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_connected_t" title="Connectivity values">cups_sc_connected_t</a></li>
 415         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 416         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 417         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 418 </ul></li>
 419 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 420         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 421         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 422         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 423         <li><a href="#cups_sc_connected_e" title="Connectivity values">cups_sc_connected_e</a></li>
 424         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 425         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 426 </ul></li>
 427 </ul>
 428 <!--
 429   "$Id$"
 430
 431   Filter and backend programming introduction for the Common UNIX Printing
 432   System (CUPS).
 433
 434   Copyright 2007-2009 by Apple Inc.
 435   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 436
 437   These coded instructions, statements, and computer programs are the
 438   property of Apple Inc. and are protected by Federal copyright
 439   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 440   which should have been included with this file.  If this file is
 441   file is missing or damaged, see the license at "http://www.cups.org/".
 442 -->
 443
 444 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 445
 446 <p>Filters (which include printer drivers and port monitors) and backends
 447 are used to convert job files to a printable format and send that data to the
 448 printer itself. All of these programs use a common interface for processing
 449 print jobs and communicating status information to the scheduler. Each is run
 450 with a standard set of command-line arguments:<p>
 451
 452 <dl class="code">
 453
 454         <dt>argv[1]</dt>
 455         <dd>The job ID</dd>
 456
 457         <dt>argv[2]</dt>
 458         <dd>The user printing the job</dd>
 459
 460         <dt>argv[3]</dt>
 461         <dd>The job name/title</dd>
 462
 463         <dt>argv[4]</dt>
 464         <dd>The number of copies to print</dd>
 465
 466         <dt>argv[5]</dt>
 467         <dd>The options that were provided when the job was submitted</dd>
 468
 469         <dt>argv[6]</dt>
 470         <dd>The file to print (first program only)</dd>
 471 </dl>
 472
 473 <p>The scheduler runs one or more of these programs to print any given job. The
 474 first filter reads from the print file and writes to the standard output, while
 475 the remaining filters read from the standard input and write to the standard
 476 output. The backend is the last filter in the chain and writes to the
 477 device.</p>
 478
 479 <p>Filters are always run as a non-privileged user, typically "lp", with no
 480 connection to the user's desktop. Backends are run either as a non-privileged
 481 user or as root if the file permissions do not allow user or group execution.
 482 The <a href="#PERMISSIONS">file permissions</a> section talks about this in
 483 more detail.</p>
 484
 485 <h3><a name="SECURITY">Security Considerations</a></h3>
 486
 487 <p>It is always important to use security programming practices. Filters and
 488 most backends are run as a non-priviledged user, so the major security
 489 consideration is resource utilization - filters should not depend on unlimited
 490 amounts of CPU, memory, or disk space, and should protect against conditions
 491 that could lead to excess usage of any resource like infinite loops and
 492 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 493 specify an arbitrary file path to a separator page, template, or other file
 494 used by the filter since that can lead to an unauthorized disclosure of
 495 information. <em>Always</em> treat input as suspect and validate it!</p>
 496
 497 <p>If you are developing a backend that runs as root, make sure to check for
 498 potential buffer overflows, integer under/overflow conditions, and file
 499 accesses since these can lead to privilege escalations. When writing files,
 500 always validate the file path and <em>never</em> allow a user to determine
 501 where to store a file.</p>
 502
 503 <blockquote><b>Note:</b>
 504
 505 <p><em>Never</em> write files to a user's home directory. Aside from the
 506 security implications, CUPS is a network print service and as such the network
 507 user may not be the same as the local user and/or there may not be a local home
 508 directory to write to.</p>
 509
 510 <p>In addition, some operating systems provide additional security mechanisms
 511 that further limit file system access, even for backends running as root. On
 512 Mac OS X, for example, no backend may write to a user's home directory.</p>
 513 </blockquote>
 514
 515 <h3><a name="PERMISSIONS">File Permissions</a></h3>
 516
 517 <p>For security reasons, CUPS will only run filters and backends that are owned
 518 by root and do not have world or group write permissions. The recommended
 519 permissions for filters and backends are 0555 - read and execute but no write.
 520 Backends that must run as root should use permissions of 0500 - read and execute
 521 by root, no access for other users. Write permissions can be enabled for the
 522 root user only.</p>
 523
 524 <p>To avoid a warning message, the directory containing your filter(s) must also
 525 be owned by root and have world and group write disabled - permissions of 0755
 526 or 0555 are strongly encouraged.</p>
 527
 528 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 529
 530 <p>Temporary files should be created in the directory specified by the
 531 "TMPDIR" environment variable. The
 532 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 533 used to safely create temporary files in this directory.</p>
 534
 535 <h3><a name="COPIES">Copy Generation</a></h3>
 536
 537 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 538 of the input file. In general, you should only generate copies if the
 539 <em>filename</em> argument is supplied. The only exception to this are
 540 filters that produce device-independent PostScript output, since the PostScript
 541 filter <var>pstops</var> is responsible for generating copies of PostScript
 542 files.</p>
 543
 544 <h3><a name="EXITCODES">Exit Codes</a></h3>
 545
 546 <p>Filters must exit with status 0 when they successfully generate print data
 547 or 1 when they encounter an error. Backends can return any of the
 548 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 549
 550 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 551
 552 <p>The following environment variables are defined by the printing system
 553 when running print filters and backends:</p>
 554
 555 <dl class="code">
 556
 557         <dt>APPLE_LANGUAGE</dt>
 558         <dd>The Apple language identifier associated with the job
 559         (Mac OS X only).</dd>
 560
 561         <dt>CHARSET</dt>
 562         <dd>The job character set, typically "utf-8".</dd>
 563
 564         <dt>CLASS</dt>
 565         <dd>When a job is submitted to a printer class, contains the name of
 566         the destination printer class. Otherwise this environment
 567         variable will not be set.</dd>
 568
 569         <dt>CONTENT_TYPE</dt>
 570         <dd>The MIME type associated with the file (e.g.
 571         application/postscript).</dd>
 572
 573         <dt>CUPS_CACHEDIR</dt>
 574         <dd>The directory where cache files can be stored. Cache files can be
 575         used to retain information between jobs or files in a job.</dd>
 576
 577         <dt>CUPS_DATADIR</dt>
 578         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 579
 580         <dt>CUPS_FILETYPE</dt>
 581         <dd>The type of file being printed: "job-sheet" for a banner page and
 582         "document" for a regular print file.</dd>
 583
 584         <dt>CUPS_SERVERROOT</dt>
 585         <dd>The root directory of the server.</dd>
 586
 587         <dt>DEVICE_URI</dt>
 588         <dd>The device-uri associated with the printer.</dd>
 589
 590         <dt>FINAL_CONTENT_TYPE</dt>
 591         <dd>The MIME type associated with the printer (e.g.
 592         application/vnd.cups-postscript).</dd>
 593
 594         <dt>LANG</dt>
 595         <dd>The language locale associated with the job.</dd>
 596
 597         <dt>PPD</dt>
 598         <dd>The full pathname of the PostScript Printer Description (PPD)
 599         file for this printer.</dd>
 600
 601         <dt>PRINTER</dt>
 602         <dd>The queue name of the class or printer.</dd>
 603
 604         <dt>RIP_CACHE</dt>
 605         <dd>The recommended amount of memory to use for Raster Image
 606         Processors (RIPs).</dd>
 607
 608         <dt>TMPDIR</dt>
 609         <dd>The directory where temporary files should be created.</dd>
 610
 611 </dl>
 612
 613 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 614
 615 <p>Filters and backends communicate with the scheduler by writing messages
 616 to the standard error file. The scheduler reads messages from all filters in
 617 a job and processes the message based on its prefix. For example, the following
 618 code sets the current printer state message to "Printing page 5":</p>
 619
 620 <pre class="example">
 621 int page = 5;
 622
 623 fprintf(stderr, "INFO: Printing page %d\n", page);
 624 </pre>
 625
 626 <p>Each message is a single line of text starting with one of the following
 627 prefix strings:</p>
 628
 629 <dl class="code">
 630
 631         <dt>ALERT: message</dt>
 632         <dd>Sets the printer-state-message attribute and adds the specified
 633         message to the current error log file using the "alert" log level.</dd>
 634
 635         <dt>ATTR: attribute=value [attribute=value]</dt>
 636         <dd>Sets the named printer or job attribute(s). Typically this is used
 637         to set the <code>marker-colors</code>, <code>marker-levels</code>,
 638         <code>marker-message</code>, <code>marker-names</code>,
 639         <code>marker-types</code>, <code>printer-alert</code>, and
 640         <code>printer-alert-description</code> printer attributes. Standard
 641         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 642         1</a>.</dd>
 643
 644         <dt>CRIT: message</dt>
 645         <dd>Sets the printer-state-message attribute and adds the specified
 646         message to the current error log file using the "critical" log
 647         level.</dd>
 648
 649         <dt>DEBUG: message</dt>
 650         <dd>Sets the printer-state-message attribute and adds the specified
 651         message to the current error log file using the "debug" log level.</dd>
 652
 653         <dt>DEBUG2: message</dt>
 654         <dd>Sets the printer-state-message attribute and adds the specified
 655         message to the current error log file using the "debug2" log level.</dd>
 656
 657         <dt>EMERG: message</dt>
 658         <dd>Sets the printer-state-message attribute and adds the specified
 659         message to the current error log file using the "emergency" log
 660         level.</dd>
 661
 662         <dt>ERROR: message</dt>
 663         <dd>Sets the printer-state-message attribute and adds the specified
 664         message to the current error log file using the "error" log level.
 665         Use "ERROR:" messages for non-persistent processing errors.</dd>
 666
 667         <dt>INFO: message</dt>
 668         <dd>Sets the printer-state-message attribute. If the current log level
 669         is set to "debug2", also adds the specified message to the current error
 670         log file using the "info" log level.</dd>
 671
 672         <dt>NOTICE: message</dt>
 673         <dd>Sets the printer-state-message attribute and adds the specified
 674         message to the current error log file using the "notice" log level.</dd>
 675
 676         <dt>PAGE: page-number #-copies</dt>
 677         <dt>PAGE: total #-pages</dt>
 678         <dd>Adds an entry to the current page log file. The first form adds
 679         #-copies to the job-media-sheets-completed attribute. The second
 680         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 681
 682         <dt>PPD: keyword=value [keyword=value ...]</dt>
 683         <dd>Changes or adds keywords to the printer's PPD file. Typically
 684         this is used to update installable options or default media settings
 685         based on the printer configuration.</dd>
 686
 687         <dt>STATE: printer-state-reason [printer-state-reason ...]</dt>
 688         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 689         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 690         <dd>Sets, adds, or removes printer-state-reason keywords to the
 691         current queue. Typically this is used to indicate persistent media,
 692         ink, toner, and configuration conditions or errors on a printer.
 693         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 694         use vendor-prefixed ("com.acme.foo") keywords for custom states.
 695
 696         <blockquote><b>Note:</b>
 697
 698         <p>"STATE:" messages often provide visible alerts to the user. For example, on
 699         Mac OS X setting a printer-state-reason value with an "-error" or "-warning"
 700         suffix will cause the printer's dock item to bounce if the corresponding reason
 701         is localized with a cupsIPPReason keyword in the printer's PPD file.</p>
 702
 703         </blockquote></dd>
 704
 705         <dt>WARNING: message</dt>
 706         <dd>Sets the printer-state-message attribute and adds the specified
 707         message to the current error log file using the "warning" log
 708         level.</dd>
 709
 710 </dl>
 711
 712 <p>Messages without one of these prefixes are treated as if they began with
 713 the "DEBUG:" prefix string.</p>
 714
 715 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 716 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 717 <thead>
 718 <tr>
 719         <th>marker-type</th>
 720         <th>Description</th>
 721 </tr>
 722 </thead>
 723 <tbody>
 724 <tr>
 725         <td>developer</td>
 726         <td>Developer unit</td>
 727 </tr>
 728 <tr>
 729         <td>fuser</td>
 730         <td>Fuser unit</td>
 731 </tr>
 732 <tr>
 733         <td>fuserCleaningPad</td>
 734         <td>Fuser cleaning pad</td>
 735 </tr>
 736 <tr>
 737         <td>fuserOil</td>
 738         <td>Fuser oil</td>
 739 </tr>
 740 <tr>
 741         <td>ink</td>
 742         <td>Ink supply</td>
 743 </tr>
 744 <tr>
 745         <td>opc</td>
 746         <td>Photo conductor</td>
 747 </tr>
 748 <tr>
 749         <td>solidWax</td>
 750         <td>Wax supply</td>
 751 </tr>
 752 <tr>
 753         <td>staples</td>
 754         <td>Staple supply</td>
 755 </tr>
 756 <tr>
 757         <td>toner</td>
 758         <td>Toner supply</td>
 759 </tr>
 760 <tr>
 761         <td>transferUnit</td>
 762         <td>Transfer unit</td>
 763 </tr>
 764 <tr>
 765         <td>wasteInk</td>
 766         <td>Waste ink tank</td>
 767 </tr>
 768 <tr>
 769         <td>wasteToner</td>
 770         <td>Waste toner tank</td>
 771 </tr>
 772 <tr>
 773         <td>wasteWax</td>
 774         <td>Waste wax tank</td>
 775 </tr>
 776 </tbody>
 777 </table></div>
 778
 779 <br>
 780
 781 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 782 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 783 <thead>
 784 <tr>
 785         <th>Keyword</th>
 786         <th>Description</th>
 787 </tr>
 788 </thead>
 789 <tbody>
 790 <tr>
 791         <td>connecting-to-device</td>
 792         <td>Connecting to printer but not printing yet</td>
 793 </tr>
 794 <tr>
 795         <td>cover-open</td>
 796         <td>A cover is open on the printer</td>
 797 </tr>
 798 <tr>
 799         <td>input-tray-missing</td>
 800         <td>An input tray is missing from the printer</td>
 801 </tr>
 802 <tr>
 803         <td>marker-supply-empty</td>
 804         <td>Out of ink</td>
 805 </tr>
 806 <tr>
 807         <td>marker-supply-low</td>
 808         <td>Low on ink</td>
 809 </tr>
 810 <tr>
 811         <td>marker-waste-almost-full</td>
 812         <td>Waste tank almost full</td>
 813 </tr>
 814 <tr>
 815         <td>marker-waste-full</td>
 816         <td>Waste tank full</td>
 817 </tr>
 818 <tr>
 819         <td>media-empty</td>
 820         <td>Out of media</td>
 821 </tr>
 822 <tr>
 823         <td>media-jam</td>
 824         <td>Media is jammed in the printer</td>
 825 </tr>
 826 <tr>
 827         <td>media-low</td>
 828         <td>Low on media</td>
 829 </tr>
 830 <tr>
 831         <td>paused</td>
 832         <td>Stop the printer</td>
 833 </tr>
 834 <tr>
 835         <td>timed-out</td>
 836         <td>Unable to connect to printer</td>
 837 </tr>
 838 <tr>
 839         <td>toner-empty</td>
 840         <td>Out of toner</td>
 841 </tr>
 842 <tr>
 843         <td>toner-low</td>
 844         <td>Low on toner</td>
 845 </tr>
 846 </tbody>
 847 </table></div>
 848
 849 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
 850
 851 <p>Filters can communicate with the backend via the
 852 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
 853 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 854 functions. The
 855 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
 856 reads data that has been sent back from the device and is typically used to
 857 obtain status and configuration information. For example, the following code
 858 polls the backend for back-channel data:</p>
 859
 860 <pre class="example">
 861 #include &lt;cups/cups.h&gt;
 862
 863 char buffer[8192];
 864 ssize_t bytes;
 865
 866 /* Use a timeout of 0.0 seconds to poll for back-channel data */
 867 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
 868 </pre>
 869
 870 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
 871 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
 872 when it is available.</p>
 873
 874 <p>The
 875 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 876 function allows you to get out-of-band status information and do synchronization
 877 with the device. For example, the following code gets the current IEEE-1284
 878 device ID string from the backend:</p>
 879
 880 <pre class="example">
 881 #include &lt;cups/sidechannel.h&gt;
 882
 883 char data[2049];
 884 int datalen;
 885 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 886
 887 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
 888    nul-termination... */
 889 datalen = sizeof(data) - 1;
 890
 891 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
 892 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
 893
 894 /* Use the returned value if OK was returned and the length is non-zero */
 895 if (status == CUPS_SC_STATUS_OK && datalen > 0)
 896   data[datalen] = '\0';
 897 else
 898   data[0] = '\0';
 899 </pre>
 900
 901 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
 902
 903 <p>Backends communicate with filters using the reciprocal functions
 904 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
 905 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
 906 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
 907 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
 908
 909 <pre class="example">
 910 #include &lt;cups/cups.h&gt;
 911
 912 char buffer[8192];
 913 ssize_t bytes;
 914
 915 /* Obtain data from printer/device */
 916 ...
 917
 918 /* Use a timeout of 1.0 seconds to give filters a chance to read */
 919 cupsBackChannelWrite(buffer, bytes, 1.0);
 920 </pre>
 921
 922 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
 923 function reads a side-channel command from a filter, driver, or port monitor.
 924 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
 925 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
 926 separate thread for that purpose), or use <code>select</code> or
 927 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
 928 input and output on several file descriptors at the same time.</p>
 929
 930 <p>Once a command is processed, the backend uses the
 931 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
 932 to send its response. For example, the following code shows how to poll for a
 933 side-channel command and respond to it:</p>
 934
 935 <pre class="example">
 936 #include &lt;cups/sidechannel.h&gt;
 937
 938 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
 939 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 940 char data[2048];
 941 int datalen = sizeof(data);
 942
 943 /* Poll for a command... */
 944 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
 945 {
 946   switch (command)
 947   {
 948     /* handle supported commands, fill data/datalen/status with values as needed */
 949
 950     default :
 951         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
 952         datalen = 0;
 953         break;
 954   }
 955
 956   /* Send a response... */
 957   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
 958 }
 959 </pre>
 960
 961 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
 962
 963 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
 964 status, page counter, and supply levels from most network printers. Every
 965 piece of information is associated with an Object Identifier (OID), and
 966 every printer has a <em>community</em> name associated with it. OIDs can be
 967 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
 968
 969 <p>The two CUPS SNMP functions provide a simple API for querying network
 970 printers through the side-channel interface. Each accepts a string containing
 971 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
 972 along with a timeout for the query.</p>
 973
 974 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
 975 function queries a single OID and returns the value as a string in a buffer
 976 you supply:</p>
 977
 978 <pre class="example">
 979 #include &lt;cups/sidechannel.h&gt;
 980
 981 char data[512];
 982 int datalen = sizeof(data);
 983
 984 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
 985         == CUPS_SC_STATUS_OK)
 986 {
 987   /* Do something with the value */
 988   printf("Page counter is: %s\n", data);
 989 }
 990 </pre>
 991
 992 <p>The
 993 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
 994 function allows you to query a whole group of OIDs, calling a function of your
 995 choice for each OID that is found:</p>
 996
 997 <pre class="example">
 998 #include &lt;cups/sidechannel.h&gt;
 999
1000 void
1001 my_callback(const char *oid, const char *data, int datalen, void *context)
1002 {
1003   /* Do something with the value */
1004   printf("%s=%s\n", oid, data);
1005 }
1006
1007 ...
1008
1009 void *my_data;
1010
1011 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
1012 </pre>
1013 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
1014 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
1015 <p class="description">Read data from the backchannel.</p>
1016 <p class="code">
1017 ssize_t cupsBackChannelRead (<br>
1018 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
1019 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1020 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1021 );</p>
1022 <h4 class="parameters">Parameters</h4>
1023 <dl>
1024 <dt>buffer</dt>
1025 <dd class="description">Buffer to read into</dd>
1026 <dt>bytes</dt>
1027 <dd class="description">Bytes to read</dd>
1028 <dt>timeout</dt>
1029 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
1030 </dl>
1031 <h4 class="returnvalue">Return Value</h4>
1032 <p class="description">Bytes read or -1 on error</p>
1033 <h4 class="discussion">Discussion</h4>
1034 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
1035 parameter controls how many seconds to wait for the data - use 0.0 to
1036 return immediately if there is no data, -1.0 to wait for data indefinitely.
1037
1038 </p>
1039 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
1040 <p class="description">Write data to the backchannel.</p>
1041 <p class="code">
1042 ssize_t cupsBackChannelWrite (<br>
1043 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
1044 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1045 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1046 );</p>
1047 <h4 class="parameters">Parameters</h4>
1048 <dl>
1049 <dt>buffer</dt>
1050 <dd class="description">Buffer to write</dd>
1051 <dt>bytes</dt>
1052 <dd class="description">Bytes to write</dd>
1053 <dt>timeout</dt>
1054 <dd class="description">Timeout in seconds, typically 1.0</dd>
1055 </dl>
1056 <h4 class="returnvalue">Return Value</h4>
1057 <p class="description">Bytes written or -1 on error</p>
1058 <h4 class="discussion">Discussion</h4>
1059 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
1060 controls how many seconds to wait for the data to be written - use
1061 0.0 to return immediately if the data cannot be written, -1.0 to wait
1062 indefinitely.
1063
1064 </p>
1065 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
1066 <p class="description">Get the device URI for a backend.</p>
1067 <p class="code">
1068 const char *cupsBackendDeviceURI (<br>
1069 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
1070 );</p>
1071 <h4 class="parameters">Parameters</h4>
1072 <dl>
1073 <dt>argv</dt>
1074 <dd class="description">Command-line arguments</dd>
1075 </dl>
1076 <h4 class="returnvalue">Return Value</h4>
1077 <p class="description">Device URI or <code>NULL</code></p>
1078 <h4 class="discussion">Discussion</h4>
1079 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
1080 function returns the device URI passed in the DEVICE_URI environment
1081 variable or the device URI passed in argv[0], whichever is found
1082 first.
1083
1084 </p>
1085 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsBackendReport">cupsBackendReport</a></h3>
1086 <p class="description">Write a device line from a backend.</p>
1087 <p class="code">
1088 void cupsBackendReport (<br>
1089 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
1090 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
1091 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
1092 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
1093 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
1094 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
1095 );</p>
1096 <h4 class="parameters">Parameters</h4>
1097 <dl>
1098 <dt>device_scheme</dt>
1099 <dd class="description">device-scheme string</dd>
1100 <dt>device_uri</dt>
1101 <dd class="description">device-uri string</dd>
1102 <dt>device_make_and_model</dt>
1103 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
1104 <dt>device_info</dt>
1105 <dd class="description">device-info string or <code>NULL</code></dd>
1106 <dt>device_id</dt>
1107 <dd class="description">device-id string or <code>NULL</code></dd>
1108 <dt>device_location</dt>
1109 <dd class="description">device-location string or <code>NULL</code></dd>
1110 </dl>
1111 <h4 class="discussion">Discussion</h4>
1112 <p class="discussion">This function writes a single device line to stdout for a backend.
1113 It handles quoting of special characters in the device-make-and-model,
1114 device-info, device-id, and device-location strings.
1115
1116 </p>
1117 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
1118 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
1119 <p class="code">
1120 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
1121 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1122 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1123 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1124 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1125 );</p>
1126 <h4 class="parameters">Parameters</h4>
1127 <dl>
1128 <dt>command</dt>
1129 <dd class="description">Command to send</dd>
1130 <dt>data</dt>
1131 <dd class="description">Response data buffer pointer</dd>
1132 <dt>datalen</dt>
1133 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1134 <dt>timeout</dt>
1135 <dd class="description">Timeout in seconds</dd>
1136 </dl>
1137 <h4 class="returnvalue">Return Value</h4>
1138 <p class="description">Status of command</p>
1139 <h4 class="discussion">Discussion</h4>
1140 <p class="discussion">This function is normally only called by filters, drivers, or port
1141 monitors in order to communicate with the backend used by the current
1142 printer.  Programs must be prepared to handle timeout or &quot;not
1143 implemented&quot; status codes, which indicate that the backend or device
1144 do not support the specified side-channel command.<br>
1145 <br>
1146 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1147 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1148 update the value to contain the number of data bytes in the buffer.
1149
1150 </p>
1151 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1152 <p class="description">Read a side-channel message.</p>
1153 <p class="code">
1154 int cupsSideChannelRead (<br>
1155 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1156 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1157 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1158 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1159 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1160 );</p>
1161 <h4 class="parameters">Parameters</h4>
1162 <dl>
1163 <dt>command</dt>
1164 <dd class="description">Command code</dd>
1165 <dt>status</dt>
1166 <dd class="description">Status code</dd>
1167 <dt>data</dt>
1168 <dd class="description">Data buffer pointer</dd>
1169 <dt>datalen</dt>
1170 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1171 <dt>timeout</dt>
1172 <dd class="description">Timeout in seconds</dd>
1173 </dl>
1174 <h4 class="returnvalue">Return Value</h4>
1175 <p class="description">0 on success, -1 on error</p>
1176 <h4 class="discussion">Discussion</h4>
1177 <p class="discussion">This function is normally only called by backend programs to read
1178 commands from a filter, driver, or port monitor program.  The
1179 caller must be prepared to handle incomplete or invalid messages
1180 and return the corresponding status codes.<br>
1181 <br>
1182 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1183 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1184 update the value to contain the number of data bytes in the buffer.
1185
1186 </p>
1187 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1188 <p class="description">Query a SNMP OID's value.</p>
1189 <p class="code">
1190 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1191 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1192 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1193 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1194 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1195 );</p>
1196 <h4 class="parameters">Parameters</h4>
1197 <dl>
1198 <dt>oid</dt>
1199 <dd class="description">OID to query</dd>
1200 <dt>data</dt>
1201 <dd class="description">Buffer for OID value</dd>
1202 <dt>datalen</dt>
1203 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1204 <dt>timeout</dt>
1205 <dd class="description">Timeout in seconds</dd>
1206 </dl>
1207 <h4 class="returnvalue">Return Value</h4>
1208 <p class="description">Query status</p>
1209 <h4 class="discussion">Discussion</h4>
1210 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1211 filter, port monitor, or backend using the default community name.<br>
1212 <br>
1213 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1214 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1215 supported and must be converted to their numeric forms.<br>
1216 <br>
1217 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1218 buffer to hold the OID value as a string. HEX-String (binary) values are
1219 converted to hexadecimal strings representing the binary data, while
1220 NULL-Value and unknown OID types are returned as the empty string.
1221 The returned &quot;datalen&quot; does not include the trailing nul.
1222
1223 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1224 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1225 the printer does not respond to the SNMP query.
1226
1227 </p>
1228 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1229 <p class="description">Query multiple SNMP OID values.</p>
1230 <p class="code">
1231 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1232 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1233 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1234 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1235 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1236 );</p>
1237 <h4 class="parameters">Parameters</h4>
1238 <dl>
1239 <dt>oid</dt>
1240 <dd class="description">First numeric OID to query</dd>
1241 <dt>timeout</dt>
1242 <dd class="description">Timeout for each query in seconds</dd>
1243 <dt>cb</dt>
1244 <dd class="description">Function to call with each value</dd>
1245 <dt>context</dt>
1246 <dd class="description">Application-defined pointer to send to callback</dd>
1247 </dl>
1248 <h4 class="returnvalue">Return Value</h4>
1249 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1250 <h4 class="discussion">Discussion</h4>
1251 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1252 of the filter, port monitor, or backend using the default community name.
1253 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1254 the callback function you provide.<br>
1255 <br>
1256 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1257 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1258 supported and must be converted to their numeric forms.<br>
1259 <br>
1260 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1261 time will depend on the number of OID values found and the time required
1262 for each query.<br>
1263 <br>
1264 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1265 is an application-defined pointer that is sent to the callback function
1266 along with the OID and current data. The data passed to the callback is the
1267 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1268
1269 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1270 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1271 the printer does not respond to the first SNMP query.
1272
1273 </p>
1274 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1275 <p class="description">Write a side-channel message.</p>
1276 <p class="code">
1277 int cupsSideChannelWrite (<br>
1278 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1279 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1280 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1281 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1282 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1283 );</p>
1284 <h4 class="parameters">Parameters</h4>
1285 <dl>
1286 <dt>command</dt>
1287 <dd class="description">Command code</dd>
1288 <dt>status</dt>
1289 <dd class="description">Status code</dd>
1290 <dt>data</dt>
1291 <dd class="description">Data buffer pointer</dd>
1292 <dt>datalen</dt>
1293 <dd class="description">Number of bytes of data</dd>
1294 <dt>timeout</dt>
1295 <dd class="description">Timeout in seconds</dd>
1296 </dl>
1297 <h4 class="returnvalue">Return Value</h4>
1298 <p class="description">0 on success, -1 on error</p>
1299 <h4 class="discussion">Discussion</h4>
1300 <p class="discussion">This function is normally only called by backend programs to send
1301 responses to a filter, driver, or port monitor program.
1302
1303 </p>
1304 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1305 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1306 <p class="description">Backend exit codes</p>
1307 <p class="code">
1308 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1309 </p>
1310 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1311 <p class="description">Bidirectional capabilities</p>
1312 <p class="code">
1313 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1314 </p>
1315 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1316 <p class="description">Request command codes</p>
1317 <p class="code">
1318 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1319 </p>
1320 <h3 class="typedef"><a name="cups_sc_connected_t">cups_sc_connected_t</a></h3>
1321 <p class="description">Connectivity values</p>
1322 <p class="code">
1323 typedef enum <a href="#cups_sc_connected_e">cups_sc_connected_e</a> cups_sc_connected_t;
1324 </p>
1325 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1326 <p class="description">Printer state bits</p>
1327 <p class="code">
1328 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1329 </p>
1330 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1331 <p class="description">Response status codes</p>
1332 <p class="code">
1333 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1334 </p>
1335 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1336 <p class="description">SNMP walk callback</p>
1337 <p class="code">
1338 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1339 </p>
1340 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1341 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1342 <p class="description">Backend exit codes</p>
1343 <h4 class="constants">Constants</h4>
1344 <dl>
1345 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1346 <dd class="description">Job failed, authentication required</dd>
1347 <dt>CUPS_BACKEND_CANCEL </dt>
1348 <dd class="description">Job failed, cancel job</dd>
1349 <dt>CUPS_BACKEND_FAILED </dt>
1350 <dd class="description">Job failed, use error-policy</dd>
1351 <dt>CUPS_BACKEND_HOLD </dt>
1352 <dd class="description">Job failed, hold job</dd>
1353 <dt>CUPS_BACKEND_OK </dt>
1354 <dd class="description">Job completed successfully</dd>
1355 <dt>CUPS_BACKEND_STOP </dt>
1356 <dd class="description">Job failed, stop queue</dd>
1357 </dl>
1358 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1359 <p class="description">Bidirectional capability values</p>
1360 <h4 class="constants">Constants</h4>
1361 <dl>
1362 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1363 <dd class="description">Bidirectional I/O is not supported</dd>
1364 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1365 <dd class="description">Bidirectional I/O is supported</dd>
1366 </dl>
1367 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1368 <p class="description">Request command codes</p>
1369 <h4 class="constants">Constants</h4>
1370 <dl>
1371 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1372 <dd class="description">Drain all pending output</dd>
1373 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1374 <dd class="description">Return bidirectional capabilities</dd>
1375 <dt>CUPS_SC_CMD_GET_CONNECTED <span class="info">&nbsp;CUPS 1.5&nbsp;</span></dt>
1376 <dd class="description">Return whether the backend is &quot;connected&quot; to the printer </dd>
1377 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1378 <dd class="description">Return the IEEE-1284 device ID</dd>
1379 <dt>CUPS_SC_CMD_GET_STATE </dt>
1380 <dd class="description">Return the device state</dd>
1381 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span></dt>
1382 <dd class="description">Query an SNMP OID </dd>
1383 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span></dt>
1384 <dd class="description">Query the next SNMP OID </dd>
1385 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1386 <dd class="description">Do a soft reset</dd>
1387 </dl>
1388 <h3 class="enumeration"><a name="cups_sc_connected_e">cups_sc_connected_e</a></h3>
1389 <p class="description">Connectivity values</p>
1390 <h4 class="constants">Constants</h4>
1391 <dl>
1392 <dt>CUPS_SC_CONNECTED </dt>
1393 <dd class="description">Backend is &quot;connected&quot; to printer</dd>
1394 <dt>CUPS_SC_NOT_CONNECTED </dt>
1395 <dd class="description">Backend is not &quot;connected&quot; to printer</dd>
1396 </dl>
1397 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1398 <p class="description">Printer state bits</p>
1399 <h4 class="constants">Constants</h4>
1400 <dl>
1401 <dt>CUPS_SC_STATE_BUSY </dt>
1402 <dd class="description">Device is busy</dd>
1403 <dt>CUPS_SC_STATE_ERROR </dt>
1404 <dd class="description">Other error condition</dd>
1405 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1406 <dd class="description">Toner/ink out condition</dd>
1407 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1408 <dd class="description">Toner/ink low condition</dd>
1409 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1410 <dd class="description">Paper out condition</dd>
1411 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1412 <dd class="description">Paper low condition</dd>
1413 <dt>CUPS_SC_STATE_OFFLINE </dt>
1414 <dd class="description">Device is offline</dd>
1415 <dt>CUPS_SC_STATE_ONLINE </dt>
1416 <dd class="description">Device is online</dd>
1417 </dl>
1418 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1419 <p class="description">Response status codes</p>
1420 <h4 class="constants">Constants</h4>
1421 <dl>
1422 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1423 <dd class="description">The command/response message was invalid</dd>
1424 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1425 <dd class="description">An I/O error occurred</dd>
1426 <dt>CUPS_SC_STATUS_NONE </dt>
1427 <dd class="description">No status</dd>
1428 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1429 <dd class="description">Command not implemented</dd>
1430 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1431 <dd class="description">The device did not respond</dd>
1432 <dt>CUPS_SC_STATUS_OK </dt>
1433 <dd class="description">Operation succeeded</dd>
1434 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1435 <dd class="description">The backend did not respond</dd>
1436 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1437 <dd class="description">Response too big</dd>
1438 </dl>
1439 </div>
1440 </body>
1441 </html>