filter(7) manual page
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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
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 "lansdscape" 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,
it will only work with the System V interface script as the only filter.
Typically the interface script will be provided via the lpadmin(8)
command
using the -i option.
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 OS X)
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)
Copyright [co] 2007-2014
by Apple Inc.
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