doc/help/api-filter.html

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 340 <!--
 341   "$Id$"
 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         Programming: <a href='postscript-driver.html' target='_top'>Developing PostScript Printer Drivers</a><br>
 377         Programming: <a href='raster-driver.html' target='_top'>Developing Raster Printer Drivers</a><br>
 378         Specifications: <a href='spec-design' target='_top'>CUPS Design Description</a></td>
 379 </tr>
 380 </tbody>
 381 </table></div>
 382 <h2 class="title">Contents</h2>
 383 <ul class="contents">
 384 <ul class="subcontents">
 385 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 386 <li><a href="#SECURITY">Security Considerations</a></li>
 387 <li><a href="#PERMISSIONS">File Permissions</a></li>
 388 <li><a href="#TEMPFILES">Temporary Files</a></li>
 389 <li><a href="#COPIES">Copy Generation</a></li>
 390 <li><a href="#EXITCODES">Exit Codes</a></li>
 391 <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 392 <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 393 <li><a href="#COMMUNICATING_BACKEND">Communicating with the Backend</a></li>
 394 <li><a href="#COMMUNICATING_FILTER">Communicating with Filters</a></li>
 395 <li><a href="#SNMP">Doing SNMP Queries with Network Printers</a></li>
 396 </ul></li>
 397 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 398 <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 399 <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 400 <li><a href="#cupsBackendDeviceURI" title="Get the device URI for a backend.">cupsBackendDeviceURI</a></li>
 401 <li><a href="#cupsBackendReport" title="Write a device line from a backend.">cupsBackendReport</a></li>
 402 <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 403 <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 404 <li><a href="#cupsSideChannelSNMPGet" title="Query a SNMP OID's value.">cupsSideChannelSNMPGet</a></li>
 405 <li><a href="#cupsSideChannelSNMPWalk" title="Query multiple SNMP OID values.">cupsSideChannelSNMPWalk</a></li>
 406 <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 407 </ul></li>
 408 <li><a href="#TYPES">Data Types</a><ul class="code">
 409         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 410         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 411         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 412         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 413         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 414         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 415 </ul></li>
 416 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 417         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 418         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 419         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 420         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 421         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 422 </ul></li>
 423 <!--
 424   "$Id$"
 425
 426   Filter and backend programming introduction for the Common UNIX Printing
 427   System (CUPS).
 428
 429   Copyright 2007-2009 by Apple Inc.
 430   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 431
 432   These coded instructions, statements, and computer programs are the
 433   property of Apple Inc. and are protected by Federal copyright
 434   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 435   which should have been included with this file.  If this file is
 436   file is missing or damaged, see the license at "http://www.cups.org/".
 437 -->
 438
 439 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 440
 441 <p>Filters (which include printer drivers and port monitors) and backends
 442 are used to convert job files to a printable format and send that data to the
 443 printer itself. All of these programs use a common interface for processing
 444 print jobs and communicating status information to the scheduler. Each is run
 445 with a standard set of command-line arguments:<p>
 446
 447 <dl class="code">
 448
 449         <dt>argv[1]</dt>
 450         <dd>The job ID</dd>
 451
 452         <dt>argv[2]</dt>
 453         <dd>The user printing the job</dd>
 454
 455         <dt>argv[3]</dt>
 456         <dd>The job name/title</dd>
 457
 458         <dt>argv[4]</dt>
 459         <dd>The number of copies to print</dd>
 460
 461         <dt>argv[5]</dt>
 462         <dd>The options that were provided when the job was submitted</dd>
 463
 464         <dt>argv[6]</dt>
 465         <dd>The file to print (first program only)</dd>
 466 </dl>
 467
 468 <p>The scheduler runs one or more of these programs to print any given job. The
 469 first filter reads from the print file and writes to the standard output, while
 470 the remaining filters read from the standard input and write to the standard
 471 output. The backend is the last filter in the chain and writes to the
 472 device.</p>
 473
 474 <p>Filters are always run as a non-privileged user, typically "lp", with no
 475 connection to the user's desktop. Backends are run either as a non-privileged
 476 user or as root if the file permissions do not allow user or group execution.
 477 The <a href="#PERMISSIONS">file permissions</a> section talks about this in
 478 more detail.</p>
 479
 480 <h3><a name="SECURITY">Security Considerations</a></h3>
 481
 482 <p>It is always important to use security programming practices. Filters and
 483 most backends are run as a non-priviledged user, so the major security
 484 consideration is resource utilization - filters should not depend on unlimited
 485 amounts of CPU, memory, or disk space, and should protect against conditions
 486 that could lead to excess usage of any resource like infinite loops and
 487 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 488 specify an arbitrary file path to a separator page, template, or other file
 489 used by the filter since that can lead to an unauthorized disclosure of
 490 information. <em>Always</em> treat input as suspect and validate it!</p>
 491
 492 <p>If you are developing a backend that runs as root, make sure to check for
 493 potential buffer overflows, integer under/overflow conditions, and file
 494 accesses since these can lead to privilege escalations. When writing files,
 495 always validate the file path and <em>never</em> allow a user to determine
 496 where to store a file.</p>
 497
 498 <blockquote><b>Note:</b>
 499
 500 <p><em>Never</em> write files to a user's home directory. Aside from the
 501 security implications, CUPS is a network print service and as such the network
 502 user may not be the same as the local user and/or there may not be a local home
 503 directory to write to.</p>
 504
 505 <p>In addition, some operating systems provide additional security mechanisms
 506 that further limit file system access, even for backends running as root. On
 507 Mac OS X, for example, no backend may write to a user's home directory.</p>
 508 </blockquote>
 509
 510 <h3><a name="PERMISSIONS">File Permissions</a></h3>
 511
 512 <p>For security reasons, CUPS will only run filters and backends that are owned
 513 by root and do not have world or group write permissions. The recommended
 514 permissions for filters and backends are 0555 - read and execute but no write.
 515 Backends that must run as root should use permissions of 0500 - read and execute
 516 by root, no access for other users. Write permissions can be enabled for the
 517 root user only.</p>
 518
 519 <p>To avoid a warning message, the directory containing your filter(s) must also
 520 be owned by root and have world and group write disabled - permissions of 0755
 521 or 0555 are strongly encouraged.</p>
 522
 523 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 524
 525 <p>Temporary files should be created in the directory specified by the
 526 "TMPDIR" environment variable. The
 527 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 528 used to safely create temporary files in this directory.</p>
 529
 530 <h3><a name="COPIES">Copy Generation</a></h3>
 531
 532 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 533 of the input file. In general, you should only generate copies if the
 534 <em>filename</em> argument is supplied. The only exception to this are
 535 filters that produce device-independent PostScript output, since the PostScript
 536 filter <var>pstops</var> is responsible for generating copies of PostScript
 537 files.</p>
 538
 539 <h3><a name="EXITCODES">Exit Codes</a></h3>
 540
 541 <p>Filters must exit with status 0 when they successfully generate print data
 542 or 1 when they encounter an error. Backends can return any of the
 543 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 544
 545 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 546
 547 <p>The following environment variables are defined by the printing system
 548 when running print filters and backends:</p>
 549
 550 <dl class="code">
 551
 552         <dt>APPLE_LANGUAGE</dt>
 553         <dd>The Apple language identifier associated with the job
 554         (Mac OS X only).</dd>
 555
 556         <dt>CHARSET</dt>
 557         <dd>The job character set, typically "utf-8".</dd>
 558
 559         <dt>CLASS</dt>
 560         <dd>When a job is submitted to a printer class, contains the name of
 561         the destination printer class. Otherwise this environment
 562         variable will not be set.</dd>
 563
 564         <dt>CONTENT_TYPE</dt>
 565         <dd>The MIME type associated with the file (e.g.
 566         application/postscript).</dd>
 567
 568         <dt>CUPS_CACHEDIR</dt>
 569         <dd>The directory where cache files can be stored. Cache files can be
 570         used to retain information between jobs or files in a job.</dd>
 571
 572         <dt>CUPS_DATADIR</dt>
 573         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 574
 575         <dt>CUPS_FILETYPE</dt>
 576         <dd>The type of file being printed: "job-sheet" for a banner page and
 577         "document" for a regular print file.</dd>
 578
 579         <dt>CUPS_SERVERROOT</dt>
 580         <dd>The root directory of the server.</dd>
 581
 582         <dt>DEVICE_URI</dt>
 583         <dd>The device-uri associated with the printer.</dd>
 584
 585         <dt>FINAL_CONTENT_TYPE</dt>
 586         <dd>The MIME type associated with the printer (e.g.
 587         application/vnd.cups-postscript).</dd>
 588
 589         <dt>LANG</dt>
 590         <dd>The language locale associated with the job.</dd>
 591
 592         <dt>PPD</dt>
 593         <dd>The full pathname of the PostScript Printer Description (PPD)
 594         file for this printer.</dd>
 595
 596         <dt>PRINTER</dt>
 597         <dd>The queue name of the class or printer.</dd>
 598
 599         <dt>RIP_CACHE</dt>
 600         <dd>The recommended amount of memory to use for Raster Image
 601         Processors (RIPs).</dd>
 602
 603         <dt>TMPDIR</dt>
 604         <dd>The directory where temporary files should be created.</dd>
 605
 606 </dl>
 607
 608 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 609
 610 <p>Filters and backends communicate with the scheduler by writing messages
 611 to the standard error file. The scheduler reads messages from all filters in
 612 a job and processes the message based on its prefix. For example, the following
 613 code sets the current printer state message to "Printing page 5":</p>
 614
 615 <pre class="example">
 616 int page = 5;
 617
 618 fprintf(stderr, "INFO: Printing page %d\n", page);
 619 </pre>
 620
 621 <p>Each message is a single line of text starting with one of the following
 622 prefix strings:</p>
 623
 624 <dl class="code">
 625
 626         <dt>ALERT: message</dt>
 627         <dd>Sets the printer-state-message attribute and adds the specified
 628         message to the current error log file using the "alert" log level.</dd>
 629
 630         <dt>ATTR: attribute=value [attribute=value]</dt>
 631         <dd>Sets the named printer or job attribute(s). Typically this is used
 632         to set the <code>marker-colors</code>, <code>marker-levels</code>,
 633         <code>marker-message</code>, <code>marker-names</code>,
 634         <code>marker-types</code>, <code>printer-alert</code>, and
 635         <code>printer-alert-description</code> printer attributes. Standard
 636         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 637         1</a>.</dd>
 638
 639         <dt>CRIT: message</dt>
 640         <dd>Sets the printer-state-message attribute and adds the specified
 641         message to the current error log file using the "critical" log
 642         level.</dd>
 643
 644         <dt>DEBUG: message</dt>
 645         <dd>Sets the printer-state-message attribute and adds the specified
 646         message to the current error log file using the "debug" log level.</dd>
 647
 648         <dt>DEBUG2: message</dt>
 649         <dd>Sets the printer-state-message attribute and adds the specified
 650         message to the current error log file using the "debug2" log level.</dd>
 651
 652         <dt>EMERG: message</dt>
 653         <dd>Sets the printer-state-message attribute and adds the specified
 654         message to the current error log file using the "emergency" log
 655         level.</dd>
 656
 657         <dt>ERROR: message</dt>
 658         <dd>Sets the printer-state-message attribute and adds the specified
 659         message to the current error log file using the "error" log level.
 660         Use "ERROR:" messages for non-persistent processing errors.</dd>
 661
 662         <dt>INFO: message</dt>
 663         <dd>Sets the printer-state-message attribute. If the current log level
 664         is set to "debug2", also adds the specified message to the current error
 665         log file using the "info" log level.</dd>
 666
 667         <dt>NOTICE: message</dt>
 668         <dd>Sets the printer-state-message attribute and adds the specified
 669         message to the current error log file using the "notice" log level.</dd>
 670
 671         <dt>PAGE: page-number #-copies</dt>
 672         <dt>PAGE: total #-pages</dt>
 673         <dd>Adds an entry to the current page log file. The first form adds
 674         #-copies to the job-media-sheets-completed attribute. The second
 675         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 676
 677         <dt>PPD: keyword=value [keyword=value ...]</dt>
 678         <dd>Changes or adds keywords to the printer's PPD file. Typically
 679         this is used to update installable options or default media settings
 680         based on the printer configuration.</dd>
 681
 682         <dt>STATE: printer-state-reason [printer-state-reason ...]</dt>
 683         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 684         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 685         <dd>Sets, adds, or removes printer-state-reason keywords to the
 686         current queue. Typically this is used to indicate persistent media,
 687         ink, toner, and configuration conditions or errors on a printer.
 688         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 689         use vendor-prefixed ("com.acme.foo") keywords for custom states.
 690
 691         <blockquote><b>Note:</b>
 692
 693         <p>"STATE:" messages often provide visible alerts to the user. For example, on
 694         Mac OS X setting a printer-state-reason value with an "-error" or "-warning"
 695         suffix will cause the printer's dock item to bounce if the corresponding reason
 696         is localized with a cupsIPPReason keyword in the printer's PPD file.</p>
 697
 698         </blockquote></dd>
 699
 700         <dt>WARNING: message</dt>
 701         <dd>Sets the printer-state-message attribute and adds the specified
 702         message to the current error log file using the "warning" log
 703         level.</dd>
 704
 705 </dl>
 706
 707 <p>Messages without one of these prefixes are treated as if they began with
 708 the "DEBUG:" prefix string.</p>
 709
 710 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 711 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 712 <thead>
 713 <tr>
 714         <th>marker-type</th>
 715         <th>Description</th>
 716 </tr>
 717 </thead>
 718 <tbody>
 719 <tr>
 720         <td>developer</td>
 721         <td>Developer unit</td>
 722 </tr>
 723 <tr>
 724         <td>fuser</td>
 725         <td>Fuser unit</td>
 726 </tr>
 727 <tr>
 728         <td>fuserCleaningPad</td>
 729         <td>Fuser cleaning pad</td>
 730 </tr>
 731 <tr>
 732         <td>fuserOil</td>
 733         <td>Fuser oil</td>
 734 </tr>
 735 <tr>
 736         <td>ink</td>
 737         <td>Ink supply</td>
 738 </tr>
 739 <tr>
 740         <td>opc</td>
 741         <td>Photo conductor</td>
 742 </tr>
 743 <tr>
 744         <td>solidWax</td>
 745         <td>Wax supply</td>
 746 </tr>
 747 <tr>
 748         <td>staples</td>
 749         <td>Staple supply</td>
 750 </tr>
 751 <tr>
 752         <td>toner</td>
 753         <td>Toner supply</td>
 754 </tr>
 755 <tr>
 756         <td>transferUnit</td>
 757         <td>Transfer unit</td>
 758 </tr>
 759 <tr>
 760         <td>wasteInk</td>
 761         <td>Waste ink tank</td>
 762 </tr>
 763 <tr>
 764         <td>wasteToner</td>
 765         <td>Waste toner tank</td>
 766 </tr>
 767 <tr>
 768         <td>wasteWax</td>
 769         <td>Waste wax tank</td>
 770 </tr>
 771 </tbody>
 772 </table></div>
 773
 774 <br>
 775
 776 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 777 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 778 <thead>
 779 <tr>
 780         <th>Keyword</th>
 781         <th>Description</th>
 782 </tr>
 783 </thead>
 784 <tbody>
 785 <tr>
 786         <td>connecting-to-device</td>
 787         <td>Connecting to printer but not printing yet</td>
 788 </tr>
 789 <tr>
 790         <td>cover-open</td>
 791         <td>A cover is open on the printer</td>
 792 </tr>
 793 <tr>
 794         <td>input-tray-missing</td>
 795         <td>An input tray is missing from the printer</td>
 796 </tr>
 797 <tr>
 798         <td>marker-supply-empty</td>
 799         <td>Out of ink</td>
 800 </tr>
 801 <tr>
 802         <td>marker-supply-low</td>
 803         <td>Low on ink</td>
 804 </tr>
 805 <tr>
 806         <td>marker-waste-almost-full</td>
 807         <td>Waste tank almost full</td>
 808 </tr>
 809 <tr>
 810         <td>marker-waste-full</td>
 811         <td>Waste tank full</td>
 812 </tr>
 813 <tr>
 814         <td>media-empty</td>
 815         <td>Out of media</td>
 816 </tr>
 817 <tr>
 818         <td>media-jam</td>
 819         <td>Media is jammed in the printer</td>
 820 </tr>
 821 <tr>
 822         <td>media-low</td>
 823         <td>Low on media</td>
 824 </tr>
 825 <tr>
 826         <td>paused</td>
 827         <td>Stop the printer</td>
 828 </tr>
 829 <tr>
 830         <td>timed-out</td>
 831         <td>Unable to connect to printer</td>
 832 </tr>
 833 <tr>
 834         <td>toner-empty</td>
 835         <td>Out of toner</td>
 836 </tr>
 837 <tr>
 838         <td>toner-low</td>
 839         <td>Low on toner</td>
 840 </tr>
 841 </tbody>
 842 </table></div>
 843
 844 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
 845
 846 <p>Filters can communicate with the backend via the
 847 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
 848 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 849 functions. The
 850 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
 851 reads data that has been sent back from the device and is typically used to
 852 obtain status and configuration information. For example, the following code
 853 polls the backend for back-channel data:</p>
 854
 855 <pre class="example">
 856 #include &lt;cups/cups.h&gt;
 857
 858 char buffer[8192];
 859 ssize_t bytes;
 860
 861 /* Use a timeout of 0.0 seconds to poll for back-channel data */
 862 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
 863 </pre>
 864
 865 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
 866 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
 867 when it is available.</p>
 868
 869 <p>The
 870 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 871 function allows you to get out-of-band status information and do synchronization
 872 with the device. For example, the following code gets the current IEEE-1284
 873 device ID string from the backend:</p>
 874
 875 <pre class="example">
 876 #include &lt;cups/sidechannel.h&gt;
 877
 878 char data[2049];
 879 int datalen;
 880 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 881
 882 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
 883    nul-termination... */
 884 datalen = sizeof(data) - 1;
 885
 886 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
 887 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
 888
 889 /* Use the returned value if OK was returned and the length is non-zero */
 890 if (status == CUPS_SC_STATUS_OK && datalen > 0)
 891   data[datalen] = '\0';
 892 else
 893   data[0] = '\0';
 894 </pre>
 895
 896 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
 897
 898 <p>Backends communicate with filters using the reciprocal functions
 899 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
 900 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
 901 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
 902 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
 903
 904 <pre class="example">
 905 #include &lt;cups/cups.h&gt;
 906
 907 char buffer[8192];
 908 ssize_t bytes;
 909
 910 /* Obtain data from printer/device */
 911 ...
 912
 913 /* Use a timeout of 1.0 seconds to give filters a chance to read */
 914 cupsBackChannelWrite(buffer, bytes, 1.0);
 915 </pre>
 916
 917 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
 918 function reads a side-channel command from a filter, driver, or port monitor.
 919 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
 920 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
 921 separate thread for that purpose), or use <code>select</code> or
 922 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
 923 input and output on several file descriptors at the same time.</p>
 924
 925 <p>Once a command is processed, the backend uses the
 926 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
 927 to send its response. For example, the following code shows how to poll for a
 928 side-channel command and respond to it:</p>
 929
 930 <pre class="example">
 931 #include &lt;cups/sidechannel.h&gt;
 932
 933 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
 934 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 935 char data[2048];
 936 int datalen = sizeof(data);
 937
 938 /* Poll for a command... */
 939 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
 940 {
 941   switch (command)
 942   {
 943     /* handle supported commands, fill data/datalen/status with values as needed */
 944
 945     default :
 946         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
 947         datalen = 0;
 948         break;
 949   }
 950
 951   /* Send a response... */
 952   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
 953 }
 954 </pre>
 955
 956 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
 957
 958 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
 959 status, page counter, and supply levels from most network printers. Every
 960 piece of information is associated with an Object Identifier (OID), and
 961 every printer has a <em>community</em> name associated with it. OIDs can be
 962 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
 963
 964 <p>The two CUPS SNMP functions provide a simple API for querying network
 965 printers through the side-channel interface. Each accepts a string containing
 966 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
 967 along with a timeout for the query.</p>
 968
 969 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
 970 function queries a single OID and returns the value as a string in a buffer
 971 you supply:</p>
 972
 973 <pre class="example">
 974 #include &lt;cups/sidechannel.h&gt;
 975
 976 char data[512];
 977 int datalen = sizeof(data);
 978
 979 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
 980         == CUPS_SC_STATUS_OK)
 981 {
 982   /* Do something with the value */
 983   printf("Page counter is: %s\n", data);
 984 }
 985 </pre>
 986
 987 <p>The
 988 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
 989 function allows you to query a whole group of OIDs, calling a function of your
 990 choice for each OID that is found:</p>
 991
 992 <pre class="example">
 993 #include &lt;cups/sidechannel.h&gt;
 994
 995 void
 996 my_callback(const char *oid, const char *data, int datalen, void *context)
 997 {
 998   /* Do something with the value */
 999   printf("%s=%s\n", oid, data);
1000 }
1001
1002 ...
1003
1004 void *my_data;
1005
1006 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
1007 </pre>
1008 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
1009 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
1010 <p class="description">Read data from the backchannel.</p>
1011 <p class="code">
1012 ssize_t cupsBackChannelRead (<br>
1013 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
1014 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1015 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1016 );</p>
1017 <h4 class="parameters">Parameters</h4>
1018 <dl>
1019 <dt>buffer</dt>
1020 <dd class="description">Buffer to read into</dd>
1021 <dt>bytes</dt>
1022 <dd class="description">Bytes to read</dd>
1023 <dt>timeout</dt>
1024 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
1025 </dl>
1026 <h4 class="returnvalue">Return Value</h4>
1027 <p class="description">Bytes read or -1 on error</p>
1028 <h4 class="discussion">Discussion</h4>
1029 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
1030 parameter controls how many seconds to wait for the data - use 0.0 to
1031 return immediately if there is no data, -1.0 to wait for data indefinitely.
1032
1033 </p>
1034 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
1035 <p class="description">Write data to the backchannel.</p>
1036 <p class="code">
1037 ssize_t cupsBackChannelWrite (<br>
1038 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
1039 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1040 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1041 );</p>
1042 <h4 class="parameters">Parameters</h4>
1043 <dl>
1044 <dt>buffer</dt>
1045 <dd class="description">Buffer to write</dd>
1046 <dt>bytes</dt>
1047 <dd class="description">Bytes to write</dd>
1048 <dt>timeout</dt>
1049 <dd class="description">Timeout in seconds, typically 1.0</dd>
1050 </dl>
1051 <h4 class="returnvalue">Return Value</h4>
1052 <p class="description">Bytes written or -1 on error</p>
1053 <h4 class="discussion">Discussion</h4>
1054 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
1055 controls how many seconds to wait for the data to be written - use
1056 0.0 to return immediately if the data cannot be written, -1.0 to wait
1057 indefinitely.
1058
1059 </p>
1060 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
1061 <p class="description">Get the device URI for a backend.</p>
1062 <p class="code">
1063 const char *cupsBackendDeviceURI (<br>
1064 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
1065 );</p>
1066 <h4 class="parameters">Parameters</h4>
1067 <dl>
1068 <dt>argv</dt>
1069 <dd class="description">Command-line arguments</dd>
1070 </dl>
1071 <h4 class="returnvalue">Return Value</h4>
1072 <p class="description">Device URI or <code>NULL</code></p>
1073 <h4 class="discussion">Discussion</h4>
1074 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
1075 function returns the device URI passed in the DEVICE_URI environment
1076 variable or the device URI passed in argv[0], whichever is found
1077 first.
1078
1079 </p>
1080 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsBackendReport">cupsBackendReport</a></h3>
1081 <p class="description">Write a device line from a backend.</p>
1082 <p class="code">
1083 void cupsBackendReport (<br>
1084 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
1085 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
1086 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
1087 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
1088 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
1089 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
1090 );</p>
1091 <h4 class="parameters">Parameters</h4>
1092 <dl>
1093 <dt>device_scheme</dt>
1094 <dd class="description">device-scheme string</dd>
1095 <dt>device_uri</dt>
1096 <dd class="description">device-uri string</dd>
1097 <dt>device_make_and_model</dt>
1098 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
1099 <dt>device_info</dt>
1100 <dd class="description">device-info string or <code>NULL</code></dd>
1101 <dt>device_id</dt>
1102 <dd class="description">device-id string or <code>NULL</code></dd>
1103 <dt>device_location</dt>
1104 <dd class="description">device-location string or <code>NULL</code></dd>
1105 </dl>
1106 <h4 class="discussion">Discussion</h4>
1107 <p class="discussion">This function writes a single device line to stdout for a backend.
1108 It handles quoting of special characters in the device-make-and-model,
1109 device-info, device-id, and device-location strings.
1110
1111 </p>
1112 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
1113 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
1114 <p class="code">
1115 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
1116 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1117 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1118 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1119 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1120 );</p>
1121 <h4 class="parameters">Parameters</h4>
1122 <dl>
1123 <dt>command</dt>
1124 <dd class="description">Command to send</dd>
1125 <dt>data</dt>
1126 <dd class="description">Response data buffer pointer</dd>
1127 <dt>datalen</dt>
1128 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1129 <dt>timeout</dt>
1130 <dd class="description">Timeout in seconds</dd>
1131 </dl>
1132 <h4 class="returnvalue">Return Value</h4>
1133 <p class="description">Status of command</p>
1134 <h4 class="discussion">Discussion</h4>
1135 <p class="discussion">This function is normally only called by filters, drivers, or port
1136 monitors in order to communicate with the backend used by the current
1137 printer.  Programs must be prepared to handle timeout or &quot;not
1138 implemented&quot; status codes, which indicate that the backend or device
1139 do not support the specified side-channel command.<br>
1140 <br>
1141 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1142 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1143 update the value to contain the number of data bytes in the buffer.
1144
1145 </p>
1146 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1147 <p class="description">Read a side-channel message.</p>
1148 <p class="code">
1149 int cupsSideChannelRead (<br>
1150 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1151 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1152 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1153 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1154 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1155 );</p>
1156 <h4 class="parameters">Parameters</h4>
1157 <dl>
1158 <dt>command</dt>
1159 <dd class="description">Command code</dd>
1160 <dt>status</dt>
1161 <dd class="description">Status code</dd>
1162 <dt>data</dt>
1163 <dd class="description">Data buffer pointer</dd>
1164 <dt>datalen</dt>
1165 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1166 <dt>timeout</dt>
1167 <dd class="description">Timeout in seconds</dd>
1168 </dl>
1169 <h4 class="returnvalue">Return Value</h4>
1170 <p class="description">0 on success, -1 on error</p>
1171 <h4 class="discussion">Discussion</h4>
1172 <p class="discussion">This function is normally only called by backend programs to read
1173 commands from a filter, driver, or port monitor program.  The
1174 caller must be prepared to handle incomplete or invalid messages
1175 and return the corresponding status codes.<br>
1176 <br>
1177 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1178 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1179 update the value to contain the number of data bytes in the buffer.
1180
1181 </p>
1182 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1183 <p class="description">Query a SNMP OID's value.</p>
1184 <p class="code">
1185 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1186 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1187 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1188 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1189 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1190 );</p>
1191 <h4 class="parameters">Parameters</h4>
1192 <dl>
1193 <dt>oid</dt>
1194 <dd class="description">OID to query</dd>
1195 <dt>data</dt>
1196 <dd class="description">Buffer for OID value</dd>
1197 <dt>datalen</dt>
1198 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1199 <dt>timeout</dt>
1200 <dd class="description">Timeout in seconds</dd>
1201 </dl>
1202 <h4 class="returnvalue">Return Value</h4>
1203 <p class="description">Query status</p>
1204 <h4 class="discussion">Discussion</h4>
1205 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1206 filter, port monitor, or backend using the default community name.<br>
1207 <br>
1208 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1209 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1210 supported and must be converted to their numeric forms.<br>
1211 <br>
1212 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1213 buffer to hold the OID value as a string. HEX-String (binary) values are
1214 converted to hexadecimal strings representing the binary data, while
1215 NULL-Value and unknown OID types are returned as the empty string.
1216 The returned &quot;datalen&quot; does not include the trailing nul.
1217
1218 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1219 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1220 the printer does not respond to the SNMP query.
1221
1222 </p>
1223 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1224 <p class="description">Query multiple SNMP OID values.</p>
1225 <p class="code">
1226 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1227 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1228 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1229 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1230 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1231 );</p>
1232 <h4 class="parameters">Parameters</h4>
1233 <dl>
1234 <dt>oid</dt>
1235 <dd class="description">First numeric OID to query</dd>
1236 <dt>timeout</dt>
1237 <dd class="description">Timeout for each query in seconds</dd>
1238 <dt>cb</dt>
1239 <dd class="description">Function to call with each value</dd>
1240 <dt>context</dt>
1241 <dd class="description">Application-defined pointer to send to callback</dd>
1242 </dl>
1243 <h4 class="returnvalue">Return Value</h4>
1244 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1245 <h4 class="discussion">Discussion</h4>
1246 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1247 of the filter, port monitor, or backend using the default community name.
1248 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1249 the callback function you provide.<br>
1250 <br>
1251 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1252 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1253 supported and must be converted to their numeric forms.<br>
1254 <br>
1255 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1256 time will depend on the number of OID values found and the time required
1257 for each query.<br>
1258 <br>
1259 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1260 is an application-defined pointer that is sent to the callback function
1261 along with the OID and current data. The data passed to the callback is the
1262 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1263
1264 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1265 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1266 the printer does not respond to the first SNMP query.
1267
1268 </p>
1269 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1270 <p class="description">Write a side-channel message.</p>
1271 <p class="code">
1272 int cupsSideChannelWrite (<br>
1273 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1274 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1275 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1276 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1277 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1278 );</p>
1279 <h4 class="parameters">Parameters</h4>
1280 <dl>
1281 <dt>command</dt>
1282 <dd class="description">Command code</dd>
1283 <dt>status</dt>
1284 <dd class="description">Status code</dd>
1285 <dt>data</dt>
1286 <dd class="description">Data buffer pointer</dd>
1287 <dt>datalen</dt>
1288 <dd class="description">Number of bytes of data</dd>
1289 <dt>timeout</dt>
1290 <dd class="description">Timeout in seconds</dd>
1291 </dl>
1292 <h4 class="returnvalue">Return Value</h4>
1293 <p class="description">0 on success, -1 on error</p>
1294 <h4 class="discussion">Discussion</h4>
1295 <p class="discussion">This function is normally only called by backend programs to send
1296 responses to a filter, driver, or port monitor program.
1297
1298 </p>
1299 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1300 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1301 <p class="description">Backend exit codes</p>
1302 <p class="code">
1303 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1304 </p>
1305 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1306 <p class="description">Bidirectional capabilities</p>
1307 <p class="code">
1308 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1309 </p>
1310 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1311 <p class="description">Request command codes</p>
1312 <p class="code">
1313 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1314 </p>
1315 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1316 <p class="description">Printer state bits</p>
1317 <p class="code">
1318 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1319 </p>
1320 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1321 <p class="description">Response status codes</p>
1322 <p class="code">
1323 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1324 </p>
1325 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1326 <p class="description">SNMP walk callback</p>
1327 <p class="code">
1328 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1329 </p>
1330 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1331 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1332 <p class="description">Backend exit codes</p>
1333 <h4 class="constants">Constants</h4>
1334 <dl>
1335 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1336 <dd class="description">Job failed, authentication required</dd>
1337 <dt>CUPS_BACKEND_CANCEL </dt>
1338 <dd class="description">Job failed, cancel job</dd>
1339 <dt>CUPS_BACKEND_FAILED </dt>
1340 <dd class="description">Job failed, use error-policy</dd>
1341 <dt>CUPS_BACKEND_HOLD </dt>
1342 <dd class="description">Job failed, hold job</dd>
1343 <dt>CUPS_BACKEND_OK </dt>
1344 <dd class="description">Job completed successfully</dd>
1345 <dt>CUPS_BACKEND_STOP </dt>
1346 <dd class="description">Job failed, stop queue</dd>
1347 </dl>
1348 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1349 <p class="description">Bidirectional capability values</p>
1350 <h4 class="constants">Constants</h4>
1351 <dl>
1352 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1353 <dd class="description">Bidirectional I/O is not supported</dd>
1354 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1355 <dd class="description">Bidirectional I/O is supported</dd>
1356 </dl>
1357 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1358 <p class="description">Request command codes</p>
1359 <h4 class="constants">Constants</h4>
1360 <dl>
1361 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1362 <dd class="description">Drain all pending output</dd>
1363 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1364 <dd class="description">Return bidirectional capabilities</dd>
1365 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1366 <dd class="description">Return the IEEE-1284 device ID</dd>
1367 <dt>CUPS_SC_CMD_GET_STATE </dt>
1368 <dd class="description">Return the device state</dd>
1369 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span></dt>
1370 <dd class="description">Query an SNMP OID </dd>
1371 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span></dt>
1372 <dd class="description">Query the next SNMP OID </dd>
1373 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1374 <dd class="description">Do a soft reset</dd>
1375 </dl>
1376 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1377 <p class="description">Printer state bits</p>
1378 <h4 class="constants">Constants</h4>
1379 <dl>
1380 <dt>CUPS_SC_STATE_BUSY </dt>
1381 <dd class="description">Device is busy</dd>
1382 <dt>CUPS_SC_STATE_ERROR </dt>
1383 <dd class="description">Other error condition</dd>
1384 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1385 <dd class="description">Toner/ink out condition</dd>
1386 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1387 <dd class="description">Toner/ink low condition</dd>
1388 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1389 <dd class="description">Paper out condition</dd>
1390 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1391 <dd class="description">Paper low condition</dd>
1392 <dt>CUPS_SC_STATE_OFFLINE </dt>
1393 <dd class="description">Device is offline</dd>
1394 <dt>CUPS_SC_STATE_ONLINE </dt>
1395 <dd class="description">Device is online</dd>
1396 </dl>
1397 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1398 <p class="description">Response status codes</p>
1399 <h4 class="constants">Constants</h4>
1400 <dl>
1401 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1402 <dd class="description">The command/response message was invalid</dd>
1403 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1404 <dd class="description">An I/O error occurred</dd>
1405 <dt>CUPS_SC_STATUS_NONE </dt>
1406 <dd class="description">No status</dd>
1407 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1408 <dd class="description">Command not implemented</dd>
1409 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1410 <dd class="description">The device did not respond</dd>
1411 <dt>CUPS_SC_STATUS_OK </dt>
1412 <dd class="description">Operation succeeded</dd>
1413 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1414 <dd class="description">The backend did not respond</dd>
1415 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1416 <dd class="description">Response too big</dd>
1417 </dl>
1418 </div>
1419 </body>
1420 </html>