On 10/24/2017 03:42 AM, Andy Bierman wrote:
On Mon, Oct 23, 2017 at 4:57 AM, Vladimir Vassilev
<vladi...@transpacket.com <mailto:vladi...@transpacket.com>> wrote:
On 10/23/2017 01:35 PM, Martin Bjorklund wrote:
Vladimir Vassilev <vladi...@transpacket.com
<mailto:vladi...@transpacket.com>> 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.
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
<bcla...@cisco.com <mailto:bcla...@cisco.com>
<mailto:bcla...@cisco.com <mailto:bcla...@cisco.com>>>
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>>
--------------------------------------
Type: Technical
Reported by: Andy Bierman <a...@yumaworks.com
<mailto:a...@yumaworks.com>
<mailto:a...@yumaworks.com
<mailto:a...@yumaworks.com>>>
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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