doc/help/api-filter.html

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 342 <div class='body'>
 343 <!--
 344   "$Id$"
 345
 346   Filter and backend programming header for the Common UNIX Printing System
 347   (CUPS).
 348
 349   Copyright 2008-2009 by Apple Inc.
 350
 351   These coded instructions, statements, and computer programs are the
 352   property of Apple Inc. and are protected by Federal copyright
 353   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 354   which should have been included with this file.  If this file is
 355   file is missing or damaged, see the license at "http://www.cups.org/".
 356 -->
 357
 358 <h1 class='title'>Filter and Backend Programming</h1>
 359
 360 <div class='summary'><table summary='General Information'>
 361 <thead>
 362 <tr>
 363         <th>Headers</th>
 364         <th>cups/backend.h<br>
 365         cups/sidechannel.h</th>
 366 </tr>
 367 </thead>
 368 <tbody>
 369 <tr>
 370         <th>Library</th>
 371         <td>-lcups</td>
 372 </tr>
 373 <tr>
 374         <th>See Also</th>
 375         <td>Programming: <a href='api-overview.html' target='_top'>Introduction to CUPS Programming</a><br>
 376         Programming: <a href='api-cups.html' target='_top'>CUPS API</a><br>
 377         Programming: <a href='api-ppd.html' target='_top'>PPD API</a><br>
 378         Programming: <a href='api-raster.html' target='_top'>Raster API</a><br>
 379         Programming: <a href='postscript-driver.html' target='_top'>Developing PostScript Printer Drivers</a><br>
 380         Programming: <a href='raster-driver.html' target='_top'>Developing Raster Printer Drivers</a><br>
 381         Specifications: <a href='spec-design.html' target='_top'>CUPS Design Description</a></td>
 382 </tr>
 383 </tbody>
 384 </table></div>
 385 <h2 class="title">Contents</h2>
 386 <ul class="contents">
 387 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 388         <li><a href="#SECURITY">Security Considerations</a></li>
 389         <li><a href="#PERMISSIONS">File Permissions</a></li>
 390         <li><a href="#TEMPFILES">Temporary Files</a></li>
 391         <li><a href="#COPIES">Copy Generation</a></li>
 392         <li><a href="#EXITCODES">Exit Codes</a></li>
 393         <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 394         <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 395         <li><a href="#COMMUNICATING_BACKEND">Communicating with the Backend</a></li>
 396         <li><a href="#COMMUNICATING_FILTER">Communicating with Filters</a></li>
 397         <li><a href="#SNMP">Doing SNMP Queries with Network Printers</a></li>
 398 </ul></li>
 399 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 400         <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 401         <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 402         <li><a href="#cupsBackendDeviceURI" title="Get the device URI for a backend.">cupsBackendDeviceURI</a></li>
 403         <li><a href="#cupsBackendReport" title="Write a device line from a backend.">cupsBackendReport</a></li>
 404         <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 405         <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 406         <li><a href="#cupsSideChannelSNMPGet" title="Query a SNMP OID's value.">cupsSideChannelSNMPGet</a></li>
 407         <li><a href="#cupsSideChannelSNMPWalk" title="Query multiple SNMP OID values.">cupsSideChannelSNMPWalk</a></li>
 408         <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 409 </ul></li>
 410 <li><a href="#TYPES">Data Types</a><ul class="code">
 411         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 412         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 413         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 414         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 415         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 416         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 417 </ul></li>
 418 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 419         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 420         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 421         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 422         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 423         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 424 </ul></li>
 425 </ul>
 426 <!--
 427   "$Id$"
 428
 429   Filter and backend programming introduction for the Common UNIX Printing
 430   System (CUPS).
 431
 432   Copyright 2007-2009 by Apple Inc.
 433   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 434
 435   These coded instructions, statements, and computer programs are the
 436   property of Apple Inc. and are protected by Federal copyright
 437   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 438   which should have been included with this file.  If this file is
 439   file is missing or damaged, see the license at "http://www.cups.org/".
 440 -->
 441
 442 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 443
 444 <p>Filters (which include printer drivers and port monitors) and backends
 445 are used to convert job files to a printable format and send that data to the
 446 printer itself. All of these programs use a common interface for processing
 447 print jobs and communicating status information to the scheduler. Each is run
 448 with a standard set of command-line arguments:<p>
 449
 450 <dl class="code">
 451
 452         <dt>argv[1]</dt>
 453         <dd>The job ID</dd>
 454
 455         <dt>argv[2]</dt>
 456         <dd>The user printing the job</dd>
 457
 458         <dt>argv[3]</dt>
 459         <dd>The job name/title</dd>
 460
 461         <dt>argv[4]</dt>
 462         <dd>The number of copies to print</dd>
 463
 464         <dt>argv[5]</dt>
 465         <dd>The options that were provided when the job was submitted</dd>
 466
 467         <dt>argv[6]</dt>
 468         <dd>The file to print (first program only)</dd>
 469 </dl>
 470
 471 <p>The scheduler runs one or more of these programs to print any given job. The
 472 first filter reads from the print file and writes to the standard output, while
 473 the remaining filters read from the standard input and write to the standard
 474 output. The backend is the last filter in the chain and writes to the
 475 device.</p>
 476
 477 <p>Filters are always run as a non-privileged user, typically "lp", with no
 478 connection to the user's desktop. Backends are run either as a non-privileged
 479 user or as root if the file permissions do not allow user or group execution.
 480 The <a href="#PERMISSIONS">file permissions</a> section talks about this in
 481 more detail.</p>
 482
 483 <h3><a name="SECURITY">Security Considerations</a></h3>
 484
 485 <p>It is always important to use security programming practices. Filters and
 486 most backends are run as a non-priviledged user, so the major security
 487 consideration is resource utilization - filters should not depend on unlimited
 488 amounts of CPU, memory, or disk space, and should protect against conditions
 489 that could lead to excess usage of any resource like infinite loops and
 490 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 491 specify an arbitrary file path to a separator page, template, or other file
 492 used by the filter since that can lead to an unauthorized disclosure of
 493 information. <em>Always</em> treat input as suspect and validate it!</p>
 494
 495 <p>If you are developing a backend that runs as root, make sure to check for
 496 potential buffer overflows, integer under/overflow conditions, and file
 497 accesses since these can lead to privilege escalations. When writing files,
 498 always validate the file path and <em>never</em> allow a user to determine
 499 where to store a file.</p>
 500
 501 <blockquote><b>Note:</b>
 502
 503 <p><em>Never</em> write files to a user's home directory. Aside from the
 504 security implications, CUPS is a network print service and as such the network
 505 user may not be the same as the local user and/or there may not be a local home
 506 directory to write to.</p>
 507
 508 <p>In addition, some operating systems provide additional security mechanisms
 509 that further limit file system access, even for backends running as root. On
 510 Mac OS X, for example, no backend may write to a user's home directory.</p>
 511 </blockquote>
 512
 513 <h3><a name="PERMISSIONS">File Permissions</a></h3>
 514
 515 <p>For security reasons, CUPS will only run filters and backends that are owned
 516 by root and do not have world or group write permissions. The recommended
 517 permissions for filters and backends are 0555 - read and execute but no write.
 518 Backends that must run as root should use permissions of 0500 - read and execute
 519 by root, no access for other users. Write permissions can be enabled for the
 520 root user only.</p>
 521
 522 <p>To avoid a warning message, the directory containing your filter(s) must also
 523 be owned by root and have world and group write disabled - permissions of 0755
 524 or 0555 are strongly encouraged.</p>
 525
 526 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 527
 528 <p>Temporary files should be created in the directory specified by the
 529 "TMPDIR" environment variable. The
 530 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 531 used to safely create temporary files in this directory.</p>
 532
 533 <h3><a name="COPIES">Copy Generation</a></h3>
 534
 535 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 536 of the input file. In general, you should only generate copies if the
 537 <em>filename</em> argument is supplied. The only exception to this are
 538 filters that produce device-independent PostScript output, since the PostScript
 539 filter <var>pstops</var> is responsible for generating copies of PostScript
 540 files.</p>
 541
 542 <h3><a name="EXITCODES">Exit Codes</a></h3>
 543
 544 <p>Filters must exit with status 0 when they successfully generate print data
 545 or 1 when they encounter an error. Backends can return any of the
 546 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 547
 548 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 549
 550 <p>The following environment variables are defined by the printing system
 551 when running print filters and backends:</p>
 552
 553 <dl class="code">
 554
 555         <dt>APPLE_LANGUAGE</dt>
 556         <dd>The Apple language identifier associated with the job
 557         (Mac OS X only).</dd>
 558
 559         <dt>CHARSET</dt>
 560         <dd>The job character set, typically "utf-8".</dd>
 561
 562         <dt>CLASS</dt>
 563         <dd>When a job is submitted to a printer class, contains the name of
 564         the destination printer class. Otherwise this environment
 565         variable will not be set.</dd>
 566
 567         <dt>CONTENT_TYPE</dt>
 568         <dd>The MIME type associated with the file (e.g.
 569         application/postscript).</dd>
 570
 571         <dt>CUPS_CACHEDIR</dt>
 572         <dd>The directory where cache files can be stored. Cache files can be
 573         used to retain information between jobs or files in a job.</dd>
 574
 575         <dt>CUPS_DATADIR</dt>
 576         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 577
 578         <dt>CUPS_FILETYPE</dt>
 579         <dd>The type of file being printed: "job-sheet" for a banner page and
 580         "document" for a regular print file.</dd>
 581
 582         <dt>CUPS_SERVERROOT</dt>
 583         <dd>The root directory of the server.</dd>
 584
 585         <dt>DEVICE_URI</dt>
 586         <dd>The device-uri associated with the printer.</dd>
 587
 588         <dt>FINAL_CONTENT_TYPE</dt>
 589         <dd>The MIME type associated with the printer (e.g.
 590         application/vnd.cups-postscript).</dd>
 591
 592         <dt>LANG</dt>
 593         <dd>The language locale associated with the job.</dd>
 594
 595         <dt>PPD</dt>
 596         <dd>The full pathname of the PostScript Printer Description (PPD)
 597         file for this printer.</dd>
 598
 599         <dt>PRINTER</dt>
 600         <dd>The queue name of the class or printer.</dd>
 601
 602         <dt>RIP_CACHE</dt>
 603         <dd>The recommended amount of memory to use for Raster Image
 604         Processors (RIPs).</dd>
 605
 606         <dt>TMPDIR</dt>
 607         <dd>The directory where temporary files should be created.</dd>
 608
 609 </dl>
 610
 611 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 612
 613 <p>Filters and backends communicate with the scheduler by writing messages
 614 to the standard error file. The scheduler reads messages from all filters in
 615 a job and processes the message based on its prefix. For example, the following
 616 code sets the current printer state message to "Printing page 5":</p>
 617
 618 <pre class="example">
 619 int page = 5;
 620
 621 fprintf(stderr, "INFO: Printing page %d\n", page);
 622 </pre>
 623
 624 <p>Each message is a single line of text starting with one of the following
 625 prefix strings:</p>
 626
 627 <dl class="code">
 628
 629         <dt>ALERT: message</dt>
 630         <dd>Sets the printer-state-message attribute and adds the specified
 631         message to the current error log file using the "alert" log level.</dd>
 632
 633         <dt>ATTR: attribute=value [attribute=value]</dt>
 634         <dd>Sets the named printer or job attribute(s). Typically this is used
 635         to set the <code>marker-colors</code>, <code>marker-levels</code>,
 636         <code>marker-message</code>, <code>marker-names</code>,
 637         <code>marker-types</code>, <code>printer-alert</code>, and
 638         <code>printer-alert-description</code> printer attributes. Standard
 639         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 640         1</a>.</dd>
 641
 642         <dt>CRIT: message</dt>
 643         <dd>Sets the printer-state-message attribute and adds the specified
 644         message to the current error log file using the "critical" log
 645         level.</dd>
 646
 647         <dt>DEBUG: message</dt>
 648         <dd>Sets the printer-state-message attribute and adds the specified
 649         message to the current error log file using the "debug" log level.</dd>
 650
 651         <dt>DEBUG2: message</dt>
 652         <dd>Sets the printer-state-message attribute and adds the specified
 653         message to the current error log file using the "debug2" log level.</dd>
 654
 655         <dt>EMERG: message</dt>
 656         <dd>Sets the printer-state-message attribute and adds the specified
 657         message to the current error log file using the "emergency" log
 658         level.</dd>
 659
 660         <dt>ERROR: message</dt>
 661         <dd>Sets the printer-state-message attribute and adds the specified
 662         message to the current error log file using the "error" log level.
 663         Use "ERROR:" messages for non-persistent processing errors.</dd>
 664
 665         <dt>INFO: message</dt>
 666         <dd>Sets the printer-state-message attribute. If the current log level
 667         is set to "debug2", also adds the specified message to the current error
 668         log file using the "info" log level.</dd>
 669
 670         <dt>NOTICE: message</dt>
 671         <dd>Sets the printer-state-message attribute and adds the specified
 672         message to the current error log file using the "notice" log level.</dd>
 673
 674         <dt>PAGE: page-number #-copies</dt>
 675         <dt>PAGE: total #-pages</dt>
 676         <dd>Adds an entry to the current page log file. The first form adds
 677         #-copies to the job-media-sheets-completed attribute. The second
 678         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 679
 680         <dt>PPD: keyword=value [keyword=value ...]</dt>
 681         <dd>Changes or adds keywords to the printer's PPD file. Typically
 682         this is used to update installable options or default media settings
 683         based on the printer configuration.</dd>
 684
 685         <dt>STATE: printer-state-reason [printer-state-reason ...]</dt>
 686         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 687         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 688         <dd>Sets, adds, or removes printer-state-reason keywords to the
 689         current queue. Typically this is used to indicate persistent media,
 690         ink, toner, and configuration conditions or errors on a printer.
 691         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 692         use vendor-prefixed ("com.acme.foo") keywords for custom states.
 693
 694         <blockquote><b>Note:</b>
 695
 696         <p>"STATE:" messages often provide visible alerts to the user. For example, on
 697         Mac OS X setting a printer-state-reason value with an "-error" or "-warning"
 698         suffix will cause the printer's dock item to bounce if the corresponding reason
 699         is localized with a cupsIPPReason keyword in the printer's PPD file.</p>
 700
 701         </blockquote></dd>
 702
 703         <dt>WARNING: message</dt>
 704         <dd>Sets the printer-state-message attribute and adds the specified
 705         message to the current error log file using the "warning" log
 706         level.</dd>
 707
 708 </dl>
 709
 710 <p>Messages without one of these prefixes are treated as if they began with
 711 the "DEBUG:" prefix string.</p>
 712
 713 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 714 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 715 <thead>
 716 <tr>
 717         <th>marker-type</th>
 718         <th>Description</th>
 719 </tr>
 720 </thead>
 721 <tbody>
 722 <tr>
 723         <td>developer</td>
 724         <td>Developer unit</td>
 725 </tr>
 726 <tr>
 727         <td>fuser</td>
 728         <td>Fuser unit</td>
 729 </tr>
 730 <tr>
 731         <td>fuserCleaningPad</td>
 732         <td>Fuser cleaning pad</td>
 733 </tr>
 734 <tr>
 735         <td>fuserOil</td>
 736         <td>Fuser oil</td>
 737 </tr>
 738 <tr>
 739         <td>ink</td>
 740         <td>Ink supply</td>
 741 </tr>
 742 <tr>
 743         <td>opc</td>
 744         <td>Photo conductor</td>
 745 </tr>
 746 <tr>
 747         <td>solidWax</td>
 748         <td>Wax supply</td>
 749 </tr>
 750 <tr>
 751         <td>staples</td>
 752         <td>Staple supply</td>
 753 </tr>
 754 <tr>
 755         <td>toner</td>
 756         <td>Toner supply</td>
 757 </tr>
 758 <tr>
 759         <td>transferUnit</td>
 760         <td>Transfer unit</td>
 761 </tr>
 762 <tr>
 763         <td>wasteInk</td>
 764         <td>Waste ink tank</td>
 765 </tr>
 766 <tr>
 767         <td>wasteToner</td>
 768         <td>Waste toner tank</td>
 769 </tr>
 770 <tr>
 771         <td>wasteWax</td>
 772         <td>Waste wax tank</td>
 773 </tr>
 774 </tbody>
 775 </table></div>
 776
 777 <br>
 778
 779 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 780 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 781 <thead>
 782 <tr>
 783         <th>Keyword</th>
 784         <th>Description</th>
 785 </tr>
 786 </thead>
 787 <tbody>
 788 <tr>
 789         <td>connecting-to-device</td>
 790         <td>Connecting to printer but not printing yet</td>
 791 </tr>
 792 <tr>
 793         <td>cover-open</td>
 794         <td>A cover is open on the printer</td>
 795 </tr>
 796 <tr>
 797         <td>input-tray-missing</td>
 798         <td>An input tray is missing from the printer</td>
 799 </tr>
 800 <tr>
 801         <td>marker-supply-empty</td>
 802         <td>Out of ink</td>
 803 </tr>
 804 <tr>
 805         <td>marker-supply-low</td>
 806         <td>Low on ink</td>
 807 </tr>
 808 <tr>
 809         <td>marker-waste-almost-full</td>
 810         <td>Waste tank almost full</td>
 811 </tr>
 812 <tr>
 813         <td>marker-waste-full</td>
 814         <td>Waste tank full</td>
 815 </tr>
 816 <tr>
 817         <td>media-empty</td>
 818         <td>Out of media</td>
 819 </tr>
 820 <tr>
 821         <td>media-jam</td>
 822         <td>Media is jammed in the printer</td>
 823 </tr>
 824 <tr>
 825         <td>media-low</td>
 826         <td>Low on media</td>
 827 </tr>
 828 <tr>
 829         <td>paused</td>
 830         <td>Stop the printer</td>
 831 </tr>
 832 <tr>
 833         <td>timed-out</td>
 834         <td>Unable to connect to printer</td>
 835 </tr>
 836 <tr>
 837         <td>toner-empty</td>
 838         <td>Out of toner</td>
 839 </tr>
 840 <tr>
 841         <td>toner-low</td>
 842         <td>Low on toner</td>
 843 </tr>
 844 </tbody>
 845 </table></div>
 846
 847 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
 848
 849 <p>Filters can communicate with the backend via the
 850 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
 851 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 852 functions. The
 853 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
 854 reads data that has been sent back from the device and is typically used to
 855 obtain status and configuration information. For example, the following code
 856 polls the backend for back-channel data:</p>
 857
 858 <pre class="example">
 859 #include &lt;cups/cups.h&gt;
 860
 861 char buffer[8192];
 862 ssize_t bytes;
 863
 864 /* Use a timeout of 0.0 seconds to poll for back-channel data */
 865 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
 866 </pre>
 867
 868 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
 869 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
 870 when it is available.</p>
 871
 872 <p>The
 873 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 874 function allows you to get out-of-band status information and do synchronization
 875 with the device. For example, the following code gets the current IEEE-1284
 876 device ID string from the backend:</p>
 877
 878 <pre class="example">
 879 #include &lt;cups/sidechannel.h&gt;
 880
 881 char data[2049];
 882 int datalen;
 883 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 884
 885 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
 886    nul-termination... */
 887 datalen = sizeof(data) - 1;
 888
 889 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
 890 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
 891
 892 /* Use the returned value if OK was returned and the length is non-zero */
 893 if (status == CUPS_SC_STATUS_OK && datalen > 0)
 894   data[datalen] = '\0';
 895 else
 896   data[0] = '\0';
 897 </pre>
 898
 899 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
 900
 901 <p>Backends communicate with filters using the reciprocal functions
 902 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
 903 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
 904 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
 905 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
 906
 907 <pre class="example">
 908 #include &lt;cups/cups.h&gt;
 909
 910 char buffer[8192];
 911 ssize_t bytes;
 912
 913 /* Obtain data from printer/device */
 914 ...
 915
 916 /* Use a timeout of 1.0 seconds to give filters a chance to read */
 917 cupsBackChannelWrite(buffer, bytes, 1.0);
 918 </pre>
 919
 920 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
 921 function reads a side-channel command from a filter, driver, or port monitor.
 922 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
 923 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
 924 separate thread for that purpose), or use <code>select</code> or
 925 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
 926 input and output on several file descriptors at the same time.</p>
 927
 928 <p>Once a command is processed, the backend uses the
 929 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
 930 to send its response. For example, the following code shows how to poll for a
 931 side-channel command and respond to it:</p>
 932
 933 <pre class="example">
 934 #include &lt;cups/sidechannel.h&gt;
 935
 936 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
 937 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 938 char data[2048];
 939 int datalen = sizeof(data);
 940
 941 /* Poll for a command... */
 942 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
 943 {
 944   switch (command)
 945   {
 946     /* handle supported commands, fill data/datalen/status with values as needed */
 947
 948     default :
 949         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
 950         datalen = 0;
 951         break;
 952   }
 953
 954   /* Send a response... */
 955   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
 956 }
 957 </pre>
 958
 959 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
 960
 961 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
 962 status, page counter, and supply levels from most network printers. Every
 963 piece of information is associated with an Object Identifier (OID), and
 964 every printer has a <em>community</em> name associated with it. OIDs can be
 965 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
 966
 967 <p>The two CUPS SNMP functions provide a simple API for querying network
 968 printers through the side-channel interface. Each accepts a string containing
 969 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
 970 along with a timeout for the query.</p>
 971
 972 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
 973 function queries a single OID and returns the value as a string in a buffer
 974 you supply:</p>
 975
 976 <pre class="example">
 977 #include &lt;cups/sidechannel.h&gt;
 978
 979 char data[512];
 980 int datalen = sizeof(data);
 981
 982 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
 983         == CUPS_SC_STATUS_OK)
 984 {
 985   /* Do something with the value */
 986   printf("Page counter is: %s\n", data);
 987 }
 988 </pre>
 989
 990 <p>The
 991 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
 992 function allows you to query a whole group of OIDs, calling a function of your
 993 choice for each OID that is found:</p>
 994
 995 <pre class="example">
 996 #include &lt;cups/sidechannel.h&gt;
 997
 998 void
 999 my_callback(const char *oid, const char *data, int datalen, void *context)
1000 {
1001   /* Do something with the value */
1002   printf("%s=%s\n", oid, data);
1003 }
1004
1005 ...
1006
1007 void *my_data;
1008
1009 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
1010 </pre>
1011 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
1012 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
1013 <p class="description">Read data from the backchannel.</p>
1014 <p class="code">
1015 ssize_t cupsBackChannelRead (<br>
1016 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
1017 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1018 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1019 );</p>
1020 <h4 class="parameters">Parameters</h4>
1021 <dl>
1022 <dt>buffer</dt>
1023 <dd class="description">Buffer to read into</dd>
1024 <dt>bytes</dt>
1025 <dd class="description">Bytes to read</dd>
1026 <dt>timeout</dt>
1027 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
1028 </dl>
1029 <h4 class="returnvalue">Return Value</h4>
1030 <p class="description">Bytes read or -1 on error</p>
1031 <h4 class="discussion">Discussion</h4>
1032 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
1033 parameter controls how many seconds to wait for the data - use 0.0 to
1034 return immediately if there is no data, -1.0 to wait for data indefinitely.
1035
1036 </p>
1037 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
1038 <p class="description">Write data to the backchannel.</p>
1039 <p class="code">
1040 ssize_t cupsBackChannelWrite (<br>
1041 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
1042 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1043 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1044 );</p>
1045 <h4 class="parameters">Parameters</h4>
1046 <dl>
1047 <dt>buffer</dt>
1048 <dd class="description">Buffer to write</dd>
1049 <dt>bytes</dt>
1050 <dd class="description">Bytes to write</dd>
1051 <dt>timeout</dt>
1052 <dd class="description">Timeout in seconds, typically 1.0</dd>
1053 </dl>
1054 <h4 class="returnvalue">Return Value</h4>
1055 <p class="description">Bytes written or -1 on error</p>
1056 <h4 class="discussion">Discussion</h4>
1057 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
1058 controls how many seconds to wait for the data to be written - use
1059 0.0 to return immediately if the data cannot be written, -1.0 to wait
1060 indefinitely.
1061
1062 </p>
1063 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
1064 <p class="description">Get the device URI for a backend.</p>
1065 <p class="code">
1066 const char *cupsBackendDeviceURI (<br>
1067 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
1068 );</p>
1069 <h4 class="parameters">Parameters</h4>
1070 <dl>
1071 <dt>argv</dt>
1072 <dd class="description">Command-line arguments</dd>
1073 </dl>
1074 <h4 class="returnvalue">Return Value</h4>
1075 <p class="description">Device URI or <code>NULL</code></p>
1076 <h4 class="discussion">Discussion</h4>
1077 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
1078 function returns the device URI passed in the DEVICE_URI environment
1079 variable or the device URI passed in argv[0], whichever is found
1080 first.
1081
1082 </p>
1083 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsBackendReport">cupsBackendReport</a></h3>
1084 <p class="description">Write a device line from a backend.</p>
1085 <p class="code">
1086 void cupsBackendReport (<br>
1087 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
1088 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
1089 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
1090 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
1091 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
1092 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
1093 );</p>
1094 <h4 class="parameters">Parameters</h4>
1095 <dl>
1096 <dt>device_scheme</dt>
1097 <dd class="description">device-scheme string</dd>
1098 <dt>device_uri</dt>
1099 <dd class="description">device-uri string</dd>
1100 <dt>device_make_and_model</dt>
1101 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
1102 <dt>device_info</dt>
1103 <dd class="description">device-info string or <code>NULL</code></dd>
1104 <dt>device_id</dt>
1105 <dd class="description">device-id string or <code>NULL</code></dd>
1106 <dt>device_location</dt>
1107 <dd class="description">device-location string or <code>NULL</code></dd>
1108 </dl>
1109 <h4 class="discussion">Discussion</h4>
1110 <p class="discussion">This function writes a single device line to stdout for a backend.
1111 It handles quoting of special characters in the device-make-and-model,
1112 device-info, device-id, and device-location strings.
1113
1114 </p>
1115 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
1116 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
1117 <p class="code">
1118 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
1119 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1120 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1121 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1122 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1123 );</p>
1124 <h4 class="parameters">Parameters</h4>
1125 <dl>
1126 <dt>command</dt>
1127 <dd class="description">Command to send</dd>
1128 <dt>data</dt>
1129 <dd class="description">Response data buffer pointer</dd>
1130 <dt>datalen</dt>
1131 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1132 <dt>timeout</dt>
1133 <dd class="description">Timeout in seconds</dd>
1134 </dl>
1135 <h4 class="returnvalue">Return Value</h4>
1136 <p class="description">Status of command</p>
1137 <h4 class="discussion">Discussion</h4>
1138 <p class="discussion">This function is normally only called by filters, drivers, or port
1139 monitors in order to communicate with the backend used by the current
1140 printer.  Programs must be prepared to handle timeout or &quot;not
1141 implemented&quot; status codes, which indicate that the backend or device
1142 do not support the specified side-channel command.<br>
1143 <br>
1144 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1145 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1146 update the value to contain the number of data bytes in the buffer.
1147
1148 </p>
1149 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1150 <p class="description">Read a side-channel message.</p>
1151 <p class="code">
1152 int cupsSideChannelRead (<br>
1153 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1154 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1155 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1156 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1157 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1158 );</p>
1159 <h4 class="parameters">Parameters</h4>
1160 <dl>
1161 <dt>command</dt>
1162 <dd class="description">Command code</dd>
1163 <dt>status</dt>
1164 <dd class="description">Status code</dd>
1165 <dt>data</dt>
1166 <dd class="description">Data buffer pointer</dd>
1167 <dt>datalen</dt>
1168 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1169 <dt>timeout</dt>
1170 <dd class="description">Timeout in seconds</dd>
1171 </dl>
1172 <h4 class="returnvalue">Return Value</h4>
1173 <p class="description">0 on success, -1 on error</p>
1174 <h4 class="discussion">Discussion</h4>
1175 <p class="discussion">This function is normally only called by backend programs to read
1176 commands from a filter, driver, or port monitor program.  The
1177 caller must be prepared to handle incomplete or invalid messages
1178 and return the corresponding status codes.<br>
1179 <br>
1180 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1181 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1182 update the value to contain the number of data bytes in the buffer.
1183
1184 </p>
1185 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1186 <p class="description">Query a SNMP OID's value.</p>
1187 <p class="code">
1188 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1189 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1190 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1191 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1192 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1193 );</p>
1194 <h4 class="parameters">Parameters</h4>
1195 <dl>
1196 <dt>oid</dt>
1197 <dd class="description">OID to query</dd>
1198 <dt>data</dt>
1199 <dd class="description">Buffer for OID value</dd>
1200 <dt>datalen</dt>
1201 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1202 <dt>timeout</dt>
1203 <dd class="description">Timeout in seconds</dd>
1204 </dl>
1205 <h4 class="returnvalue">Return Value</h4>
1206 <p class="description">Query status</p>
1207 <h4 class="discussion">Discussion</h4>
1208 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1209 filter, port monitor, or backend using the default community name.<br>
1210 <br>
1211 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1212 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1213 supported and must be converted to their numeric forms.<br>
1214 <br>
1215 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1216 buffer to hold the OID value as a string. HEX-String (binary) values are
1217 converted to hexadecimal strings representing the binary data, while
1218 NULL-Value and unknown OID types are returned as the empty string.
1219 The returned &quot;datalen&quot; does not include the trailing nul.
1220
1221 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1222 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1223 the printer does not respond to the SNMP query.
1224
1225 </p>
1226 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1227 <p class="description">Query multiple SNMP OID values.</p>
1228 <p class="code">
1229 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1230 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1231 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1232 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1233 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1234 );</p>
1235 <h4 class="parameters">Parameters</h4>
1236 <dl>
1237 <dt>oid</dt>
1238 <dd class="description">First numeric OID to query</dd>
1239 <dt>timeout</dt>
1240 <dd class="description">Timeout for each query in seconds</dd>
1241 <dt>cb</dt>
1242 <dd class="description">Function to call with each value</dd>
1243 <dt>context</dt>
1244 <dd class="description">Application-defined pointer to send to callback</dd>
1245 </dl>
1246 <h4 class="returnvalue">Return Value</h4>
1247 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1248 <h4 class="discussion">Discussion</h4>
1249 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1250 of the filter, port monitor, or backend using the default community name.
1251 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1252 the callback function you provide.<br>
1253 <br>
1254 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1255 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1256 supported and must be converted to their numeric forms.<br>
1257 <br>
1258 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1259 time will depend on the number of OID values found and the time required
1260 for each query.<br>
1261 <br>
1262 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1263 is an application-defined pointer that is sent to the callback function
1264 along with the OID and current data. The data passed to the callback is the
1265 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1266
1267 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1268 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1269 the printer does not respond to the first SNMP query.
1270
1271 </p>
1272 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1273 <p class="description">Write a side-channel message.</p>
1274 <p class="code">
1275 int cupsSideChannelWrite (<br>
1276 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1277 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1278 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1279 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1280 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1281 );</p>
1282 <h4 class="parameters">Parameters</h4>
1283 <dl>
1284 <dt>command</dt>
1285 <dd class="description">Command code</dd>
1286 <dt>status</dt>
1287 <dd class="description">Status code</dd>
1288 <dt>data</dt>
1289 <dd class="description">Data buffer pointer</dd>
1290 <dt>datalen</dt>
1291 <dd class="description">Number of bytes of data</dd>
1292 <dt>timeout</dt>
1293 <dd class="description">Timeout in seconds</dd>
1294 </dl>
1295 <h4 class="returnvalue">Return Value</h4>
1296 <p class="description">0 on success, -1 on error</p>
1297 <h4 class="discussion">Discussion</h4>
1298 <p class="discussion">This function is normally only called by backend programs to send
1299 responses to a filter, driver, or port monitor program.
1300
1301 </p>
1302 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1303 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1304 <p class="description">Backend exit codes</p>
1305 <p class="code">
1306 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1307 </p>
1308 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1309 <p class="description">Bidirectional capabilities</p>
1310 <p class="code">
1311 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1312 </p>
1313 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1314 <p class="description">Request command codes</p>
1315 <p class="code">
1316 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1317 </p>
1318 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1319 <p class="description">Printer state bits</p>
1320 <p class="code">
1321 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1322 </p>
1323 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1324 <p class="description">Response status codes</p>
1325 <p class="code">
1326 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1327 </p>
1328 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1329 <p class="description">SNMP walk callback</p>
1330 <p class="code">
1331 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1332 </p>
1333 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1334 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1335 <p class="description">Backend exit codes</p>
1336 <h4 class="constants">Constants</h4>
1337 <dl>
1338 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1339 <dd class="description">Job failed, authentication required</dd>
1340 <dt>CUPS_BACKEND_CANCEL </dt>
1341 <dd class="description">Job failed, cancel job</dd>
1342 <dt>CUPS_BACKEND_FAILED </dt>
1343 <dd class="description">Job failed, use error-policy</dd>
1344 <dt>CUPS_BACKEND_HOLD </dt>
1345 <dd class="description">Job failed, hold job</dd>
1346 <dt>CUPS_BACKEND_OK </dt>
1347 <dd class="description">Job completed successfully</dd>
1348 <dt>CUPS_BACKEND_STOP </dt>
1349 <dd class="description">Job failed, stop queue</dd>
1350 </dl>
1351 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1352 <p class="description">Bidirectional capability values</p>
1353 <h4 class="constants">Constants</h4>
1354 <dl>
1355 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1356 <dd class="description">Bidirectional I/O is not supported</dd>
1357 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1358 <dd class="description">Bidirectional I/O is supported</dd>
1359 </dl>
1360 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1361 <p class="description">Request command codes</p>
1362 <h4 class="constants">Constants</h4>
1363 <dl>
1364 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1365 <dd class="description">Drain all pending output</dd>
1366 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1367 <dd class="description">Return bidirectional capabilities</dd>
1368 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1369 <dd class="description">Return the IEEE-1284 device ID</dd>
1370 <dt>CUPS_SC_CMD_GET_STATE </dt>
1371 <dd class="description">Return the device state</dd>
1372 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span></dt>
1373 <dd class="description">Query an SNMP OID </dd>
1374 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span></dt>
1375 <dd class="description">Query the next SNMP OID </dd>
1376 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1377 <dd class="description">Do a soft reset</dd>
1378 </dl>
1379 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1380 <p class="description">Printer state bits</p>
1381 <h4 class="constants">Constants</h4>
1382 <dl>
1383 <dt>CUPS_SC_STATE_BUSY </dt>
1384 <dd class="description">Device is busy</dd>
1385 <dt>CUPS_SC_STATE_ERROR </dt>
1386 <dd class="description">Other error condition</dd>
1387 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1388 <dd class="description">Toner/ink out condition</dd>
1389 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1390 <dd class="description">Toner/ink low condition</dd>
1391 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1392 <dd class="description">Paper out condition</dd>
1393 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1394 <dd class="description">Paper low condition</dd>
1395 <dt>CUPS_SC_STATE_OFFLINE </dt>
1396 <dd class="description">Device is offline</dd>
1397 <dt>CUPS_SC_STATE_ONLINE </dt>
1398 <dd class="description">Device is online</dd>
1399 </dl>
1400 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1401 <p class="description">Response status codes</p>
1402 <h4 class="constants">Constants</h4>
1403 <dl>
1404 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1405 <dd class="description">The command/response message was invalid</dd>
1406 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1407 <dd class="description">An I/O error occurred</dd>
1408 <dt>CUPS_SC_STATUS_NONE </dt>
1409 <dd class="description">No status</dd>
1410 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1411 <dd class="description">Command not implemented</dd>
1412 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1413 <dd class="description">The device did not respond</dd>
1414 <dt>CUPS_SC_STATUS_OK </dt>
1415 <dd class="description">Operation succeeded</dd>
1416 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1417 <dd class="description">The backend did not respond</dd>
1418 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1419 <dd class="description">Response too big</dd>
1420 </dl>
1421 </div>
1422 </body>
1423 </html>