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 343 <!--
 344   "$Id: api-filter.header 7616 2008-05-28 00:34:13Z mike $"
 345
 346   Filter and backend programming header for CUPS.
 347
 348   Copyright 2008-2011 by Apple Inc.
 349
 350   These coded instructions, statements, and computer programs are the
 351   property of Apple Inc. and are protected by Federal copyright
 352   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 353   which should have been included with this file.  If this file is
 354   file is missing or damaged, see the license at "http://www.cups.org/".
 355 -->
 356
 357 <h1 class='title'>Filter and Backend Programming</h1>
 358
 359 <div class='summary'><table summary='General Information'>
 360 <thead>
 361 <tr>
 362         <th>Headers</th>
 363         <th>cups/backend.h<br>
 364         cups/sidechannel.h</th>
 365 </tr>
 366 </thead>
 367 <tbody>
 368 <tr>
 369         <th>Library</th>
 370         <td>-lcups</td>
 371 </tr>
 372 <tr>
 373         <th>See Also</th>
 374         <td>Programming: <a href='api-overview.html' target='_top'>Introduction to CUPS Programming</a><br>
 375         Programming: <a href='api-cups.html' target='_top'>CUPS API</a><br>
 376         Programming: <a href='api-ppd.html' target='_top'>PPD API</a><br>
 377         Programming: <a href='api-raster.html' target='_top'>Raster API</a><br>
 378         Programming: <a href='postscript-driver.html' target='_top'>Developing PostScript Printer Drivers</a><br>
 379         Programming: <a href='raster-driver.html' target='_top'>Developing Raster Printer Drivers</a><br>
 380         Specifications: <a href='spec-design.html' target='_top'>CUPS Design Description</a></td>
 381 </tr>
 382 </tbody>
 383 </table></div>
 384 <h2 class="title">Contents</h2>
 385 <ul class="contents">
 386 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 387         <li><a href="#SECURITY">Security Considerations</a></li>
 388         <li><a href="#SIGNALS">Canceled Jobs and Signal Handling</a></li>
 389         <li><a href="#PERMISSIONS">File Permissions</a></li>
 390         <li><a href="#TEMPFILES">Temporary Files</a></li>
 391         <li><a href="#COPIES">Copy Generation</a></li>
 392         <li><a href="#EXITCODES">Exit Codes</a></li>
 393         <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 394         <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 395         <li><a href="#COMMUNICATING_BACKEND">Communicating with the Backend</a></li>
 396         <li><a href="#COMMUNICATING_FILTER">Communicating with Filters</a></li>
 397         <li><a href="#SNMP">Doing SNMP Queries with Network Printers</a></li>
 398 </ul></li>
 399 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 400         <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 401         <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 402         <li><a href="#cupsBackendDeviceURI" title="Get the device URI for a backend.">cupsBackendDeviceURI</a></li>
 403         <li><a href="#cupsBackendReport" title="Write a device line from a backend.">cupsBackendReport</a></li>
 404         <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 405         <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 406         <li><a href="#cupsSideChannelSNMPGet" title="Query a SNMP OID's value.">cupsSideChannelSNMPGet</a></li>
 407         <li><a href="#cupsSideChannelSNMPWalk" title="Query multiple SNMP OID values.">cupsSideChannelSNMPWalk</a></li>
 408         <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 409 </ul></li>
 410 <li><a href="#TYPES">Data Types</a><ul class="code">
 411         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 412         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 413         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 414         <li><a href="#cups_sc_connected_t" title="Connectivity values">cups_sc_connected_t</a></li>
 415         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 416         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 417         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 418 </ul></li>
 419 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 420         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 421         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 422         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 423         <li><a href="#cups_sc_connected_e" title="Connectivity values">cups_sc_connected_e</a></li>
 424         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 425         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 426 </ul></li>
 427 </ul>
 428 <!--
 429   "$Id: api-filter.shtml 7677 2008-06-19 23:22:19Z mike $"
 430
 431   Filter and backend programming introduction for CUPS.
 432
 433   Copyright 2007-2013 by Apple Inc.
 434   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 435
 436   These coded instructions, statements, and computer programs are the
 437   property of Apple Inc. and are protected by Federal copyright
 438   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 439   which should have been included with this file.  If this file is
 440   file is missing or damaged, see the license at "http://www.cups.org/".
 441 -->
 442
 443 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 444
 445 <p>Filters (which include printer drivers and port monitors) and backends
 446 are used to convert job files to a printable format and send that data to the
 447 printer itself. All of these programs use a common interface for processing
 448 print jobs and communicating status information to the scheduler. Each is run
 449 with a standard set of command-line arguments:<p>
 450
 451 <dl class="code">
 452
 453         <dt>argv[1]</dt>
 454         <dd>The job ID</dd>
 455
 456         <dt>argv[2]</dt>
 457         <dd>The user printing the job</dd>
 458
 459         <dt>argv[3]</dt>
 460         <dd>The job name/title</dd>
 461
 462         <dt>argv[4]</dt>
 463         <dd>The number of copies to print</dd>
 464
 465         <dt>argv[5]</dt>
 466         <dd>The options that were provided when the job was submitted</dd>
 467
 468         <dt>argv[6]</dt>
 469         <dd>The file to print (first program only)</dd>
 470 </dl>
 471
 472 <p>The scheduler runs one or more of these programs to print any given job. The
 473 first filter reads from the print file and writes to the standard output, while
 474 the remaining filters read from the standard input and write to the standard
 475 output. The backend is the last filter in the chain and writes to the
 476 device.</p>
 477
 478 <p>Filters are always run as a non-privileged user, typically "lp", with no
 479 connection to the user's desktop. Backends are run either as a non-privileged
 480 user or as root if the file permissions do not allow user or group execution.
 481 The <a href="#PERMISSIONS">file permissions</a> section talks about this in
 482 more detail.</p>
 483
 484 <h3><a name="SECURITY">Security Considerations</a></h3>
 485
 486 <p>It is always important to use security programming practices. Filters and
 487 most backends are run as a non-privileged user, so the major security
 488 consideration is resource utilization - filters should not depend on unlimited
 489 amounts of CPU, memory, or disk space, and should protect against conditions
 490 that could lead to excess usage of any resource like infinite loops and
 491 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 492 specify an arbitrary file path to a separator page, template, or other file
 493 used by the filter since that can lead to an unauthorized disclosure of
 494 information. <em>Always</em> treat input as suspect and validate it!</p>
 495
 496 <p>If you are developing a backend that runs as root, make sure to check for
 497 potential buffer overflows, integer under/overflow conditions, and file
 498 accesses since these can lead to privilege escalations. When writing files,
 499 always validate the file path and <em>never</em> allow a user to determine
 500 where to store a file.</p>
 501
 502 <blockquote><b>Note:</b>
 503
 504 <p><em>Never</em> write files to a user's home directory. Aside from the
 505 security implications, CUPS is a network print service and as such the network
 506 user may not be the same as the local user and/or there may not be a local home
 507 directory to write to.</p>
 508
 509 <p>In addition, some operating systems provide additional security mechanisms
 510 that further limit file system access, even for backends running as root. On
 511 OS X, for example, no backend may write to a user's home directory.</p>
 512 </blockquote>
 513
 514 <h3><a name="SIGNALS">Canceled Jobs and Signal Handling</a></h3>
 515
 516 <p>The scheduler sends <code>SIGTERM</code> when a printing job is canceled or
 517 held. Filters, backends, and port monitors <em>must</em> catch
 518 <code>SIGTERM</code> and perform any cleanup necessary to produce a valid output
 519 file or return the printer to a known good state. The recommended behavior is to
 520 end the output on the current page, preferably on the current line or object
 521 being printed.</p>
 522
 523 <p>Filters and backends may also receive <code>SIGPIPE</code> when an upstream or downstream filter/backend exits with a non-zero status. Developers should generally ignore <code>SIGPIPE</code> at the beginning of <code>main()</code> with the following function call:</p>
 524
 525 <pre class="example">
 526 #include &lt;signal.h&gt;>
 527
 528 ...
 529
 530 int
 531 main(int argc, char *argv[])
 532 {
 533   signal(SIGPIPE, SIG_IGN);
 534
 535   ...
 536 }
 537 </pre>
 538
 539 <h3><a name="PERMISSIONS">File Permissions</a></h3>
 540
 541 <p>For security reasons, CUPS will only run filters and backends that are owned
 542 by root and do not have world or group write permissions. The recommended
 543 permissions for filters and backends are 0555 - read and execute but no write.
 544 Backends that must run as root should use permissions of 0500 - read and execute
 545 by root, no access for other users. Write permissions can be enabled for the
 546 root user only.</p>
 547
 548 <p>To avoid a warning message, the directory containing your filter(s) must also
 549 be owned by root and have world and group write disabled - permissions of 0755
 550 or 0555 are strongly encouraged.</p>
 551
 552 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 553
 554 <p>Temporary files should be created in the directory specified by the
 555 "TMPDIR" environment variable. The
 556 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 557 used to safely create temporary files in this directory.</p>
 558
 559 <h3><a name="COPIES">Copy Generation</a></h3>
 560
 561 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 562 of the input file. In general, you should only generate copies if the
 563 <em>filename</em> argument is supplied. The only exception to this are
 564 filters that produce device-independent PostScript output, since the PostScript
 565 filter <var>pstops</var> is responsible for generating copies of PostScript
 566 files.</p>
 567
 568 <h3><a name="EXITCODES">Exit Codes</a></h3>
 569
 570 <p>Filters must exit with status 0 when they successfully generate print data
 571 or 1 when they encounter an error. Backends can return any of the
 572 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 573
 574 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 575
 576 <p>The following environment variables are defined by the printing system
 577 when running print filters and backends:</p>
 578
 579 <dl class="code">
 580
 581         <dt>APPLE_LANGUAGE</dt>
 582         <dd>The Apple language identifier associated with the job
 583         (OS X only).</dd>
 584
 585         <dt>CHARSET</dt>
 586         <dd>The job character set, typically "utf-8".</dd>
 587
 588         <dt>CLASS</dt>
 589         <dd>When a job is submitted to a printer class, contains the name of
 590         the destination printer class. Otherwise this environment
 591         variable will not be set.</dd>
 592
 593         <dt>CONTENT_TYPE</dt>
 594         <dd>The MIME type associated with the file (e.g.
 595         application/postscript).</dd>
 596
 597         <dt>CUPS_CACHEDIR</dt>
 598         <dd>The directory where cache files can be stored. Cache files can be
 599         used to retain information between jobs or files in a job.</dd>
 600
 601         <dt>CUPS_DATADIR</dt>
 602         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 603
 604         <dt>CUPS_FILETYPE</dt>
 605         <dd>The type of file being printed: "job-sheet" for a banner page and
 606         "document" for a regular print file.</dd>
 607
 608         <dt>CUPS_SERVERROOT</dt>
 609         <dd>The root directory of the server.</dd>
 610
 611         <dt>DEVICE_URI</dt>
 612         <dd>The device-uri associated with the printer.</dd>
 613
 614         <dt>FINAL_CONTENT_TYPE</dt>
 615         <dd>The MIME type associated with the printer (e.g.
 616         application/vnd.cups-postscript).</dd>
 617
 618         <dt>LANG</dt>
 619         <dd>The language locale associated with the job.</dd>
 620
 621         <dt>PPD</dt>
 622         <dd>The full pathname of the PostScript Printer Description (PPD)
 623         file for this printer.</dd>
 624
 625         <dt>PRINTER</dt>
 626         <dd>The queue name of the class or printer.</dd>
 627
 628         <dt>RIP_CACHE</dt>
 629         <dd>The recommended amount of memory to use for Raster Image
 630         Processors (RIPs).</dd>
 631
 632         <dt>TMPDIR</dt>
 633         <dd>The directory where temporary files should be created.</dd>
 634
 635 </dl>
 636
 637 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 638
 639 <p>Filters and backends communicate with the scheduler by writing messages
 640 to the standard error file. The scheduler reads messages from all filters in
 641 a job and processes the message based on its prefix. For example, the following
 642 code sets the current printer state message to "Printing page 5":</p>
 643
 644 <pre class="example">
 645 int page = 5;
 646
 647 fprintf(stderr, "INFO: Printing page %d\n", page);
 648 </pre>
 649
 650 <p>Each message is a single line of text starting with one of the following
 651 prefix strings:</p>
 652
 653 <dl class="code">
 654
 655         <dt>ALERT: message</dt>
 656         <dd>Sets the printer-state-message attribute and adds the specified
 657         message to the current error log file using the "alert" log level.</dd>
 658
 659         <dt>ATTR: attribute=value [attribute=value]</dt>
 660         <dd>Sets the named printer or job attribute(s). Typically this is used
 661         to set the <code>marker-colors</code>, <code>marker-high-levels</code>,
 662         <code>marker-levels</code>, <code>marker-low-levels</code>,
 663         <code>marker-message</code>, <code>marker-names</code>,
 664         <code>marker-types</code>, <code>printer-alert</code>, and
 665         <code>printer-alert-description</code> printer attributes. Standard
 666         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 667         1</a>.</dd>
 668
 669         <dt>CRIT: message</dt>
 670         <dd>Sets the printer-state-message attribute and adds the specified
 671         message to the current error log file using the "critical" log
 672         level.</dd>
 673
 674         <dt>DEBUG: message</dt>
 675         <dd>Sets the printer-state-message attribute and adds the specified
 676         message to the current error log file using the "debug" log level.</dd>
 677
 678         <dt>DEBUG2: message</dt>
 679         <dd>Sets the printer-state-message attribute and adds the specified
 680         message to the current error log file using the "debug2" log level.</dd>
 681
 682         <dt>EMERG: message</dt>
 683         <dd>Sets the printer-state-message attribute and adds the specified
 684         message to the current error log file using the "emergency" log
 685         level.</dd>
 686
 687         <dt>ERROR: message</dt>
 688         <dd>Sets the printer-state-message attribute and adds the specified
 689         message to the current error log file using the "error" log level.
 690         Use "ERROR:" messages for non-persistent processing errors.</dd>
 691
 692         <dt>INFO: message</dt>
 693         <dd>Sets the printer-state-message attribute. If the current log level
 694         is set to "debug2", also adds the specified message to the current error
 695         log file using the "info" log level.</dd>
 696
 697         <dt>NOTICE: message</dt>
 698         <dd>Sets the printer-state-message attribute and adds the specified
 699         message to the current error log file using the "notice" log level.</dd>
 700
 701         <dt>PAGE: page-number #-copies</dt>
 702         <dt>PAGE: total #-pages</dt>
 703         <dd>Adds an entry to the current page log file. The first form adds
 704         #-copies to the job-media-sheets-completed attribute. The second
 705         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 706
 707         <dt>PPD: keyword=value [keyword=value ...]</dt>
 708         <dd>Changes or adds keywords to the printer's PPD file. Typically
 709         this is used to update installable options or default media settings
 710         based on the printer configuration.</dd>
 711
 712         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 713         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 714         <dd>Sets or clears printer-state-reason keywords for the current queue.
 715         Typically this is used to indicate persistent media, ink, toner, and
 716         configuration conditions or errors on a printer.
 717         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 718         use vendor-prefixed ("com.example.foo") keywords for custom states. See
 719         <a href="#MANAGING_STATE">Managing Printer State in a Filter</a> for more
 720         information.
 721
 722         <dt>WARNING: message</dt>
 723         <dd>Sets the printer-state-message attribute and adds the specified
 724         message to the current error log file using the "warning" log
 725         level.</dd>
 726
 727 </dl>
 728
 729 <p>Messages without one of these prefixes are treated as if they began with
 730 the "DEBUG:" prefix string.</p>
 731
 732 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 733 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 734 <thead>
 735 <tr>
 736         <th>marker-type</th>
 737         <th>Description</th>
 738 </tr>
 739 </thead>
 740 <tbody>
 741 <tr>
 742         <td>developer</td>
 743         <td>Developer unit</td>
 744 </tr>
 745 <tr>
 746         <td>fuser</td>
 747         <td>Fuser unit</td>
 748 </tr>
 749 <tr>
 750         <td>fuserCleaningPad</td>
 751         <td>Fuser cleaning pad</td>
 752 </tr>
 753 <tr>
 754         <td>fuserOil</td>
 755         <td>Fuser oil</td>
 756 </tr>
 757 <tr>
 758         <td>ink</td>
 759         <td>Ink supply</td>
 760 </tr>
 761 <tr>
 762         <td>opc</td>
 763         <td>Photo conductor</td>
 764 </tr>
 765 <tr>
 766         <td>solidWax</td>
 767         <td>Wax supply</td>
 768 </tr>
 769 <tr>
 770         <td>staples</td>
 771         <td>Staple supply</td>
 772 </tr>
 773 <tr>
 774         <td>toner</td>
 775         <td>Toner supply</td>
 776 </tr>
 777 <tr>
 778         <td>transferUnit</td>
 779         <td>Transfer unit</td>
 780 </tr>
 781 <tr>
 782         <td>wasteInk</td>
 783         <td>Waste ink tank</td>
 784 </tr>
 785 <tr>
 786         <td>wasteToner</td>
 787         <td>Waste toner tank</td>
 788 </tr>
 789 <tr>
 790         <td>wasteWax</td>
 791         <td>Waste wax tank</td>
 792 </tr>
 793 </tbody>
 794 </table></div>
 795
 796 <br>
 797
 798 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 799 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 800 <thead>
 801 <tr>
 802         <th>Keyword</th>
 803         <th>Description</th>
 804 </tr>
 805 </thead>
 806 <tbody>
 807 <tr>
 808         <td>connecting-to-device</td>
 809         <td>Connecting to printer but not printing yet.</td>
 810 </tr>
 811 <tr>
 812         <td>cover-open</td>
 813         <td>The printer's cover is open.</td>
 814 </tr>
 815 <tr>
 816         <td>input-tray-missing</td>
 817         <td>The paper tray is missing.</td>
 818 </tr>
 819 <tr>
 820         <td>marker-supply-empty</td>
 821         <td>The printer is out of ink.</td>
 822 </tr>
 823 <tr>
 824         <td>marker-supply-low</td>
 825         <td>The printer is almost out of ink.</td>
 826 </tr>
 827 <tr>
 828         <td>marker-waste-almost-full</td>
 829         <td>The printer's waste bin is almost full.</td>
 830 </tr>
 831 <tr>
 832         <td>marker-waste-full</td>
 833         <td>The printer's waste bin is full.</td>
 834 </tr>
 835 <tr>
 836         <td>media-empty</td>
 837         <td>The paper tray (any paper tray) is empty.</td>
 838 </tr>
 839 <tr>
 840         <td>media-jam</td>
 841         <td>There is a paper jam.</td>
 842 </tr>
 843 <tr>
 844         <td>media-low</td>
 845         <td>The paper tray (any paper tray) is almost empty.</td>
 846 </tr>
 847 <tr>
 848         <td>media-needed</td>
 849         <td>The paper tray needs to be filled (for a job that is printing).</td>
 850 </tr>
 851 <tr>
 852         <td>paused</td>
 853         <td>Stop the printer.</td>
 854 </tr>
 855 <tr>
 856         <td>timed-out</td>
 857         <td>Unable to connect to printer.</td>
 858 </tr>
 859 <tr>
 860         <td>toner-empty</td>
 861         <td>The printer is out of toner.</td>
 862 </tr>
 863 <tr>
 864         <td>toner-low</td>
 865         <td>The printer is low on toner.</td>
 866 </tr>
 867 </tbody>
 868 </table></div>
 869
 870 <h4><a name="MANAGING_STATE">Managing Printer State in a Filter</a></h4>
 871
 872 <p>Filters are responsible for managing the state keywords they set using
 873 "STATE:" messages. Typically you will update <em>all</em> of the keywords that
 874 are used by the filter at startup, for example:</p>
 875
 876 <pre class="example">
 877 if (foo_condition != 0)
 878   fputs("STATE: +com.example.foo\n", stderr);
 879 else
 880   fputs("STATE: -com.example.foo\n", stderr);
 881
 882 if (bar_condition != 0)
 883   fputs("STATE: +com.example.bar\n", stderr);
 884 else
 885   fputs("STATE: -com.example.bar\n", stderr);
 886 </pre>
 887
 888 <p>Then as conditions change, your filter sends "STATE: +keyword" or "STATE:
 889 -keyword" messages as necessary to set or clear the corresponding keyword,
 890 respectively.</p>
 891
 892 <p>State keywords are often used to notify the user of issues that span across
 893 jobs, for example "media-empty-warning" that indicates one or more paper trays
 894 are empty. These keywords should not be cleared unless the corresponding issue
 895 no longer exists.</p>
 896
 897 <p>Filters should clear job-related keywords on startup and exit so that they
 898 do not remain set between jobs.  For example, "connecting-to-device" is a job
 899 sub-state and not an issue that applies when a job is not printing.</p>
 900
 901 <blockquote><b>Note:</b>
 902
 903 <p>"STATE:" messages often provide visible alerts to the user. For example,
 904 on OS X setting a printer-state-reason value with an "-error" or
 905 "-warning" suffix will cause the printer's dock item to bounce if the
 906 corresponding reason is localized with a cupsIPPReason keyword in the
 907 printer's PPD file.</p>
 908
 909 <p>When providing a vendor-prefixed keyword, <em>always</em> provide the
 910 corresponding standard keyword (if any) to allow clients to respond to the
 911 condition correctly. For example, if you provide a vendor-prefixed keyword
 912 for a low cyan ink condition ("com.example.cyan-ink-low") you must also set the
 913 "marker-supply-low-warning" keyword. In such cases you should also refrain
 914 from localizing the vendor-prefixed keyword in the PPD file - otherwise both
 915 the generic and vendor-specific keyword will be shown in the user
 916 interface.</p>
 917
 918 </blockquote>
 919
 920 <h4><a name="REPORTING_SUPPLIES">Reporting Supply Levels</a></h4>
 921
 922 <p>CUPS tracks several "marker-*" attributes for ink/toner supply level
 923 reporting. These attributes allow applications to display the current supply
 924 levels for a printer without printer-specific software. <a href="#TABLE3">Table 3</a> lists the marker attributes and what they represent.</p>
 925
 926 <p>Filters set marker attributes by sending "ATTR:" messages to stderr. For
 927 example, a filter supporting an inkjet printer with black and tri-color ink
 928 cartridges would use the following to initialize the supply attributes:</p>
 929
 930 <pre class="example">
 931 fputs("ATTR: marker-colors=#000000,#00FFFF#FF00FF#FFFF00\n", stderr);
 932 fputs("ATTR: marker-low-levels=5,10\n", stderr);
 933 fputs("ATTR: marker-names=Black,Tri-Color\n", stderr);
 934 fputs("ATTR: marker-types=ink,ink\n", stderr);
 935 </pre>
 936
 937 <p>Then periodically the filter queries the printer for its current supply
 938 levels and updates them with a separate "ATTR:" message:</p>
 939
 940 <pre class="example">
 941 int black_level, tri_level;
 942 ...
 943 fprintf(stderr, "ATTR: marker-levels=%d,%d\n", black_level, tri_level);
 944 </pre>
 945
 946 <div class='table'><table width='80%' summary='Table 3: Supply Level Attributes'>
 947 <caption>Table 3: <a name='TABLE3'>Supply Level Attributes</a></caption>
 948 <thead>
 949 <tr>
 950         <th>Attribute</th>
 951         <th>Description</th>
 952 </tr>
 953 </thead>
 954 <tbody>
 955 <tr>
 956         <td>marker-colors</td>
 957         <td>A list of comma-separated colors; each color is either "none" or one or
 958         more hex-encoded sRGB colors of the form "#RRGGBB".</td>
 959 </tr>
 960 <tr>
 961         <td>marker-high-levels</td>
 962         <td>A list of comma-separated "almost full" level values from 0 to 100; a
 963         value of 100 should be used for supplies that are consumed/emptied like ink
 964         cartridges.</td>
 965 </tr>
 966 <tr>
 967         <td>marker-levels</td>
 968         <td>A list of comma-separated level values for each supply. A value of -1
 969         indicates the level is unavailable, -2 indicates unknown, and -3 indicates
 970         the level is unknown but has not yet reached capacity. Values from 0 to 100
 971         indicate the corresponding percentage.</td>
 972 </tr>
 973 <tr>
 974         <td>marker-low-levels</td>
 975         <td>A list of comma-separated "almost empty" level values from 0 to 100; a
 976         value of 0 should be used for supplies that are filled like waste ink
 977         tanks.</td>
 978 </tr>
 979 <tr>
 980         <td>marker-message</td>
 981         <td>A human-readable supply status message for the user like "12 pages of
 982         ink remaining."</td>
 983 </tr>
 984 <tr>
 985         <td>marker-names</td>
 986         <td>A list of comma-separated supply names like "Cyan Ink", "Fuser",
 987         etc.</td>
 988 </tr>
 989 <tr>
 990         <td>marker-types</td>
 991         <td>A list of comma-separated supply types; the types are listed in
 992         <a href="#TABLE1">Table 1</a>.</td>
 993 </tr>
 994 </tbody>
 995 </table></div>
 996
 997 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
 998
 999 <p>Filters can communicate with the backend via the
1000 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
1001 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
1002 functions. The
1003 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
1004 reads data that has been sent back from the device and is typically used to
1005 obtain status and configuration information. For example, the following code
1006 polls the backend for back-channel data:</p>
1007
1008 <pre class="example">
1009 #include &lt;cups/cups.h&gt;
1010
1011 char buffer[8192];
1012 ssize_t bytes;
1013
1014 /* Use a timeout of 0.0 seconds to poll for back-channel data */
1015 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
1016 </pre>
1017
1018 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
1019 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
1020 when it is available.</p>
1021
1022 <p>The
1023 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
1024 function allows you to get out-of-band status information and do synchronization
1025 with the device. For example, the following code gets the current IEEE-1284
1026 device ID string from the backend:</p>
1027
1028 <pre class="example">
1029 #include &lt;cups/sidechannel.h&gt;
1030
1031 char data[2049];
1032 int datalen;
1033 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
1034
1035 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
1036    nul-termination... */
1037 datalen = sizeof(data) - 1;
1038
1039 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
1040 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
1041
1042 /* Use the returned value if OK was returned and the length is non-zero */
1043 if (status == CUPS_SC_STATUS_OK &amp;&amp; datalen > 0)
1044   data[datalen] = '\0';
1045 else
1046   data[0] = '\0';
1047 </pre>
1048
1049 <h4><a name="DRAIN_OUTPUT">Forcing All Output to a Printer</a></h4>
1050
1051 <p>The
1052 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
1053 function allows you to tell the backend to send all pending data to the printer.
1054 This is most often needed when sending query commands to the printer. For example:</p>
1055
1056 <pre class="example">
1057 #include &lt;cups/cups.h&gt;
1058 #include &lt;cups/sidechannel.h&gt;
1059
1060 char data[1024];
1061 int datalen = sizeof(data);
1062 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
1063
1064 /* Flush pending output to stdout */
1065 fflush(stdout);
1066
1067 /* Drain output to backend, waiting for up to 30 seconds */
1068 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_DRAIN_OUTPUT, data, &amp;datalen, 30.0);
1069
1070 /* Read the response if the output was sent */
1071 if (status == CUPS_SC_STATUS_OK)
1072 {
1073   ssize_t bytes;
1074
1075   /* Wait up to 10.0 seconds for back-channel data */
1076   bytes = cupsBackChannelRead(data, sizeof(data), 10.0);
1077   /* do something with the data from the printer */
1078 }
1079 </pre>
1080
1081 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
1082
1083 <p>Backends communicate with filters using the reciprocal functions
1084 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
1085 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
1086 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
1087 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
1088
1089 <pre class="example">
1090 #include &lt;cups/cups.h&gt;
1091
1092 char buffer[8192];
1093 ssize_t bytes;
1094
1095 /* Obtain data from printer/device */
1096 ...
1097
1098 /* Use a timeout of 1.0 seconds to give filters a chance to read */
1099 cupsBackChannelWrite(buffer, bytes, 1.0);
1100 </pre>
1101
1102 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
1103 function reads a side-channel command from a filter, driver, or port monitor.
1104 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
1105 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
1106 separate thread for that purpose), or use <code>select</code> or
1107 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
1108 input and output on several file descriptors at the same time.</p>
1109
1110 <p>Once a command is processed, the backend uses the
1111 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
1112 to send its response. For example, the following code shows how to poll for a
1113 side-channel command and respond to it:</p>
1114
1115 <pre class="example">
1116 #include &lt;cups/sidechannel.h&gt;
1117
1118 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
1119 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
1120 char data[2048];
1121 int datalen = sizeof(data);
1122
1123 /* Poll for a command... */
1124 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
1125 {
1126   switch (command)
1127   {
1128     /* handle supported commands, fill data/datalen/status with values as needed */
1129
1130     default :
1131         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
1132         datalen = 0;
1133         break;
1134   }
1135
1136   /* Send a response... */
1137   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
1138 }
1139 </pre>
1140
1141 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
1142
1143 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
1144 status, page counter, and supply levels from most network printers. Every
1145 piece of information is associated with an Object Identifier (OID), and
1146 every printer has a <em>community</em> name associated with it. OIDs can be
1147 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
1148
1149 <p>The two CUPS SNMP functions provide a simple API for querying network
1150 printers through the side-channel interface. Each accepts a string containing
1151 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
1152 along with a timeout for the query.</p>
1153
1154 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
1155 function queries a single OID and returns the value as a string in a buffer
1156 you supply:</p>
1157
1158 <pre class="example">
1159 #include &lt;cups/sidechannel.h&gt;
1160
1161 char data[512];
1162 int datalen = sizeof(data);
1163
1164 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
1165         == CUPS_SC_STATUS_OK)
1166 {
1167   /* Do something with the value */
1168   printf("Page counter is: %s\n", data);
1169 }
1170 </pre>
1171
1172 <p>The
1173 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
1174 function allows you to query a whole group of OIDs, calling a function of your
1175 choice for each OID that is found:</p>
1176
1177 <pre class="example">
1178 #include &lt;cups/sidechannel.h&gt;
1179
1180 void
1181 my_callback(const char *oid, const char *data, int datalen, void *context)
1182 {
1183   /* Do something with the value */
1184   printf("%s=%s\n", oid, data);
1185 }
1186
1187 ...
1188
1189 void *my_data;
1190
1191 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
1192 </pre>
1193 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
1194 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/OS X 10.5&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
1195 <p class="description">Read data from the backchannel.</p>
1196 <p class="code">
1197 ssize_t cupsBackChannelRead (<br>
1198 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
1199 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1200 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1201 );</p>
1202 <h4 class="parameters">Parameters</h4>
1203 <dl>
1204 <dt>buffer</dt>
1205 <dd class="description">Buffer to read into</dd>
1206 <dt>bytes</dt>
1207 <dd class="description">Bytes to read</dd>
1208 <dt>timeout</dt>
1209 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
1210 </dl>
1211 <h4 class="returnvalue">Return Value</h4>
1212 <p class="description">Bytes read or -1 on error</p>
1213 <h4 class="discussion">Discussion</h4>
1214 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
1215 parameter controls how many seconds to wait for the data - use 0.0 to
1216 return immediately if there is no data, -1.0 to wait for data indefinitely.
1217
1218 </p>
1219 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/OS X 10.5&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
1220 <p class="description">Write data to the backchannel.</p>
1221 <p class="code">
1222 ssize_t cupsBackChannelWrite (<br>
1223 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
1224 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1225 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1226 );</p>
1227 <h4 class="parameters">Parameters</h4>
1228 <dl>
1229 <dt>buffer</dt>
1230 <dd class="description">Buffer to write</dd>
1231 <dt>bytes</dt>
1232 <dd class="description">Bytes to write</dd>
1233 <dt>timeout</dt>
1234 <dd class="description">Timeout in seconds, typically 1.0</dd>
1235 </dl>
1236 <h4 class="returnvalue">Return Value</h4>
1237 <p class="description">Bytes written or -1 on error</p>
1238 <h4 class="discussion">Discussion</h4>
1239 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
1240 controls how many seconds to wait for the data to be written - use
1241 0.0 to return immediately if the data cannot be written, -1.0 to wait
1242 indefinitely.
1243
1244 </p>
1245 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/OS X 10.5&nbsp;</span><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
1246 <p class="description">Get the device URI for a backend.</p>
1247 <p class="code">
1248 const char *cupsBackendDeviceURI (<br>
1249 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
1250 );</p>
1251 <h4 class="parameters">Parameters</h4>
1252 <dl>
1253 <dt>argv</dt>
1254 <dd class="description">Command-line arguments</dd>
1255 </dl>
1256 <h4 class="returnvalue">Return Value</h4>
1257 <p class="description">Device URI or <code>NULL</code></p>
1258 <h4 class="discussion">Discussion</h4>
1259 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
1260 function returns the device URI passed in the DEVICE_URI environment
1261 variable or the device URI passed in argv[0], whichever is found
1262 first.
1263
1264 </p>
1265 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span><a name="cupsBackendReport">cupsBackendReport</a></h3>
1266 <p class="description">Write a device line from a backend.</p>
1267 <p class="code">
1268 void cupsBackendReport (<br>
1269 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
1270 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
1271 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
1272 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
1273 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
1274 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
1275 );</p>
1276 <h4 class="parameters">Parameters</h4>
1277 <dl>
1278 <dt>device_scheme</dt>
1279 <dd class="description">device-scheme string</dd>
1280 <dt>device_uri</dt>
1281 <dd class="description">device-uri string</dd>
1282 <dt>device_make_and_model</dt>
1283 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
1284 <dt>device_info</dt>
1285 <dd class="description">device-info string or <code>NULL</code></dd>
1286 <dt>device_id</dt>
1287 <dd class="description">device-id string or <code>NULL</code></dd>
1288 <dt>device_location</dt>
1289 <dd class="description">device-location string or <code>NULL</code></dd>
1290 </dl>
1291 <h4 class="discussion">Discussion</h4>
1292 <p class="discussion">This function writes a single device line to stdout for a backend.
1293 It handles quoting of special characters in the device-make-and-model,
1294 device-info, device-id, and device-location strings.
1295
1296 </p>
1297 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/OS X 10.5&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
1298 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
1299 <p class="code">
1300 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
1301 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1302 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1303 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1304 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1305 );</p>
1306 <h4 class="parameters">Parameters</h4>
1307 <dl>
1308 <dt>command</dt>
1309 <dd class="description">Command to send</dd>
1310 <dt>data</dt>
1311 <dd class="description">Response data buffer pointer</dd>
1312 <dt>datalen</dt>
1313 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1314 <dt>timeout</dt>
1315 <dd class="description">Timeout in seconds</dd>
1316 </dl>
1317 <h4 class="returnvalue">Return Value</h4>
1318 <p class="description">Status of command</p>
1319 <h4 class="discussion">Discussion</h4>
1320 <p class="discussion">This function is normally only called by filters, drivers, or port
1321 monitors in order to communicate with the backend used by the current
1322 printer.  Programs must be prepared to handle timeout or &quot;not
1323 implemented&quot; status codes, which indicate that the backend or device
1324 do not support the specified side-channel command.<br>
1325 <br>
1326 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1327 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1328 update the value to contain the number of data bytes in the buffer.
1329
1330 </p>
1331 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/OS X 10.5&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1332 <p class="description">Read a side-channel message.</p>
1333 <p class="code">
1334 int cupsSideChannelRead (<br>
1335 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1336 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1337 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1338 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1339 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1340 );</p>
1341 <h4 class="parameters">Parameters</h4>
1342 <dl>
1343 <dt>command</dt>
1344 <dd class="description">Command code</dd>
1345 <dt>status</dt>
1346 <dd class="description">Status code</dd>
1347 <dt>data</dt>
1348 <dd class="description">Data buffer pointer</dd>
1349 <dt>datalen</dt>
1350 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1351 <dt>timeout</dt>
1352 <dd class="description">Timeout in seconds</dd>
1353 </dl>
1354 <h4 class="returnvalue">Return Value</h4>
1355 <p class="description">0 on success, -1 on error</p>
1356 <h4 class="discussion">Discussion</h4>
1357 <p class="discussion">This function is normally only called by backend programs to read
1358 commands from a filter, driver, or port monitor program.  The
1359 caller must be prepared to handle incomplete or invalid messages
1360 and return the corresponding status codes.<br>
1361 <br>
1362 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1363 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1364 update the value to contain the number of data bytes in the buffer.
1365
1366 </p>
1367 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1368 <p class="description">Query a SNMP OID's value.</p>
1369 <p class="code">
1370 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1371 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1372 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1373 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1374 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1375 );</p>
1376 <h4 class="parameters">Parameters</h4>
1377 <dl>
1378 <dt>oid</dt>
1379 <dd class="description">OID to query</dd>
1380 <dt>data</dt>
1381 <dd class="description">Buffer for OID value</dd>
1382 <dt>datalen</dt>
1383 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1384 <dt>timeout</dt>
1385 <dd class="description">Timeout in seconds</dd>
1386 </dl>
1387 <h4 class="returnvalue">Return Value</h4>
1388 <p class="description">Query status</p>
1389 <h4 class="discussion">Discussion</h4>
1390 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1391 filter, port monitor, or backend using the default community name.<br>
1392 <br>
1393 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1394 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1395 supported and must be converted to their numeric forms.<br>
1396 <br>
1397 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1398 buffer to hold the OID value as a string. HEX-String (binary) values are
1399 converted to hexadecimal strings representing the binary data, while
1400 NULL-Value and unknown OID types are returned as the empty string.
1401 The returned &quot;datalen&quot; does not include the trailing nul.
1402
1403 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1404 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1405 the printer does not respond to the SNMP query.
1406
1407 </p>
1408 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1409 <p class="description">Query multiple SNMP OID values.</p>
1410 <p class="code">
1411 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1412 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1413 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1414 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1415 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1416 );</p>
1417 <h4 class="parameters">Parameters</h4>
1418 <dl>
1419 <dt>oid</dt>
1420 <dd class="description">First numeric OID to query</dd>
1421 <dt>timeout</dt>
1422 <dd class="description">Timeout for each query in seconds</dd>
1423 <dt>cb</dt>
1424 <dd class="description">Function to call with each value</dd>
1425 <dt>context</dt>
1426 <dd class="description">Application-defined pointer to send to callback</dd>
1427 </dl>
1428 <h4 class="returnvalue">Return Value</h4>
1429 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1430 <h4 class="discussion">Discussion</h4>
1431 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1432 of the filter, port monitor, or backend using the default community name.
1433 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1434 the callback function you provide.<br>
1435 <br>
1436 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1437 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1438 supported and must be converted to their numeric forms.<br>
1439 <br>
1440 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1441 time will depend on the number of OID values found and the time required
1442 for each query.<br>
1443 <br>
1444 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1445 is an application-defined pointer that is sent to the callback function
1446 along with the OID and current data. The data passed to the callback is the
1447 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1448
1449 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1450 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1451 the printer does not respond to the first SNMP query.
1452
1453 </p>
1454 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/OS X 10.5&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1455 <p class="description">Write a side-channel message.</p>
1456 <p class="code">
1457 int cupsSideChannelWrite (<br>
1458 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1459 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1460 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1461 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1462 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1463 );</p>
1464 <h4 class="parameters">Parameters</h4>
1465 <dl>
1466 <dt>command</dt>
1467 <dd class="description">Command code</dd>
1468 <dt>status</dt>
1469 <dd class="description">Status code</dd>
1470 <dt>data</dt>
1471 <dd class="description">Data buffer pointer</dd>
1472 <dt>datalen</dt>
1473 <dd class="description">Number of bytes of data</dd>
1474 <dt>timeout</dt>
1475 <dd class="description">Timeout in seconds</dd>
1476 </dl>
1477 <h4 class="returnvalue">Return Value</h4>
1478 <p class="description">0 on success, -1 on error</p>
1479 <h4 class="discussion">Discussion</h4>
1480 <p class="discussion">This function is normally only called by backend programs to send
1481 responses to a filter, driver, or port monitor program.
1482
1483 </p>
1484 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1485 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1486 <p class="description">Backend exit codes</p>
1487 <p class="code">
1488 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1489 </p>
1490 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1491 <p class="description">Bidirectional capabilities</p>
1492 <p class="code">
1493 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1494 </p>
1495 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1496 <p class="description">Request command codes</p>
1497 <p class="code">
1498 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1499 </p>
1500 <h3 class="typedef"><a name="cups_sc_connected_t">cups_sc_connected_t</a></h3>
1501 <p class="description">Connectivity values</p>
1502 <p class="code">
1503 typedef enum <a href="#cups_sc_connected_e">cups_sc_connected_e</a> cups_sc_connected_t;
1504 </p>
1505 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1506 <p class="description">Printer state bits</p>
1507 <p class="code">
1508 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1509 </p>
1510 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1511 <p class="description">Response status codes</p>
1512 <p class="code">
1513 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1514 </p>
1515 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1516 <p class="description">SNMP walk callback</p>
1517 <p class="code">
1518 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1519 </p>
1520 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1521 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1522 <p class="description">Backend exit codes</p>
1523 <h4 class="constants">Constants</h4>
1524 <dl>
1525 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1526 <dd class="description">Job failed, authentication required</dd>
1527 <dt>CUPS_BACKEND_CANCEL </dt>
1528 <dd class="description">Job failed, cancel job</dd>
1529 <dt>CUPS_BACKEND_FAILED </dt>
1530 <dd class="description">Job failed, use error-policy</dd>
1531 <dt>CUPS_BACKEND_HOLD </dt>
1532 <dd class="description">Job failed, hold job</dd>
1533 <dt>CUPS_BACKEND_OK </dt>
1534 <dd class="description">Job completed successfully</dd>
1535 <dt>CUPS_BACKEND_RETRY </dt>
1536 <dd class="description">Job failed, retry this job later</dd>
1537 <dt>CUPS_BACKEND_RETRY_CURRENT </dt>
1538 <dd class="description">Job failed, retry this job immediately</dd>
1539 <dt>CUPS_BACKEND_STOP </dt>
1540 <dd class="description">Job failed, stop queue</dd>
1541 </dl>
1542 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1543 <p class="description">Bidirectional capability values</p>
1544 <h4 class="constants">Constants</h4>
1545 <dl>
1546 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1547 <dd class="description">Bidirectional I/O is not supported</dd>
1548 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1549 <dd class="description">Bidirectional I/O is supported</dd>
1550 </dl>
1551 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1552 <p class="description">Request command codes</p>
1553 <h4 class="constants">Constants</h4>
1554 <dl>
1555 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1556 <dd class="description">Drain all pending output</dd>
1557 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1558 <dd class="description">Return bidirectional capabilities</dd>
1559 <dt>CUPS_SC_CMD_GET_CONNECTED <span class="info">&nbsp;CUPS 1.5/OS X 10.7&nbsp;</span></dt>
1560 <dd class="description">Return whether the backend is &quot;connected&quot; to the printer </dd>
1561 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1562 <dd class="description">Return the IEEE-1284 device ID</dd>
1563 <dt>CUPS_SC_CMD_GET_STATE </dt>
1564 <dd class="description">Return the device state</dd>
1565 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span></dt>
1566 <dd class="description">Query an SNMP OID </dd>
1567 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span></dt>
1568 <dd class="description">Query the next SNMP OID </dd>
1569 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1570 <dd class="description">Do a soft reset</dd>
1571 </dl>
1572 <h3 class="enumeration"><a name="cups_sc_connected_e">cups_sc_connected_e</a></h3>
1573 <p class="description">Connectivity values</p>
1574 <h4 class="constants">Constants</h4>
1575 <dl>
1576 <dt>CUPS_SC_CONNECTED </dt>
1577 <dd class="description">Backend is &quot;connected&quot; to printer</dd>
1578 <dt>CUPS_SC_NOT_CONNECTED </dt>
1579 <dd class="description">Backend is not &quot;connected&quot; to printer</dd>
1580 </dl>
1581 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1582 <p class="description">Printer state bits</p>
1583 <h4 class="constants">Constants</h4>
1584 <dl>
1585 <dt>CUPS_SC_STATE_BUSY </dt>
1586 <dd class="description">Device is busy</dd>
1587 <dt>CUPS_SC_STATE_ERROR </dt>
1588 <dd class="description">Other error condition</dd>
1589 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1590 <dd class="description">Toner/ink out condition</dd>
1591 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1592 <dd class="description">Toner/ink low condition</dd>
1593 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1594 <dd class="description">Paper out condition</dd>
1595 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1596 <dd class="description">Paper low condition</dd>
1597 <dt>CUPS_SC_STATE_OFFLINE </dt>
1598 <dd class="description">Device is offline</dd>
1599 <dt>CUPS_SC_STATE_ONLINE </dt>
1600 <dd class="description">Device is online</dd>
1601 </dl>
1602 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1603 <p class="description">Response status codes</p>
1604 <h4 class="constants">Constants</h4>
1605 <dl>
1606 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1607 <dd class="description">The command/response message was invalid</dd>
1608 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1609 <dd class="description">An I/O error occurred</dd>
1610 <dt>CUPS_SC_STATUS_NONE </dt>
1611 <dd class="description">No status</dd>
1612 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1613 <dd class="description">Command not implemented</dd>
1614 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1615 <dd class="description">The device did not respond</dd>
1616 <dt>CUPS_SC_STATUS_OK </dt>
1617 <dd class="description">Operation succeeded</dd>
1618 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1619 <dd class="description">The backend did not respond</dd>
1620 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1621 <dd class="description">Response too big</dd>
1622 </dl>
1623 </div>
1624 </body>
1625 </html>