filter - cups file conversion filter interface
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);
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 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.
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.
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.
While the filter interface is compatible with System V interface scripts, CUPS
does not support System V interface scripts.
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.
backend(7),
cups(1),
cups-files.conf(5),
cupsd(8),
cupsfilter(8),
CUPS Online Help (http://localhost:631/help)
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