Re: IPP Validate-Job operation and its implementation in CUPS

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From: Zdenek Dohnal <[email protected]>
To: Michael Sweet <[email protected]>
Cc: "The CUPS developer list." <[email protected]>,
 "[email protected]"
 <[email protected]>,
 "The CUPS user discussion list." <[email protected]>,
 Ira McDonald <[email protected]>
Message-ID: <[email protected]>
Subject: Re: [Printing-architecture] IPP Validate-Job operation and its
 implementation in CUPS
References: <[email protected]>
 <[email protected]>
In-Reply-To: <[email protected]>

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Hi Mike,

thank you for the comments!

I'll implement both approaches for option 2 (validate two times and end
with error if fails x validate once and move to printing no matter of
the result), see what will work for the customer and then create PR in
Openprinting/cups for review.

Thank you again and have a nice day!

Zdenek

On 10/21/20 10:49 PM, Michael Sweet wrote:
> Zdenek,
>
>> On Oct 21, 2020, at 9:18 AM, Zdenek Dohnal <[email protected]> wrote:
>> ...
>> In this email I would like to ask if there can be a way how to work arou=
nd such printer issues within CUPS, which can be aligned with RFC and PWG s=
tandards, 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=20
>
>> I have several ideas:
>>
>> 1) Validate-Job operation is 'only' recommended since IPP 2.0, so the ba=
ckend would have printed only warning if Validate-Job failed and the IPP pr=
otocol used for communication is 2.0 or newer
> Actually, while Validate-Job was listed as RECOMMENDED in IPP 2.0, IPP Ev=
erywhere 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 f=
rom printer behavior (Validate-Job works after N retries) and from knowledg=
e there are already configurable variables in backends via device uri
> I'd rather it be automatic - either retry the Validate-Job operation or j=
ust 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 "gra=
cefully degrade" in these situations, which would basically mean option 2 w=
ithout the retry (just attempt to validate and continue if we don't get a v=
alid response.
>
> ________________________
> Michael Sweet
>
>
>
--=20
Zdenek Dohnal
Software Engineer
Red Hat Czech - Brno TPB-C


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