Re: [DNSOP] [Ext] I-D Action: draft-ietf-dnsop-svcb-https-05.txt

Ben Schwartz <bemasc@google.com> Mon, 10 May 2021 22:38 UTC

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From: Ben Schwartz <bemasc@google.com>
Date: Mon, 10 May 2021 15:38:11 -0700
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To: Mark Andrews <marka@isc.org>
Cc: Joe Abley <jabley@hopcount.ca>, dnsop <dnsop@ietf.org>, Pieter Lexis <pieter.lexis@powerdns.com>
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Subject: Re: [DNSOP] [Ext] I-D Action: draft-ietf-dnsop-svcb-https-05.txt
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On Mon, May 10, 2021 at 3:14 PM Mark Andrews <marka@isc.org> wrote:

>
>
> > On 11 May 2021, at 02:56, Ben Schwartz <bemasc=
> 40google.com@dmarc.ietf.org> wrote:
>
...

> > To see why I favor two-pass, consider a SvcParam whose wire format value
> is defined to be CBOR, represented as JSON in the zone file.  JSON is
> defined as UTF-16, and allows strings containing any character from the
> Basic Multilingual Plane.  It also allows various kinds of backslash
> escaping including " \" " for quotes within strings, and "\uD834\uDD1E" for
> extended unicode codepoints.  A one-pass parser must somehow integrate this
> into the flow of zone file parsing.  The easiest way is to simply disable
> all RFC1035-style escapes and line-breaks for the duration of the
> SvcParamValue, but this is a major breach of standard zone file practice,
> and raises questions about how to store UTF-16 characters in a zone file.
> Alternatively, we could somehow combine both RFC1035 and JSON escaping, but
> if this is even possible, it would seem to require writing a new
> RFC1035+JSON hybrid parser.  I also think these behaviors would be
> confusing to users, who would have to try to understand how this new
> integrated escaping works in order to author zone files containing either
> kind of escape.
>
> Yet you fail to mention that the following
>
> 3. Encoding
>
>    JSON text SHALL be encoded in Unicode.  The default encoding is
>    UTF-8.
>
> The UTF-16 JSON strings values are encoded as UTF-8.  UTF-8 in zone files
> usually ends up being \DDD for non-ASCII and ASCII control octets once it
> has gone from text -> wire -> text to put everything into ASCII printable.
> Zone files are ASCII documents.  If you are using the values in other
> contexts you may convert the
> wire forms differently.
>

It sounds like you're saying that \DDD escape processing would happen
entirely before JSON parsing.  That would be a two-pass design, just like
what the current draft says.  Consider a json value of {"a":"\\123"} (two
'\' due to escaping within a JSON string).  It sounds like, in your plan,
this would be escaped to something like jsonKey={"a":"\092\092123"}, or
perhaps jsonKey={"a":"\\\\123"}.  Those are both valid in the current SVCB
draft.

I think your solution here is exactly what is proposed in the current SVCB
draft, so I fully support it.  However, it necessarily results in
double-escaping, which is the initial concern raised in this thread.