Re: [netmod] Whitespace in XML encoding - allowed ?

Ladislav Lhotka <lhotka@nic.cz> Tue, 09 October 2018 10:37 UTC

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From: Ladislav Lhotka <lhotka@nic.cz>
To: =?utf-8?Q?Bal=C3=A1zs?= Lengyel <balazs.lengyel@ericsson.com>, "netmod\@ietf.org" <netmod@ietf.org>
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Date: Tue, 09 Oct 2018 12:37:37 +0200
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Subject: Re: [netmod] Whitespace in XML encoding - allowed ?
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Balázs Lengyel <balazs.lengyel@ericsson.com> writes:

> Hello,
>
> Recently we came up against a problem where a certain implementation did not accept the
> following:
>
> <with-defaults xmlns="...">
>     report-all
> </with-defaults>
>
> while it did accept 
>
> <with-defaults xmlns="...">report-all</with-defaults>

The "with-defaults" leaf is modelled as an enumeration in RFC 6243
(sec. 5), so the lexical representation is the assigned name,
i.e. "report-all". So the behaviour above is correct according to the
spec.

On the other hand, this looks like a good place for applying the Postel
principle because enum names must not have any leading or trailing
whitespace, so no confusion can ever arise if this whitespace is
stripped.

Lada

>
> I am unsure whether YANG's XML encoding allows whitespace before and after a leaf's value? In
> RFC7950 it does not say yes or no. I have found the following examples that seem to allow
> preceding/following whitespace:
>
> https://tools.ietf.org/html/rfc7950#section-4.2.9
>
>        <status xmlns="http://example.com/system">
>          The image example-fw-2.3 is being installed.
>        </status>
>
> https://tools.ietf.org/html/rfc7950#section-7.16.3
>
>          <reporting-entity>
>            /ex:interface[ex:name='Ethernet0']
>          </reporting-entity>
>
> https://tools.ietf.org/html/rfc6243#appendix-A.3.1
>
>         <with-defaults
>          xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-with-defaults">
>           report-all
>         </with-defaults>
>
> It is problematic that this is not clarified. IMHO this should be clarified in an errata to rfc7950.
> Chose one:
>
> 1 It is not allowed to add preceding or following whitespace after the value of a leaf/leaf-list. 
>  Note that some text documents may add whitespace to Netconf examples to avoid long
>  lines, 
>  however this extra whitespace MUST NOT be present in the actual Netconf encoding.
> 2 It is not allowed to add preceding or following whitespace after the value of a leaf/leaf-list.
> 3 It is allowed to add preceding or following whitespace after the value of a leaf/leaf-list except
>  for string based types, where the whitespace could be part of the leaf's value itself..
>
> What do you think?
>
> regards Balazs
>
> -- 
> Balazs Lengyel                       Ericsson Hungary Ltd.
> Senior Specialist
> Mobile: +36-70-330-7909              email: Balazs.Lengyel@ericsson.com 
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-- 
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67