PostScript Printer Application

INTRODUCTION

This repository contains a Printer Application for PostScript printers that uses PAPPL to support IPP printing from multiple operating systems. In addition, it uses the resources of cups-filters 2.x (filter functions in libcupsfilters, libppd) and pappl-retrofit (encapsulating classic CUPS drivers in Printer Applications). This work (or now the code of pappl-retrofit) is derived from the hp-printer-app.

Your contributions are welcome. Please post issues and pull requests.

This Printer Application is a working model for

A non-raster Printer Application: Destination format is PostScript, a high-level/vector format. Input data in PostScript or PDF is accepted and needed conversion is done without any inbetween raster steps.
A Printer Application which uses the new filter functions of cups-filters 2.x. Filter functions are library functions derived from the CUPS filters and contain decades of development and refinement starting from the introduction of CUPS in 2000.
A retro-fit Printer Application for classic CUPS drivers, in this case the simplest form of only PPD files for PostScript printers. It lists PPD files from repositories included in the Snap, loads the PPD needed for the actual printer, extracts options from the PPD to display them in the web interface, accepts job settings as IPP attributes, and inserts the PostScript code provided by the PPD correctly into the output data stream.
A Printer Application which does not pass through raw (input format is printer's native format) jobs. To assure that always the PostScript code of the PPD file is inserted into the output stream, we call the printer's native format "application/vnd.printer-specific" which does not exist as input format, so "application/postscript" input is forced through the pstops() filter function.
An expandable Printer Application: The user can add PPD files via the administration web interface to support additional printer models.

Further properties are:

To avoid the need to re-invent the code for forking into sub-processes so that we can pass data through a sequence of filters, we create a filter function to send the data off to the printer and form a chain of the actually converting filter function (one of pstops() and pdftops()) with this filter function using the filterChain() filter function.
For PWG/Apple Raster input we use raster callbacks so that the processing is streaming, allowing for large and even infinitely long jobs. We use libppd functions to insert the PPD option's PostScript code in the output stream and the filterPOpen() function to create a file descriptor for the libppd functions to send data off to the device.
The PostScript Printer Application Snap has all PostScript PPD files of the foomatic-db and HPLIP projects built-in, so most PostScript printer PPDs which usually come with Linux Distributions. To avoid that this vast number of PPDs blows up the size of the Snap, we highly compress them using pyppd. Note that some PPDs use certain CUPS filters for extra functionality. These filters are included in the Snap, so the extra functionality is supported (in most cases PIN-protected printing). The user can add additional PPDs without needing to rebuild the Snap (see below).
We use the printer's IEEE-1284 device ID to identify at first that it is a PostScript printer (via CMD: field) to see whether it is supported at all and only then check via make and model whether we explicitly support it with a PPD. PostScript printers for which there is no PPD get a generic PPD assigned. By the check of the CMD: field before make/model lookup we assure that if PostScript is provided by an add-on module that the module is actually installed.
Standard job IPP attributes are mapped to the PPD option settings best fitting to them so that users can print from any type of client (like for example a phone or IoT device) which only supports standard IPP attributes and cannot retrive the PPD options. Trays, media sizes, media types, and duplex can get mapped easily, but when it comes to color and quality it gets more complex, as relevant options differ a lot in the PPD files. Here we use an algorithm which automatically (who wants hand-edit ~10000 PPDs for the assignments) finds the right set of option settings for each combination of print-color-mode (color/monochrome), print-quality (draft/normal/high), and print-content-optimize (auto/photo/graphics/text/text-and-graphics) in the PPD of the current printer. So you have easy access to the full quality or speed of your printer without needing to deal with printer-specific option settings (the original options are still accessible via web admin interface).
The printer capabilities for a given printer model (a "driver" in the Printer Application) are not static throughout the life of the print queue set up in the Printer Application. The user can configure via a page in the web admin interface which hardware accessories (extra paper trays, duplex unit, finishers, ...) are installed on the printer and the Printer Application updates the driver data structure and with this the printer capabilities. The response to a get-printer-attributes IPP request gets updated appropriately.
PostScript is a full-fledged programming language and many PostScript printers allow querying settings of options and the presence of installable hardware accessories executing appropriate PostScript code. If a setting can get queried, the manufacturer puts the needed PostScript code into the PPD file, together with the queriable option. These queries are supported by the web interface of the Printer Application.
Available printer devices are discovered (and used) with CUPS' backends and not with PAPPL's own backends. This way quirk workarounds for USB printers with compatibility problems are used (and are editable) and PostScript output can get sent to the printer via IPP, IPPS (encrypted!), and LPD in addition to socket (usually port 9100). The SNMP backend can get configured (community, address scope).
If you have an unusual system configuration or a personal firewall your printer will perhaps not get discovered. In this situation the fully manual "Network Printer" entry in combination with the hostname/IP field can be helpful.

Remark

This Printer Application and its snapping is derived from the hp-printer-app, which uses the "avahi-observe" Snap interface to access DNS-SD. This does not work for registering printers. In this Printer Application this is already corrected to "avahi-control".

To Do

On the "Add PPD files" page in the list of already added user PPD files mark which ones are actually used by a printer which got set up in the Printer Application, to avoid that the user removes these files.
Human-readable strings for vendor options (Needs support by PAPPL: Issue #58: Localization support)
Internationalization/Localization (Needs support by PAPPL: [Issue

58: Localization

support](https://github.com/michaelrsweet/pappl/issues/58))
SNMP Ink level check via ps_status() function (Needs support by PAPPL: Issue #83: CUPS does IPP and SNMP ink level polls via backends, PAPPL should have functions for this)
Build options for cups-filters, to build without libqpdf and/or without libppd, the former will allow to create the Snap of this Printer Application without downloading and building QPDF

THE SNAP

Installing and building

To just run and use this Printer Application, simply install it from the Snap Store:

sudo snap install --edge ps-printer-app

Then follow the instructions below for setting it up.

To build the Snap by yourself, in the main directory of this repository run

snapcraft snap

This will download all needed packages and build the PostScript Printer Application. Note that PAPPL (upcoming 1.0) and cups-filters (upcoming 2.0) are pulled directly from their GIT repositories, as there are no appropriate releases yet. This can also lead to the fact that this Printer Application will suddenly not build any more.

NOTE: There is a bug in Ubuntu Groovy (20.10) that prevents it from building Snaps, see this discussion on the Snapcraft forum. The problem is already solved but did not make it into Groovy yet.

Any older (like 20.04) or newer (like 21.04) Ubuntu version should work.

To install the resulting Snap run

sudo snap install --dangerous ps-printer-app_1.0_amd64.snap

Setting up

The Printer Application will automatically be started as a server daemon.

Enter the web interface

http://localhost:8000/

Use the web interface to add a printer. Supply a name, select the discovered printer, then select make and model. Also set the installed accessories, loaded media and the option defaults. Accessory configuration and option defaults can also offen get polled from the printer.

Then print PDF, PostScript, JPEG, Apple Raster, or PWG Raster files with

ps-printer-app FILE

or print with CUPS, CUPS (and also cups-browsed) discover and treat the printers set up with this Printer Application as driverless IPP printers (IPP Everywhere and AirPrint).

You can also add PPD files without rebuilding the Snap, either by using the "Add PPD files" button in the web interface or by manually copying PPD files:

sudo cp PPDFILE /var/snap/ps-printer-app/common/ppd/

After manually copying (or removing) PPD files you need to restart the server or in the web interface, on the "Add PPD files" page click the "Refresh" button at the bottom. This adds the changes to the internal driver list.

On the "Add Printer" page in the drop-down to select the driver, user-added PPD files are marked "USER-ADDED". When setting up a printer with automatic driver selection, user-added PPD files are preferred.

PPDFILE in the command line above cannot only be a single PPD file but any number of single PPD files, .tar.gz files containing PPDs (in arbitrary directory structure) and PPD-gemerating executables which are usually put into /usr/lib/cups/driver. You can also create arbitrary sub-directory structures in /var/snap/ps-printer-app/current/ppd/ containing the mentioned types of files. Only make sure to not put any executables there which do anything else than listing and generating PPD files.

Note that with the web interface you can only manage individual PPDs (uncompressed or compressed with gzip) in the /var/snap/ps-printer-app/current/ppd/ itself. Archives, executables, or sub-directories are not shown and appropriate uploads not accepted. This especially prevents adding executables without root rights.

Any added PPD file must be for PostScript printers, as non-PostScript PPD files are for CUPS drivers and so they would need additional files in order to work and such files are not supported by this Printer Application. The "Add PPD files" page shows warnings if such files get uploaded.

See

ps-printer-app --help

for more options.

Use the "-o log-level=debug" argument for verbose logging in your terminal window.

You can add files to /var/snap/ps-printer-app/common/usb/ for additional USB quirk rules. Edit the existing files only for quick tests, as they get replaced at every update of the Snap (to introduce new rules).

You can edit the /var/snap/ps-printer-app/common/cups/snmp.conf file for configuring SNMP network printer discovery.

BUILDING WITHOUT SNAP

You can also do a "quick-and-dirty" build without snapping and without needing to install PAPPL, cups-filters 2.x, and pappl-retrofit into your system. You need a directory with the latest GIT snapshot of PAPPL, the latest GIT snapshot of cups-filters, and the latest GIT snapshot of pappl-retrofit (master branches of each). They all need to be compiled (./autogen.sh; ./configure; make), installing not needed. Also install the header files of all needed libraries (installing "libcups2-dev" should do it).

In the directory with ps-printer-app.c run the command line

gcc -o ps-printer-app ps-printer-app.c $PAPPL_SRC/pappl/libpappl.a $CUPS_FILTERS_SRC/.libs/libppd.a $CUPS_FILTERS_SRC/.libs/libcupsfilters.a $PAPPL_RETROFIT_SRC/.libs/libpappl-retrofit.a -ldl -lpthread  -lppd -lcups -lavahi-common -lavahi-client -lgnutls -ljpeg -lpng16 -ltiff -lz -lm -lusb-1.0 -lpam -lqpdf -lstdc++ -I. -I$PAPPL_SRC/pappl -I$CUPS_FILTERS_SRC/ppd -I$CUPS_FILTERS_SRC/cupsfilters -I$PAPPL_RETROFIT_SRC/pappl/retrofit -L$CUPS_FILTERS_SRC/.libs/ -L$PAPPL_RETROFIT_SRC/.libs/

There is also a Makefile, but this needs PAPPL, cups-filters 2.x, and pappl-retrofit to be installed into your system.

Run

./ps-printer-app --help

When running the non-snapped version, by default, PPD files are searched for in

/usr/share/ppd/
/usr/lib/cups/driver/
/var/lib/ps-printer-app/ppd/

The last path is used when adding PPD files using the "Add PPD files" page in the web interface.

You can set the PPD_PATHS environment variable to search other places instead:

PPD_PATHS=/path/to/my/ppds:/my/second/place ./ps-printer-app server

Simply put a colon-separated list of any amount of paths into the variable, always the last being used by the "Add PPD files" page. Creating a wrapper script is recommended.

This Printer Application uses CUPS' backends and not PAPPL's, meaning that for USB printers CUPS' USB quirk workarounds for compatibility problems are used, network printers can also be used with IPP, IPPS, and LPD protocols, and SNMP printer discovery is configurable.

USB Quirk rules in /usr/share/cups/usb and the /etc/cups/snmp.conf file can get edited if needed.

Make sure you have CUPS (at least its backends) installed.

You also need Ghostscript to print PDF jobs.

For access to the test page testpage.ps use the TESTPAGE_DIR environment variable:

TESTPAGE_DIR=`pwd` PPD_PATHS=/path/to/my/ppds:/my/second/place ./ps-printer-app server

or for your own creation of a test page (PostScript, PDF, PNG, JPEG, Apple Raster, PWG Raster):

TESTPAGE=/path/to/my/testpage/my_testpage.ps PPD_PATHS=/path/to/my/ppds:/my/second/place ./ps-printer-app server

LEGAL STUFF

It is derived from the HP PCL Printer Application, a first working model of a raster Printer Application using PAPPL. It is available here:

https://github.com/michaelrsweet/hp-printer-app

This software is licensed under the Apache License Version 2.0 with an exception to allow linking against GPL2/LGPL2 software (like older versions of CUPS). See the files "LICENSE" and "NOTICE" for more information.

OpenPrinting / ps-printer-app

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