[cups] [Printing-architecture] IPP Validate-Job operation and its implementation in CUPS

[Zdenek Dohnal]

Hi Ira,

thanks for the heads-up! I only checked IPP 2.0 standard and didn't
follow documents created later, which is a mistake...

Zdenek

On 10/22/20 2:48 AM, Ira McDonald wrote:
> Hi,
>
> Note that IPP/2.0 reducing Validate-Job from REQUIRED is a known
> technical error.
>
> IPP/2.0 (or any other later IPP spec) CANNOT reduce any REQUIRED operation
> conformance from IETF Standard IPP/1.1 (STD92/RFC 8010/RFC 8011).
>
> Cheers,
> - Ira
>
> /Ira McDonald (Musician / Software Architect)/
> /Chair - SAE Trust Anchors and Authentication TF
> /
> /Co-Chair - TCG Trusted Mobility Solutions WG/
> /Co-Chair - TCG Metadata Access Protocol SG
> /
> /Chair - Linux Foundation Open Printing WG
> Secretary - IEEE-ISTO Printer Working Group
> Co-Chair - IEEE-ISTO PWG Internet Printing Protocol WG
> IETF Designated Expert - IPP & Printer MIB
> Blue Roof Music / High North Inc
> http://sites.google.com/site/blueroofmusic
> <http://sites.google.com/site/blueroofmusic>
> http://sites.google.com/site/highnorthinc
> <http://sites.google.com/site/highnorthinc>
> mailto: blueroofmusic at gmail.com <mailto:blueroofmusic at gmail.com>
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>
>
> On Wed, Oct 21, 2020 at 4:49 PM Michael Sweet <msweet at msweet.org
> <mailto:msweet at msweet.org>> wrote:
>
>     Zdenek,
>
>     > On Oct 21, 2020, at 9:18 AM, Zdenek Dohnal <zdohnal at redhat.com
>     <mailto:zdohnal at redhat.com>> wrote:
>     > ...
>     > In this email I would like to ask if there can be a way how to
>     work around such printer issues within CUPS, which can be aligned
>     with RFC and PWG standards, and can be merged into
>     OpenPrinting/cups project.
>
>     Aside from maybe retrying the Validate-Job request if it fails the
>     first time, I'm not sure
>
>     > I have several ideas:
>     >
>     > 1) Validate-Job operation is 'only' recommended since IPP 2.0,
>     so the backend would have printed only warning if Validate-Job
>     failed and the IPP protocol used for communication is 2.0 or newer
>
>     Actually, while Validate-Job was listed as RECOMMENDED in IPP 2.0,
>     IPP Everywhere restores it to REQUIRED, just as STD 92 has
>     required it going all the way back to the IPP/1.0 experimental
>     version.
>
>     > 2) configurable retries for Validate-Job operation - this idea
>     came up from printer behavior (Validate-Job works after N retries)
>     and from knowledge there are already configurable variables in
>     backends via device uri
>
>     I'd rather it be automatic - either retry the Validate-Job
>     operation or just move on to printing without validation.
>
>     > 3) define a specific IPP_STATUS_* enum variable for failing
>     Validate-Job, let the backend fail if ipp_status is that variable
>     and let error-policy handle the possible retry
>
>     I'm not keen on "supporting" broken behavior.  Usually I've tried
>     to "gracefully degrade" in these situations, which would basically
>     mean option 2 without the retry (just attempt to validate and
>     continue if we don't get a valid response.
>
>     ________________________
>     Michael Sweet
>
>
>
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>
-- 
Zdenek Dohnal
Software Engineer
Red Hat Czech - Brno TPB-C