type.
>
>                     And this can be fixed if:
>
>                     1. white spaces in instance-identifiers are prohibited
>
>
>                     2. list key predicates are required in
>         alphabetical order
>
>                 Or perhaps use the order the keys are defined in the data
>                 model (the
>                 "keys" statement").
>
>             This is an option but then the e.g. xpath2instid() function
>             implementations will need schema support.
>
>
>
>         All the YANG tools I have seen generate the predicates in YANG
>         key order.
>
>     Yes.
>
>     If Xpath came with a canonical form definition (prohibiting
>     spaces, redundant duplication of namespace prefixes in children,
>     order of predicates, canonical quotation rule, and some
>     flexibility as of the node prefix semantics) we would not need to
>     have this discussion. Seems no other modeling language of
>     hierarchical data has reusable instance-identifier datatype with
>     the necessary properties and I can see this as something that can
>     go in separate RFC specifying generic data type making canonic
>     definition from Xpath that YANG can reuse. In that case the
>     alphabetic order makes sense moving some constraints into the
>     generic definition of the type one can validate without the
>     context schema but it is not of significant importance.
>
>         The issue of canonical instance-identifier has been discussed
>         many times,
>         and it is not possible to require the usage of specific
>         prefixes in XML.
>         (Note that Lada fixed this for JSON in RFC 7951)
>
>     Yes.
>
>
>         Only the string + expanded names can be properly compared in
>         XML, not the literal string
>         representing the XPath expression.
>
>     Yes.
>
>     I do not see the need of major rework just making the Xpath subset
>     rules stricter with canonical requirement and either allowing
>     concat() (also with canonic rule producing predictable result e.g.
>     to be used only for escaping single quotes and prohibiting double
>     quotes in predicates otherwise). Even with RFC7951 prefix rules
>     added in the instance-identifier can still be a valid Xpath subset
>     requiring trivial prefix replacements so that it can be used with
>     non-YANG aware XML tools keeping that option open.
>
>     Vladimir
>
>
>
>             Vladimir
>
>
>
>         Andy
>
>
>                     3. strict quotation convention with escape option is
>                     added. (only
>                     3. contradicts the sec. 9.13 "..
>         instance-identifier is a
>                     subset of
>                     the XPath ..")
>
>                 I would like to change one more thing - I think it is
>                 unfortunate that
>                 the lexical representation depends on the lexical context;
>                 specifically that prefixes declared in the XML instance
>                 document is
>                 used.  This applies also to identityref.  YANG 2.0
>         should use
>                 the same
>                 encoding as JSON does for these datatypes.
>
>
>
>                 /martin
>
>
>
>                     Vladimir
>
>                     On 10/21/2017 08:16 PM, Andy Bierman wrote:
>
>
>                         On Sat, Oct 21, 2017 at 12:28 AM, Benoit Claise
>                         <[e-mail] <mailto:[e-mail]>
>         <mailto:[e-mail] <mailto:[e-mail]>>
>                         <mailto:[e-mail]
>         <mailto:[e-mail]> <mailto:[e-mail]
>         <mailto:[e-mail]>>>>
>                         wrote:
>
>                              Dear all,
>
>                              Shall I validate this one?
>
>
>
>                         To add more context, this relates to the the
>         RESTCONF
>                         JSON vs. XML
>                         discussions in the NETCONF WG.
>
>                            leaf broken {
>                                type union {
>                                  type int32;
>                                  type string;
>                               }
>                            }
>
>                         If all values of key leaf "broken" are sent as
>         strings
>                         in an
>                         instance-identifier,
>                         then the int32 value may not match in all
>                         implementations, instead of
>                         the string.
>                         Allowing numbers as literals in addition to quoted
>                         strings allows the
>                         sender
>                         to be specific, and all implementations to be
>         consistent.
>
>
>                              Regards, Benoit
>
>
>
>                         Andy
>
>                                  The following errata report has been
>                         submitted for RFC7950,
>                                  "The YANG 1.1 Data Modeling Language".
>
>                                  --------------------------------------
>                                  You may review the report below and at:
>         http://www.rfc-editor.org/errata/eid5157
>         <http://www.rfc-editor.org/errata/eid5157>
>                         <http://www.rfc-editor.org/errata/eid5157
>         <http://www.rfc-editor.org/errata/eid5157>>
>                                
>          <http://www.rfc-editor.org/errata/eid5157
>         <http://www.rfc-editor.org/errata/eid5157>
>                         <http://www.rfc-editor.org/errata/eid5157
>         <http://www.rfc-editor.org/errata/eid5157>>>
>
>                                  --------------------------------------
>                                  Type: Technical
>                                  Reported by: Andy Bierman
>         <[e-mail] <mailto:[e-mail]>
>                         <mailto:[e-mail]
>         <mailto:[e-mail]>>
>                                  <mailto:[e-mail]
>         <mailto:[e-mail]>
>                         <mailto:[e-mail]
>         <mailto:[e-mail]>>>>
>
>                                  Section: 14
>
>                                  Original Text
>                                  -------------
>                                     key-predicate-expr  =
>         node-identifier *WSP
>                         "=" *WSP
>                                  quoted-string
>
>                                  Corrected Text
>                                  --------------
>                                     key-predicate-expr  =
>         node-identifier *WSP
>                         "=" *WSP
>                                           (quoted-string / integer-value /
>                         decimal-value)
>
>                                  Notes
>                                  -----
>                                  An instance identifier is forced to
>         specify
>                         every key value to
>                                  be a string
>                                  even though the YANG key leaf type
>         could be a
>                         numeric type.
>                                  XPath does not require a quoted
>         string here,
>                         just YANG.
>
>                                  Old:  /top/list[idx="4"]
>                                  New: /top/list[idx=4]
>
>                                  Instructions:
>                                  -------------
>                                  This erratum 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
>                                  can log in to change the status and
>         edit the
>                         report, if necessary.
>
>                                  --------------------------------------
>                                  RFC7950 (draft-ietf-netmod-rfc6020bis-14)
>                                  --------------------------------------
>                                  Title               : The YANG 1.1 Data
>                         Modeling Language
>                                  Publication Date    : August 2016
>                                  Author(s)           : M. Bjorklund, Ed.
>                                  Category            : PROPOSED STANDARD
>                                  Source              : NETCONF Data
>         Modeling
>                         Language
>                                  Area                : Operations and
>         Management
>                                  Stream              : IETF
>                                  Verifying Party     : IESG
>                                  .
>
>
>
>
>
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