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 337 <!--
 338   "$Id: api-filter.header 8087 2008-10-27 21:37:05Z mike $"
 339
 340   Filter and backend programming header for the Common UNIX Printing System
 341   (CUPS).
 342
 343   Copyright 2008 by Apple Inc.
 344
 345   These coded instructions, statements, and computer programs are the
 346   property of Apple Inc. and are protected by Federal copyright
 347   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 348   which should have been included with this file.  If this file is
 349   file is missing or damaged, see the license at "http://www.cups.org/".
 350 -->
 351
 352 <div class='summary'><table summary='General Information'>
 353 <thead>
 354 <tr>
 355         <th>Headers</th>
 356         <th>cups/backend.h<br>
 357         cups/sidechannel.h</th>
 358 </tr>
 359 </thead>
 360 <tbody>
 361 <tr>
 362         <th>Library</th>
 363         <td>-lcups</td>
 364 </tr>
 365 <tr>
 366         <th>See Also</th>
 367         <td>Programming: <a href='api-overview.html' target='_top'>Introduction to CUPS Programming</a><br>
 368         Programming: <a href='api-cups.html' target='_top'>CUPS API</a><br>
 369         Programming: <a href='api-ppd.html' target='_top'>PPD API</a><br>
 370         Programming: <a href='api-raster.html' target='_top'>Raster API</a><br>
 371         Specifications: <a href='spec-design' target='_top'>CUPS Design Description</a></td>
 372 </tr>
 373 </tbody>
 374 </table></div>
 375 <h2 class="title">Contents</h2>
 376 <ul class="contents">
 377 <ul class="subcontents">
 378 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 379 <li><a href="#SECURITY">Security Considerations</a></li>
 380 <li><a href="#TEMPFILES">Temporary Files</a></li>
 381 <li><a href="#COPIES">Copy Generation</a></li>
 382 <li><a href="#EXITCODES">Exit Codes</a></li>
 383 <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 384 <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 385 <li><a href="#COMMUNICATING_BACKEND">Communicating with the Backend</a></li>
 386 <li><a href="#COMMUNICATING_FILTER">Communicating with Filters</a></li>
 387 <li><a href="#SNMP">Doing SNMP Queries with Network Printers</a></li>
 388 </ul></li>
 389 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 390 <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 391 <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 392 <li><a href="#cupsBackendDeviceURI" title="Get the device URI for a backend.">cupsBackendDeviceURI</a></li>
 393 <li><a href="#cupsBackendReport" title="Write a device line from a backend.">cupsBackendReport</a></li>
 394 <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 395 <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 396 <li><a href="#cupsSideChannelSNMPGet" title="Query a SNMP OID's value.">cupsSideChannelSNMPGet</a></li>
 397 <li><a href="#cupsSideChannelSNMPWalk" title="Query multiple SNMP OID values.">cupsSideChannelSNMPWalk</a></li>
 398 <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 399 </ul></li>
 400 <li><a href="#TYPES">Data Types</a><ul class="code">
 401         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 402         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 403         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 404         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 405         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 406         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 407 </ul></li>
 408 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 409         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 410         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 411         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 412         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 413         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 414 </ul></li>
 415 <!--
 416   "$Id: api-filter.shtml 7962 2008-09-18 17:31:33Z mike $"
 417
 418   Filter and backend programming introduction for the Common UNIX Printing
 419   System (CUPS).
 420
 421   Copyright 2007-2008 by Apple Inc.
 422   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 423
 424   These coded instructions, statements, and computer programs are the
 425   property of Apple Inc. and are protected by Federal copyright
 426   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 427   which should have been included with this file.  If this file is
 428   file is missing or damaged, see the license at "http://www.cups.org/".
 429 -->
 430
 431 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 432
 433 <p>Filters (which include printer drivers and port monitors) and backends
 434 are used to convert job files to a printable format and send that data to the
 435 printer itself. All of these programs use a common interface for processing
 436 print jobs and communicating status information to the scheduler. Each is run
 437 with a standard set of command-line arguments:<p>
 438
 439 <dl class="code">
 440
 441         <dt>argv[1]</dt>
 442         <dd>The job ID</dd>
 443
 444         <dt>argv[2]</dt>
 445         <dd>The user printing the job</dd>
 446
 447         <dt>argv[3]</dt>
 448         <dd>The job name/title</dd>
 449
 450         <dt>argv[4]</dt>
 451         <dd>The number of copies to print</dd>
 452
 453         <dt>argv[5]</dt>
 454         <dd>The options that were provided when the job was submitted</dd>
 455
 456         <dt>argv[6]</dt>
 457         <dd>The file to print (first program only)</dd>
 458 </dl>
 459
 460 <p>The scheduler runs one or more of these programs to print any given job. The
 461 first filter reads from the print file and writes to the standard output, while
 462 the remaining filters read from the standard input and write to the standard
 463 output. The backend is the last filter in the chain and writes to the
 464 device.</p>
 465
 466 <h3><a name="SECURITY">Security Considerations</a></h3>
 467
 468 <p>It is always important to use security programming practices. Filters and
 469 most backends are run as a non-priviledged user, so the major security
 470 consideration is resource utilization - filters should not depend on unlimited
 471 amounts of CPU, memory, or disk space, and should protect against conditions
 472 that could lead to excess usage of any resource like infinite loops and
 473 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 474 specify an arbitrary file path to a separator page, template, or other file
 475 used by the filter since that can lead to an unauthorized disclosure of
 476 information. <em>Always</em> treat input as suspect and validate it!</p>
 477
 478 <p>If you are developing a backend that runs as root, make sure to check for
 479 potential buffer overflows, integer under/overflow conditions, and file
 480 accesses since these can lead to privilege escalations. When writing files,
 481 always validate the file path and <em>never</em> allow a user to determine
 482 where to store a file.</p>
 483
 484 <blockquote><b>Note:</b>
 485
 486 <p><em>Never</em> write files to a user's home directory. Aside from the
 487 security implications, CUPS is a network print service and as such the network
 488 user may not be the same as the local user and/or there may not be a local home
 489 directory to write to.</p>
 490
 491 <p>In addition, some operating systems provide additional security mechanisms
 492 that further limit file system access, even for backends running as root.  On
 493 Mac OS X, for example, no backend may write to a user's home directory.</p>
 494 </blockquote>
 495
 496 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 497
 498 <p>Temporary files should be created in the directory specified by the
 499 "TMPDIR" environment variable. The
 500 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 501 used to safely create temporary files in this directory.</p>
 502
 503 <h3><a name="COPIES">Copy Generation</a></h3>
 504
 505 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 506 of the input file. In general, you should only generate copies if the
 507 <em>filename</em> argument is supplied. The only exception to this are
 508 filters that produce device-independent PostScript output, since the PostScript
 509 filter <var>pstops</var> is responsible for generating copies of PostScript
 510 files.</p>
 511
 512 <h3><a name="EXITCODES">Exit Codes</a></h3>
 513
 514 <p>Filters must exit with status 0 when they successfully generate print data
 515 or 1 when they encounter an error. Backends can return any of the
 516 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 517
 518 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 519
 520 <p>The following environment variables are defined by the printing system
 521 when running print filters and backends:</p>
 522
 523 <dl class="code">
 524
 525         <dt>APPLE_LANGUAGES</dt>
 526         <dd>The Apple language identifier associated with the job
 527         (Mac OS X only).</dd>
 528
 529         <dt>CHARSET</dt>
 530         <dd>The job character set, typically "utf-8".</dd>
 531
 532         <dt>CLASS</dt>
 533         <dd>When a job is submitted to a printer class, contains the name of
 534         the destination printer class. Otherwise this environment
 535         variable will not be set.</dd>
 536
 537         <dt>CONTENT_TYPE</dt>
 538         <dd>The MIME type associated with the file (e.g.
 539         application/postscript).</dd>
 540
 541         <dt>CUPS_CACHEDIR</dt>
 542         <dd>The directory where cache files can be stored. Cache files can be
 543         used to retain information between jobs or files in a job.</dd>
 544
 545         <dt>CUPS_DATADIR</dt>
 546         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 547
 548         <dt>CUPS_FILETYPE</dt>
 549         <dd>The type of file being printed: "job-sheet" for a banner page and
 550         "document" for a regular print file.</dd>
 551
 552         <dt>CUPS_SERVERROOT</dt>
 553         <dd>The root directory of the server.</dd>
 554
 555         <dt>DEVICE_URI</dt>
 556         <dd>The device-uri associated with the printer.</dd>
 557
 558         <dt>FINAL_CONTENT_TYPE</dt>
 559         <dd>The MIME type associated with the printer (e.g.
 560         application/vnd.cups-postscript).</dd>
 561
 562         <dt>LANG</dt>
 563         <dd>The language locale associated with the job.</dd>
 564
 565         <dt>PPD</dt>
 566         <dd>The full pathname of the PostScript Printer Description (PPD)
 567         file for this printer.</dd>
 568
 569         <dt>PRINTER</dt>
 570         <dd>The queue name of the class or printer.</dd>
 571
 572         <dt>RIP_CACHE</dt>
 573         <dd>The recommended amount of memory to use for Raster Image
 574         Processors (RIPs).</dd>
 575
 576         <dt>TMPDIR</dt>
 577         <dd>The directory where temporary files should be created.</dd>
 578
 579 </dl>
 580
 581 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 582
 583 <p>Filters and backends communicate with the scheduler by writing messages
 584 to the standard error file. The scheduler reads messages from all filters in
 585 a job and processes the message based on its prefix. For example, the following
 586 code sets the current printer state message to "Printing page 5":</p>
 587
 588 <pre class="example">
 589 int page = 5;
 590
 591 fprintf(stderr, "INFO: Printing page %d\n", page);
 592 </pre>
 593
 594 <p>Each message is a single line of text starting with one of the following
 595 prefix strings:</p>
 596
 597 <dl class="code">
 598
 599         <dt>ALERT: message</dt>
 600         <dd>Sets the printer-state-message attribute and adds the specified
 601         message to the current error log file using the "alert" log level.</dd>
 602
 603         <dt>ATTR: attribute=value [attribute=value]</dt>
 604         <dd>Sets the named printer or job attribute(s). Typically this is used
 605         to set the <code>marker-colors</code>, <code>marker-levels</code>,
 606         <code>marker-message</code>, <code>marker-names</code>,
 607         <code>marker-types</code>, <code>printer-alert</code>, and
 608         <code>printer-alert-description</code> printer attributes. Standard
 609         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 610         1</a>.</dd>
 611
 612         <dt>CRIT: message</dt>
 613         <dd>Sets the printer-state-message attribute and adds the specified
 614         message to the current error log file using the "critical" log
 615         level.</dd>
 616
 617         <dt>DEBUG: message</dt>
 618         <dd>Sets the printer-state-message attribute and adds the specified
 619         message to the current error log file using the "debug" log level.</dd>
 620
 621         <dt>DEBUG2: message</dt>
 622         <dd>Sets the printer-state-message attribute and adds the specified
 623         message to the current error log file using the "debug2" log level.</dd>
 624
 625         <dt>EMERG: message</dt>
 626         <dd>Sets the printer-state-message attribute and adds the specified
 627         message to the current error log file using the "emergency" log
 628         level.</dd>
 629
 630         <dt>ERROR: message</dt>
 631         <dd>Sets the printer-state-message attribute and adds the specified
 632         message to the current error log file using the "error" log level.
 633         Use "ERROR:" messages for non-persistent processing errors.</dd>
 634
 635         <dt>INFO: message</dt>
 636         <dd>Sets the printer-state-message attribute. If the current log level
 637         is set to "debug2", also adds the specified message to the current error
 638         log file using the "info" log level.</dd>
 639
 640         <dt>NOTICE: message</dt>
 641         <dd>Sets the printer-state-message attribute and adds the specified
 642         message to the current error log file using the "notice" log level.</dd>
 643
 644         <dt>PAGE: page-number #-copies</dt>
 645         <dt>PAGE: total #-pages</dt>
 646         <dd>Adds an entry to the current page log file. The first form adds
 647         #-copies to the job-media-sheets-completed attribute. The second
 648         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 649
 650         <dt>PPD: keyword=value [keyword=value ...]</dt>
 651         <dd>Changes or adds keywords to the printer's PPD file. Typically
 652         this is used to update installable options or default media settings
 653         based on the printer configuration.</dd>
 654
 655         <dt>STATE: printer-state-reason [printer-state-reason ...]</dt>
 656         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 657         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 658         <dd>Sets, adds, or removes printer-state-reason keywords to the
 659         current queue. Typically this is used to indicate persistent media,
 660         ink, toner, and configuration conditions or errors on a printer.
 661         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 662         use vendor-prefixed ("com.acme.foo") keywords for custom states.</dd>
 663
 664         <dt>WARNING: message</dt>
 665         <dd>Sets the printer-state-message attribute and adds the specified
 666         message to the current error log file using the "warning" log
 667         level.</dd>
 668
 669 </dl>
 670
 671 <p>Messages without one of these prefixes are treated as if they began with
 672 the "DEBUG:" prefix string.</p>
 673
 674
 675 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 676 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 677 <thead>
 678 <tr>
 679         <th>marker-type</th>
 680         <th>Description</th>
 681 </tr>
 682 </thead>
 683 <tbody>
 684 <tr>
 685         <td>developer</td>
 686         <td>Developer unit</td>
 687 </tr>
 688 <tr>
 689         <td>fuser</td>
 690         <td>Fuser unit</td>
 691 </tr>
 692 <tr>
 693         <td>fuserCleaningPad</td>
 694         <td>Fuser cleaning pad</td>
 695 </tr>
 696 <tr>
 697         <td>fuserOil</td>
 698         <td>Fuser oil</td>
 699 </tr>
 700 <tr>
 701         <td>ink</td>
 702         <td>Ink supply</td>
 703 </tr>
 704 <tr>
 705         <td>opc</td>
 706         <td>Photo conductor</td>
 707 </tr>
 708 <tr>
 709         <td>solidWax</td>
 710         <td>Wax supply</td>
 711 </tr>
 712 <tr>
 713         <td>staples</td>
 714         <td>Staple supply</td>
 715 </tr>
 716 <tr>
 717         <td>toner</td>
 718         <td>Toner supply</td>
 719 </tr>
 720 <tr>
 721         <td>transferUnit</td>
 722         <td>Transfer unit</td>
 723 </tr>
 724 <tr>
 725         <td>wasteInk</td>
 726         <td>Waste ink tank</td>
 727 </tr>
 728 <tr>
 729         <td>wasteToner</td>
 730         <td>Waste toner tank</td>
 731 </tr>
 732 <tr>
 733         <td>wasteWax</td>
 734         <td>Waste wax tank</td>
 735 </tr>
 736 </tbody>
 737 </table></div>
 738
 739 <br>
 740
 741 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 742 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 743 <thead>
 744 <tr>
 745         <th>Keyword</th>
 746         <th>Description</th>
 747 </tr>
 748 </thead>
 749 <tbody>
 750 <tr>
 751         <td>connecting-to-device</td>
 752         <td>Connecting to printer but not printing yet</td>
 753 </tr>
 754 <tr>
 755         <td>cover-open</td>
 756         <td>A cover is open on the printer</td>
 757 </tr>
 758 <tr>
 759         <td>input-tray-missing</td>
 760         <td>An input tray is missing from the printer</td>
 761 </tr>
 762 <tr>
 763         <td>marker-supply-empty</td>
 764         <td>Out of ink</td>
 765 </tr>
 766 <tr>
 767         <td>marker-supply-low</td>
 768         <td>Low on ink</td>
 769 </tr>
 770 <tr>
 771         <td>marker-waste-almost-full</td>
 772         <td>Waste tank almost full</td>
 773 </tr>
 774 <tr>
 775         <td>marker-waste-full</td>
 776         <td>Waste tank full</td>
 777 </tr>
 778 <tr>
 779         <td>media-empty</td>
 780         <td>Out of media</td>
 781 </tr>
 782 <tr>
 783         <td>media-jam</td>
 784         <td>Media is jammed in the printer</td>
 785 </tr>
 786 <tr>
 787         <td>media-low</td>
 788         <td>Low on media</td>
 789 </tr>
 790 <tr>
 791         <td>paused</td>
 792         <td>Stop the printer</td>
 793 </tr>
 794 <tr>
 795         <td>timed-out</td>
 796         <td>Unable to connect to printer</td>
 797 </tr>
 798 <tr>
 799         <td>toner-empty</td>
 800         <td>Out of toner</td>
 801 </tr>
 802 <tr>
 803         <td>toner-low</td>
 804         <td>Low on toner</td>
 805 </tr>
 806 </tbody>
 807 </table></div>
 808
 809 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
 810
 811 <p>Filters can communicate with the backend via the
 812 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
 813 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 814 functions. The
 815 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
 816 reads data that has been sent back from the device and is typically used to
 817 obtain status and configuration information. For example, the following code
 818 polls the backend for back-channel data:</p>
 819
 820 <pre class="example">
 821 #include &lt;cups/cups.h&gt;
 822
 823 char buffer[8192];
 824 ssize_t bytes;
 825
 826 /* Use a timeout of 0.0 seconds to poll for back-channel data */
 827 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
 828 </pre>
 829
 830 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
 831 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
 832 when it is available.</p>
 833
 834 <p>The
 835 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 836 function allows you to get out-of-band status information and do synchronization
 837 with the device. For example, the following code gets the current IEEE-1284
 838 device ID string from the backend:</p>
 839
 840 <pre class="example">
 841 #include &lt;cups/sidechannel.h&gt;
 842
 843 char data[2049];
 844 int datalen;
 845 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 846
 847 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
 848    nul-termination... */
 849 datalen = sizeof(data) - 1;
 850
 851 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
 852 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
 853
 854 /* Use the returned value if OK was returned and the length is non-zero */
 855 if (status == CUPS_SC_STATUS_OK && datalen > 0)
 856   data[datalen] = '\0';
 857 else
 858   data[0] = '\0';
 859 </pre>
 860
 861 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
 862
 863 <p>Backends communicate with filters using the reciprocal functions
 864 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
 865 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
 866 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
 867 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
 868
 869 <pre class="example">
 870 #include &lt;cups/cups.h&gt;
 871
 872 char buffer[8192];
 873 ssize_t bytes;
 874
 875 /* Obtain data from printer/device */
 876 ...
 877
 878 /* Use a timeout of 1.0 seconds to give filters a chance to read */
 879 cupsBackChannelWrite(buffer, bytes, 1.0);
 880 </pre>
 881
 882 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
 883 function reads a side-channel command from a filter, driver, or port monitor.
 884 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
 885 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
 886 separate thread for that purpose), or use <code>select</code> or
 887 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
 888 input and output on several file descriptors at the same time.</p>
 889
 890 <p>Once a command is processed, the backend uses the
 891 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
 892 to send its response. For example, the following code shows how to poll for a
 893 side-channel command and respond to it:</p>
 894
 895 <pre class="example">
 896 #include &lt;cups/sidechannel.h&gt;
 897
 898 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
 899 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 900 char data[2048];
 901 int datalen = sizeof(data);
 902
 903 /* Poll for a command... */
 904 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
 905 {
 906   switch (command)
 907   {
 908     /* handle supported commands, fill data/datalen/status with values as needed */
 909
 910     default :
 911         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
 912         datalen = 0;
 913         break;
 914   }
 915
 916   /* Send a response... */
 917   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
 918 }
 919 </pre>
 920
 921 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
 922
 923 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
 924 status, page counter, and supply levels from most network printers. Every
 925 piece of information is associated with an Object Identifier (OID), and
 926 every printer has a <em>community</em> name associated with it. OIDs can be
 927 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
 928
 929 <p>The two CUPS SNMP functions provide a simple API for querying network
 930 printers through the side-channel interface. Each accepts a string containing
 931 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
 932 along with a timeout for the query.</p>
 933
 934 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
 935 function queries a single OID and returns the value as a string in a buffer
 936 you supply:</p>
 937
 938 <pre class="example">
 939 #include &lt;cups/sidechannel.h&gt;
 940
 941 char data[512];
 942 int datalen = sizeof(data);
 943
 944 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
 945         == CUPS_SC_STATUS_OK)
 946 {
 947   /* Do something with the value */
 948   printf("Page counter is: %s\n", data);
 949 }
 950 </pre>
 951
 952 <p>The
 953 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
 954 function allows you to query a whole group of OIDs, calling a function of your
 955 choice for each OID that is found:</p>
 956
 957 <pre class="example">
 958 #include &lt;cups/sidechannel.h&gt;
 959
 960 void
 961 my_callback(const char *oid, const char *data, int datalen, void *context)
 962 {
 963   /* Do something with the value */
 964   printf("%s=%s\n", oid, data);
 965 }
 966
 967 ...
 968
 969 void *my_data;
 970
 971 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
 972 </pre>
 973 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
 974 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
 975 <p class="description">Read data from the backchannel.</p>
 976 <p class="code">
 977 ssize_t cupsBackChannelRead (<br>
 978 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
 979 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
 980 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
 981 );</p>
 982 <h4 class="parameters">Parameters</h4>
 983 <dl>
 984 <dt>buffer</dt>
 985 <dd class="description">Buffer to read into</dd>
 986 <dt>bytes</dt>
 987 <dd class="description">Bytes to read</dd>
 988 <dt>timeout</dt>
 989 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
 990 </dl>
 991 <h4 class="returnvalue">Return Value</h4>
 992 <p class="description">Bytes read or -1 on error</p>
 993 <h4 class="discussion">Discussion</h4>
 994 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
 995 parameter controls how many seconds to wait for the data - use 0.0 to
 996 return immediately if there is no data, -1.0 to wait for data indefinitely.
 997
 998 </p>
 999 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
1000 <p class="description">Write data to the backchannel.</p>
1001 <p class="code">
1002 ssize_t cupsBackChannelWrite (<br>
1003 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
1004 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1005 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1006 );</p>
1007 <h4 class="parameters">Parameters</h4>
1008 <dl>
1009 <dt>buffer</dt>
1010 <dd class="description">Buffer to write</dd>
1011 <dt>bytes</dt>
1012 <dd class="description">Bytes to write</dd>
1013 <dt>timeout</dt>
1014 <dd class="description">Timeout in seconds, typically 1.0</dd>
1015 </dl>
1016 <h4 class="returnvalue">Return Value</h4>
1017 <p class="description">Bytes written or -1 on error</p>
1018 <h4 class="discussion">Discussion</h4>
1019 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
1020 controls how many seconds to wait for the data to be written - use
1021 0.0 to return immediately if the data cannot be written, -1.0 to wait
1022 indefinitely.
1023
1024 </p>
1025 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
1026 <p class="description">Get the device URI for a backend.</p>
1027 <p class="code">
1028 const char *cupsBackendDeviceURI (<br>
1029 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
1030 );</p>
1031 <h4 class="parameters">Parameters</h4>
1032 <dl>
1033 <dt>argv</dt>
1034 <dd class="description">Command-line arguments</dd>
1035 </dl>
1036 <h4 class="returnvalue">Return Value</h4>
1037 <p class="description">Device URI or <code>NULL</code></p>
1038 <h4 class="discussion">Discussion</h4>
1039 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
1040 function returns the device URI passed in the DEVICE_URI environment
1041 variable or the device URI passed in argv[0], whichever is found
1042 first.
1043
1044 </p>
1045 <h3 class="function"><span class="info">&nbsp;CUPS 1.4&nbsp;</span><a name="cupsBackendReport">cupsBackendReport</a></h3>
1046 <p class="description">Write a device line from a backend.</p>
1047 <p class="code">
1048 void cupsBackendReport (<br>
1049 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
1050 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
1051 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
1052 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
1053 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
1054 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
1055 );</p>
1056 <h4 class="parameters">Parameters</h4>
1057 <dl>
1058 <dt>device_scheme</dt>
1059 <dd class="description">device-scheme string</dd>
1060 <dt>device_uri</dt>
1061 <dd class="description">device-uri string</dd>
1062 <dt>device_make_and_model</dt>
1063 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
1064 <dt>device_info</dt>
1065 <dd class="description">device-info string or <code>NULL</code></dd>
1066 <dt>device_id</dt>
1067 <dd class="description">device-id string or <code>NULL</code></dd>
1068 <dt>device_location</dt>
1069 <dd class="description">device-location string or <code>NULL</code></dd>
1070 </dl>
1071 <h4 class="discussion">Discussion</h4>
1072 <p class="discussion">This function writes a single device line to stdout for a backend.
1073 It handles quoting of special characters in the device-make-and-model,
1074 device-info, device-id, and device-location strings.
1075
1076 </p>
1077 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
1078 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
1079 <p class="code">
1080 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
1081 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1082 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1083 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1084 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1085 );</p>
1086 <h4 class="parameters">Parameters</h4>
1087 <dl>
1088 <dt>command</dt>
1089 <dd class="description">Command to send</dd>
1090 <dt>data</dt>
1091 <dd class="description">Response data buffer pointer</dd>
1092 <dt>datalen</dt>
1093 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1094 <dt>timeout</dt>
1095 <dd class="description">Timeout in seconds</dd>
1096 </dl>
1097 <h4 class="returnvalue">Return Value</h4>
1098 <p class="description">Status of command</p>
1099 <h4 class="discussion">Discussion</h4>
1100 <p class="discussion">This function is normally only called by filters, drivers, or port
1101 monitors in order to communicate with the backend used by the current
1102 printer.  Programs must be prepared to handle timeout or &quot;not
1103 implemented&quot; status codes, which indicate that the backend or device
1104 do not support the specified side-channel command.<br>
1105 <br>
1106 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1107 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1108 update the value to contain the number of data bytes in the buffer.
1109
1110 </p>
1111 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1112 <p class="description">Read a side-channel message.</p>
1113 <p class="code">
1114 int cupsSideChannelRead (<br>
1115 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1116 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1117 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1118 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1119 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1120 );</p>
1121 <h4 class="parameters">Parameters</h4>
1122 <dl>
1123 <dt>command</dt>
1124 <dd class="description">Command code</dd>
1125 <dt>status</dt>
1126 <dd class="description">Status code</dd>
1127 <dt>data</dt>
1128 <dd class="description">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">0 on success, -1 on error</p>
1136 <h4 class="discussion">Discussion</h4>
1137 <p class="discussion">This function is normally only called by backend programs to read
1138 commands from a filter, driver, or port monitor program.  The
1139 caller must be prepared to handle incomplete or invalid messages
1140 and return the corresponding status codes.<br>
1141 <br>
1142 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1143 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1144 update the value to contain the number of data bytes in the buffer.
1145
1146 </p>
1147 <h3 class="function"><span class="info">&nbsp;CUPS 1.4&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1148 <p class="description">Query a SNMP OID's value.</p>
1149 <p class="code">
1150 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1151 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1152 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1153 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1154 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1155 );</p>
1156 <h4 class="parameters">Parameters</h4>
1157 <dl>
1158 <dt>oid</dt>
1159 <dd class="description">OID to query</dd>
1160 <dt>data</dt>
1161 <dd class="description">Buffer for OID value</dd>
1162 <dt>datalen</dt>
1163 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1164 <dt>timeout</dt>
1165 <dd class="description">Timeout in seconds</dd>
1166 </dl>
1167 <h4 class="returnvalue">Return Value</h4>
1168 <p class="description">Query status</p>
1169 <h4 class="discussion">Discussion</h4>
1170 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1171 filter, port monitor, or backend using the default community name.<br>
1172 <br>
1173 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1174 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1175 supported and must be converted to their numeric forms.<br>
1176 <br>
1177 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1178 buffer to hold the OID value as a string. HEX-String (binary) values are
1179 converted to hexadecimal strings representing the binary data, while
1180 NULL-Value and unknown OID types are returned as the empty string.
1181 The returned &quot;datalen&quot; does not include the trailing nul.
1182
1183 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1184 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1185 the printer does not respond to the SNMP query.
1186
1187 </p>
1188 <h3 class="function"><span class="info">&nbsp;CUPS 1.4&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1189 <p class="description">Query multiple SNMP OID values.</p>
1190 <p class="code">
1191 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1192 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1193 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1194 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1195 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1196 );</p>
1197 <h4 class="parameters">Parameters</h4>
1198 <dl>
1199 <dt>oid</dt>
1200 <dd class="description">First numeric OID to query</dd>
1201 <dt>timeout</dt>
1202 <dd class="description">Timeout for each query in seconds</dd>
1203 <dt>cb</dt>
1204 <dd class="description">Function to call with each value</dd>
1205 <dt>context</dt>
1206 <dd class="description">Application-defined pointer to send to callback</dd>
1207 </dl>
1208 <h4 class="returnvalue">Return Value</h4>
1209 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1210 <h4 class="discussion">Discussion</h4>
1211 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1212 of the filter, port monitor, or backend using the default community name.
1213 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1214 the callback function you provide.<br>
1215 <br>
1216 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1217 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1218 supported and must be converted to their numeric forms.<br>
1219 <br>
1220 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1221 time will depend on the number of OID values found and the time required
1222 for each query.<br>
1223 <br>
1224 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1225 is an application-defined pointer that is sent to the callback function
1226 along with the OID and current data. The data passed to the callback is the
1227 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1228
1229 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1230 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1231 the printer does not respond to the first SNMP query.
1232
1233 </p>
1234 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1235 <p class="description">Write a side-channel message.</p>
1236 <p class="code">
1237 int cupsSideChannelWrite (<br>
1238 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1239 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1240 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1241 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1242 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1243 );</p>
1244 <h4 class="parameters">Parameters</h4>
1245 <dl>
1246 <dt>command</dt>
1247 <dd class="description">Command code</dd>
1248 <dt>status</dt>
1249 <dd class="description">Status code</dd>
1250 <dt>data</dt>
1251 <dd class="description">Data buffer pointer</dd>
1252 <dt>datalen</dt>
1253 <dd class="description">Number of bytes of data</dd>
1254 <dt>timeout</dt>
1255 <dd class="description">Timeout in seconds</dd>
1256 </dl>
1257 <h4 class="returnvalue">Return Value</h4>
1258 <p class="description">0 on success, -1 on error</p>
1259 <h4 class="discussion">Discussion</h4>
1260 <p class="discussion">This function is normally only called by backend programs to send
1261 responses to a filter, driver, or port monitor program.
1262
1263 </p>
1264 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1265 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1266 <p class="description">Backend exit codes</p>
1267 <p class="code">
1268 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1269 </p>
1270 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1271 <p class="description">Bidirectional capabilities</p>
1272 <p class="code">
1273 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1274 </p>
1275 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1276 <p class="description">Request command codes</p>
1277 <p class="code">
1278 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1279 </p>
1280 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1281 <p class="description">Printer state bits</p>
1282 <p class="code">
1283 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1284 </p>
1285 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1286 <p class="description">Response status codes</p>
1287 <p class="code">
1288 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1289 </p>
1290 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1291 <p class="description">SNMP walk callback</p>
1292 <p class="code">
1293 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1294 </p>
1295 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1296 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1297 <p class="description">Backend exit codes</p>
1298 <h4 class="constants">Constants</h4>
1299 <dl>
1300 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1301 <dd class="description">Job failed, authentication required</dd>
1302 <dt>CUPS_BACKEND_CANCEL </dt>
1303 <dd class="description">Job failed, cancel job</dd>
1304 <dt>CUPS_BACKEND_FAILED </dt>
1305 <dd class="description">Job failed, use error-policy</dd>
1306 <dt>CUPS_BACKEND_HOLD </dt>
1307 <dd class="description">Job failed, hold job</dd>
1308 <dt>CUPS_BACKEND_OK </dt>
1309 <dd class="description">Job completed successfully</dd>
1310 <dt>CUPS_BACKEND_STOP </dt>
1311 <dd class="description">Job failed, stop queue</dd>
1312 </dl>
1313 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1314 <p class="description">Bidirectional capability values</p>
1315 <h4 class="constants">Constants</h4>
1316 <dl>
1317 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1318 <dd class="description">Bidirectional I/O is not supported</dd>
1319 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1320 <dd class="description">Bidirectional I/O is supported</dd>
1321 </dl>
1322 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1323 <p class="description">Request command codes</p>
1324 <h4 class="constants">Constants</h4>
1325 <dl>
1326 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1327 <dd class="description">Drain all pending output</dd>
1328 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1329 <dd class="description">Return bidirectional capabilities</dd>
1330 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1331 <dd class="description">Return the IEEE-1284 device ID</dd>
1332 <dt>CUPS_SC_CMD_GET_STATE </dt>
1333 <dd class="description">Return the device state</dd>
1334 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4&nbsp;</span></dt>
1335 <dd class="description">Query an SNMP OID </dd>
1336 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4&nbsp;</span></dt>
1337 <dd class="description">Query the next SNMP OID </dd>
1338 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1339 <dd class="description">Do a soft reset</dd>
1340 </dl>
1341 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1342 <p class="description">Printer state bits</p>
1343 <h4 class="constants">Constants</h4>
1344 <dl>
1345 <dt>CUPS_SC_STATE_BUSY </dt>
1346 <dd class="description">Device is busy</dd>
1347 <dt>CUPS_SC_STATE_ERROR </dt>
1348 <dd class="description">Other error condition</dd>
1349 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1350 <dd class="description">Toner/ink out condition</dd>
1351 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1352 <dd class="description">Toner/ink low condition</dd>
1353 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1354 <dd class="description">Paper out condition</dd>
1355 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1356 <dd class="description">Paper low condition</dd>
1357 <dt>CUPS_SC_STATE_OFFLINE </dt>
1358 <dd class="description">Device is offline</dd>
1359 <dt>CUPS_SC_STATE_ONLINE </dt>
1360 <dd class="description">Device is online</dd>
1361 </dl>
1362 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1363 <p class="description">Response status codes</p>
1364 <h4 class="constants">Constants</h4>
1365 <dl>
1366 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1367 <dd class="description">The command/response message was invalid</dd>
1368 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1369 <dd class="description">An I/O error occurred</dd>
1370 <dt>CUPS_SC_STATUS_NONE </dt>
1371 <dd class="description">No status</dd>
1372 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1373 <dd class="description">Command not implemented</dd>
1374 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1375 <dd class="description">The device did not respond</dd>
1376 <dt>CUPS_SC_STATUS_OK </dt>
1377 <dd class="description">Operation succeeded</dd>
1378 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1379 <dd class="description">The backend did not respond</dd>
1380 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1381 <dd class="description">Response too big</dd>
1382 </dl>
1383 </div>
1384 </body>
1385 </html>