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;
}
}
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
3. strict quotation convention with escape option is added. (only 3.
contradicts the sec. 9.13 ".. instance-identifier is a subset of the
XPath ..")
Vladimir
On 10/21/2017 08:16 PM, Andy Bierman wrote:
On Sat, Oct 21, 2017 at 12:28 AM, Benoit Claise <[email protected]
<mailto:[email protected]>> 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>
--------------------------------------
Type: Technical
Reported by: Andy Bierman <[email protected]
<mailto:[email protected]>>
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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