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 333 <!--
 334   "$Id: api-filter.header 8087 2008-10-27 21:37:05Z mike $"
 335
 336   Filter and backend programming header for the Common UNIX Printing System
 337   (CUPS).
 338
 339   Copyright 2008 by Apple Inc.
 340
 341   These coded instructions, statements, and computer programs are the
 342   property of Apple Inc. and are protected by Federal copyright
 343   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 344   which should have been included with this file.  If this file is
 345   file is missing or damaged, see the license at "http://www.cups.org/".
 346 -->
 347
 348 <div class='summary'><table summary='General Information'>
 349 <thead>
 350 <tr>
 351         <th>Headers</th>
 352         <th>cups/backend.h<br>
 353         cups/sidechannel.h</th>
 354 </tr>
 355 </thead>
 356 <tbody>
 357 <tr>
 358         <th>Library</th>
 359         <td>-lcups</td>
 360 </tr>
 361 <tr>
 362         <th>See Also</th>
 363         <td>Programming: <a href='api-overview.html' target='_top'>Introduction to CUPS Programming</a><br>
 364         Programming: <a href='api-cups.html' target='_top'>CUPS API</a><br>
 365         Programming: <a href='api-ppd.html' target='_top'>PPD API</a><br>
 366         Programming: <a href='api-raster.html' target='_top'>Raster API</a><br>
 367         Specifications: <a href='spec-design' target='_top'>CUPS Design Description</a></td>
 368 </tr>
 369 </tbody>
 370 </table></div>
 371 <h2 class="title">Contents</h2>
 372 <ul class="contents">
 373 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 374 <li><a href="#SECURITY">Security Considerations</a></li>
 375 <li><a href="#TEMPFILES">Temporary Files</a></li>
 376 <li><a href="#COPIES">Copy Generation</a></li>
 377 <li><a href="#EXITCODES">Exit Codes</a></li>
 378 <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 379 <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 380 <li><a href="#COMMUNICATING_BACKEND">Communicating with the Backend</a></li>
 381 <li><a href="#COMMUNICATING_FILTER">Communicating with Filters</a></li>
 382 <li><a href="#SNMP">Doing SNMP Queries with Network Printers</a></li>
 383 </ul></li>
 384 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 385 <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 386 <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 387 <li><a href="#cupsBackendDeviceURI" title="Get the device URI for a backend.">cupsBackendDeviceURI</a></li>
 388 <li><a href="#cupsBackendReport" title="Write a device line from a backend.">cupsBackendReport</a></li>
 389 <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 390 <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 391 <li><a href="#cupsSideChannelSNMPGet" title="Query a SNMP OID's value.">cupsSideChannelSNMPGet</a></li>
 392 <li><a href="#cupsSideChannelSNMPWalk" title="Query multiple SNMP OID values.">cupsSideChannelSNMPWalk</a></li>
 393 <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 394 </ul></li>
 395 <li><a href="#TYPES">Data Types</a><ul class="code">
 396         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 397         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 398         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 399         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 400         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 401         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 402 </ul></li>
 403 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 404         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 405         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 406         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 407         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 408         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 409 </ul></li>
 410 </ul>
 411 <!--
 412   "$Id: api-filter.shtml 7962 2008-09-18 17:31:33Z mike $"
 413
 414   Filter and backend programming introduction for the Common UNIX Printing
 415   System (CUPS).
 416
 417   Copyright 2007-2008 by Apple Inc.
 418   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 419
 420   These coded instructions, statements, and computer programs are the
 421   property of Apple Inc. and are protected by Federal copyright
 422   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 423   which should have been included with this file.  If this file is
 424   file is missing or damaged, see the license at "http://www.cups.org/".
 425 -->
 426
 427 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 428
 429 <p>Filters (which include printer drivers and port monitors) and backends
 430 are used to convert job files to a printable format and send that data to the
 431 printer itself. All of these programs use a common interface for processing
 432 print jobs and communicating status information to the scheduler. Each is run
 433 with a standard set of command-line arguments:<p>
 434
 435 <dl class="code">
 436
 437         <dt>argv[1]</dt>
 438         <dd>The job ID</dd>
 439
 440         <dt>argv[2]</dt>
 441         <dd>The user printing the job</dd>
 442
 443         <dt>argv[3]</dt>
 444         <dd>The job name/title</dd>
 445
 446         <dt>argv[4]</dt>
 447         <dd>The number of copies to print</dd>
 448
 449         <dt>argv[5]</dt>
 450         <dd>The options that were provided when the job was submitted</dd>
 451
 452         <dt>argv[6]</dt>
 453         <dd>The file to print (first program only)</dd>
 454 </dl>
 455
 456 <p>The scheduler runs one or more of these programs to print any given job. The
 457 first filter reads from the print file and writes to the standard output, while
 458 the remaining filters read from the standard input and write to the standard
 459 output. The backend is the last filter in the chain and writes to the
 460 device.</p>
 461
 462 <h3><a name="SECURITY">Security Considerations</a></h3>
 463
 464 <p>It is always important to use security programming practices. Filters and
 465 most backends are run as a non-priviledged user, so the major security
 466 consideration is resource utilization - filters should not depend on unlimited
 467 amounts of CPU, memory, or disk space, and should protect against conditions
 468 that could lead to excess usage of any resource like infinite loops and
 469 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 470 specify an arbitrary file path to a separator page, template, or other file
 471 used by the filter since that can lead to an unauthorized disclosure of
 472 information. <em>Always</em> treat input as suspect and validate it!</p>
 473
 474 <p>If you are developing a backend that runs as root, make sure to check for
 475 potential buffer overflows, integer under/overflow conditions, and file
 476 accesses since these can lead to privilege escalations. When writing files,
 477 always validate the file path and <em>never</em> allow a user to determine
 478 where to store a file.</p>
 479
 480 <blockquote><b>Note:</b>
 481
 482 <p><em>Never</em> write files to a user's home directory. Aside from the
 483 security implications, CUPS is a network print service and as such the network
 484 user may not be the same as the local user and/or there may not be a local home
 485 directory to write to.</p>
 486
 487 <p>In addition, some operating systems provide additional security mechanisms
 488 that further limit file system access, even for backends running as root.  On
 489 Mac OS X, for example, no backend may write to a user's home directory.</p>
 490 </blockquote>
 491
 492 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 493
 494 <p>Temporary files should be created in the directory specified by the
 495 "TMPDIR" environment variable. The
 496 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 497 used to safely create temporary files in this directory.</p>
 498
 499 <h3><a name="COPIES">Copy Generation</a></h3>
 500
 501 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 502 of the input file. In general, you should only generate copies if the
 503 <em>filename</em> argument is supplied. The only exception to this are
 504 filters that produce device-independent PostScript output, since the PostScript
 505 filter <var>pstops</var> is responsible for generating copies of PostScript
 506 files.</p>
 507
 508 <h3><a name="EXITCODES">Exit Codes</a></h3>
 509
 510 <p>Filters must exit with status 0 when they successfully generate print data
 511 or 1 when they encounter an error. Backends can return any of the
 512 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 513
 514 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 515
 516 <p>The following environment variables are defined by the printing system
 517 when running print filters and backends:</p>
 518
 519 <dl class="code">
 520
 521         <dt>APPLE_LANGUAGES</dt>
 522         <dd>The Apple language identifier associated with the job
 523         (Mac OS X only).</dd>
 524
 525         <dt>CHARSET</dt>
 526         <dd>The job character set, typically "utf-8".</dd>
 527
 528         <dt>CLASS</dt>
 529         <dd>When a job is submitted to a printer class, contains the name of
 530         the destination printer class. Otherwise this environment
 531         variable will not be set.</dd>
 532
 533         <dt>CONTENT_TYPE</dt>
 534         <dd>The MIME type associated with the file (e.g.
 535         application/postscript).</dd>
 536
 537         <dt>CUPS_CACHEDIR</dt>
 538         <dd>The directory where cache files can be stored. Cache files can be
 539         used to retain information between jobs or files in a job.</dd>
 540
 541         <dt>CUPS_DATADIR</dt>
 542         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 543
 544         <dt>CUPS_FILETYPE</dt>
 545         <dd>The type of file being printed: "job-sheet" for a banner page and
 546         "document" for a regular print file.</dd>
 547
 548         <dt>CUPS_SERVERROOT</dt>
 549         <dd>The root directory of the server.</dd>
 550
 551         <dt>DEVICE_URI</dt>
 552         <dd>The device-uri associated with the printer.</dd>
 553
 554         <dt>FINAL_CONTENT_TYPE</dt>
 555         <dd>The MIME type associated with the printer (e.g.
 556         application/vnd.cups-postscript).</dd>
 557
 558         <dt>LANG</dt>
 559         <dd>The language locale associated with the job.</dd>
 560
 561         <dt>PPD</dt>
 562         <dd>The full pathname of the PostScript Printer Description (PPD)
 563         file for this printer.</dd>
 564
 565         <dt>PRINTER</dt>
 566         <dd>The queue name of the class or printer.</dd>
 567
 568         <dt>RIP_CACHE</dt>
 569         <dd>The recommended amount of memory to use for Raster Image
 570         Processors (RIPs).</dd>
 571
 572         <dt>TMPDIR</dt>
 573         <dd>The directory where temporary files should be created.</dd>
 574
 575 </dl>
 576
 577 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 578
 579 <p>Filters and backends communicate with the scheduler by writing messages
 580 to the standard error file. The scheduler reads messages from all filters in
 581 a job and processes the message based on its prefix. For example, the following
 582 code sets the current printer state message to "Printing page 5":</p>
 583
 584 <pre class="example">
 585 int page = 5;
 586
 587 fprintf(stderr, "INFO: Printing page %d\n", page);
 588 </pre>
 589
 590 <p>Each message is a single line of text starting with one of the following
 591 prefix strings:</p>
 592
 593 <dl class="code">
 594
 595         <dt>ALERT: message</dt>
 596         <dd>Sets the printer-state-message attribute and adds the specified
 597         message to the current error log file using the "alert" log level.</dd>
 598
 599         <dt>ATTR: attribute=value [attribute=value]</dt>
 600         <dd>Sets the named printer or job attribute(s). Typically this is used
 601         to set the <code>marker-colors</code>, <code>marker-levels</code>,
 602         <code>marker-message</code>, <code>marker-names</code>,
 603         <code>marker-types</code>, <code>printer-alert</code>, and
 604         <code>printer-alert-description</code> printer attributes. Standard
 605         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 606         1</a>.</dd>
 607
 608         <dt>CRIT: message</dt>
 609         <dd>Sets the printer-state-message attribute and adds the specified
 610         message to the current error log file using the "critical" log
 611         level.</dd>
 612
 613         <dt>DEBUG: message</dt>
 614         <dd>Sets the printer-state-message attribute and adds the specified
 615         message to the current error log file using the "debug" log level.</dd>
 616
 617         <dt>DEBUG2: message</dt>
 618         <dd>Sets the printer-state-message attribute and adds the specified
 619         message to the current error log file using the "debug2" log level.</dd>
 620
 621         <dt>EMERG: message</dt>
 622         <dd>Sets the printer-state-message attribute and adds the specified
 623         message to the current error log file using the "emergency" log
 624         level.</dd>
 625
 626         <dt>ERROR: message</dt>
 627         <dd>Sets the printer-state-message attribute and adds the specified
 628         message to the current error log file using the "error" log level.
 629         Use "ERROR:" messages for non-persistent processing errors.</dd>
 630
 631         <dt>INFO: message</dt>
 632         <dd>Sets the printer-state-message attribute. If the current log level
 633         is set to "debug2", also adds the specified message to the current error
 634         log file using the "info" log level.</dd>
 635
 636         <dt>NOTICE: message</dt>
 637         <dd>Sets the printer-state-message attribute and adds the specified
 638         message to the current error log file using the "notice" log level.</dd>
 639
 640         <dt>PAGE: page-number #-copies</dt>
 641         <dt>PAGE: total #-pages</dt>
 642         <dd>Adds an entry to the current page log file. The first form adds
 643         #-copies to the job-media-sheets-completed attribute. The second
 644         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 645
 646         <dt>PPD: keyword=value [keyword=value ...]</dt>
 647         <dd>Changes or adds keywords to the printer's PPD file. Typically
 648         this is used to update installable options or default media settings
 649         based on the printer configuration.</dd>
 650
 651         <dt>STATE: printer-state-reason [printer-state-reason ...]</dt>
 652         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 653         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 654         <dd>Sets, adds, or removes printer-state-reason keywords to the
 655         current queue. Typically this is used to indicate persistent media,
 656         ink, toner, and configuration conditions or errors on a printer.
 657         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 658         use vendor-prefixed ("com.acme.foo") keywords for custom states.</dd>
 659
 660         <dt>WARNING: message</dt>
 661         <dd>Sets the printer-state-message attribute and adds the specified
 662         message to the current error log file using the "warning" log
 663         level.</dd>
 664
 665 </dl>
 666
 667 <p>Messages without one of these prefixes are treated as if they began with
 668 the "DEBUG:" prefix string.</p>
 669
 670
 671 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 672 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 673 <thead>
 674 <tr>
 675         <th>marker-type</th>
 676         <th>Description</th>
 677 </tr>
 678 </thead>
 679 <tbody>
 680 <tr>
 681         <td>developer</td>
 682         <td>Developer unit</td>
 683 </tr>
 684 <tr>
 685         <td>fuser</td>
 686         <td>Fuser unit</td>
 687 </tr>
 688 <tr>
 689         <td>fuserCleaningPad</td>
 690         <td>Fuser cleaning pad</td>
 691 </tr>
 692 <tr>
 693         <td>fuserOil</td>
 694         <td>Fuser oil</td>
 695 </tr>
 696 <tr>
 697         <td>ink</td>
 698         <td>Ink supply</td>
 699 </tr>
 700 <tr>
 701         <td>opc</td>
 702         <td>Photo conductor</td>
 703 </tr>
 704 <tr>
 705         <td>solidWax</td>
 706         <td>Wax supply</td>
 707 </tr>
 708 <tr>
 709         <td>staples</td>
 710         <td>Staple supply</td>
 711 </tr>
 712 <tr>
 713         <td>toner</td>
 714         <td>Toner supply</td>
 715 </tr>
 716 <tr>
 717         <td>transferUnit</td>
 718         <td>Transfer unit</td>
 719 </tr>
 720 <tr>
 721         <td>wasteInk</td>
 722         <td>Waste ink tank</td>
 723 </tr>
 724 <tr>
 725         <td>wasteToner</td>
 726         <td>Waste toner tank</td>
 727 </tr>
 728 <tr>
 729         <td>wasteWax</td>
 730         <td>Waste wax tank</td>
 731 </tr>
 732 </tbody>
 733 </table></div>
 734
 735 <br>
 736
 737 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 738 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 739 <thead>
 740 <tr>
 741         <th>Keyword</th>
 742         <th>Description</th>
 743 </tr>
 744 </thead>
 745 <tbody>
 746 <tr>
 747         <td>connecting-to-device</td>
 748         <td>Connecting to printer but not printing yet</td>
 749 </tr>
 750 <tr>
 751         <td>cover-open</td>
 752         <td>A cover is open on the printer</td>
 753 </tr>
 754 <tr>
 755         <td>input-tray-missing</td>
 756         <td>An input tray is missing from the printer</td>
 757 </tr>
 758 <tr>
 759         <td>marker-supply-empty</td>
 760         <td>Out of ink</td>
 761 </tr>
 762 <tr>
 763         <td>marker-supply-low</td>
 764         <td>Low on ink</td>
 765 </tr>
 766 <tr>
 767         <td>marker-waste-almost-full</td>
 768         <td>Waste tank almost full</td>
 769 </tr>
 770 <tr>
 771         <td>marker-waste-full</td>
 772         <td>Waste tank full</td>
 773 </tr>
 774 <tr>
 775         <td>media-empty</td>
 776         <td>Out of media</td>
 777 </tr>
 778 <tr>
 779         <td>media-jam</td>
 780         <td>Media is jammed in the printer</td>
 781 </tr>
 782 <tr>
 783         <td>media-low</td>
 784         <td>Low on media</td>
 785 </tr>
 786 <tr>
 787         <td>paused</td>
 788         <td>Stop the printer</td>
 789 </tr>
 790 <tr>
 791         <td>timed-out</td>
 792         <td>Unable to connect to printer</td>
 793 </tr>
 794 <tr>
 795         <td>toner-empty</td>
 796         <td>Out of toner</td>
 797 </tr>
 798 <tr>
 799         <td>toner-low</td>
 800         <td>Low on toner</td>
 801 </tr>
 802 </tbody>
 803 </table></div>
 804
 805 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
 806
 807 <p>Filters can communicate with the backend via the
 808 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
 809 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 810 functions. The
 811 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
 812 reads data that has been sent back from the device and is typically used to
 813 obtain status and configuration information. For example, the following code
 814 polls the backend for back-channel data:</p>
 815
 816 <pre class="example">
 817 #include &lt;cups/cups.h&gt;
 818
 819 char buffer[8192];
 820 ssize_t bytes;
 821
 822 /* Use a timeout of 0.0 seconds to poll for back-channel data */
 823 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
 824 </pre>
 825
 826 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
 827 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
 828 when it is available.</p>
 829
 830 <p>The
 831 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 832 function allows you to get out-of-band status information and do synchronization
 833 with the device. For example, the following code gets the current IEEE-1284
 834 device ID string from the backend:</p>
 835
 836 <pre class="example">
 837 #include &lt;cups/sidechannel.h&gt;
 838
 839 char data[2049];
 840 int datalen;
 841 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 842
 843 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
 844    nul-termination... */
 845 datalen = sizeof(data) - 1;
 846
 847 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
 848 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
 849
 850 /* Use the returned value if OK was returned and the length is non-zero */
 851 if (status == CUPS_SC_STATUS_OK && datalen > 0)
 852   data[datalen] = '\0';
 853 else
 854   data[0] = '\0';
 855 </pre>
 856
 857 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
 858
 859 <p>Backends communicate with filters using the reciprocal functions
 860 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
 861 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
 862 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
 863 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
 864
 865 <pre class="example">
 866 #include &lt;cups/cups.h&gt;
 867
 868 char buffer[8192];
 869 ssize_t bytes;
 870
 871 /* Obtain data from printer/device */
 872 ...
 873
 874 /* Use a timeout of 1.0 seconds to give filters a chance to read */
 875 cupsBackChannelWrite(buffer, bytes, 1.0);
 876 </pre>
 877
 878 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
 879 function reads a side-channel command from a filter, driver, or port monitor.
 880 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
 881 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
 882 separate thread for that purpose), or use <code>select</code> or
 883 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
 884 input and output on several file descriptors at the same time.</p>
 885
 886 <p>Once a command is processed, the backend uses the
 887 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
 888 to send its response. For example, the following code shows how to poll for a
 889 side-channel command and respond to it:</p>
 890
 891 <pre class="example">
 892 #include &lt;cups/sidechannel.h&gt;
 893
 894 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
 895 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 896 char data[2048];
 897 int datalen = sizeof(data);
 898
 899 /* Poll for a command... */
 900 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
 901 {
 902   switch (command)
 903   {
 904     /* handle supported commands, fill data/datalen/status with values as needed */
 905
 906     default :
 907         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
 908         datalen = 0;
 909         break;
 910   }
 911
 912   /* Send a response... */
 913   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
 914 }
 915 </pre>
 916
 917 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
 918
 919 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
 920 status, page counter, and supply levels from most network printers. Every
 921 piece of information is associated with an Object Identifier (OID), and
 922 every printer has a <em>community</em> name associated with it. OIDs can be
 923 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
 924
 925 <p>The two CUPS SNMP functions provide a simple API for querying network
 926 printers through the side-channel interface. Each accepts a string containing
 927 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
 928 along with a timeout for the query.</p>
 929
 930 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
 931 function queries a single OID and returns the value as a string in a buffer
 932 you supply:</p>
 933
 934 <pre class="example">
 935 #include &lt;cups/sidechannel.h&gt;
 936
 937 char data[512];
 938 int datalen = sizeof(data);
 939
 940 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
 941         == CUPS_SC_STATUS_OK)
 942 {
 943   /* Do something with the value */
 944   printf("Page counter is: %s\n", data);
 945 }
 946 </pre>
 947
 948 <p>The
 949 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
 950 function allows you to query a whole group of OIDs, calling a function of your
 951 choice for each OID that is found:</p>
 952
 953 <pre class="example">
 954 #include &lt;cups/sidechannel.h&gt;
 955
 956 void
 957 my_callback(const char *oid, const char *data, int datalen, void *context)
 958 {
 959   /* Do something with the value */
 960   printf("%s=%s\n", oid, data);
 961 }
 962
 963 ...
 964
 965 void *my_data;
 966
 967 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
 968 </pre>
 969 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
 970 <h3 class="function"><span class="info">&nbsp;CUPS 1.2&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
 971 <p class="description">Read data from the backchannel.</p>
 972 <p class="code">
 973 ssize_t cupsBackChannelRead (<br>
 974 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
 975 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
 976 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
 977 );</p>
 978 <h4 class="parameters">Parameters</h4>
 979 <dl>
 980 <dt>buffer</dt>
 981 <dd class="description">Buffer to read into</dd>
 982 <dt>bytes</dt>
 983 <dd class="description">Bytes to read</dd>
 984 <dt>timeout</dt>
 985 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
 986 </dl>
 987 <h4 class="returnvalue">Return Value</h4>
 988 <p class="description">Bytes read or -1 on error</p>
 989 <h4 class="discussion">Discussion</h4>
 990 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
 991 parameter controls how many seconds to wait for the data - use 0.0 to
 992 return immediately if there is no data, -1.0 to wait for data indefinitely.
 993
 994 </p>
 995 <h3 class="function"><span class="info">&nbsp;CUPS 1.2&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
 996 <p class="description">Write data to the backchannel.</p>
 997 <p class="code">
 998 ssize_t cupsBackChannelWrite (<br>
 999 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
1000 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1001 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1002 );</p>
1003 <h4 class="parameters">Parameters</h4>
1004 <dl>
1005 <dt>buffer</dt>
1006 <dd class="description">Buffer to write</dd>
1007 <dt>bytes</dt>
1008 <dd class="description">Bytes to write</dd>
1009 <dt>timeout</dt>
1010 <dd class="description">Timeout in seconds, typically 1.0</dd>
1011 </dl>
1012 <h4 class="returnvalue">Return Value</h4>
1013 <p class="description">Bytes written or -1 on error</p>
1014 <h4 class="discussion">Discussion</h4>
1015 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
1016 controls how many seconds to wait for the data to be written - use
1017 0.0 to return immediately if the data cannot be written, -1.0 to wait
1018 indefinitely.
1019
1020 </p>
1021 <h3 class="function"><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
1022 <p class="description">Get the device URI for a backend.</p>
1023 <p class="code">
1024 const char *cupsBackendDeviceURI (<br>
1025 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
1026 );</p>
1027 <h4 class="parameters">Parameters</h4>
1028 <dl>
1029 <dt>argv</dt>
1030 <dd class="description">Command-line arguments</dd>
1031 </dl>
1032 <h4 class="returnvalue">Return Value</h4>
1033 <p class="description">Device URI or <code>NULL</code></p>
1034 <h4 class="discussion">Discussion</h4>
1035 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
1036 function returns the device URI passed in the DEVICE_URI environment
1037 variable or the device URI passed in argv[0], whichever is found
1038 first.</p>
1039 <h3 class="function"><a name="cupsBackendReport">cupsBackendReport</a></h3>
1040 <p class="description">Write a device line from a backend.</p>
1041 <p class="code">
1042 void cupsBackendReport (<br>
1043 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
1044 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
1045 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
1046 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
1047 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
1048 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
1049 );</p>
1050 <h4 class="parameters">Parameters</h4>
1051 <dl>
1052 <dt>device_scheme</dt>
1053 <dd class="description">device-scheme string</dd>
1054 <dt>device_uri</dt>
1055 <dd class="description">device-uri string</dd>
1056 <dt>device_make_and_model</dt>
1057 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
1058 <dt>device_info</dt>
1059 <dd class="description">device-info string or <code>NULL</code></dd>
1060 <dt>device_id</dt>
1061 <dd class="description">device-id string or <code>NULL</code></dd>
1062 <dt>device_location</dt>
1063 <dd class="description">device-location string or <code>NULL</code></dd>
1064 </dl>
1065 <h4 class="discussion">Discussion</h4>
1066 <p class="discussion">This function writes a single device line to stdout for a backend.
1067 It handles quoting of special characters in the device-make-and-model,
1068 device-info, device-id, and device-location strings.</p>
1069 <h3 class="function"><span class="info">&nbsp;CUPS 1.3&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
1070 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
1071 <p class="code">
1072 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
1073 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1074 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1075 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1076 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1077 );</p>
1078 <h4 class="parameters">Parameters</h4>
1079 <dl>
1080 <dt>command</dt>
1081 <dd class="description">Command to send</dd>
1082 <dt>data</dt>
1083 <dd class="description">Response data buffer pointer</dd>
1084 <dt>datalen</dt>
1085 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1086 <dt>timeout</dt>
1087 <dd class="description">Timeout in seconds</dd>
1088 </dl>
1089 <h4 class="returnvalue">Return Value</h4>
1090 <p class="description">Status of command</p>
1091 <h4 class="discussion">Discussion</h4>
1092 <p class="discussion">This function is normally only called by filters, drivers, or port
1093 monitors in order to communicate with the backend used by the current
1094 printer.  Programs must be prepared to handle timeout or &quot;not
1095 implemented&quot; status codes, which indicate that the backend or device
1096 do not support the specified side-channel command.<br>
1097 <br>
1098 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1099 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1100 update the value to contain the number of data bytes in the buffer.
1101
1102 </p>
1103 <h3 class="function"><span class="info">&nbsp;CUPS 1.3&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1104 <p class="description">Read a side-channel message.</p>
1105 <p class="code">
1106 int cupsSideChannelRead (<br>
1107 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1108 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1109 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1110 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1111 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1112 );</p>
1113 <h4 class="parameters">Parameters</h4>
1114 <dl>
1115 <dt>command</dt>
1116 <dd class="description">Command code</dd>
1117 <dt>status</dt>
1118 <dd class="description">Status code</dd>
1119 <dt>data</dt>
1120 <dd class="description">Data buffer pointer</dd>
1121 <dt>datalen</dt>
1122 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1123 <dt>timeout</dt>
1124 <dd class="description">Timeout in seconds</dd>
1125 </dl>
1126 <h4 class="returnvalue">Return Value</h4>
1127 <p class="description">0 on success, -1 on error</p>
1128 <h4 class="discussion">Discussion</h4>
1129 <p class="discussion">This function is normally only called by backend programs to read
1130 commands from a filter, driver, or port monitor program.  The
1131 caller must be prepared to handle incomplete or invalid messages
1132 and return the corresponding status codes.<br>
1133 <br>
1134 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1135 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1136 update the value to contain the number of data bytes in the buffer.
1137
1138 </p>
1139 <h3 class="function"><span class="info">&nbsp;CUPS 1.4&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1140 <p class="description">Query a SNMP OID's value.</p>
1141 <p class="code">
1142 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1143 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1144 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1145 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1146 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1147 );</p>
1148 <h4 class="parameters">Parameters</h4>
1149 <dl>
1150 <dt>oid</dt>
1151 <dd class="description">OID to query</dd>
1152 <dt>data</dt>
1153 <dd class="description">Buffer for OID value</dd>
1154 <dt>datalen</dt>
1155 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1156 <dt>timeout</dt>
1157 <dd class="description">Timeout in seconds</dd>
1158 </dl>
1159 <h4 class="returnvalue">Return Value</h4>
1160 <p class="description">Query status</p>
1161 <h4 class="discussion">Discussion</h4>
1162 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1163 filter, port monitor, or backend using the default community name.<br>
1164 <br>
1165 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1166 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1167 supported and must be converted to their numeric forms.<br>
1168 <br>
1169 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1170 buffer to hold the OID value as a string. HEX-String (binary) values are
1171 converted to hexadecimal strings representing the binary data, while
1172 NULL-Value and unknown OID types are returned as the empty string.
1173 The returned &quot;datalen&quot; does not include the trailing nul.
1174
1175 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1176 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1177 the printer does not respond to the SNMP query.
1178
1179 </p>
1180 <h3 class="function"><span class="info">&nbsp;CUPS 1.4&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1181 <p class="description">Query multiple SNMP OID values.</p>
1182 <p class="code">
1183 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1184 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1185 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1186 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1187 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1188 );</p>
1189 <h4 class="parameters">Parameters</h4>
1190 <dl>
1191 <dt>oid</dt>
1192 <dd class="description">First numeric OID to query</dd>
1193 <dt>timeout</dt>
1194 <dd class="description">Timeout for each query in seconds</dd>
1195 <dt>cb</dt>
1196 <dd class="description">Function to call with each value</dd>
1197 <dt>context</dt>
1198 <dd class="description">Application-defined pointer to send to callback</dd>
1199 </dl>
1200 <h4 class="returnvalue">Return Value</h4>
1201 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1202 <h4 class="discussion">Discussion</h4>
1203 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1204 of the filter, port monitor, or backend using the default community name.
1205 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1206 the callback function you provide.<br>
1207 <br>
1208 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1209 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1210 supported and must be converted to their numeric forms.<br>
1211 <br>
1212 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1213 time will depend on the number of OID values found and the time required
1214 for each query.<br>
1215 <br>
1216 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1217 is an application-defined pointer that is sent to the callback function
1218 along with the OID and current data. The data passed to the callback is the
1219 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1220
1221 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1222 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1223 the printer does not respond to the first SNMP query.
1224
1225 </p>
1226 <h3 class="function"><span class="info">&nbsp;CUPS 1.3&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1227 <p class="description">Write a side-channel message.</p>
1228 <p class="code">
1229 int cupsSideChannelWrite (<br>
1230 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1231 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1232 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1233 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1234 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1235 );</p>
1236 <h4 class="parameters">Parameters</h4>
1237 <dl>
1238 <dt>command</dt>
1239 <dd class="description">Command code</dd>
1240 <dt>status</dt>
1241 <dd class="description">Status code</dd>
1242 <dt>data</dt>
1243 <dd class="description">Data buffer pointer</dd>
1244 <dt>datalen</dt>
1245 <dd class="description">Number of bytes of data</dd>
1246 <dt>timeout</dt>
1247 <dd class="description">Timeout in seconds</dd>
1248 </dl>
1249 <h4 class="returnvalue">Return Value</h4>
1250 <p class="description">0 on success, -1 on error</p>
1251 <h4 class="discussion">Discussion</h4>
1252 <p class="discussion">This function is normally only called by backend programs to send
1253 responses to a filter, driver, or port monitor program.
1254
1255 </p>
1256 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1257 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1258 <p class="description">Backend exit codes</p>
1259 <p class="code">
1260 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1261 </p>
1262 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1263 <p class="description">Bidirectional capabilities</p>
1264 <p class="code">
1265 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1266 </p>
1267 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1268 <p class="description">Request command codes</p>
1269 <p class="code">
1270 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1271 </p>
1272 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1273 <p class="description">Printer state bits</p>
1274 <p class="code">
1275 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1276 </p>
1277 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1278 <p class="description">Response status codes</p>
1279 <p class="code">
1280 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1281 </p>
1282 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1283 <p class="description">SNMP walk callback</p>
1284 <p class="code">
1285 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1286 </p>
1287 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1288 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1289 <p class="description">Backend exit codes</p>
1290 <h4 class="constants">Constants</h4>
1291 <dl>
1292 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1293 <dd class="description">Job failed, authentication required</dd>
1294 <dt>CUPS_BACKEND_CANCEL </dt>
1295 <dd class="description">Job failed, cancel job</dd>
1296 <dt>CUPS_BACKEND_FAILED </dt>
1297 <dd class="description">Job failed, use error-policy</dd>
1298 <dt>CUPS_BACKEND_HOLD </dt>
1299 <dd class="description">Job failed, hold job</dd>
1300 <dt>CUPS_BACKEND_OK </dt>
1301 <dd class="description">Job completed successfully</dd>
1302 <dt>CUPS_BACKEND_STOP </dt>
1303 <dd class="description">Job failed, stop queue</dd>
1304 </dl>
1305 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1306 <p class="description">Bidirectional capability values</p>
1307 <h4 class="constants">Constants</h4>
1308 <dl>
1309 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1310 <dd class="description">Bidirectional I/O is not supported</dd>
1311 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1312 <dd class="description">Bidirectional I/O is supported</dd>
1313 </dl>
1314 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1315 <p class="description">Request command codes</p>
1316 <h4 class="constants">Constants</h4>
1317 <dl>
1318 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1319 <dd class="description">Drain all pending output</dd>
1320 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1321 <dd class="description">Return bidirectional capabilities</dd>
1322 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1323 <dd class="description">Return the IEEE-1284 device ID</dd>
1324 <dt>CUPS_SC_CMD_GET_STATE </dt>
1325 <dd class="description">Return the device state</dd>
1326 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4&nbsp;</span></dt>
1327 <dd class="description">Query an SNMP OID </dd>
1328 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4&nbsp;</span></dt>
1329 <dd class="description">Query the next SNMP OID </dd>
1330 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1331 <dd class="description">Do a soft reset</dd>
1332 </dl>
1333 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1334 <p class="description">Printer state bits</p>
1335 <h4 class="constants">Constants</h4>
1336 <dl>
1337 <dt>CUPS_SC_STATE_BUSY </dt>
1338 <dd class="description">Device is busy</dd>
1339 <dt>CUPS_SC_STATE_ERROR </dt>
1340 <dd class="description">Other error condition</dd>
1341 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1342 <dd class="description">Toner/ink out condition</dd>
1343 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1344 <dd class="description">Toner/ink low condition</dd>
1345 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1346 <dd class="description">Paper out condition</dd>
1347 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1348 <dd class="description">Paper low condition</dd>
1349 <dt>CUPS_SC_STATE_OFFLINE </dt>
1350 <dd class="description">Device is offline</dd>
1351 <dt>CUPS_SC_STATE_ONLINE </dt>
1352 <dd class="description">Device is online</dd>
1353 </dl>
1354 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1355 <p class="description">Response status codes</p>
1356 <h4 class="constants">Constants</h4>
1357 <dl>
1358 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1359 <dd class="description">The command/response message was invalid</dd>
1360 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1361 <dd class="description">An I/O error occurred</dd>
1362 <dt>CUPS_SC_STATUS_NONE </dt>
1363 <dd class="description">No status</dd>
1364 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1365 <dd class="description">Command not implemented</dd>
1366 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1367 <dd class="description">The device did not respond</dd>
1368 <dt>CUPS_SC_STATUS_OK </dt>
1369 <dd class="description">Operation succeeded</dd>
1370 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1371 <dd class="description">The backend did not respond</dd>
1372 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1373 <dd class="description">Response too big</dd>
1374 </dl>
1375 </div>
1376 </body>
1377 </html>