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 © 2021-2022 by OpenPrinting.