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256 "$Id: api-filter.header 7285 2008-02-01 23:57:39Z mike $"
258 Filter and backend programming header for the Common UNIX Printing System
261 Copyright 2008 by Apple Inc.
263 These coded instructions, statements, and computer programs are the
264 property of Apple Inc. and are protected by Federal copyright
265 law. Distribution and use rights are outlined in the file "LICENSE.txt"
266 which should have been included with this file. If this file is
267 file is missing or damaged, see the license at "http://www.cups.org/".
270 <h1 class=
"title">Filter and Backend Programming
</h1>
272 <div class='summary'
><table summary='General Information'
>
276 <th>cups/backend.h
<br>
277 cups/sidechannel.h
<br>
288 <td>Programming:
<a href='api-overview.html' target='_top'
>Introduction to CUPS Programming
</a><br>
289 Programming:
<a href='api-cups.html' target='_top'
>CUPS API
</a><br>
290 Programming:
<a href='api-ppd.html' target='_top'
>PPD API
</a><br>
291 Programming:
<a href='api-raster.html' target='_top'
>Raster API
</a></td>
295 <h2 class=
"title">Contents
</h2>
296 <ul class=
"contents">
298 <li><a href=
"#OVERVIEW">Overview
</a><ul class=
"subcontents">
299 <li><a href=
"#SECURITY">Security Considerations
</a></li>
300 <li><a href=
"#TEMPFILES">Temporary Files
</a></li>
301 <li><a href=
"#COPIES">Copy Generation
</a></li>
302 <li><a href=
"#EXITCODES">Exit Codes
</a></li>
303 <li><a href=
"#ENVIRONMENT">Environment Variables
</a></li>
304 <li><a href=
"#MESSAGES">Communicating with the Scheduler
</a></li>
305 <li><a href=
"#COMMUNICATING_BACKEND">Communicating with the Backend
</a></li>
306 <li><a href=
"#COMMUNICATING_FILTER">Communicating with Filters
</a></li>
307 <li><a href=
"#SNMP">Doing SNMP Queries with Network Printers
</a></li>
309 <li><a href=
"#FUNCTIONS">Functions
</a><ul class=
"code">
310 <li><a href=
"#cupsBackChannelRead" title=
"Read data from the backchannel.">cupsBackChannelRead
</a></li>
311 <li><a href=
"#cupsBackChannelWrite" title=
"Write data to the backchannel.">cupsBackChannelWrite
</a></li>
312 <li><a href=
"#cupsBackendDeviceURI" title=
"Get the device URI for a backend.">cupsBackendDeviceURI
</a></li>
313 <li><a href=
"#cupsSideChannelDoRequest" title=
"Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest
</a></li>
314 <li><a href=
"#cupsSideChannelRead" title=
"Read a side-channel message.">cupsSideChannelRead
</a></li>
315 <li><a href=
"#cupsSideChannelSNMPGet" title=
"Query a SNMP OID's value.">cupsSideChannelSNMPGet
</a></li>
316 <li><a href=
"#cupsSideChannelSNMPWalk" title=
"Query multiple SNMP OID values.">cupsSideChannelSNMPWalk
</a></li>
317 <li><a href=
"#cupsSideChannelWrite" title=
"Write a side-channel message.">cupsSideChannelWrite
</a></li>
319 <li><a href=
"#TYPES">Data Types
</a><ul class=
"code">
320 <li><a href=
"#cups_backend_t" title=
"Backend exit codes">cups_backend_t
</a></li>
321 <li><a href=
"#cups_sc_bidi_t" title=
"Bidirectional capabilities">cups_sc_bidi_t
</a></li>
322 <li><a href=
"#cups_sc_command_t" title=
"Request command codes">cups_sc_command_t
</a></li>
323 <li><a href=
"#cups_sc_state_t" title=
"Printer state bits">cups_sc_state_t
</a></li>
324 <li><a href=
"#cups_sc_status_t" title=
"Response status codes">cups_sc_status_t
</a></li>
325 <li><a href=
"#cups_sc_walk_func_t" title=
"SNMP walk callback">cups_sc_walk_func_t
</a></li>
327 <li><a href=
"#ENUMERATIONS">Constants
</a><ul class=
"code">
328 <li><a href=
"#cups_backend_e" title=
"Backend exit codes">cups_backend_e
</a></li>
329 <li><a href=
"#cups_sc_bidi_e" title=
"Bidirectional capabilities">cups_sc_bidi_e
</a></li>
330 <li><a href=
"#cups_sc_command_e" title=
"Request command codes">cups_sc_command_e
</a></li>
331 <li><a href=
"#cups_sc_state_e" title=
"Printer state bits">cups_sc_state_e
</a></li>
332 <li><a href=
"#cups_sc_status_e" title=
"Response status codes">cups_sc_status_e
</a></li>
336 "$Id: api-filter.shtml 7502 2008-04-28 21:30:12Z mike $"
338 Filter and backend programming introduction for the Common UNIX Printing
341 Copyright 2007-2008 by Apple Inc.
342 Copyright 1997-2006 by Easy Software Products, all rights reserved.
344 These coded instructions, statements, and computer programs are the
345 property of Apple Inc. and are protected by Federal copyright
346 law. Distribution and use rights are outlined in the file "LICENSE.txt"
347 which should have been included with this file. If this file is
348 file is missing or damaged, see the license at "http://www.cups.org/".
351 <h2 class='title'
><a name=
"OVERVIEW">Overview
</a></h2>
353 <p>Filters, printer drivers, port monitors, and backends use a common interface
354 for processing print jobs and communicating status information to the scheduler.
355 Each filter is run with a standard set of command-line arguments:
<p>
363 <dd>The user printing the job
</dd>
366 <dd>The job name/title
</dd>
369 <dd>The number of copies to print
</dd>
372 <dd>The options that were provided when the job was submitted
</dd>
375 <dd>The file to print (first filter only)
</dd>
378 <p>The scheduler runs one or more of these programs to print any given job. The
379 first filter reads from the print file and writes to the standard output, while
380 the remaining filters read from the standard input and write to the standard
381 output. The backend is the last filter in the chain and writes to the
384 <h3><a name=
"SECURITY">Security Considerations
</a></h3>
386 <p>It is always important to use security programming practices. Filters and
387 most backends are run as a non-priviledged user, so the major security
388 consideration is resource utilization - filters should not depend on unlimited
389 amounts of CPU, memory, or disk space, and should protect against conditions
390 that could lead to excess usage of any resource like infinite loops and
391 unbounded recursion. In addition, filters must
<em>never
</em> allow the user to
392 specify an arbitrary file path to a separator page, template, or other file
393 used by the filter since that can lead to an unauthorized disclosure of
394 information.
<em>Always
</em> treat input as suspect and validate it!
</p>
396 <p>If you are developing a backend that runs as root, make sure to check for
397 potential buffer overflows, integer under/overflow conditions, and file
398 accesses since these can lead to privilege escalations. When writing files,
399 always validate the file path and
<em>never
</em> allow a user to determine
400 where to store a file.
</p>
402 <blockquote><b>Note:
</b>
404 <p><em>Never
</em> write files to a user's home directory. Aside from the
405 security implications, CUPS is a network print service and as such the network
406 user may not be the same as the local user and/or there may not be a local home
407 directory to write to.
</p>
409 <p>In addition, some operating systems provide additional security mechanisms
410 that further limit file system access, even for backends running as root. On
411 Mac OS X, for example, no backend may write to a user's home directory.
</p>
414 <h3><a name=
"TEMPFILES">Temporary Files
</a></h3>
416 <p>Temporary files should be created in the directory specified by the
417 "TMPDIR" environment variable. The
418 <a href=
"#cupsTempFile2"><code>cupsTempFile2
</code></a> function can be
419 used to safely create temporary files in this directory.
</p>
421 <h3><a name=
"COPIES">Copy Generation
</a></h3>
423 <p>The
<code>argv[
4]
</code> argument specifies the number of copies to produce
424 of the input file. In general, you should only generate copies if the
425 <em>filename
</em> argument is supplied. The only exception to this are
426 filters that produce device-independent PostScript output, since the PostScript
427 filter
<var>pstops
</var> is responsible for generating copies of PostScript
430 <h3><a name=
"EXITCODES">Exit Codes
</a></h3>
432 <p>Filters must exit with status
0 when they successfully generate print data
433 or
1 when they encounter an error. Backends can return any of the
434 <a href=
"#cups_backend_t"><code>cups_backend_t
</code></a> constants.
</p>
436 <h3><a name=
"ENVIRONMENT">Environment Variables
</a></h3>
438 <p>The following environment variables are defined by the printing system:
</p>
442 <dt>APPLE_LANGUAGES
</dt>
443 <dd>The Apple language identifier associated with the job
444 (Mac OS X only).
</dd>
447 <dd>The job character set, typically
"utf-8".
</dd>
450 <dd>When a job is submitted to a printer class, contains the name of
451 the destination printer class. Otherwise this environment
452 variable will not be set.
</dd>
454 <dt>CONTENT_TYPE
</dt>
455 <dd>The MIME type associated with the file (e.g.
456 application/postscript).
</dd>
458 <dt>CUPS_CACHEDIR
</dt>
459 <dd>The directory where cache files can be stored.
</dd>
461 <dt>CUPS_DATADIR
</dt>
462 <dd>The directory where data files can be found.
</dd>
464 <dt>CUPS_SERVERROOT
</dt>
465 <dd>The root directory of the server.
</dd>
468 <dd>The device-uri associated with the printer.
</dd>
470 <dt>FINAL_CONTENT_TYPE
</dt>
471 <dd>The MIME type associated with the printer (e.g.
472 application/vnd.cups-postscript).
</dd>
475 <dd>The language locale associated with the job.
</dd>
478 <dd>The full pathname of the PostScript Printer Description (PPD)
479 file for this printer.
</dd>
482 <dd>The name of the printer.
</dd>
485 <dd>The recommended amount of memory to use for Raster Image
486 Processors (RIPs).
</dd>
490 <h3><a name=
"MESSAGES">Communicating with the Scheduler
</a></h3>
492 <p>Filters and backends communicate wih the scheduler by writing messages
493 to the standard error file. For example, the following code sets the current
494 printer state message to
"Printing page 5":
</p>
496 <pre class=
"example">
499 fprintf(stderr,
"INFO: Printing page %d\n", page);
502 <p>Each message is a single line of text starting with one of the following
507 <dt>ALERT: message
</dt>
508 <dd>Sets the printer-state-message attribute and adds the specified
509 message to the current error log file using the
"alert" log level.
</dd>
511 <dt>ATTR: attribute=value [attribute=value]
</dt>
512 <dd>Sets the named printer or job attribute(s). Typically this is used
513 to set the
<code>marker-colors
</code>,
<code>marker-levels
</code>,
514 <code>marker-names
</code>,
<code>marker-types
</code>,
515 <code>printer-alert
</code>, and
<code>printer-alert-description
</code>
516 printer attributes.
</dd>
518 <dt>CRIT: message
</dt>
519 <dd>Sets the printer-state-message attribute and adds the specified
520 message to the current error log file using the
"critical" log
523 <dt>DEBUG: message
</dt>
524 <dd>Sets the printer-state-message attribute and adds the specified
525 message to the current error log file using the
"debug" log level.
</dd>
527 <dt>DEBUG2: message
</dt>
528 <dd>Sets the printer-state-message attribute and adds the specified
529 message to the current error log file using the
"debug2" log level.
</dd>
531 <dt>EMERG: message
</dt>
532 <dd>Sets the printer-state-message attribute and adds the specified
533 message to the current error log file using the
"emergency" log
536 <dt>ERROR: message
</dt>
537 <dd>Sets the printer-state-message attribute and adds the specified
538 message to the current error log file using the
"error" log level.
</dd>
540 <dt>INFO: message
</dt>
541 <dd>Sets the printer-state-message attribute. If the current log level
542 is set to
"debug2", also adds the specified message to the current error
543 log file using the
"info" log level.
</dd>
545 <dt>NOTICE: message
</dt>
546 <dd>Sets the printer-state-message attribute and adds the specified
547 message to the current error log file using the
"notice" log level.
</dd>
549 <dt>PAGE: page-number #-copies
</dt>
550 <dt>PAGE: total #-pages
</dt>
551 <dd>Adds an entry to the current page log file. The first form adds
552 #-copies to the job-media-sheets-completed attribute. The second
553 form sets the job-media-sheets-completed attribute to #-pages.
</dd>
555 <dt>PPD: keyword=value [keyword=value ...]
</dt>
556 <dd>Changes or adds keywords to the printer's PPD file. Typically
557 this is used to update installable options or default media settings
558 based on the printer configuration.
</dd>
560 <dt>STATE: printer-state-reason [printer-state-reason ...]
</dt>
561 <dt>STATE: + printer-state-reason [printer-state-reason ...]
</dt>
562 <dt>STATE: - printer-state-reason [printer-state-reason ...]
</dt>
563 <dd>Sets, adds, or removes printer-state-reason keywords to the
564 current queue. Typically this is used to indicate media, ink, and
565 toner conditions on a printer.
</dd>
567 <dt>WARNING: message
</dt>
568 <dd>Sets the printer-state-message attribute and adds the specified
569 message to the current error log file using the
"warning" log
574 <p>Messages without one of these prefixes are treated as if they began with
575 the
"DEBUG:" prefix string.
</p>
577 <h3><a name=
"COMMUNICATING_BACKEND">Communicating with the Backend
</a></h3>
579 <p>Filters can communicate with the backend via the
580 <a href=
"#cupsBackChannelRead"><code>cupsBackChannelRead
</code></a> and
581 <a href=
"#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest
</code></a>
583 <a href=
"#cupsBackChannelRead"><code>cupsBackChannelRead
</code></a> function
584 reads data that has been sent back from the device and is typically used to
585 obtain status and configuration information. For example, the following code
586 polls the backend for back-channel data:
</p>
588 <pre class=
"example">
589 #include
<cups/cups.h
>
594 /* Use a timeout of
0.0 seconds to poll for back-channel data */
595 bytes = cupsBackChannelRead(buffer, sizeof(buffer),
0.0);
599 <a href=
"#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest
</code></a>
600 function allows you to get out-of-band status information and do synchronization
601 with the device. For example, the following code gets the current IEEE-
1284
602 device ID string from the backend:
</p>
604 <pre class=
"example">
605 #include
<cups/sidechannel.h
>
609 <a href=
"#cups_sc_status_t">cups_sc_status_t
</a> status;
611 /* Tell cupsSideChannelDoRequest() how big our buffer is, less
1 byte for nul-termination... */
612 datalen = sizeof(data) -
1;
614 /* Get the IEEE-
1284 device ID, waiting for up to
1 second */
615 status =
<a href=
"#cupsSideChannelDoRequest">cupsSideChannelDoRequest
</a>(CUPS_SC_CMD_GET_DEVICE_ID, data,
&datalen,
1.0);
617 /* Use the returned value if OK was returned and the length is non-zero */
618 if (status == CUPS_SC_STATUS_OK && datalen
> 0)
619 data[datalen] = '\
0';
624 <h3><a name=
"COMMUNICATING_FILTER">Communicating with Filters
</a></h3>
626 <p>Backends communicate with filters using the reciprocal functions
627 <a href=
"#cupsBackChannelWrite"><code>cupsBackChannelWrite
</code></a>,
628 <a href=
"#cupsSideChannelRead"><code>cupsSideChannelRead
</code></a>, and
629 <a href=
"#cupsSideChannelWrite"><code>cupsSideChannelWrite
</code></a>. We
630 recommend writing back-channel data using a timeout of
1.0 seconds:
</p>
632 <pre class=
"example">
633 #include
<cups/cups.h
>
638 /* Use a timeout of
1.0 seconds to give filters a chance to read */
639 cupsBackChannelWrite(buffer, bytes,
1.0);
642 <p>The
<a href=
"#cupsSideChannelRead"><code>cupsSideChannelRead
</code></a>
643 function reads a side-channel command from a filter, driver, or port monitor.
644 Backends can either poll for commands using a
<code>timeout
</code> of
0.0, wait
645 indefinitely for commands using a
<code>timeout
</code> of -
1.0 (probably in a
646 separate thread for that purpose), or use
<code>select
</code> or
647 <code>poll
</code> on the
<code>CUPS_SC_FD
</code> file descriptor (
4) to handle
648 input and output on several file descriptors at the same time.
</p>
650 <p>Once a command is processed, the backend uses the
651 <a href=
"#cupsSideChannelWrite"><code>cupsSideChannelWrite
</code></a> function
652 to send its response. For example, the following code shows how to poll for a
653 side-channel command and respond to it:
</p>
655 <pre class=
"example">
656 #include
<cups/sidechannel.h
>
658 <a href=
"#cups_sc_command_t">cups_sc_command_t
</a> command;
659 <a href=
"#cups_sc_status_t">cups_sc_status_t
</a> status;
661 int datalen = sizeof(data);
663 /* Poll for a command... */
664 if (!
<a href=
"#cupsSideChannelRead">cupsSideChannelRead
</a>(
&command,
&status, data,
&datalen,
0.0))
668 /* handle supported commands, fill data/datalen/status with values as needed */
671 status = CUPS_SC_STATUS_NOT_IMPLEMENTED;
676 /* Send a response... */
677 <a href=
"#cupsSideChannelWrite">cupsSideChannelWrite
</a>(command, status, data, datalen,
1.0);
681 <h3><a name=
"SNMP">Doing SNMP Queries with Network Printers
</a></h3>
683 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
684 status, page counter, and supply levels from most network printers. Every
685 piece of information is associated with an Object Identifier (OID), and
686 every printer has a
<em>community
</em> name associated with it. OIDs can be
687 queried directly or by
"walking" over a range of OIDs with a common prefix.
</p>
689 <p>The two CUPS SNMP functions provide a simple API for querying network
690 printers through the side-channel interface. Each accepts a string containing
691 an OID like
".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
692 along with a timeout for the query.
</p>
694 <p>The
<a href=
"#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet
</code></a>
695 function queries a single OID and returns the value as a string in a buffer
698 <pre class=
"example">
699 #include
<cups/sidechannel.h
>
702 int datalen = sizeof(data);
704 if (
<a href=
"#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet
</a>(
".1.3.6.1.2.1.43.10.2.1.4.1.1", data,
&datalen,
5.0)
705 == CUPS_SC_STATUS_OK)
707 /* Do something with the value */
708 printf(
"Page counter is: %s\n", data);
713 <a href=
"#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk
</code></a>
714 function allows you to query a whole group of OIDs, calling a function of your
715 choice for each OID that is found:
</p>
717 <pre class=
"example">
718 #include
<cups/sidechannel.h
>
721 my_callback(const char *oid, const char *data, int datalen, void *context)
723 /* Do something with the value */
724 printf(
"%s=%s\n", oid, data);
731 <a href=
"#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk
</a>(
".1.3.6.1.2.1.43",
5.0, my_callback, my_data);
733 <h2 class=
"title"><a name=
"FUNCTIONS">Functions
</a></h2>
734 <h3 class=
"function"><span class=
"info"> CUPS
1.2 </span><a name=
"cupsBackChannelRead">cupsBackChannelRead
</a></h3>
735 <p class=
"description">Read data from the backchannel.
</p>
737 ssize_t cupsBackChannelRead (
<br>
738 char *buffer,
<br>
739 size_t bytes,
<br>
740 double timeout
<br>
742 <h4 class=
"parameters">Parameters
</h4>
745 <dd class=
"description">Buffer to read
</dd>
747 <dd class=
"description">Bytes to read
</dd>
749 <dd class=
"description">Timeout in seconds
</dd>
751 <h4 class=
"returnvalue">Return Value
</h4>
752 <p class=
"description">Bytes read or -
1 on error
</p>
753 <h4 class=
"discussion">Discussion
</h4>
754 <p class=
"discussion">Reads up to
"bytes
" bytes from the backchannel. The
"timeout
"
755 parameter controls how many seconds to wait for the data - use
756 0.0 to return immediately if there is no data, -
1.0 to wait
757 for data indefinitely.
760 <h3 class=
"function"><span class=
"info"> CUPS
1.2 </span><a name=
"cupsBackChannelWrite">cupsBackChannelWrite
</a></h3>
761 <p class=
"description">Write data to the backchannel.
</p>
763 ssize_t cupsBackChannelWrite (
<br>
764 const char *buffer,
<br>
765 size_t bytes,
<br>
766 double timeout
<br>
768 <h4 class=
"parameters">Parameters
</h4>
771 <dd class=
"description">Buffer to write
</dd>
773 <dd class=
"description">Bytes to write
</dd>
775 <dd class=
"description">Timeout in seconds
</dd>
777 <h4 class=
"returnvalue">Return Value
</h4>
778 <p class=
"description">Bytes written or -
1 on error
</p>
779 <h4 class=
"discussion">Discussion
</h4>
780 <p class=
"discussion">Writes
"bytes
" bytes to the backchannel. The
"timeout
" parameter
781 controls how many seconds to wait for the data to be written - use
782 0.0 to return immediately if the data cannot be written, -
1.0 to wait
786 <h3 class=
"function"><a name=
"cupsBackendDeviceURI">cupsBackendDeviceURI
</a></h3>
787 <p class=
"description">Get the device URI for a backend.
</p>
789 const char *cupsBackendDeviceURI (
<br>
790 char **argv
<br>
792 <h4 class=
"parameters">Parameters
</h4>
795 <dd class=
"description">Command-line arguments
</dd>
797 <h4 class=
"returnvalue">Return Value
</h4>
798 <p class=
"description">Device URI or
<code>NULL
</code></p>
799 <h4 class=
"discussion">Discussion
</h4>
800 <p class=
"discussion">The
"argv
" argument is the argv argument passed to main(). This
801 function returns the device URI passed in the DEVICE_URI environment
802 variable or the device URI passed in argv[
0], whichever is found
804 <h3 class=
"function"><span class=
"info"> CUPS
1.3 </span><a name=
"cupsSideChannelDoRequest">cupsSideChannelDoRequest
</a></h3>
805 <p class=
"description">Send a side-channel command to a backend and wait for a response.
</p>
807 <a href=
"#cups_sc_status_t">cups_sc_status_t
</a> cupsSideChannelDoRequest (
<br>
808 <a href=
"#cups_sc_command_t">cups_sc_command_t
</a> command,
<br>
809 char *data,
<br>
810 int *datalen,
<br>
811 double timeout
<br>
813 <h4 class=
"parameters">Parameters
</h4>
816 <dd class=
"description">Command to send
</dd>
818 <dd class=
"description">Response data buffer pointer
</dd>
820 <dd class=
"description">Size of data buffer on entry, number of bytes in buffer on return
</dd>
822 <dd class=
"description">Timeout in seconds
</dd>
824 <h4 class=
"returnvalue">Return Value
</h4>
825 <p class=
"description">Status of command
</p>
826 <h4 class=
"discussion">Discussion
</h4>
827 <p class=
"discussion">This function is normally only called by filters, drivers, or port
828 monitors in order to communicate with the backend used by the current
829 printer. Programs must be prepared to handle timeout or
"not
830 implemented
" status codes, which indicate that the backend or device
831 do not support the specified side-channel command.
<br>
833 The
"datalen
" parameter must be initialized to the size of the buffer
834 pointed to by the
"data
" parameter. cupsSideChannelDoRequest() will
835 update the value to contain the number of data bytes in the buffer.
838 <h3 class=
"function"><span class=
"info"> CUPS
1.3 </span><a name=
"cupsSideChannelRead">cupsSideChannelRead
</a></h3>
839 <p class=
"description">Read a side-channel message.
</p>
841 int cupsSideChannelRead (
<br>
842 <a href=
"#cups_sc_command_t">cups_sc_command_t
</a> *command,
<br>
843 <a href=
"#cups_sc_status_t">cups_sc_status_t
</a> *status,
<br>
844 char *data,
<br>
845 int *datalen,
<br>
846 double timeout
<br>
848 <h4 class=
"parameters">Parameters
</h4>
851 <dd class=
"description">Command code
</dd>
853 <dd class=
"description">Status code
</dd>
855 <dd class=
"description">Data buffer pointer
</dd>
857 <dd class=
"description">Size of data buffer on entry, number of bytes in buffer on return
</dd>
859 <dd class=
"description">Timeout in seconds
</dd>
861 <h4 class=
"returnvalue">Return Value
</h4>
862 <p class=
"description">0 on success, -
1 on error
</p>
863 <h4 class=
"discussion">Discussion
</h4>
864 <p class=
"discussion">This function is normally only called by backend programs to read
865 commands from a filter, driver, or port monitor program. The
866 caller must be prepared to handle incomplete or invalid messages
867 and return the corresponding status codes.
<br>
869 The
"datalen
" parameter must be initialized to the size of the buffer
870 pointed to by the
"data
" parameter. cupsSideChannelDoRequest() will
871 update the value to contain the number of data bytes in the buffer.
874 <h3 class=
"function"><span class=
"info"> CUPS
1.4 </span><a name=
"cupsSideChannelSNMPGet">cupsSideChannelSNMPGet
</a></h3>
875 <p class=
"description">Query a SNMP OID's value.
</p>
877 <a href=
"#cups_sc_status_t">cups_sc_status_t
</a> cupsSideChannelSNMPGet (
<br>
878 const char *oid,
<br>
879 char *data,
<br>
880 int *datalen,
<br>
881 double timeout
<br>
883 <h4 class=
"parameters">Parameters
</h4>
886 <dd class=
"description">OID to query
</dd>
888 <dd class=
"description">Buffer for OID value
</dd>
890 <dd class=
"description">Size of OID buffer on entry, size of value on return
</dd>
892 <dd class=
"description">Timeout in seconds
</dd>
894 <h4 class=
"returnvalue">Return Value
</h4>
895 <p class=
"description">Query status
</p>
896 <h4 class=
"discussion">Discussion
</h4>
897 <p class=
"discussion">This function asks the backend to do a SNMP OID query on behalf of the
898 filter, port monitor, or backend using the default community name.
<br>
900 "oid
" contains a numeric OID consisting of integers separated by periods,
901 for example
".1.3.6.1.2.1.43". Symbolic names from SNMP MIBs are not
902 supported and must be converted to their numeric forms.
<br>
904 On input,
"data
" and
"datalen
" provide the location and size of the
905 buffer to hold the OID value as a string. HEX-String (binary) values are
906 converted to hexadecimal strings representing the binary data, while
907 NULL-Value and unknown OID types are returned as the empty string.
908 The returned
"datalen
" does not include the trailing nul.
910 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED
</code> is returned by backends that do not
911 support SNMP queries.
<code>CUPS_SC_STATUS_NO_RESPONSE
</code> is returned when
912 the printer does not respond to the SNMP query.
915 <h3 class=
"function"><span class=
"info"> CUPS
1.4 </span><a name=
"cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk
</a></h3>
916 <p class=
"description">Query multiple SNMP OID values.
</p>
918 <a href=
"#cups_sc_status_t">cups_sc_status_t
</a> cupsSideChannelSNMPWalk (
<br>
919 const char *oid,
<br>
920 double timeout,
<br>
921 <a href=
"#cups_sc_walk_func_t">cups_sc_walk_func_t
</a> cb,
<br>
922 void *context
<br>
924 <h4 class=
"parameters">Parameters
</h4>
927 <dd class=
"description">First numeric OID to query
</dd>
929 <dd class=
"description">Timeout for each query in seconds
</dd>
931 <dd class=
"description">Function to call with each value
</dd>
933 <dd class=
"description">Application-defined pointer to send to callback
</dd>
935 <h4 class=
"returnvalue">Return Value
</h4>
936 <p class=
"description">Status of first query of
<code>CUPS_SC_STATUS_OK
</code> on success
</p>
937 <h4 class=
"discussion">Discussion
</h4>
938 <p class=
"discussion">This function asks the backend to do multiple SNMP OID queries on behalf
939 of the filter, port monitor, or backend using the default community name.
940 All OIDs under the
"parent
" OID are queried and the results are sent to
941 the callback function you provide.
<br>
943 "oid
" contains a numeric OID consisting of integers separated by periods,
944 for example
".1.3.6.1.2.1.43". Symbolic names from SNMP MIBs are not
945 supported and must be converted to their numeric forms.
<br>
947 "timeout
" specifies the timeout for each OID query. The total amount of
948 time will depend on the number of OID values found and the time required
951 "cb
" provides a function to call for every value that is found.
"context
"
952 is an application-defined pointer that is sent to the callback function
953 along with the OID and current data. The data passed to the callback is the
954 same as returned by
<a href=
"#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet
</code></a>.
956 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED
</code> is returned by backends that do not
957 support SNMP queries.
<code>CUPS_SC_STATUS_NO_RESPONSE
</code> is returned when
958 the printer does not respond to the first SNMP query.
961 <h3 class=
"function"><span class=
"info"> CUPS
1.3 </span><a name=
"cupsSideChannelWrite">cupsSideChannelWrite
</a></h3>
962 <p class=
"description">Write a side-channel message.
</p>
964 int cupsSideChannelWrite (
<br>
965 <a href=
"#cups_sc_command_t">cups_sc_command_t
</a> command,
<br>
966 <a href=
"#cups_sc_status_t">cups_sc_status_t
</a> status,
<br>
967 const char *data,
<br>
968 int datalen,
<br>
969 double timeout
<br>
971 <h4 class=
"parameters">Parameters
</h4>
974 <dd class=
"description">Command code
</dd>
976 <dd class=
"description">Status code
</dd>
978 <dd class=
"description">Data buffer pointer
</dd>
980 <dd class=
"description">Number of bytes of data
</dd>
982 <dd class=
"description">Timeout in seconds
</dd>
984 <h4 class=
"returnvalue">Return Value
</h4>
985 <p class=
"description">0 on success, -
1 on error
</p>
986 <h4 class=
"discussion">Discussion
</h4>
987 <p class=
"discussion">This function is normally only called by backend programs to send
988 responses to a filter, driver, or port monitor program.
991 <h2 class=
"title"><a name=
"TYPES">Data Types
</a></h2>
992 <h3 class=
"typedef"><a name=
"cups_backend_t">cups_backend_t
</a></h3>
993 <p class=
"description">Backend exit codes
</p>
995 typedef enum
<a href=
"#cups_backend_e">cups_backend_e
</a> cups_backend_t;
997 <h3 class=
"typedef"><a name=
"cups_sc_bidi_t">cups_sc_bidi_t
</a></h3>
998 <p class=
"description">Bidirectional capabilities
</p>
1000 typedef enum
<a href=
"#cups_sc_bidi_e">cups_sc_bidi_e
</a> cups_sc_bidi_t;
1002 <h3 class=
"typedef"><a name=
"cups_sc_command_t">cups_sc_command_t
</a></h3>
1003 <p class=
"description">Request command codes
</p>
1005 typedef enum
<a href=
"#cups_sc_command_e">cups_sc_command_e
</a> cups_sc_command_t;
1007 <h3 class=
"typedef"><a name=
"cups_sc_state_t">cups_sc_state_t
</a></h3>
1008 <p class=
"description">Printer state bits
</p>
1010 typedef enum
<a href=
"#cups_sc_state_e">cups_sc_state_e
</a> cups_sc_state_t;
1012 <h3 class=
"typedef"><a name=
"cups_sc_status_t">cups_sc_status_t
</a></h3>
1013 <p class=
"description">Response status codes
</p>
1015 typedef enum
<a href=
"#cups_sc_status_e">cups_sc_status_e
</a> cups_sc_status_t;
1017 <h3 class=
"typedef"><a name=
"cups_sc_walk_func_t">cups_sc_walk_func_t
</a></h3>
1018 <p class=
"description">SNMP walk callback
</p>
1020 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1022 <h2 class=
"title"><a name=
"ENUMERATIONS">Constants
</a></h2>
1023 <h3 class=
"enumeration"><a name=
"cups_backend_e">cups_backend_e
</a></h3>
1024 <p class=
"description">Backend exit codes
</p>
1025 <h4 class=
"constants">Constants
</h4>
1027 <dt>CUPS_BACKEND_AUTH_REQUIRED
</dt>
1028 <dd class=
"description">Job failed, authentication required
</dd>
1029 <dt>CUPS_BACKEND_CANCEL
</dt>
1030 <dd class=
"description">Job failed, cancel job
</dd>
1031 <dt>CUPS_BACKEND_FAILED
</dt>
1032 <dd class=
"description">Job failed, use error-policy
</dd>
1033 <dt>CUPS_BACKEND_HOLD
</dt>
1034 <dd class=
"description">Job failed, hold job
</dd>
1035 <dt>CUPS_BACKEND_OK
</dt>
1036 <dd class=
"description">Job completed successfully
</dd>
1037 <dt>CUPS_BACKEND_STOP
</dt>
1038 <dd class=
"description">Job failed, stop queue
</dd>
1040 <h3 class=
"enumeration"><a name=
"cups_sc_bidi_e">cups_sc_bidi_e
</a></h3>
1041 <p class=
"description">Bidirectional capabilities
</p>
1042 <h4 class=
"constants">Constants
</h4>
1044 <dt>CUPS_SC_BIDI_NOT_SUPPORTED
</dt>
1045 <dd class=
"description">Bidirectional I/O is not supported
</dd>
1046 <dt>CUPS_SC_BIDI_SUPPORTED
</dt>
1047 <dd class=
"description">Bidirectional I/O is supported
</dd>
1049 <h3 class=
"enumeration"><a name=
"cups_sc_command_e">cups_sc_command_e
</a></h3>
1050 <p class=
"description">Request command codes
</p>
1051 <h4 class=
"constants">Constants
</h4>
1053 <dt>CUPS_SC_CMD_DRAIN_OUTPUT
</dt>
1054 <dd class=
"description">Drain all pending output
</dd>
1055 <dt>CUPS_SC_CMD_GET_BIDI
</dt>
1056 <dd class=
"description">Return bidirectional capabilities
</dd>
1057 <dt>CUPS_SC_CMD_GET_DEVICE_ID
</dt>
1058 <dd class=
"description">Return the IEEE-
1284 device ID
</dd>
1059 <dt>CUPS_SC_CMD_GET_STATE
</dt>
1060 <dd class=
"description">Return the device state
</dd>
1061 <dt>CUPS_SC_CMD_SNMP_GET
<span class=
"info"> CUPS
1.4 </span></dt>
1062 <dd class=
"description">Query an SNMP OID
</dd>
1063 <dt>CUPS_SC_CMD_SNMP_GET_NEXT
<span class=
"info"> CUPS
1.4 </span></dt>
1064 <dd class=
"description">Query the next SNMP OID
</dd>
1065 <dt>CUPS_SC_CMD_SOFT_RESET
</dt>
1066 <dd class=
"description">Do a soft reset
</dd>
1068 <h3 class=
"enumeration"><a name=
"cups_sc_state_e">cups_sc_state_e
</a></h3>
1069 <p class=
"description">Printer state bits
</p>
1070 <h4 class=
"constants">Constants
</h4>
1072 <dt>CUPS_SC_STATE_BUSY
</dt>
1073 <dd class=
"description">Device is busy
</dd>
1074 <dt>CUPS_SC_STATE_ERROR
</dt>
1075 <dd class=
"description">Other error condition
</dd>
1076 <dt>CUPS_SC_STATE_MARKER_EMPTY
</dt>
1077 <dd class=
"description">Toner/ink out condition
</dd>
1078 <dt>CUPS_SC_STATE_MARKER_LOW
</dt>
1079 <dd class=
"description">Toner/ink low condition
</dd>
1080 <dt>CUPS_SC_STATE_MEDIA_EMPTY
</dt>
1081 <dd class=
"description">Paper out condition
</dd>
1082 <dt>CUPS_SC_STATE_MEDIA_LOW
</dt>
1083 <dd class=
"description">Paper low condition
</dd>
1084 <dt>CUPS_SC_STATE_OFFLINE
</dt>
1085 <dd class=
"description">Device is off-line
</dd>
1086 <dt>CUPS_SC_STATE_ONLINE
</dt>
1087 <dd class=
"description">Device is on-line
</dd>
1089 <h3 class=
"enumeration"><a name=
"cups_sc_status_e">cups_sc_status_e
</a></h3>
1090 <p class=
"description">Response status codes
</p>
1091 <h4 class=
"constants">Constants
</h4>
1093 <dt>CUPS_SC_STATUS_BAD_MESSAGE
</dt>
1094 <dd class=
"description">The command/response message was invalid
</dd>
1095 <dt>CUPS_SC_STATUS_IO_ERROR
</dt>
1096 <dd class=
"description">An I/O error occurred
</dd>
1097 <dt>CUPS_SC_STATUS_NONE
</dt>
1098 <dd class=
"description">No status
</dd>
1099 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED
</dt>
1100 <dd class=
"description">Command not implemented
</dd>
1101 <dt>CUPS_SC_STATUS_NO_RESPONSE
</dt>
1102 <dd class=
"description">The device did not respond
</dd>
1103 <dt>CUPS_SC_STATUS_OK
</dt>
1104 <dd class=
"description">Operation succeeded
</dd>
1105 <dt>CUPS_SC_STATUS_TIMEOUT
</dt>
1106 <dd class=
"description">The backend did not respond
</dd>
1107 <dt>CUPS_SC_STATUS_TOO_BIG
</dt>
1108 <dd class=
"description">Response too big
</dd>