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

[Martin Bjorklund <[e-mail]>]

Balázs Lengyel <[e-mail]> wrote:
> 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>
> 
> 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.

For example, RFC 7950 says about integers in 9.2.1:

   An integer value is lexically represented as an optional sign ("+" or
   "-"), followed by a sequence of decimal digits.  If no sign is
   specified, "+" is assumed.

So, space characters (and other characters) are not allowed.  In XML,
whitespace has meaning, so:

   <foo>42</foo>

is not the same as

   <foo> 42 </foo>

Since the string " 42 " is not a legal integer lexical representation
according to 9.2.1, <foo> 42 </foo> is not a valid XML representation
for the integer foo.

> 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>

Yes, to be strict, these examples should have had some text that
explained that whitespace was added for readability.  New documents
will hopefully use the new artwork draft's rules instead.



/martin


> 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: [phone]              email: [e-mail]