PostScript Printer Application

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). This work 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 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.

• To do not 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. Note that some PPDs use certain CUPS filters for extra functionality. These filters are not included. The user can add additional PPDs without needing to rebuild the Snap.

• 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.

• 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.

KNOWN ISSUES

• 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".

TODO:

• Automatic start of the Printer Application as a daemon

• Add printer auto-setup for all supported printers

• Correct locations for the state file, the log file, and user-added PPD files

• Add PPD files via web interface

• 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

• Better way to download HPLIP for grabbing the PostScript PPD files for HP printers

• Use pyppd to compress the built-in PPD repositories

• In ps-printer-app.c many places are marked with XXX. These are points to be improved.

BUILDING AND INSTALLING

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 Ubuntu version (like 20.04) should work.

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.

To install the resulting Snap run

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

Then connect the interfaces:

sudo snap connect ps-printer-app:avahi-control
sudo snap connect ps-printer-app:log-observe
sudo snap connect ps-printer-app:network-manager
sudo snap connect ps-printer-app:raw-usb

Now fire up the Printer Application as a server daemon:

ps-printer-app server

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 loaded media and the option defaults.

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

ps-printer-app FILE

You can also add PPD files without rebuilding the Snap. Do

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

PPDFILE 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/ containing the mentioned types of files. Only make sure to not put any executables there which do something else than listing and generating PPD files.

If you have a ps-printer-app server running you have to restart it to get your added PPD files visible in the list when adding a printer.

See

ps-printer-app --help

for more options, use the "--debug" info for verbose logging in your terminal window.

You can also do a "quick-and-dirty" build wothout snapping. You need a directory with the latest GIT snapshot of PAPPL and the latest GIT snapshot of cups-filters (master branch). Both PAPPL and cups-filters need to be compiled (./cnfigure; make), installing not needed. Also install the header files of all needed libraries (installing "libcups2-dev" should do it).

In the directory with the attached 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 $CUPS_FILTERS_SRC/.libs/libcupsfilters.a -ldl -lpthread  -lppd -lcups -lavahi-common -lavahi-client -lgnutls -ljpeg -lpng16 -ltiff -lz -lm -lusb-1.0 -lpam -lqpdf -lstdc++ -I. -I$PAPPL_SRC/pappl -I$CUPS_FILTERS_SRC/ppd -I$CUPS_FILTERS_SRC/cupsfilters

Then 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/

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. Creating a wrapper script is recommended.

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

The PostScript Printer Application is Copyright © 2020 by Till Kamppeter.

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

The HP PCL Printer Application is Copyright © 2019-2020 by Michael R Sweet.

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.