doc/help/api-filter.html

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 255 <!--
 256   "$Id: api-filter.header 7616 2008-05-28 00:34:13Z mike $"
 257
 258   Filter and backend programming header for the Common UNIX Printing System
 259   (CUPS).
 260
 261   Copyright 2008 by Apple Inc.
 262
 263   These coded instructions, statements, and computer programs are the
 264   property of Apple Inc. and are protected by Federal copyright
 265   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 266   which should have been included with this file.  If this file is
 267   file is missing or damaged, see the license at "http://www.cups.org/".
 268 -->
 269
 270 <h1 class="title">Filter and Backend Programming</h1>
 271
 272 <div class='summary'><table summary='General Information'>
 273 <thead>
 274 <tr>
 275         <th>Headers</th>
 276         <th>cups/backend.h<br>
 277         cups/sidechannel.h</th>
 278 </tr>
 279 </thead>
 280 <tbody>
 281 <tr>
 282         <th>Library</th>
 283         <td>-lcups</td>
 284 </tr>
 285 <tr>
 286         <th>See Also</th>
 287         <td>Programming: <a href='api-overview.html' target='_top'>Introduction to CUPS Programming</a><br>
 288         Programming: <a href='api-cups.html' target='_top'>CUPS API</a><br>
 289         Programming: <a href='api-ppd.html' target='_top'>PPD API</a><br>
 290         Programming: <a href='api-raster.html' target='_top'>Raster API</a><br>
 291         Specifications: <a href='spec-design' target='_top'>CUPS Design Description</a></td>
 292 </tr>
 293 </tbody>
 294 </table></div>
 295 <h2 class="title">Contents</h2>
 296 <ul class="contents">
 297 </li>
 298 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 299 <li><a href="#SECURITY">Security Considerations</a></li>
 300 <li><a href="#TEMPFILES">Temporary Files</a></li>
 301 <li><a href="#COPIES">Copy Generation</a></li>
 302 <li><a href="#EXITCODES">Exit Codes</a></li>
 303 <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 304 <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 305 <li><a href="#COMMUNICATING_BACKEND">Communicating with the Backend</a></li>
 306 <li><a href="#COMMUNICATING_FILTER">Communicating with Filters</a></li>
 307 <li><a href="#SNMP">Doing SNMP Queries with Network Printers</a></li>
 308 </ul></li>
 309 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 310 <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 311 <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 312 <li><a href="#cupsBackendDeviceURI" title="Get the device URI for a backend.">cupsBackendDeviceURI</a></li>
 313 <li><a href="#cupsBackendReport" title="Write a device line from a backend.">cupsBackendReport</a></li>
 314 <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 315 <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 316 <li><a href="#cupsSideChannelSNMPGet" title="Query a SNMP OID's value.">cupsSideChannelSNMPGet</a></li>
 317 <li><a href="#cupsSideChannelSNMPWalk" title="Query multiple SNMP OID values.">cupsSideChannelSNMPWalk</a></li>
 318 <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 319 </ul>
 320 <li><a href="#TYPES">Data Types</a><ul class="code">
 321         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 322         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 323         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 324         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 325         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 326         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 327 </ul></li>
 328 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 329         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 330         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 331         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 332         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 333         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 334 </ul></li>
 335 </ul>
 336 <!--
 337   "$Id: api-filter.shtml 7677 2008-06-19 23:22:19Z mike $"
 338
 339   Filter and backend programming introduction for the Common UNIX Printing
 340   System (CUPS).
 341
 342   Copyright 2007-2008 by Apple Inc.
 343   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 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 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 353
 354 <p>Filters (which include printer drivers and port monitors) and backends
 355 are used to convert job files to a printable format and send that data to the
 356 printer itself. All of these programs use a common interface for processing
 357 print jobs and communicating status information to the scheduler. Each is run
 358 with a standard set of command-line arguments:<p>
 359
 360 <dl class="code">
 361
 362         <dt>argv[1]</dt>
 363         <dd>The job ID</dd>
 364
 365         <dt>argv[2]</dt>
 366         <dd>The user printing the job</dd>
 367
 368         <dt>argv[3]</dt>
 369         <dd>The job name/title</dd>
 370
 371         <dt>argv[4]</dt>
 372         <dd>The number of copies to print</dd>
 373
 374         <dt>argv[5]</dt>
 375         <dd>The options that were provided when the job was submitted</dd>
 376
 377         <dt>argv[6]</dt>
 378         <dd>The file to print (first program only)</dd>
 379 </dl>
 380
 381 <p>The scheduler runs one or more of these programs to print any given job. The
 382 first filter reads from the print file and writes to the standard output, while
 383 the remaining filters read from the standard input and write to the standard
 384 output. The backend is the last filter in the chain and writes to the
 385 device.</p>
 386
 387 <h3><a name="SECURITY">Security Considerations</a></h3>
 388
 389 <p>It is always important to use security programming practices. Filters and
 390 most backends are run as a non-priviledged user, so the major security
 391 consideration is resource utilization - filters should not depend on unlimited
 392 amounts of CPU, memory, or disk space, and should protect against conditions
 393 that could lead to excess usage of any resource like infinite loops and
 394 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 395 specify an arbitrary file path to a separator page, template, or other file
 396 used by the filter since that can lead to an unauthorized disclosure of
 397 information. <em>Always</em> treat input as suspect and validate it!</p>
 398
 399 <p>If you are developing a backend that runs as root, make sure to check for
 400 potential buffer overflows, integer under/overflow conditions, and file
 401 accesses since these can lead to privilege escalations. When writing files,
 402 always validate the file path and <em>never</em> allow a user to determine
 403 where to store a file.</p>
 404
 405 <blockquote><b>Note:</b>
 406
 407 <p><em>Never</em> write files to a user's home directory. Aside from the
 408 security implications, CUPS is a network print service and as such the network
 409 user may not be the same as the local user and/or there may not be a local home
 410 directory to write to.</p>
 411
 412 <p>In addition, some operating systems provide additional security mechanisms
 413 that further limit file system access, even for backends running as root.  On
 414 Mac OS X, for example, no backend may write to a user's home directory.</p>
 415 </blockquote>
 416
 417 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 418
 419 <p>Temporary files should be created in the directory specified by the
 420 "TMPDIR" environment variable. The
 421 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 422 used to safely create temporary files in this directory.</p>
 423
 424 <h3><a name="COPIES">Copy Generation</a></h3>
 425
 426 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 427 of the input file. In general, you should only generate copies if the
 428 <em>filename</em> argument is supplied. The only exception to this are
 429 filters that produce device-independent PostScript output, since the PostScript
 430 filter <var>pstops</var> is responsible for generating copies of PostScript
 431 files.</p>
 432
 433 <h3><a name="EXITCODES">Exit Codes</a></h3>
 434
 435 <p>Filters must exit with status 0 when they successfully generate print data
 436 or 1 when they encounter an error. Backends can return any of the
 437 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 438
 439 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 440
 441 <p>The following environment variables are defined by the printing system
 442 when running print filters and backends:</p>
 443
 444 <dl class="code">
 445
 446         <dt>APPLE_LANGUAGES</dt>
 447         <dd>The Apple language identifier associated with the job
 448         (Mac OS X only).</dd>
 449
 450         <dt>CHARSET</dt>
 451         <dd>The job character set, typically "utf-8".</dd>
 452
 453         <dt>CLASS</dt>
 454         <dd>When a job is submitted to a printer class, contains the name of
 455         the destination printer class. Otherwise this environment
 456         variable will not be set.</dd>
 457
 458         <dt>CONTENT_TYPE</dt>
 459         <dd>The MIME type associated with the file (e.g.
 460         application/postscript).</dd>
 461
 462         <dt>CUPS_CACHEDIR</dt>
 463         <dd>The directory where cache files can be stored. Cache files can be
 464         used to retain information between jobs or files in a job.</dd>
 465
 466         <dt>CUPS_DATADIR</dt>
 467         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 468
 469         <dt>CUPS_SERVERROOT</dt>
 470         <dd>The root directory of the server.</dd>
 471
 472         <dt>DEVICE_URI</dt>
 473         <dd>The device-uri associated with the printer.</dd>
 474
 475         <dt>FINAL_CONTENT_TYPE</dt>
 476         <dd>The MIME type associated with the printer (e.g.
 477         application/vnd.cups-postscript).</dd>
 478
 479         <dt>LANG</dt>
 480         <dd>The language locale associated with the job.</dd>
 481
 482         <dt>PPD</dt>
 483         <dd>The full pathname of the PostScript Printer Description (PPD)
 484         file for this printer.</dd>
 485
 486         <dt>PRINTER</dt>
 487         <dd>The queue name of the class or printer.</dd>
 488
 489         <dt>RIP_CACHE</dt>
 490         <dd>The recommended amount of memory to use for Raster Image
 491         Processors (RIPs).</dd>
 492
 493         <dt>TMPDIR</dt>
 494         <dd>The directory where temporary files should be created.</dd>
 495
 496 </dl>
 497
 498 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 499
 500 <p>Filters and backends communicate with the scheduler by writing messages
 501 to the standard error file. The scheduler reads messages from all filters in
 502 a job and processes the message based on its prefix. For example, the following
 503 code sets the current printer state message to "Printing page 5":</p>
 504
 505 <pre class="example">
 506 int page = 5;
 507
 508 fprintf(stderr, "INFO: Printing page %d\n", page);
 509 </pre>
 510
 511 <p>Each message is a single line of text starting with one of the following
 512 prefix strings:</p>
 513
 514 <dl class="code">
 515
 516         <dt>ALERT: message</dt>
 517         <dd>Sets the printer-state-message attribute and adds the specified
 518         message to the current error log file using the "alert" log level.</dd>
 519
 520         <dt>ATTR: attribute=value [attribute=value]</dt>
 521         <dd>Sets the named printer or job attribute(s). Typically this is used
 522         to set the <code>marker-colors</code>, <code>marker-levels</code>,
 523         <code>marker-message</code>, <code>marker-names</code>,
 524         <code>marker-types</code>, <code>printer-alert</code>, and
 525         <code>printer-alert-description</code> printer attributes. Standard
 526         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 527         1</a>.</dd>
 528
 529         <dt>CRIT: message</dt>
 530         <dd>Sets the printer-state-message attribute and adds the specified
 531         message to the current error log file using the "critical" log
 532         level.</dd>
 533
 534         <dt>DEBUG: message</dt>
 535         <dd>Sets the printer-state-message attribute and adds the specified
 536         message to the current error log file using the "debug" log level.</dd>
 537
 538         <dt>DEBUG2: message</dt>
 539         <dd>Sets the printer-state-message attribute and adds the specified
 540         message to the current error log file using the "debug2" log level.</dd>
 541
 542         <dt>EMERG: message</dt>
 543         <dd>Sets the printer-state-message attribute and adds the specified
 544         message to the current error log file using the "emergency" log
 545         level.</dd>
 546
 547         <dt>ERROR: message</dt>
 548         <dd>Sets the printer-state-message attribute and adds the specified
 549         message to the current error log file using the "error" log level.
 550         Use "ERROR:" messages for non-persistent processing errors.</dd>
 551
 552         <dt>INFO: message</dt>
 553         <dd>Sets the printer-state-message attribute. If the current log level
 554         is set to "debug2", also adds the specified message to the current error
 555         log file using the "info" log level.</dd>
 556
 557         <dt>NOTICE: message</dt>
 558         <dd>Sets the printer-state-message attribute and adds the specified
 559         message to the current error log file using the "notice" log level.</dd>
 560
 561         <dt>PAGE: page-number #-copies</dt>
 562         <dt>PAGE: total #-pages</dt>
 563         <dd>Adds an entry to the current page log file. The first form adds
 564         #-copies to the job-media-sheets-completed attribute. The second
 565         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 566
 567         <dt>PPD: keyword=value [keyword=value ...]</dt>
 568         <dd>Changes or adds keywords to the printer's PPD file. Typically
 569         this is used to update installable options or default media settings
 570         based on the printer configuration.</dd>
 571
 572         <dt>STATE: printer-state-reason [printer-state-reason ...]</dt>
 573         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 574         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 575         <dd>Sets, adds, or removes printer-state-reason keywords to the
 576         current queue. Typically this is used to indicate persistent media,
 577         ink, toner, and configuration conditions or errors on a printer.
 578         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 579         use vendor-prefixed ("com.acme.foo") keywords for custom states.</dd>
 580
 581         <dt>WARNING: message</dt>
 582         <dd>Sets the printer-state-message attribute and adds the specified
 583         message to the current error log file using the "warning" log
 584         level.</dd>
 585
 586 </dl>
 587
 588 <p>Messages without one of these prefixes are treated as if they began with
 589 the "DEBUG:" prefix string.</p>
 590
 591
 592 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 593 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 594 <thead>
 595 <tr>
 596         <th>marker-type</th>
 597         <th>Description</th>
 598 </tr>
 599 </thead>
 600 <tbody>
 601 <tr>
 602         <td>developer</td>
 603         <td>Developer unit</td>
 604 </tr>
 605 <tr>
 606         <td>fuser</td>
 607         <td>Fuser unit</td>
 608 </tr>
 609 <tr>
 610         <td>fuserCleaningPad</td>
 611         <td>Fuser cleaning pad</td>
 612 </tr>
 613 <tr>
 614         <td>fuserOil</td>
 615         <td>Fuser oil</td>
 616 </tr>
 617 <tr>
 618         <td>ink</td>
 619         <td>Ink supply</td>
 620 </tr>
 621 <tr>
 622         <td>opc</td>
 623         <td>Photo conductor</td>
 624 </tr>
 625 <tr>
 626         <td>solidWax</td>
 627         <td>Wax supply</td>
 628 </tr>
 629 <tr>
 630         <td>staples</td>
 631         <td>Staple supply</td>
 632 </tr>
 633 <tr>
 634         <td>toner</td>
 635         <td>Toner supply</td>
 636 </tr>
 637 <tr>
 638         <td>transferUnit</td>
 639         <td>Transfer unit</td>
 640 </tr>
 641 <tr>
 642         <td>wasteInk</td>
 643         <td>Waste ink tank</td>
 644 </tr>
 645 <tr>
 646         <td>wasteToner</td>
 647         <td>Waste toner tank</td>
 648 </tr>
 649 <tr>
 650         <td>wasteWax</td>
 651         <td>Waste wax tank</td>
 652 </tr>
 653 </tbody>
 654 </table></div>
 655
 656 <br>
 657
 658 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 659 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 660 <thead>
 661 <tr>
 662         <th>Keyword</th>
 663         <th>Description</th>
 664 </tr>
 665 </thead>
 666 <tbody>
 667 <tr>
 668         <td>connecting-to-device</td>
 669         <td>Connecting to printer but not printing yet</td>
 670 </tr>
 671 <tr>
 672         <td>cover-open</td>
 673         <td>A cover is open on the printer</td>
 674 </tr>
 675 <tr>
 676         <td>input-tray-missing</td>
 677         <td>An input tray is missing from the printer</td>
 678 </tr>
 679 <tr>
 680         <td>marker-supply-empty</td>
 681         <td>Out of ink</td>
 682 </tr>
 683 <tr>
 684         <td>marker-supply-low</td>
 685         <td>Low on ink</td>
 686 </tr>
 687 <tr>
 688         <td>marker-waste-almost-full</td>
 689         <td>Waste tank almost full</td>
 690 </tr>
 691 <tr>
 692         <td>marker-waste-full</td>
 693         <td>Waste tank full</td>
 694 </tr>
 695 <tr>
 696         <td>media-empty</td>
 697         <td>Out of media</td>
 698 </tr>
 699 <tr>
 700         <td>media-jam</td>
 701         <td>Media is jammed in the printer</td>
 702 </tr>
 703 <tr>
 704         <td>media-low</td>
 705         <td>Low on media</td>
 706 </tr>
 707 <tr>
 708         <td>paused</td>
 709         <td>Stop the printer</td>
 710 </tr>
 711 <tr>
 712         <td>timed-out</td>
 713         <td>Unable to connect to printer</td>
 714 </tr>
 715 <tr>
 716         <td>toner-empty</td>
 717         <td>Out of toner</td>
 718 </tr>
 719 <tr>
 720         <td>toner-low</td>
 721         <td>Low on toner</td>
 722 </tr>
 723 </tbody>
 724 </table></div>
 725
 726 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
 727
 728 <p>Filters can communicate with the backend via the
 729 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
 730 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 731 functions. The
 732 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
 733 reads data that has been sent back from the device and is typically used to
 734 obtain status and configuration information. For example, the following code
 735 polls the backend for back-channel data:</p>
 736
 737 <pre class="example">
 738 #include &lt;cups/cups.h&gt;
 739
 740 char buffer[8192];
 741 ssize_t bytes;
 742
 743 /* Use a timeout of 0.0 seconds to poll for back-channel data */
 744 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
 745 </pre>
 746
 747 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
 748 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
 749 when it is available.</p>
 750
 751 <p>The
 752 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 753 function allows you to get out-of-band status information and do synchronization
 754 with the device. For example, the following code gets the current IEEE-1284
 755 device ID string from the backend:</p>
 756
 757 <pre class="example">
 758 #include &lt;cups/sidechannel.h&gt;
 759
 760 char data[2049];
 761 int datalen;
 762 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 763
 764 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
 765    nul-termination... */
 766 datalen = sizeof(data) - 1;
 767
 768 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
 769 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
 770
 771 /* Use the returned value if OK was returned and the length is non-zero */
 772 if (status == CUPS_SC_STATUS_OK && datalen > 0)
 773   data[datalen] = '\0';
 774 else
 775   data[0] = '\0';
 776 </pre>
 777
 778 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
 779
 780 <p>Backends communicate with filters using the reciprocal functions
 781 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
 782 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
 783 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
 784 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
 785
 786 <pre class="example">
 787 #include &lt;cups/cups.h&gt;
 788
 789 char buffer[8192];
 790 ssize_t bytes;
 791
 792 /* Obtain data from printer/device */
 793 ...
 794
 795 /* Use a timeout of 1.0 seconds to give filters a chance to read */
 796 cupsBackChannelWrite(buffer, bytes, 1.0);
 797 </pre>
 798
 799 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
 800 function reads a side-channel command from a filter, driver, or port monitor.
 801 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
 802 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
 803 separate thread for that purpose), or use <code>select</code> or
 804 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
 805 input and output on several file descriptors at the same time.</p>
 806
 807 <p>Once a command is processed, the backend uses the
 808 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
 809 to send its response. For example, the following code shows how to poll for a
 810 side-channel command and respond to it:</p>
 811
 812 <pre class="example">
 813 #include &lt;cups/sidechannel.h&gt;
 814
 815 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
 816 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 817 char data[2048];
 818 int datalen = sizeof(data);
 819
 820 /* Poll for a command... */
 821 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
 822 {
 823   switch (command)
 824   {
 825     /* handle supported commands, fill data/datalen/status with values as needed */
 826
 827     default :
 828         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
 829         datalen = 0;
 830         break;
 831   }
 832
 833   /* Send a response... */
 834   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
 835 }
 836 </pre>
 837
 838 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
 839
 840 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
 841 status, page counter, and supply levels from most network printers. Every
 842 piece of information is associated with an Object Identifier (OID), and
 843 every printer has a <em>community</em> name associated with it. OIDs can be
 844 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
 845
 846 <p>The two CUPS SNMP functions provide a simple API for querying network
 847 printers through the side-channel interface. Each accepts a string containing
 848 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
 849 along with a timeout for the query.</p>
 850
 851 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
 852 function queries a single OID and returns the value as a string in a buffer
 853 you supply:</p>
 854
 855 <pre class="example">
 856 #include &lt;cups/sidechannel.h&gt;
 857
 858 char data[512];
 859 int datalen = sizeof(data);
 860
 861 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
 862         == CUPS_SC_STATUS_OK)
 863 {
 864   /* Do something with the value */
 865   printf("Page counter is: %s\n", data);
 866 }
 867 </pre>
 868
 869 <p>The
 870 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
 871 function allows you to query a whole group of OIDs, calling a function of your
 872 choice for each OID that is found:</p>
 873
 874 <pre class="example">
 875 #include &lt;cups/sidechannel.h&gt;
 876
 877 void
 878 my_callback(const char *oid, const char *data, int datalen, void *context)
 879 {
 880   /* Do something with the value */
 881   printf("%s=%s\n", oid, data);
 882 }
 883
 884 ...
 885
 886 void *my_data;
 887
 888 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
 889 </pre>
 890 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
 891 <h3 class="function"><span class="info">&nbsp;CUPS 1.2&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
 892 <p class="description">Read data from the backchannel.</p>
 893 <p class="code">
 894 ssize_t cupsBackChannelRead (<br>
 895 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
 896 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
 897 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
 898 );</p>
 899 <h4 class="parameters">Parameters</h4>
 900 <dl>
 901 <dt>buffer</dt>
 902 <dd class="description">Buffer to read into</dd>
 903 <dt>bytes</dt>
 904 <dd class="description">Bytes to read</dd>
 905 <dt>timeout</dt>
 906 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
 907 </dl>
 908 <h4 class="returnvalue">Return Value</h4>
 909 <p class="description">Bytes read or -1 on error</p>
 910 <h4 class="discussion">Discussion</h4>
 911 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
 912 parameter controls how many seconds to wait for the data - use 0.0 to
 913 return immediately if there is no data, -1.0 to wait for data indefinitely.
 914
 915 </p>
 916 <h3 class="function"><span class="info">&nbsp;CUPS 1.2&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
 917 <p class="description">Write data to the backchannel.</p>
 918 <p class="code">
 919 ssize_t cupsBackChannelWrite (<br>
 920 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
 921 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
 922 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
 923 );</p>
 924 <h4 class="parameters">Parameters</h4>
 925 <dl>
 926 <dt>buffer</dt>
 927 <dd class="description">Buffer to write</dd>
 928 <dt>bytes</dt>
 929 <dd class="description">Bytes to write</dd>
 930 <dt>timeout</dt>
 931 <dd class="description">Timeout in seconds, typically 1.0</dd>
 932 </dl>
 933 <h4 class="returnvalue">Return Value</h4>
 934 <p class="description">Bytes written or -1 on error</p>
 935 <h4 class="discussion">Discussion</h4>
 936 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
 937 controls how many seconds to wait for the data to be written - use
 938 0.0 to return immediately if the data cannot be written, -1.0 to wait
 939 indefinitely.
 940
 941 </p>
 942 <h3 class="function"><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
 943 <p class="description">Get the device URI for a backend.</p>
 944 <p class="code">
 945 const char *cupsBackendDeviceURI (<br>
 946 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
 947 );</p>
 948 <h4 class="parameters">Parameters</h4>
 949 <dl>
 950 <dt>argv</dt>
 951 <dd class="description">Command-line arguments</dd>
 952 </dl>
 953 <h4 class="returnvalue">Return Value</h4>
 954 <p class="description">Device URI or <code>NULL</code></p>
 955 <h4 class="discussion">Discussion</h4>
 956 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
 957 function returns the device URI passed in the DEVICE_URI environment
 958 variable or the device URI passed in argv[0], whichever is found
 959 first.</p>
 960 <h3 class="function"><a name="cupsBackendReport">cupsBackendReport</a></h3>
 961 <p class="description">Write a device line from a backend.</p>
 962 <p class="code">
 963 void cupsBackendReport (<br>
 964 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
 965 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
 966 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
 967 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
 968 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
 969 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
 970 );</p>
 971 <h4 class="parameters">Parameters</h4>
 972 <dl>
 973 <dt>device_scheme</dt>
 974 <dd class="description">device-scheme string</dd>
 975 <dt>device_uri</dt>
 976 <dd class="description">device-uri string</dd>
 977 <dt>device_make_and_model</dt>
 978 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
 979 <dt>device_info</dt>
 980 <dd class="description">device-info string or <code>NULL</code></dd>
 981 <dt>device_id</dt>
 982 <dd class="description">device-id string or <code>NULL</code></dd>
 983 <dt>device_location</dt>
 984 <dd class="description">device-location string or <code>NULL</code></dd>
 985 </dl>
 986 <h4 class="discussion">Discussion</h4>
 987 <p class="discussion">This function writes a single device line to stdout for a backend.
 988 It handles quoting of special characters in the device-make-and-model,
 989 device-info, device-id, and device-location strings.</p>
 990 <h3 class="function"><span class="info">&nbsp;CUPS 1.3&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
 991 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
 992 <p class="code">
 993 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
 994 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
 995 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
 996 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
 997 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
 998 );</p>
 999 <h4 class="parameters">Parameters</h4>
1000 <dl>
1001 <dt>command</dt>
1002 <dd class="description">Command to send</dd>
1003 <dt>data</dt>
1004 <dd class="description">Response data buffer pointer</dd>
1005 <dt>datalen</dt>
1006 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1007 <dt>timeout</dt>
1008 <dd class="description">Timeout in seconds</dd>
1009 </dl>
1010 <h4 class="returnvalue">Return Value</h4>
1011 <p class="description">Status of command</p>
1012 <h4 class="discussion">Discussion</h4>
1013 <p class="discussion">This function is normally only called by filters, drivers, or port
1014 monitors in order to communicate with the backend used by the current
1015 printer.  Programs must be prepared to handle timeout or &quot;not
1016 implemented&quot; status codes, which indicate that the backend or device
1017 do not support the specified side-channel command.<br>
1018 <br>
1019 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1020 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1021 update the value to contain the number of data bytes in the buffer.
1022
1023 </p>
1024 <h3 class="function"><span class="info">&nbsp;CUPS 1.3&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1025 <p class="description">Read a side-channel message.</p>
1026 <p class="code">
1027 int cupsSideChannelRead (<br>
1028 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1029 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1030 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1031 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1032 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1033 );</p>
1034 <h4 class="parameters">Parameters</h4>
1035 <dl>
1036 <dt>command</dt>
1037 <dd class="description">Command code</dd>
1038 <dt>status</dt>
1039 <dd class="description">Status code</dd>
1040 <dt>data</dt>
1041 <dd class="description">Data buffer pointer</dd>
1042 <dt>datalen</dt>
1043 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1044 <dt>timeout</dt>
1045 <dd class="description">Timeout in seconds</dd>
1046 </dl>
1047 <h4 class="returnvalue">Return Value</h4>
1048 <p class="description">0 on success, -1 on error</p>
1049 <h4 class="discussion">Discussion</h4>
1050 <p class="discussion">This function is normally only called by backend programs to read
1051 commands from a filter, driver, or port monitor program.  The
1052 caller must be prepared to handle incomplete or invalid messages
1053 and return the corresponding status codes.<br>
1054 <br>
1055 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1056 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1057 update the value to contain the number of data bytes in the buffer.
1058
1059 </p>
1060 <h3 class="function"><span class="info">&nbsp;CUPS 1.4&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1061 <p class="description">Query a SNMP OID's value.</p>
1062 <p class="code">
1063 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1064 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1065 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1066 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1067 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1068 );</p>
1069 <h4 class="parameters">Parameters</h4>
1070 <dl>
1071 <dt>oid</dt>
1072 <dd class="description">OID to query</dd>
1073 <dt>data</dt>
1074 <dd class="description">Buffer for OID value</dd>
1075 <dt>datalen</dt>
1076 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1077 <dt>timeout</dt>
1078 <dd class="description">Timeout in seconds</dd>
1079 </dl>
1080 <h4 class="returnvalue">Return Value</h4>
1081 <p class="description">Query status</p>
1082 <h4 class="discussion">Discussion</h4>
1083 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1084 filter, port monitor, or backend using the default community name.<br>
1085 <br>
1086 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1087 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1088 supported and must be converted to their numeric forms.<br>
1089 <br>
1090 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1091 buffer to hold the OID value as a string. HEX-String (binary) values are
1092 converted to hexadecimal strings representing the binary data, while
1093 NULL-Value and unknown OID types are returned as the empty string.
1094 The returned &quot;datalen&quot; does not include the trailing nul.
1095
1096 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1097 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1098 the printer does not respond to the SNMP query.
1099
1100 </p>
1101 <h3 class="function"><span class="info">&nbsp;CUPS 1.4&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1102 <p class="description">Query multiple SNMP OID values.</p>
1103 <p class="code">
1104 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1105 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1106 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1107 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1108 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1109 );</p>
1110 <h4 class="parameters">Parameters</h4>
1111 <dl>
1112 <dt>oid</dt>
1113 <dd class="description">First numeric OID to query</dd>
1114 <dt>timeout</dt>
1115 <dd class="description">Timeout for each query in seconds</dd>
1116 <dt>cb</dt>
1117 <dd class="description">Function to call with each value</dd>
1118 <dt>context</dt>
1119 <dd class="description">Application-defined pointer to send to callback</dd>
1120 </dl>
1121 <h4 class="returnvalue">Return Value</h4>
1122 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1123 <h4 class="discussion">Discussion</h4>
1124 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1125 of the filter, port monitor, or backend using the default community name.
1126 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1127 the callback function you provide.<br>
1128 <br>
1129 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1130 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1131 supported and must be converted to their numeric forms.<br>
1132 <br>
1133 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1134 time will depend on the number of OID values found and the time required
1135 for each query.<br>
1136 <br>
1137 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1138 is an application-defined pointer that is sent to the callback function
1139 along with the OID and current data. The data passed to the callback is the
1140 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1141
1142 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1143 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1144 the printer does not respond to the first SNMP query.
1145
1146 </p>
1147 <h3 class="function"><span class="info">&nbsp;CUPS 1.3&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1148 <p class="description">Write a side-channel message.</p>
1149 <p class="code">
1150 int cupsSideChannelWrite (<br>
1151 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1152 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1153 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1154 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1155 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1156 );</p>
1157 <h4 class="parameters">Parameters</h4>
1158 <dl>
1159 <dt>command</dt>
1160 <dd class="description">Command code</dd>
1161 <dt>status</dt>
1162 <dd class="description">Status code</dd>
1163 <dt>data</dt>
1164 <dd class="description">Data buffer pointer</dd>
1165 <dt>datalen</dt>
1166 <dd class="description">Number of bytes of data</dd>
1167 <dt>timeout</dt>
1168 <dd class="description">Timeout in seconds</dd>
1169 </dl>
1170 <h4 class="returnvalue">Return Value</h4>
1171 <p class="description">0 on success, -1 on error</p>
1172 <h4 class="discussion">Discussion</h4>
1173 <p class="discussion">This function is normally only called by backend programs to send
1174 responses to a filter, driver, or port monitor program.
1175
1176 </p>
1177 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1178 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1179 <p class="description">Backend exit codes</p>
1180 <p class="code">
1181 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1182 </p>
1183 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1184 <p class="description">Bidirectional capabilities</p>
1185 <p class="code">
1186 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1187 </p>
1188 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1189 <p class="description">Request command codes</p>
1190 <p class="code">
1191 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1192 </p>
1193 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1194 <p class="description">Printer state bits</p>
1195 <p class="code">
1196 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1197 </p>
1198 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1199 <p class="description">Response status codes</p>
1200 <p class="code">
1201 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1202 </p>
1203 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1204 <p class="description">SNMP walk callback</p>
1205 <p class="code">
1206 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1207 </p>
1208 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1209 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1210 <p class="description">Backend exit codes</p>
1211 <h4 class="constants">Constants</h4>
1212 <dl>
1213 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1214 <dd class="description">Job failed, authentication required</dd>
1215 <dt>CUPS_BACKEND_CANCEL </dt>
1216 <dd class="description">Job failed, cancel job</dd>
1217 <dt>CUPS_BACKEND_FAILED </dt>
1218 <dd class="description">Job failed, use error-policy</dd>
1219 <dt>CUPS_BACKEND_HOLD </dt>
1220 <dd class="description">Job failed, hold job</dd>
1221 <dt>CUPS_BACKEND_OK </dt>
1222 <dd class="description">Job completed successfully</dd>
1223 <dt>CUPS_BACKEND_STOP </dt>
1224 <dd class="description">Job failed, stop queue</dd>
1225 </dl>
1226 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1227 <p class="description">Bidirectional capability values</p>
1228 <h4 class="constants">Constants</h4>
1229 <dl>
1230 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1231 <dd class="description">Bidirectional I/O is not supported</dd>
1232 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1233 <dd class="description">Bidirectional I/O is supported</dd>
1234 </dl>
1235 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1236 <p class="description">Request command codes</p>
1237 <h4 class="constants">Constants</h4>
1238 <dl>
1239 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1240 <dd class="description">Drain all pending output</dd>
1241 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1242 <dd class="description">Return bidirectional capabilities</dd>
1243 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1244 <dd class="description">Return the IEEE-1284 device ID</dd>
1245 <dt>CUPS_SC_CMD_GET_STATE </dt>
1246 <dd class="description">Return the device state</dd>
1247 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4&nbsp;</span></dt>
1248 <dd class="description">Query an SNMP OID </dd>
1249 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4&nbsp;</span></dt>
1250 <dd class="description">Query the next SNMP OID </dd>
1251 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1252 <dd class="description">Do a soft reset</dd>
1253 </dl>
1254 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1255 <p class="description">Printer state bits</p>
1256 <h4 class="constants">Constants</h4>
1257 <dl>
1258 <dt>CUPS_SC_STATE_BUSY </dt>
1259 <dd class="description">Device is busy</dd>
1260 <dt>CUPS_SC_STATE_ERROR </dt>
1261 <dd class="description">Other error condition</dd>
1262 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1263 <dd class="description">Toner/ink out condition</dd>
1264 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1265 <dd class="description">Toner/ink low condition</dd>
1266 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1267 <dd class="description">Paper out condition</dd>
1268 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1269 <dd class="description">Paper low condition</dd>
1270 <dt>CUPS_SC_STATE_OFFLINE </dt>
1271 <dd class="description">Device is offline</dd>
1272 <dt>CUPS_SC_STATE_ONLINE </dt>
1273 <dd class="description">Device is online</dd>
1274 </dl>
1275 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1276 <p class="description">Response status codes</p>
1277 <h4 class="constants">Constants</h4>
1278 <dl>
1279 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1280 <dd class="description">The command/response message was invalid</dd>
1281 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1282 <dd class="description">An I/O error occurred</dd>
1283 <dt>CUPS_SC_STATUS_NONE </dt>
1284 <dd class="description">No status</dd>
1285 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1286 <dd class="description">Command not implemented</dd>
1287 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1288 <dd class="description">The device did not respond</dd>
1289 <dt>CUPS_SC_STATUS_OK </dt>
1290 <dd class="description">Operation succeeded</dd>
1291 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1292 <dd class="description">The backend did not respond</dd>
1293 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1294 <dd class="description">Response too big</dd>
1295 </dl>
1296 </div>
1297 </body>
1298 </html>