doc/help/api-filter.html

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