Tribblix: manual page: filter.7

filter(7) OpenPrinting filter(7)

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.