doc/help/api-filter.html

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 340 <!--
 341   "$Id: api-filter.header 8627 2009-05-13 21:39:17Z mike $"
 342
 343   Filter and backend programming header for the Common UNIX Printing System
 344   (CUPS).
 345
 346   Copyright 2008-2009 by Apple Inc.
 347
 348   These coded instructions, statements, and computer programs are the
 349   property of Apple Inc. and are protected by Federal copyright
 350   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 351   which should have been included with this file.  If this file is
 352   file is missing or damaged, see the license at "http://www.cups.org/".
 353 -->
 354
 355 <h1 class='title'>Filter and Backend Programming</h1>
 356
 357 <div class='summary'><table summary='General Information'>
 358 <thead>
 359 <tr>
 360         <th>Headers</th>
 361         <th>cups/backend.h<br>
 362         cups/sidechannel.h</th>
 363 </tr>
 364 </thead>
 365 <tbody>
 366 <tr>
 367         <th>Library</th>
 368         <td>-lcups</td>
 369 </tr>
 370 <tr>
 371         <th>See Also</th>
 372         <td>Programming: <a href='api-overview.html' target='_top'>Introduction to CUPS Programming</a><br>
 373         Programming: <a href='api-cups.html' target='_top'>CUPS API</a><br>
 374         Programming: <a href='api-ppd.html' target='_top'>PPD API</a><br>
 375         Programming: <a href='api-raster.html' target='_top'>Raster API</a><br>
 376         Specifications: <a href='spec-design' target='_top'>CUPS Design Description</a></td>
 377 </tr>
 378 </tbody>
 379 </table></div>
 380 <h2 class="title">Contents</h2>
 381 <ul class="contents">
 382 <ul class="subcontents">
 383 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 384 <li><a href="#SECURITY">Security Considerations</a></li>
 385 <li><a href="#PERMISSIONS">File Permissions</a></li>
 386 <li><a href="#TEMPFILES">Temporary Files</a></li>
 387 <li><a href="#COPIES">Copy Generation</a></li>
 388 <li><a href="#EXITCODES">Exit Codes</a></li>
 389 <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 390 <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 391 <li><a href="#COMMUNICATING_BACKEND">Communicating with the Backend</a></li>
 392 <li><a href="#COMMUNICATING_FILTER">Communicating with Filters</a></li>
 393 <li><a href="#SNMP">Doing SNMP Queries with Network Printers</a></li>
 394 </ul></li>
 395 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 396 <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 397 <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 398 <li><a href="#cupsBackendDeviceURI" title="Get the device URI for a backend.">cupsBackendDeviceURI</a></li>
 399 <li><a href="#cupsBackendReport" title="Write a device line from a backend.">cupsBackendReport</a></li>
 400 <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 401 <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 402 <li><a href="#cupsSideChannelSNMPGet" title="Query a SNMP OID's value.">cupsSideChannelSNMPGet</a></li>
 403 <li><a href="#cupsSideChannelSNMPWalk" title="Query multiple SNMP OID values.">cupsSideChannelSNMPWalk</a></li>
 404 <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 405 </ul></li>
 406 <li><a href="#TYPES">Data Types</a><ul class="code">
 407         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 408         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 409         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 410         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 411         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 412         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 413 </ul></li>
 414 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 415         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 416         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 417         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 418         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 419         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 420 </ul></li>
 421 <!--
 422   "$Id: api-filter.shtml 7962 2008-09-18 17:31:33Z mike $"
 423
 424   Filter and backend programming introduction for the Common UNIX Printing
 425   System (CUPS).
 426
 427   Copyright 2007-2009 by Apple Inc.
 428   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 429
 430   These coded instructions, statements, and computer programs are the
 431   property of Apple Inc. and are protected by Federal copyright
 432   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 433   which should have been included with this file.  If this file is
 434   file is missing or damaged, see the license at "http://www.cups.org/".
 435 -->
 436
 437 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 438
 439 <p>Filters (which include printer drivers and port monitors) and backends
 440 are used to convert job files to a printable format and send that data to the
 441 printer itself. All of these programs use a common interface for processing
 442 print jobs and communicating status information to the scheduler. Each is run
 443 with a standard set of command-line arguments:<p>
 444
 445 <dl class="code">
 446
 447         <dt>argv[1]</dt>
 448         <dd>The job ID</dd>
 449
 450         <dt>argv[2]</dt>
 451         <dd>The user printing the job</dd>
 452
 453         <dt>argv[3]</dt>
 454         <dd>The job name/title</dd>
 455
 456         <dt>argv[4]</dt>
 457         <dd>The number of copies to print</dd>
 458
 459         <dt>argv[5]</dt>
 460         <dd>The options that were provided when the job was submitted</dd>
 461
 462         <dt>argv[6]</dt>
 463         <dd>The file to print (first program only)</dd>
 464 </dl>
 465
 466 <p>The scheduler runs one or more of these programs to print any given job. The
 467 first filter reads from the print file and writes to the standard output, while
 468 the remaining filters read from the standard input and write to the standard
 469 output. The backend is the last filter in the chain and writes to the
 470 device.</p>
 471
 472 <p>Filters are always run as a non-privileged user, typically "lp", with no
 473 connection to the user's desktop. Backends are run either as a non-privileged
 474 user or as root if the file permissions do not allow user or group execution.
 475 The <a href="#PERMISSIONS">file permissions</a> section talks about this in
 476 more detail.</p>
 477
 478 <h3><a name="SECURITY">Security Considerations</a></h3>
 479
 480 <p>It is always important to use security programming practices. Filters and
 481 most backends are run as a non-priviledged user, so the major security
 482 consideration is resource utilization - filters should not depend on unlimited
 483 amounts of CPU, memory, or disk space, and should protect against conditions
 484 that could lead to excess usage of any resource like infinite loops and
 485 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 486 specify an arbitrary file path to a separator page, template, or other file
 487 used by the filter since that can lead to an unauthorized disclosure of
 488 information. <em>Always</em> treat input as suspect and validate it!</p>
 489
 490 <p>If you are developing a backend that runs as root , make sure to check for
 491 potential buffer overflows, integer under/overflow conditions, and file
 492 accesses since these can lead to privilege escalations. When writing files,
 493 always validate the file path and <em>never</em> allow a user to determine
 494 where to store a file.</p>
 495
 496 <blockquote><b>Note:</b>
 497
 498 <p><em>Never</em> write files to a user's home directory. Aside from the
 499 security implications, CUPS is a network print service and as such the network
 500 user may not be the same as the local user and/or there may not be a local home
 501 directory to write to.</p>
 502
 503 <p>In addition, some operating systems provide additional security mechanisms
 504 that further limit file system access, even for backends running as root. On
 505 Mac OS X, for example, no backend may write to a user's home directory.</p>
 506 </blockquote>
 507
 508 <h3><a name="PERMISSIONS">File Permissions</a></h3>
 509
 510 <p>For security reasons, CUPS will only run filters and backends that are owned
 511 by root and do not have world write permissions. The recommended permissions for
 512 filters and backends are 0555 - read and execute but no write. Backends that
 513 must run as root should use permissions of 0500 - read and execute by root, no
 514 access for other users. Write permissions can be enabled for the root user
 515 only.</p>
 516
 517 <p>To avoid a warning message, the directory containing your filter(s) must also
 518 be owned by root and have world write disabled - permissions of 0755 or 0555 are
 519 strongly encouraged.</p>
 520
 521 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 522
 523 <p>Temporary files should be created in the directory specified by the
 524 "TMPDIR" environment variable. The
 525 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 526 used to safely create temporary files in this directory.</p>
 527
 528 <h3><a name="COPIES">Copy Generation</a></h3>
 529
 530 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 531 of the input file. In general, you should only generate copies if the
 532 <em>filename</em> argument is supplied. The only exception to this are
 533 filters that produce device-independent PostScript output, since the PostScript
 534 filter <var>pstops</var> is responsible for generating copies of PostScript
 535 files.</p>
 536
 537 <h3><a name="EXITCODES">Exit Codes</a></h3>
 538
 539 <p>Filters must exit with status 0 when they successfully generate print data
 540 or 1 when they encounter an error. Backends can return any of the
 541 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 542
 543 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 544
 545 <p>The following environment variables are defined by the printing system
 546 when running print filters and backends:</p>
 547
 548 <dl class="code">
 549
 550         <dt>APPLE_LANGUAGES</dt>
 551         <dd>The Apple language identifier associated with the job
 552         (Mac OS X only).</dd>
 553
 554         <dt>CHARSET</dt>
 555         <dd>The job character set, typically "utf-8".</dd>
 556
 557         <dt>CLASS</dt>
 558         <dd>When a job is submitted to a printer class, contains the name of
 559         the destination printer class. Otherwise this environment
 560         variable will not be set.</dd>
 561
 562         <dt>CONTENT_TYPE</dt>
 563         <dd>The MIME type associated with the file (e.g.
 564         application/postscript).</dd>
 565
 566         <dt>CUPS_CACHEDIR</dt>
 567         <dd>The directory where cache files can be stored. Cache files can be
 568         used to retain information between jobs or files in a job.</dd>
 569
 570         <dt>CUPS_DATADIR</dt>
 571         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 572
 573         <dt>CUPS_FILETYPE</dt>
 574         <dd>The type of file being printed: "job-sheet" for a banner page and
 575         "document" for a regular print file.</dd>
 576
 577         <dt>CUPS_SERVERROOT</dt>
 578         <dd>The root directory of the server.</dd>
 579
 580         <dt>DEVICE_URI</dt>
 581         <dd>The device-uri associated with the printer.</dd>
 582
 583         <dt>FINAL_CONTENT_TYPE</dt>
 584         <dd>The MIME type associated with the printer (e.g.
 585         application/vnd.cups-postscript).</dd>
 586
 587         <dt>LANG</dt>
 588         <dd>The language locale associated with the job.</dd>
 589
 590         <dt>PPD</dt>
 591         <dd>The full pathname of the PostScript Printer Description (PPD)
 592         file for this printer.</dd>
 593
 594         <dt>PRINTER</dt>
 595         <dd>The queue name of the class or printer.</dd>
 596
 597         <dt>RIP_CACHE</dt>
 598         <dd>The recommended amount of memory to use for Raster Image
 599         Processors (RIPs).</dd>
 600
 601         <dt>TMPDIR</dt>
 602         <dd>The directory where temporary files should be created.</dd>
 603
 604 </dl>
 605
 606 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 607
 608 <p>Filters and backends communicate with the scheduler by writing messages
 609 to the standard error file. The scheduler reads messages from all filters in
 610 a job and processes the message based on its prefix. For example, the following
 611 code sets the current printer state message to "Printing page 5":</p>
 612
 613 <pre class="example">
 614 int page = 5;
 615
 616 fprintf(stderr, "INFO: Printing page %d\n", page);
 617 </pre>
 618
 619 <p>Each message is a single line of text starting with one of the following
 620 prefix strings:</p>
 621
 622 <dl class="code">
 623
 624         <dt>ALERT: message</dt>
 625         <dd>Sets the printer-state-message attribute and adds the specified
 626         message to the current error log file using the "alert" log level.</dd>
 627
 628         <dt>ATTR: attribute=value [attribute=value]</dt>
 629         <dd>Sets the named printer or job attribute(s). Typically this is used
 630         to set the <code>marker-colors</code>, <code>marker-levels</code>,
 631         <code>marker-message</code>, <code>marker-names</code>,
 632         <code>marker-types</code>, <code>printer-alert</code>, and
 633         <code>printer-alert-description</code> printer attributes. Standard
 634         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 635         1</a>.</dd>
 636
 637         <dt>CRIT: message</dt>
 638         <dd>Sets the printer-state-message attribute and adds the specified
 639         message to the current error log file using the "critical" log
 640         level.</dd>
 641
 642         <dt>DEBUG: message</dt>
 643         <dd>Sets the printer-state-message attribute and adds the specified
 644         message to the current error log file using the "debug" log level.</dd>
 645
 646         <dt>DEBUG2: message</dt>
 647         <dd>Sets the printer-state-message attribute and adds the specified
 648         message to the current error log file using the "debug2" log level.</dd>
 649
 650         <dt>EMERG: message</dt>
 651         <dd>Sets the printer-state-message attribute and adds the specified
 652         message to the current error log file using the "emergency" log
 653         level.</dd>
 654
 655         <dt>ERROR: message</dt>
 656         <dd>Sets the printer-state-message attribute and adds the specified
 657         message to the current error log file using the "error" log level.
 658         Use "ERROR:" messages for non-persistent processing errors.</dd>
 659
 660         <dt>INFO: message</dt>
 661         <dd>Sets the printer-state-message attribute. If the current log level
 662         is set to "debug2", also adds the specified message to the current error
 663         log file using the "info" log level.</dd>
 664
 665         <dt>NOTICE: message</dt>
 666         <dd>Sets the printer-state-message attribute and adds the specified
 667         message to the current error log file using the "notice" log level.</dd>
 668
 669         <dt>PAGE: page-number #-copies</dt>
 670         <dt>PAGE: total #-pages</dt>
 671         <dd>Adds an entry to the current page log file. The first form adds
 672         #-copies to the job-media-sheets-completed attribute. The second
 673         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 674
 675         <dt>PPD: keyword=value [keyword=value ...]</dt>
 676         <dd>Changes or adds keywords to the printer's PPD file. Typically
 677         this is used to update installable options or default media settings
 678         based on the printer configuration.</dd>
 679
 680         <dt>STATE: printer-state-reason [printer-state-reason ...]</dt>
 681         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 682         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 683         <dd>Sets, adds, or removes printer-state-reason keywords to the
 684         current queue. Typically this is used to indicate persistent media,
 685         ink, toner, and configuration conditions or errors on a printer.
 686         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 687         use vendor-prefixed ("com.acme.foo") keywords for custom states.</dd>
 688
 689         <dt>WARNING: message</dt>
 690         <dd>Sets the printer-state-message attribute and adds the specified
 691         message to the current error log file using the "warning" log
 692         level.</dd>
 693
 694 </dl>
 695
 696 <p>Messages without one of these prefixes are treated as if they began with
 697 the "DEBUG:" prefix string.</p>
 698
 699
 700 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 701 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 702 <thead>
 703 <tr>
 704         <th>marker-type</th>
 705         <th>Description</th>
 706 </tr>
 707 </thead>
 708 <tbody>
 709 <tr>
 710         <td>developer</td>
 711         <td>Developer unit</td>
 712 </tr>
 713 <tr>
 714         <td>fuser</td>
 715         <td>Fuser unit</td>
 716 </tr>
 717 <tr>
 718         <td>fuserCleaningPad</td>
 719         <td>Fuser cleaning pad</td>
 720 </tr>
 721 <tr>
 722         <td>fuserOil</td>
 723         <td>Fuser oil</td>
 724 </tr>
 725 <tr>
 726         <td>ink</td>
 727         <td>Ink supply</td>
 728 </tr>
 729 <tr>
 730         <td>opc</td>
 731         <td>Photo conductor</td>
 732 </tr>
 733 <tr>
 734         <td>solidWax</td>
 735         <td>Wax supply</td>
 736 </tr>
 737 <tr>
 738         <td>staples</td>
 739         <td>Staple supply</td>
 740 </tr>
 741 <tr>
 742         <td>toner</td>
 743         <td>Toner supply</td>
 744 </tr>
 745 <tr>
 746         <td>transferUnit</td>
 747         <td>Transfer unit</td>
 748 </tr>
 749 <tr>
 750         <td>wasteInk</td>
 751         <td>Waste ink tank</td>
 752 </tr>
 753 <tr>
 754         <td>wasteToner</td>
 755         <td>Waste toner tank</td>
 756 </tr>
 757 <tr>
 758         <td>wasteWax</td>
 759         <td>Waste wax tank</td>
 760 </tr>
 761 </tbody>
 762 </table></div>
 763
 764 <br>
 765
 766 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 767 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 768 <thead>
 769 <tr>
 770         <th>Keyword</th>
 771         <th>Description</th>
 772 </tr>
 773 </thead>
 774 <tbody>
 775 <tr>
 776         <td>connecting-to-device</td>
 777         <td>Connecting to printer but not printing yet</td>
 778 </tr>
 779 <tr>
 780         <td>cover-open</td>
 781         <td>A cover is open on the printer</td>
 782 </tr>
 783 <tr>
 784         <td>input-tray-missing</td>
 785         <td>An input tray is missing from the printer</td>
 786 </tr>
 787 <tr>
 788         <td>marker-supply-empty</td>
 789         <td>Out of ink</td>
 790 </tr>
 791 <tr>
 792         <td>marker-supply-low</td>
 793         <td>Low on ink</td>
 794 </tr>
 795 <tr>
 796         <td>marker-waste-almost-full</td>
 797         <td>Waste tank almost full</td>
 798 </tr>
 799 <tr>
 800         <td>marker-waste-full</td>
 801         <td>Waste tank full</td>
 802 </tr>
 803 <tr>
 804         <td>media-empty</td>
 805         <td>Out of media</td>
 806 </tr>
 807 <tr>
 808         <td>media-jam</td>
 809         <td>Media is jammed in the printer</td>
 810 </tr>
 811 <tr>
 812         <td>media-low</td>
 813         <td>Low on media</td>
 814 </tr>
 815 <tr>
 816         <td>paused</td>
 817         <td>Stop the printer</td>
 818 </tr>
 819 <tr>
 820         <td>timed-out</td>
 821         <td>Unable to connect to printer</td>
 822 </tr>
 823 <tr>
 824         <td>toner-empty</td>
 825         <td>Out of toner</td>
 826 </tr>
 827 <tr>
 828         <td>toner-low</td>
 829         <td>Low on toner</td>
 830 </tr>
 831 </tbody>
 832 </table></div>
 833
 834 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
 835
 836 <p>Filters can communicate with the backend via the
 837 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
 838 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 839 functions. The
 840 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
 841 reads data that has been sent back from the device and is typically used to
 842 obtain status and configuration information. For example, the following code
 843 polls the backend for back-channel data:</p>
 844
 845 <pre class="example">
 846 #include &lt;cups/cups.h&gt;
 847
 848 char buffer[8192];
 849 ssize_t bytes;
 850
 851 /* Use a timeout of 0.0 seconds to poll for back-channel data */
 852 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
 853 </pre>
 854
 855 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
 856 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
 857 when it is available.</p>
 858
 859 <p>The
 860 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 861 function allows you to get out-of-band status information and do synchronization
 862 with the device. For example, the following code gets the current IEEE-1284
 863 device ID string from the backend:</p>
 864
 865 <pre class="example">
 866 #include &lt;cups/sidechannel.h&gt;
 867
 868 char data[2049];
 869 int datalen;
 870 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 871
 872 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
 873    nul-termination... */
 874 datalen = sizeof(data) - 1;
 875
 876 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
 877 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
 878
 879 /* Use the returned value if OK was returned and the length is non-zero */
 880 if (status == CUPS_SC_STATUS_OK && datalen > 0)
 881   data[datalen] = '\0';
 882 else
 883   data[0] = '\0';
 884 </pre>
 885
 886 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
 887
 888 <p>Backends communicate with filters using the reciprocal functions
 889 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
 890 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
 891 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
 892 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
 893
 894 <pre class="example">
 895 #include &lt;cups/cups.h&gt;
 896
 897 char buffer[8192];
 898 ssize_t bytes;
 899
 900 /* Obtain data from printer/device */
 901 ...
 902
 903 /* Use a timeout of 1.0 seconds to give filters a chance to read */
 904 cupsBackChannelWrite(buffer, bytes, 1.0);
 905 </pre>
 906
 907 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
 908 function reads a side-channel command from a filter, driver, or port monitor.
 909 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
 910 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
 911 separate thread for that purpose), or use <code>select</code> or
 912 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
 913 input and output on several file descriptors at the same time.</p>
 914
 915 <p>Once a command is processed, the backend uses the
 916 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
 917 to send its response. For example, the following code shows how to poll for a
 918 side-channel command and respond to it:</p>
 919
 920 <pre class="example">
 921 #include &lt;cups/sidechannel.h&gt;
 922
 923 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
 924 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 925 char data[2048];
 926 int datalen = sizeof(data);
 927
 928 /* Poll for a command... */
 929 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
 930 {
 931   switch (command)
 932   {
 933     /* handle supported commands, fill data/datalen/status with values as needed */
 934
 935     default :
 936         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
 937         datalen = 0;
 938         break;
 939   }
 940
 941   /* Send a response... */
 942   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
 943 }
 944 </pre>
 945
 946 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
 947
 948 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
 949 status, page counter, and supply levels from most network printers. Every
 950 piece of information is associated with an Object Identifier (OID), and
 951 every printer has a <em>community</em> name associated with it. OIDs can be
 952 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
 953
 954 <p>The two CUPS SNMP functions provide a simple API for querying network
 955 printers through the side-channel interface. Each accepts a string containing
 956 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
 957 along with a timeout for the query.</p>
 958
 959 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
 960 function queries a single OID and returns the value as a string in a buffer
 961 you supply:</p>
 962
 963 <pre class="example">
 964 #include &lt;cups/sidechannel.h&gt;
 965
 966 char data[512];
 967 int datalen = sizeof(data);
 968
 969 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
 970         == CUPS_SC_STATUS_OK)
 971 {
 972   /* Do something with the value */
 973   printf("Page counter is: %s\n", data);
 974 }
 975 </pre>
 976
 977 <p>The
 978 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
 979 function allows you to query a whole group of OIDs, calling a function of your
 980 choice for each OID that is found:</p>
 981
 982 <pre class="example">
 983 #include &lt;cups/sidechannel.h&gt;
 984
 985 void
 986 my_callback(const char *oid, const char *data, int datalen, void *context)
 987 {
 988   /* Do something with the value */
 989   printf("%s=%s\n", oid, data);
 990 }
 991
 992 ...
 993
 994 void *my_data;
 995
 996 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
 997 </pre>
 998 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
 999 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
1000 <p class="description">Read data from the backchannel.</p>
1001 <p class="code">
1002 ssize_t cupsBackChannelRead (<br>
1003 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
1004 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1005 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1006 );</p>
1007 <h4 class="parameters">Parameters</h4>
1008 <dl>
1009 <dt>buffer</dt>
1010 <dd class="description">Buffer to read into</dd>
1011 <dt>bytes</dt>
1012 <dd class="description">Bytes to read</dd>
1013 <dt>timeout</dt>
1014 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
1015 </dl>
1016 <h4 class="returnvalue">Return Value</h4>
1017 <p class="description">Bytes read or -1 on error</p>
1018 <h4 class="discussion">Discussion</h4>
1019 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
1020 parameter controls how many seconds to wait for the data - use 0.0 to
1021 return immediately if there is no data, -1.0 to wait for data indefinitely.
1022
1023 </p>
1024 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
1025 <p class="description">Write data to the backchannel.</p>
1026 <p class="code">
1027 ssize_t cupsBackChannelWrite (<br>
1028 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
1029 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1030 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1031 );</p>
1032 <h4 class="parameters">Parameters</h4>
1033 <dl>
1034 <dt>buffer</dt>
1035 <dd class="description">Buffer to write</dd>
1036 <dt>bytes</dt>
1037 <dd class="description">Bytes to write</dd>
1038 <dt>timeout</dt>
1039 <dd class="description">Timeout in seconds, typically 1.0</dd>
1040 </dl>
1041 <h4 class="returnvalue">Return Value</h4>
1042 <p class="description">Bytes written or -1 on error</p>
1043 <h4 class="discussion">Discussion</h4>
1044 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
1045 controls how many seconds to wait for the data to be written - use
1046 0.0 to return immediately if the data cannot be written, -1.0 to wait
1047 indefinitely.
1048
1049 </p>
1050 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
1051 <p class="description">Get the device URI for a backend.</p>
1052 <p class="code">
1053 const char *cupsBackendDeviceURI (<br>
1054 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
1055 );</p>
1056 <h4 class="parameters">Parameters</h4>
1057 <dl>
1058 <dt>argv</dt>
1059 <dd class="description">Command-line arguments</dd>
1060 </dl>
1061 <h4 class="returnvalue">Return Value</h4>
1062 <p class="description">Device URI or <code>NULL</code></p>
1063 <h4 class="discussion">Discussion</h4>
1064 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
1065 function returns the device URI passed in the DEVICE_URI environment
1066 variable or the device URI passed in argv[0], whichever is found
1067 first.
1068
1069 </p>
1070 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsBackendReport">cupsBackendReport</a></h3>
1071 <p class="description">Write a device line from a backend.</p>
1072 <p class="code">
1073 void cupsBackendReport (<br>
1074 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
1075 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
1076 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
1077 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
1078 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
1079 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
1080 );</p>
1081 <h4 class="parameters">Parameters</h4>
1082 <dl>
1083 <dt>device_scheme</dt>
1084 <dd class="description">device-scheme string</dd>
1085 <dt>device_uri</dt>
1086 <dd class="description">device-uri string</dd>
1087 <dt>device_make_and_model</dt>
1088 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
1089 <dt>device_info</dt>
1090 <dd class="description">device-info string or <code>NULL</code></dd>
1091 <dt>device_id</dt>
1092 <dd class="description">device-id string or <code>NULL</code></dd>
1093 <dt>device_location</dt>
1094 <dd class="description">device-location string or <code>NULL</code></dd>
1095 </dl>
1096 <h4 class="discussion">Discussion</h4>
1097 <p class="discussion">This function writes a single device line to stdout for a backend.
1098 It handles quoting of special characters in the device-make-and-model,
1099 device-info, device-id, and device-location strings.
1100
1101 </p>
1102 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
1103 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
1104 <p class="code">
1105 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
1106 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1107 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1108 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1109 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1110 );</p>
1111 <h4 class="parameters">Parameters</h4>
1112 <dl>
1113 <dt>command</dt>
1114 <dd class="description">Command to send</dd>
1115 <dt>data</dt>
1116 <dd class="description">Response data buffer pointer</dd>
1117 <dt>datalen</dt>
1118 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1119 <dt>timeout</dt>
1120 <dd class="description">Timeout in seconds</dd>
1121 </dl>
1122 <h4 class="returnvalue">Return Value</h4>
1123 <p class="description">Status of command</p>
1124 <h4 class="discussion">Discussion</h4>
1125 <p class="discussion">This function is normally only called by filters, drivers, or port
1126 monitors in order to communicate with the backend used by the current
1127 printer.  Programs must be prepared to handle timeout or &quot;not
1128 implemented&quot; status codes, which indicate that the backend or device
1129 do not support the specified side-channel command.<br>
1130 <br>
1131 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1132 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1133 update the value to contain the number of data bytes in the buffer.
1134
1135 </p>
1136 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1137 <p class="description">Read a side-channel message.</p>
1138 <p class="code">
1139 int cupsSideChannelRead (<br>
1140 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1141 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1142 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1143 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1144 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1145 );</p>
1146 <h4 class="parameters">Parameters</h4>
1147 <dl>
1148 <dt>command</dt>
1149 <dd class="description">Command code</dd>
1150 <dt>status</dt>
1151 <dd class="description">Status code</dd>
1152 <dt>data</dt>
1153 <dd class="description">Data buffer pointer</dd>
1154 <dt>datalen</dt>
1155 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1156 <dt>timeout</dt>
1157 <dd class="description">Timeout in seconds</dd>
1158 </dl>
1159 <h4 class="returnvalue">Return Value</h4>
1160 <p class="description">0 on success, -1 on error</p>
1161 <h4 class="discussion">Discussion</h4>
1162 <p class="discussion">This function is normally only called by backend programs to read
1163 commands from a filter, driver, or port monitor program.  The
1164 caller must be prepared to handle incomplete or invalid messages
1165 and return the corresponding status codes.<br>
1166 <br>
1167 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1168 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1169 update the value to contain the number of data bytes in the buffer.
1170
1171 </p>
1172 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1173 <p class="description">Query a SNMP OID's value.</p>
1174 <p class="code">
1175 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1176 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1177 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1178 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1179 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1180 );</p>
1181 <h4 class="parameters">Parameters</h4>
1182 <dl>
1183 <dt>oid</dt>
1184 <dd class="description">OID to query</dd>
1185 <dt>data</dt>
1186 <dd class="description">Buffer for OID value</dd>
1187 <dt>datalen</dt>
1188 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1189 <dt>timeout</dt>
1190 <dd class="description">Timeout in seconds</dd>
1191 </dl>
1192 <h4 class="returnvalue">Return Value</h4>
1193 <p class="description">Query status</p>
1194 <h4 class="discussion">Discussion</h4>
1195 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1196 filter, port monitor, or backend using the default community name.<br>
1197 <br>
1198 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1199 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1200 supported and must be converted to their numeric forms.<br>
1201 <br>
1202 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1203 buffer to hold the OID value as a string. HEX-String (binary) values are
1204 converted to hexadecimal strings representing the binary data, while
1205 NULL-Value and unknown OID types are returned as the empty string.
1206 The returned &quot;datalen&quot; does not include the trailing nul.
1207
1208 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1209 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1210 the printer does not respond to the SNMP query.
1211
1212 </p>
1213 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1214 <p class="description">Query multiple SNMP OID values.</p>
1215 <p class="code">
1216 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1217 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1218 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1219 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1220 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1221 );</p>
1222 <h4 class="parameters">Parameters</h4>
1223 <dl>
1224 <dt>oid</dt>
1225 <dd class="description">First numeric OID to query</dd>
1226 <dt>timeout</dt>
1227 <dd class="description">Timeout for each query in seconds</dd>
1228 <dt>cb</dt>
1229 <dd class="description">Function to call with each value</dd>
1230 <dt>context</dt>
1231 <dd class="description">Application-defined pointer to send to callback</dd>
1232 </dl>
1233 <h4 class="returnvalue">Return Value</h4>
1234 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1235 <h4 class="discussion">Discussion</h4>
1236 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1237 of the filter, port monitor, or backend using the default community name.
1238 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1239 the callback function you provide.<br>
1240 <br>
1241 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1242 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1243 supported and must be converted to their numeric forms.<br>
1244 <br>
1245 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1246 time will depend on the number of OID values found and the time required
1247 for each query.<br>
1248 <br>
1249 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1250 is an application-defined pointer that is sent to the callback function
1251 along with the OID and current data. The data passed to the callback is the
1252 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1253
1254 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1255 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1256 the printer does not respond to the first SNMP query.
1257
1258 </p>
1259 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1260 <p class="description">Write a side-channel message.</p>
1261 <p class="code">
1262 int cupsSideChannelWrite (<br>
1263 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1264 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1265 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1266 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1267 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1268 );</p>
1269 <h4 class="parameters">Parameters</h4>
1270 <dl>
1271 <dt>command</dt>
1272 <dd class="description">Command code</dd>
1273 <dt>status</dt>
1274 <dd class="description">Status code</dd>
1275 <dt>data</dt>
1276 <dd class="description">Data buffer pointer</dd>
1277 <dt>datalen</dt>
1278 <dd class="description">Number of bytes of data</dd>
1279 <dt>timeout</dt>
1280 <dd class="description">Timeout in seconds</dd>
1281 </dl>
1282 <h4 class="returnvalue">Return Value</h4>
1283 <p class="description">0 on success, -1 on error</p>
1284 <h4 class="discussion">Discussion</h4>
1285 <p class="discussion">This function is normally only called by backend programs to send
1286 responses to a filter, driver, or port monitor program.
1287
1288 </p>
1289 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1290 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1291 <p class="description">Backend exit codes</p>
1292 <p class="code">
1293 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1294 </p>
1295 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1296 <p class="description">Bidirectional capabilities</p>
1297 <p class="code">
1298 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1299 </p>
1300 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1301 <p class="description">Request command codes</p>
1302 <p class="code">
1303 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1304 </p>
1305 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1306 <p class="description">Printer state bits</p>
1307 <p class="code">
1308 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1309 </p>
1310 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1311 <p class="description">Response status codes</p>
1312 <p class="code">
1313 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1314 </p>
1315 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1316 <p class="description">SNMP walk callback</p>
1317 <p class="code">
1318 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1319 </p>
1320 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1321 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1322 <p class="description">Backend exit codes</p>
1323 <h4 class="constants">Constants</h4>
1324 <dl>
1325 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1326 <dd class="description">Job failed, authentication required</dd>
1327 <dt>CUPS_BACKEND_CANCEL </dt>
1328 <dd class="description">Job failed, cancel job</dd>
1329 <dt>CUPS_BACKEND_FAILED </dt>
1330 <dd class="description">Job failed, use error-policy</dd>
1331 <dt>CUPS_BACKEND_HOLD </dt>
1332 <dd class="description">Job failed, hold job</dd>
1333 <dt>CUPS_BACKEND_OK </dt>
1334 <dd class="description">Job completed successfully</dd>
1335 <dt>CUPS_BACKEND_STOP </dt>
1336 <dd class="description">Job failed, stop queue</dd>
1337 </dl>
1338 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1339 <p class="description">Bidirectional capability values</p>
1340 <h4 class="constants">Constants</h4>
1341 <dl>
1342 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1343 <dd class="description">Bidirectional I/O is not supported</dd>
1344 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1345 <dd class="description">Bidirectional I/O is supported</dd>
1346 </dl>
1347 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1348 <p class="description">Request command codes</p>
1349 <h4 class="constants">Constants</h4>
1350 <dl>
1351 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1352 <dd class="description">Drain all pending output</dd>
1353 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1354 <dd class="description">Return bidirectional capabilities</dd>
1355 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1356 <dd class="description">Return the IEEE-1284 device ID</dd>
1357 <dt>CUPS_SC_CMD_GET_STATE </dt>
1358 <dd class="description">Return the device state</dd>
1359 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span></dt>
1360 <dd class="description">Query an SNMP OID </dd>
1361 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span></dt>
1362 <dd class="description">Query the next SNMP OID </dd>
1363 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1364 <dd class="description">Do a soft reset</dd>
1365 </dl>
1366 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1367 <p class="description">Printer state bits</p>
1368 <h4 class="constants">Constants</h4>
1369 <dl>
1370 <dt>CUPS_SC_STATE_BUSY </dt>
1371 <dd class="description">Device is busy</dd>
1372 <dt>CUPS_SC_STATE_ERROR </dt>
1373 <dd class="description">Other error condition</dd>
1374 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1375 <dd class="description">Toner/ink out condition</dd>
1376 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1377 <dd class="description">Toner/ink low condition</dd>
1378 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1379 <dd class="description">Paper out condition</dd>
1380 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1381 <dd class="description">Paper low condition</dd>
1382 <dt>CUPS_SC_STATE_OFFLINE </dt>
1383 <dd class="description">Device is offline</dd>
1384 <dt>CUPS_SC_STATE_ONLINE </dt>
1385 <dd class="description">Device is online</dd>
1386 </dl>
1387 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1388 <p class="description">Response status codes</p>
1389 <h4 class="constants">Constants</h4>
1390 <dl>
1391 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1392 <dd class="description">The command/response message was invalid</dd>
1393 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1394 <dd class="description">An I/O error occurred</dd>
1395 <dt>CUPS_SC_STATUS_NONE </dt>
1396 <dd class="description">No status</dd>
1397 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1398 <dd class="description">Command not implemented</dd>
1399 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1400 <dd class="description">The device did not respond</dd>
1401 <dt>CUPS_SC_STATUS_OK </dt>
1402 <dd class="description">Operation succeeded</dd>
1403 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1404 <dd class="description">The backend did not respond</dd>
1405 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1406 <dd class="description">Response too big</dd>
1407 </dl>
1408 </div>
1409 </body>
1410 </html>