Ubuntu Manpage: filter - cups file conversion filter interface

NAME

       filter - cups file conversion filter interface

SYNOPSIS

       filter job user title num-copies options [ filename ]

       #include <cups/cups.h>

       ssize_t cupsBackChannelRead(char *buffer, size_t bytes,
                                   double timeout);

       cups_sc_status_t cupsSideChannelDoRequest(cups_sc_command_t command,
                                                 char *data, int *datalen,
                                                 double timeout);

       #include <cups/ppd.h>

       const char *cupsGetOption(const char *name, int num_options,
                        cups_option_t *options);

       int cupsMarkOptions(ppd_file_t *ppd, int num_options,
                           cups_option_t *options);

       int cupsParseOptions(const char *arg, int num_options,
                            cups_option_t **options);

       ppd_choice_t *ppdFindMarkedChoice(ppd_file_t *ppd, const char *keyword);

       void ppdMarkDefaults(ppd_file_t *ppd);

       ppd_file_t *ppdOpenFile(const char *filename);

DESCRIPTION

       The  CUPS  filter  interface  provides  a  standard  method  for adding support for new document types or
       printers to CUPS.  Each filter is capable of converting from one or more input formats to another  format
       that can either be printed directly or piped into another filter to get it to a printable format.

       Filters  MUST  be  capable  of  reading  from  a filename on the command-line or from the standard input,
       copying the standard input to a temporary file as required by the file format.  All output MUST  be  sent
       to  the  standard  output.   Filters  MUST  NOT  attempt  to communicate directly with the printer, other
       processes, or other services.

       The command name (argv[0]) is set to the name of the destination printer but is  also  available  in  the
       PRINTER environment variable.

OPTIONS

       Options are passed in argv[5] and are encoded from the corresponding IPP attributes used when the job was
       submitted. Use the cupsParseOptions() function to load the options into a  cups_option_t  array  and  the
       cupsGetOption() function to get the value of a specific attribute.  Be careful to look for common aliases
       of IPP attributes such as "landscape" for the IPP "orientation-requested" attribute.

       Options passed on the command-line typically do not include the default choices the printer's  PPD  file.
       Use the ppdMarkDefaults() and cupsMarkOptions() functions in the CUPS library to apply the options to the
       PPD defaults and map any IPP attributes to the corresponding PPD options.  Use  ppdFindMarkedChoice()  to
       get  the  user-selected  choice  for  a PPD option. For example, a filter might use the following code to
       determine the current value of the Duplex PPD option:

           ppd_file_t *ppd = ppdOpenFile(getenv("PPD"));
           cups_option_t *options = NULL;
           int num_options = cupsParseOptions(argv[5], 0, &options);

           ppdMarkDefaults(ppd);
           cupsMarkOptions(ppd, num_options, options);

           ppd_choice_t *choice = ppdFindMarkedChoice(ppd, "Duplex");

       Raster filters should use option choices set through the raster page header, as those reflect the options
       in  effect  for a given page.  Options specified on the command-line determine the default values for the
       entire job, which can be overridden on a per-page basis.

LOG MESSAGES

Messages sent to the standard error are generally stored in the printer's "printer-state-message"
attribute and the current ErrorLog file. Each line begins with a standard prefix:

ALERT: message
Sets the "printer-state-message" attribute and adds the specified message to the current ErrorLog
using the "alert" log level.

ATTR: attribute=value [ ... attribute=value]
Sets the named job or printer attribute(s). The following job attributes can be set: "job-media-
progress". The following printer attributes can be set: "auth-info-required", "marker-colors",
"marker-high-levels", "marker-levels", "marker-low-levels", "marker-message", "marker-names",
"marker-types", "printer-alert", and "printer-alert-description".

CRIT: message
Sets the "printer-state-message" attribute and adds the specified message to the current ErrorLog
using the "critical" log level.

DEBUG: message
Adds the specified message to the current ErrorLog using the "debug" log level. DEBUG messages are
never stored in the "printer-state-message" attribute.

DEBUG2: message
Adds the specified message to the current ErrorLog using the "debug2" log level. DEBUG2 messages
are never stored in the "printer-state-message" attribute.

EMERG: message
Sets the "printer-state-message" attribute and adds the specified message to the current ErrorLog
using the "emergency" log level.

ERROR: message
Sets the "printer-state-message" attribute and adds the specified message to the current ErrorLog
using the "error" log level.

INFO: message
Sets the "printer-state-message" attribute. If the current LogLevel is set to "debug2", also adds
the specified message to the current ErrorLog using the "info" log level.

NOTICE: message
Sets the "printer-state-message" attribute and adds the specified message to the current ErrorLog
using the "notice" log level.

PAGE: page-number #-copies

PAGE: total #-pages
Adds an entry to the current PageLog. The first form adds #-copies to the "job-media-sheets-
completed" attribute. The second form sets the "job-media-sheets-completed" attribute to #-pages.

PPD: Keyword=Value [ ... KeywordN=Value ]
Sets the named keywords in the printer's PPD file. This is typically used to update default option
keywords such as DefaultPageSize and the various installable options in the PPD file.

STATE: printer-state-reason [ ... printer-state-reason ]

STATE: + printer-state-reason [ ... printer-state-reason ]

STATE: - printer-state-reason [ ... printer-state-reason ]
Sets, adds, or removes "printer-state-reason" keywords for the current queue. Typically this is used
to indicate media, ink, and toner conditions on a printer.

WARNING: message
Sets the "printer-state-message" attribute and adds the specified message to the current ErrorLog
using the "warning" log level.

ENVIRONMENT VARIABLES

The following environment variables are defined by the CUPS server when executing the filter:

CHARSET
The default text character set, typically "utf-8".

CLASS
When a job is submitted to a printer class, contains the name of the destination printer class.
Otherwise this environment variable will not be set.

CONTENT_TYPE
The MIME media type associated with the submitted job file, for example "application/postscript".

CUPS_CACHEDIR
The directory where semi-persistent cache files can be found and stored.

CUPS_DATADIR
The directory where data files can be found.

CUPS_FILETYPE
The type of file being printed: "job-sheet" for a banner page and "document" for a regular print
file.

CUPS_MAX_MESSAGE
The maximum size of a message sent to stderr, including any leading prefix and the trailing newline.

CUPS_SERVERROOT
The root directory of the server.

FINAL_CONTENT_TYPE
The MIME media type associated with the output destined for the printer, for example
"application/vnd.cups-postscript".

LANG The default language locale (typically C or en).

PATH The standard execution path for external programs that may be run by the filter.

PPD The full pathname of the PostScript Printer Description (PPD) file for this printer.

PRINTER
The name of the printer.

RIP_CACHE
The recommended amount of memory to use for Raster Image Processors (RIPs).

SOFTWARE
The name and version number of the server (typically CUPS/major.minor).

TZ The timezone of the server.

USER The user executing the filter, typically "lp" or "root"; consult the cups-files.conf file for the
current setting.

CONFORMING TO

       While the filter interface is compatible with System V interface scripts, CUPS does not support System  V
       interface scripts.

NOTES

       CUPS  printer  drivers  and  backends  are deprecated and will no longer be supported in a future feature
       release of CUPS.  Printers that  do  not  support  IPP  can  be  supported  using  applications  such  as
       ippeveprinter(1).

       CUPS  filters  are  not  meant  to be run directly by the user.  Aside from the legacy System V interface
       issues (argv[0] is the printer name), CUPS filters also expect specific environment  variables  and  file
       descriptors,  and typically run in a user session that (on macOS) has additional restrictions that affect
       how it runs.  Unless you are a developer and know what you are doing, please do not run filters directly.
       Instead, use the cupsfilter(8) program to use the appropriate filters to do the conversions you need.

COPYRIGHT

       Copyright © 2020-2024 by OpenPrinting.