[cups] PPD API: Status, future and alternatives to handle printer-specific options

[Till Kamppeter]

On 01/31/2017 12:19 PM, Michael Sweet wrote:
>> 2) What is the recommended way to handle printer-specific options in a print dialog? Which API should be used? (The implementation should support both "traditional" printers set up via PPD files and PPD-less printers like IPP Everywhere printers.)
>
> Use the new API.  CUPS maps old PPD options to IPP/IPP Everywhere options.
>

I have done some tests concerning getting capabilities and options via 
IPP, by taking several of my CUPS queues.

First, I run

ippfind

and see all my CUPS queues represented by ipp://... URIs plus some IPP 
network printers.

Then I select one of my CUPS queues and run

lpadmin -p ippcupstest -E -v ipp://... -m everywhere

with the respective ipp://... URI from the output of ippfind.

This makes CUPS polling the IPP get-printer-attributes record and 
generate a PPD file from this information. With one queue this failed, 
with others I got a PPD file but it has less options and choices than 
the original PPD file of the queue, meaning that building a print dialog 
based on the IPP record instead of the original PPD seems to be inferior.

To be sure that it is not the fault of CUPS' PPD generator I polled the 
IPP record directly via

ipptool -tv ipp://... get-printer-attributes.test > ipp-rec.txt

Now I got the attributes and found out that for the missing items in the 
generated PPD partially the IPP get-printer-attributes output and 
partially CUPS' PPD generator is the culprit. So I reported the 
following CUPS issues:

https://github.com/apple/cups/issues/4950

CUPS queues emulate IPP Everywhere printers: Required IPP attributes not 
provided

https://github.com/apple/cups/issues/4951

CUPS queues emulate IPP Everywhere printers: Number of color modes in 
capabilities reported by IPP very restricted

https://github.com/apple/cups/issues/4952

CUPS queues emulate IPP Everywhere printers: Not all details of the PPD 
file made available as IPP attributes

https://github.com/apple/cups/issues/4953

CUPS PPD generator for driverless printing does not find all options and 
choices

With this fixed one could probably very well use IPP Everywhere to 
populate print dialogs with the printer-specific information.

But to completely get rid of PPDs one would need to have CUPS support 
print queues with filters but without PPDs, where the data format list 
which the printer reports by IPP determines the destination format for 
the filter chain.

I tried already an approach like this in cups-filters, but it used a 
System V Interface script and this concept was removed from CUPS for 
security reasons.

    Till