Re: [netmod] instance file format and etags/timestamps, xml attributes

Balázs Lengyel <balazs.lengyel@ericsson.com> Fri, 30 November 2018 12:28 UTC

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Thread-Topic: [netmod] instance file format and etags/timestamps, xml attributes
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Subject: Re: [netmod] instance file format and etags/timestamps, xml attributes
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Hello Jurgen,

Thanks for the comments. See answers below.

regards Balazs

On 2018. 11. 28. 11:01, Juergen Schoenwaelder wrote:
draft-ietf-netmod-yang-instance-file-format-00.txt says:

   The JSON format SHALL follow the format of the reply returmed for a
   RESTCONF GET request directed at the datastore resource:
   {+restconf}/data.  ETags and Timestamps SHOULD NOT be included, but
   if present SHOULD be ignored.

I assume that you mean the JSON content in the message-body of the
HTTP Response message for GET message. My understanding is that ETags
and Timestamps (what are these precisely?) are carried in the HTTP
header. So how could the ETag or 'Timestamps' be in the JSON data?  We
should not mess up the HTTP difference between header data and payload
data.
BALAZS: OK, I will correct it. Yes, it is the payload that I want to include in the instance data.
I thought that lower level etags/timestamps are returned inside the get-response payload. On re-reading RFC8040 I see my mistake.


I also do not fully understand the text concerning the XML format.

   The XML format SHALL follow the format returned for a NETCONF GET
   operation.  The <data> anydata (which is not part of the real data
   itself) SHALL contain all data that would be inside the <data>
   wrapper element of a reply to the <get> operation.  XML attributes
   SHOULD NOT be present, however if a SW receiving a YANG Based
   Instance data file encounters XML attributes unknown to it, it MUST
   ignore them, allowing them to be used later for other purposes.

It is unclear what exactly is the instance data - the entire reponse?
Everything inside <data>? Everything inside and including <data>? I
assume the second sentence is trying to say the later but I do not
find it very clear not does it seem to be right. The examples show to
content of the NETCONF <rpc-reply><data/></rpc-reply> inside a <data>
container that belongs to the instance data format (two times <data>
but in different namespaces).

BALAZS: I will try to reword it to clarify the issue. How about:

An instance data set is made up of header part and content-data. The content-data is all data inside the anydata data node.

The header part is defined by the -ietf-instance-data module while the content-data is defined by the target YANG modules. The content-data  SHALL contain all data that would be inside the <data> wrapper element of a reply to the <get> operation .  

I hope this conveys that content data excludes the <data> wrapper element from the get-reply.


It is also unclear to me why XML attributes are to be removed. Why is
that? If I snapshot <operational>, why should I remove important
information such origin annotations? And removing attributes is
actually plain wrong if you consider that attributes carry XML
namespaces.

BALAZS: You are right, although some attributes might be absent in some use cases.  E.g. namespace as you pointed out is always needed. However e.g. origin may be present if the instance data is a snapshot of the operational datastore, but it may be absent if the instance data is used to document readOnly server capabilities.

So I propose to change the text to:

Some XML attributes (e.g. metadata like origin) MAY be absent. 
        SW handling YANG Instance data MUST ignore   
        XML attributes unknown to it, allowing them to be used 
        later for other purposes.
/js

PS: I am also concerned about the revision being not fine grained
    enough to be useful. I would love to have a much more precise
    timestamp telling me when the instance data was recorded. I would
    probably replace 'revision' with simply a 'timestamp' or add next
    to a 'revision' a more fine grained 'timestamp'.

BALAZS: I agree that in some use cases a timestamp would be useful e.g. diagnostic data from a real live YANG server.
However in other use cases like documenting factory default, defining default configuration to be preloaded or documenting server capabilities I see no need for the timestamp. It is not interesting exactly at which hour/minute/second the server capabilities were documented.
So while I would not like to add the timestamp in the draft, the draft documents, that additional metadata like a timestamp may be added to the instance data set.


-- 
Balazs Lengyel                       Ericsson Hungary Ltd.
Senior Specialist
Mobile: +36-70-330-7909              email: Balazs.Lengyel@ericsson.com