doc/help/api-filter.html

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 355 <!--
 356   Filter and backend programming header for CUPS.
 357
 358   Copyright 2008-2014 by Apple Inc.
 359
 360   These coded instructions, statements, and computer programs are the
 361   property of Apple Inc. and are protected by Federal copyright
 362   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 363   which should have been included with this file.  If this file is
 364   file is missing or damaged, see the license at "http://www.cups.org/".
 365 -->
 366
 367 <h1 class='title'>Filter and Backend Programming</h1>
 368
 369 <div class='summary'><table summary='General Information'>
 370 <thead>
 371 <tr>
 372         <th>Headers</th>
 373         <th>cups/backend.h<br>
 374         cups/sidechannel.h</th>
 375 </tr>
 376 </thead>
 377 <tbody>
 378 <tr>
 379         <th>Library</th>
 380         <td>-lcups</td>
 381 </tr>
 382 <tr>
 383         <th>See Also</th>
 384         <td>Programming: <a href='api-overview.html' target='_top'>Introduction to CUPS Programming</a><br>
 385         Programming: <a href='api-cups.html' target='_top'>CUPS API</a><br>
 386         Programming: <a href='api-ppd.html' target='_top'>PPD API</a><br>
 387         Programming: <a href='api-raster.html' target='_top'>Raster API</a><br>
 388         Programming: <a href='postscript-driver.html' target='_top'>Developing PostScript Printer Drivers</a><br>
 389         Programming: <a href='raster-driver.html' target='_top'>Developing Raster Printer Drivers</a><br>
 390         Specifications: <a href='spec-design.html' target='_top'>CUPS Design Description</a></td>
 391 </tr>
 392 </tbody>
 393 </table></div>
 394 <h2 class="title">Contents</h2>
 395 <ul class="contents">
 396 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 397         <li><a href="#SECURITY">Security Considerations</a></li>
 398         <li><a href="#SIGNALS">Canceled Jobs and Signal Handling</a></li>
 399         <li><a href="#PERMISSIONS">File Permissions</a></li>
 400         <li><a href="#TEMPFILES">Temporary Files</a></li>
 401         <li><a href="#COPIES">Copy Generation</a></li>
 402         <li><a href="#EXITCODES">Exit Codes</a></li>
 403         <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 404         <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 405         <li><a href="#COMMUNICATING_BACKEND">Communicating with the Backend</a></li>
 406         <li><a href="#COMMUNICATING_FILTER">Communicating with Filters</a></li>
 407         <li><a href="#SNMP">Doing SNMP Queries with Network Printers</a></li>
 408 </ul></li>
 409 <li><a href="#SANDBOXING">Sandboxing on OS X</a></li>
 410 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 411         <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 412         <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 413         <li><a href="#cupsBackendDeviceURI" title="Get the device URI for a backend.">cupsBackendDeviceURI</a></li>
 414         <li><a href="#cupsBackendReport" title="Write a device line from a backend.">cupsBackendReport</a></li>
 415         <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 416         <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 417         <li><a href="#cupsSideChannelSNMPGet" title="Query a SNMP OID's value.">cupsSideChannelSNMPGet</a></li>
 418         <li><a href="#cupsSideChannelSNMPWalk" title="Query multiple SNMP OID values.">cupsSideChannelSNMPWalk</a></li>
 419         <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 420 </ul></li>
 421 <li><a href="#TYPES">Data Types</a><ul class="code">
 422         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 423         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 424         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 425         <li><a href="#cups_sc_connected_t" title="Connectivity values">cups_sc_connected_t</a></li>
 426         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 427         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 428         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 429 </ul></li>
 430 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 431         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 432         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 433         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 434         <li><a href="#cups_sc_connected_e" title="Connectivity values">cups_sc_connected_e</a></li>
 435         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 436         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 437 </ul></li>
 438 </ul>
 439 <!--
 440   Filter and backend programming introduction for CUPS.
 441
 442   Copyright 2007-2014 by Apple Inc.
 443   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 444
 445   These coded instructions, statements, and computer programs are the
 446   property of Apple Inc. and are protected by Federal copyright
 447   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 448   which should have been included with this file.  If this file is
 449   file is missing or damaged, see the license at "http://www.cups.org/".
 450 -->
 451
 452 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 453
 454 <p>Filters (which include printer drivers and port monitors) and backends
 455 are used to convert job files to a printable format and send that data to the
 456 printer itself. All of these programs use a common interface for processing
 457 print jobs and communicating status information to the scheduler. Each is run
 458 with a standard set of command-line arguments:<p>
 459
 460 <dl class="code">
 461
 462         <dt>argv[1]</dt>
 463         <dd>The job ID</dd>
 464
 465         <dt>argv[2]</dt>
 466         <dd>The user printing the job</dd>
 467
 468         <dt>argv[3]</dt>
 469         <dd>The job name/title</dd>
 470
 471         <dt>argv[4]</dt>
 472         <dd>The number of copies to print</dd>
 473
 474         <dt>argv[5]</dt>
 475         <dd>The options that were provided when the job was submitted</dd>
 476
 477         <dt>argv[6]</dt>
 478         <dd>The file to print (first program only)</dd>
 479 </dl>
 480
 481 <p>The scheduler runs one or more of these programs to print any given job. The
 482 first filter reads from the print file and writes to the standard output, while
 483 the remaining filters read from the standard input and write to the standard
 484 output. The backend is the last filter in the chain and writes to the
 485 device.</p>
 486
 487 <p>Filters are always run as a non-privileged user, typically "lp", with no
 488 connection to the user's desktop. Backends are run either as a non-privileged
 489 user or as root if the file permissions do not allow user or group execution.
 490 The <a href="#PERMISSIONS">file permissions</a> section talks about this in
 491 more detail.</p>
 492
 493 <h3><a name="SECURITY">Security Considerations</a></h3>
 494
 495 <p>It is always important to use security programming practices. Filters and
 496 most backends are run as a non-privileged user, so the major security
 497 consideration is resource utilization - filters should not depend on unlimited
 498 amounts of CPU, memory, or disk space, and should protect against conditions
 499 that could lead to excess usage of any resource like infinite loops and
 500 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 501 specify an arbitrary file path to a separator page, template, or other file
 502 used by the filter since that can lead to an unauthorized disclosure of
 503 information. <em>Always</em> treat input as suspect and validate it!</p>
 504
 505 <p>If you are developing a backend that runs as root, make sure to check for
 506 potential buffer overflows, integer under/overflow conditions, and file
 507 accesses since these can lead to privilege escalations. When writing files,
 508 always validate the file path and <em>never</em> allow a user to determine
 509 where to store a file.</p>
 510
 511 <blockquote><b>Note:</b>
 512
 513 <p><em>Never</em> write files to a user's home directory. Aside from the
 514 security implications, CUPS is a network print service and as such the network
 515 user may not be the same as the local user and/or there may not be a local home
 516 directory to write to.</p>
 517
 518 <p>In addition, some operating systems provide additional security mechanisms
 519 that further limit file system access, even for backends running as root. On
 520 OS X, for example, no backend may write to a user's home directory. See the <a href="#SANDBOXING">Sandboxing on OS X</a> section for more information.</p>
 521 </blockquote>
 522
 523 <h3><a name="SIGNALS">Canceled Jobs and Signal Handling</a></h3>
 524
 525 <p>The scheduler sends <code>SIGTERM</code> when a printing job is canceled or
 526 held. Filters, backends, and port monitors <em>must</em> catch
 527 <code>SIGTERM</code> and perform any cleanup necessary to produce a valid output
 528 file or return the printer to a known good state. The recommended behavior is to
 529 end the output on the current page, preferably on the current line or object
 530 being printed.</p>
 531
 532 <p>Filters and backends may also receive <code>SIGPIPE</code> when an upstream or downstream filter/backend exits with a non-zero status. Developers should generally ignore <code>SIGPIPE</code> at the beginning of <code>main()</code> with the following function call:</p>
 533
 534 <pre class="example">
 535 #include &lt;signal.h&gt;>
 536
 537 ...
 538
 539 int
 540 main(int argc, char *argv[])
 541 {
 542   signal(SIGPIPE, SIG_IGN);
 543
 544   ...
 545 }
 546 </pre>
 547
 548 <h3><a name="PERMISSIONS">File Permissions</a></h3>
 549
 550 <p>For security reasons, CUPS will only run filters and backends that are owned
 551 by root and do not have world or group write permissions. The recommended
 552 permissions for filters and backends are 0555 - read and execute but no write.
 553 Backends that must run as root should use permissions of 0500 - read and execute
 554 by root, no access for other users. Write permissions can be enabled for the
 555 root user only.</p>
 556
 557 <p>To avoid a warning message, the directory containing your filter(s) must also
 558 be owned by root and have world and group write disabled - permissions of 0755
 559 or 0555 are strongly encouraged.</p>
 560
 561 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 562
 563 <p>Temporary files should be created in the directory specified by the
 564 "TMPDIR" environment variable. The
 565 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 566 used to safely create temporary files in this directory.</p>
 567
 568 <h3><a name="COPIES">Copy Generation</a></h3>
 569
 570 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 571 of the input file. In general, you should only generate copies if the
 572 <em>filename</em> argument is supplied. The only exception to this are
 573 filters that produce device-independent PostScript output, since the PostScript
 574 filter <var>pstops</var> is responsible for generating copies of PostScript
 575 files.</p>
 576
 577 <h3><a name="EXITCODES">Exit Codes</a></h3>
 578
 579 <p>Filters must exit with status 0 when they successfully generate print data
 580 or 1 when they encounter an error. Backends can return any of the
 581 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 582
 583 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 584
 585 <p>The following environment variables are defined by the printing system
 586 when running print filters and backends:</p>
 587
 588 <dl class="code">
 589
 590         <dt>APPLE_LANGUAGE</dt>
 591         <dd>The Apple language identifier associated with the job
 592         (OS X only).</dd>
 593
 594         <dt>CHARSET</dt>
 595         <dd>The job character set, typically "utf-8".</dd>
 596
 597         <dt>CLASS</dt>
 598         <dd>When a job is submitted to a printer class, contains the name of
 599         the destination printer class. Otherwise this environment
 600         variable will not be set.</dd>
 601
 602         <dt>CONTENT_TYPE</dt>
 603         <dd>The MIME type associated with the file (e.g.
 604         application/postscript).</dd>
 605
 606         <dt>CUPS_CACHEDIR</dt>
 607         <dd>The directory where cache files can be stored. Cache files can be
 608         used to retain information between jobs or files in a job.</dd>
 609
 610         <dt>CUPS_DATADIR</dt>
 611         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 612
 613         <dt>CUPS_FILETYPE</dt>
 614         <dd>The type of file being printed: "job-sheet" for a banner page and
 615         "document" for a regular print file.</dd>
 616
 617         <dt>CUPS_SERVERROOT</dt>
 618         <dd>The root directory of the server.</dd>
 619
 620         <dt>DEVICE_URI</dt>
 621         <dd>The device-uri associated with the printer.</dd>
 622
 623         <dt>FINAL_CONTENT_TYPE</dt>
 624         <dd>The MIME type associated with the printer (e.g.
 625         application/vnd.cups-postscript).</dd>
 626
 627         <dt>LANG</dt>
 628         <dd>The language locale associated with the job.</dd>
 629
 630         <dt>PPD</dt>
 631         <dd>The full pathname of the PostScript Printer Description (PPD)
 632         file for this printer.</dd>
 633
 634         <dt>PRINTER</dt>
 635         <dd>The queue name of the class or printer.</dd>
 636
 637         <dt>RIP_CACHE</dt>
 638         <dd>The recommended amount of memory to use for Raster Image
 639         Processors (RIPs).</dd>
 640
 641         <dt>TMPDIR</dt>
 642         <dd>The directory where temporary files should be created.</dd>
 643
 644 </dl>
 645
 646 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 647
 648 <p>Filters and backends communicate with the scheduler by writing messages
 649 to the standard error file. The scheduler reads messages from all filters in
 650 a job and processes the message based on its prefix. For example, the following
 651 code sets the current printer state message to "Printing page 5":</p>
 652
 653 <pre class="example">
 654 int page = 5;
 655
 656 fprintf(stderr, "INFO: Printing page %d\n", page);
 657 </pre>
 658
 659 <p>Each message is a single line of text starting with one of the following
 660 prefix strings:</p>
 661
 662 <dl class="code">
 663
 664         <dt>ALERT: message</dt>
 665         <dd>Sets the printer-state-message attribute and adds the specified
 666         message to the current error log file using the "alert" log level.</dd>
 667
 668         <dt>ATTR: attribute=value [attribute=value]</dt>
 669         <dd>Sets the named printer or job attribute(s). Typically this is used
 670         to set the <code>marker-colors</code>, <code>marker-high-levels</code>,
 671         <code>marker-levels</code>, <code>marker-low-levels</code>,
 672         <code>marker-message</code>, <code>marker-names</code>,
 673         <code>marker-types</code>, <code>printer-alert</code>, and
 674         <code>printer-alert-description</code> printer attributes. Standard
 675         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 676         1</a>. String values need special handling - see <a href="#ATTR_STRINGS">Reporting Attribute String Values</a> below.</dd>
 677
 678         <dt>CRIT: message</dt>
 679         <dd>Sets the printer-state-message attribute and adds the specified
 680         message to the current error log file using the "critical" log
 681         level.</dd>
 682
 683         <dt>DEBUG: message</dt>
 684         <dd>Sets the printer-state-message attribute and adds the specified
 685         message to the current error log file using the "debug" log level.</dd>
 686
 687         <dt>DEBUG2: message</dt>
 688         <dd>Sets the printer-state-message attribute and adds the specified
 689         message to the current error log file using the "debug2" log level.</dd>
 690
 691         <dt>EMERG: message</dt>
 692         <dd>Sets the printer-state-message attribute and adds the specified
 693         message to the current error log file using the "emergency" log
 694         level.</dd>
 695
 696         <dt>ERROR: message</dt>
 697         <dd>Sets the printer-state-message attribute and adds the specified
 698         message to the current error log file using the "error" log level.
 699         Use "ERROR:" messages for non-persistent processing errors.</dd>
 700
 701         <dt>INFO: message</dt>
 702         <dd>Sets the printer-state-message attribute. If the current log level
 703         is set to "debug2", also adds the specified message to the current error
 704         log file using the "info" log level.</dd>
 705
 706         <dt>NOTICE: message</dt>
 707         <dd>Sets the printer-state-message attribute and adds the specified
 708         message to the current error log file using the "notice" log level.</dd>
 709
 710         <dt>PAGE: page-number #-copies</dt>
 711         <dt>PAGE: total #-pages</dt>
 712         <dd>Adds an entry to the current page log file. The first form adds
 713         #-copies to the job-media-sheets-completed attribute. The second
 714         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 715
 716         <dt>PPD: keyword=value [keyword=value ...]</dt>
 717         <dd>Changes or adds keywords to the printer's PPD file. Typically
 718         this is used to update installable options or default media settings
 719         based on the printer configuration.</dd>
 720
 721         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 722         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 723         <dd>Sets or clears printer-state-reason keywords for the current queue.
 724         Typically this is used to indicate persistent media, ink, toner, and
 725         configuration conditions or errors on a printer.
 726         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 727         use vendor-prefixed ("com.example.foo") keywords for custom states. See
 728         <a href="#MANAGING_STATE">Managing Printer State in a Filter</a> for more
 729         information.
 730
 731         <dt>WARNING: message</dt>
 732         <dd>Sets the printer-state-message attribute and adds the specified
 733         message to the current error log file using the "warning" log
 734         level.</dd>
 735
 736 </dl>
 737
 738 <p>Messages without one of these prefixes are treated as if they began with
 739 the "DEBUG:" prefix string.</p>
 740
 741 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 742 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 743 <thead>
 744 <tr>
 745         <th>marker-type</th>
 746         <th>Description</th>
 747 </tr>
 748 </thead>
 749 <tbody>
 750 <tr>
 751         <td>developer</td>
 752         <td>Developer unit</td>
 753 </tr>
 754 <tr>
 755         <td>fuser</td>
 756         <td>Fuser unit</td>
 757 </tr>
 758 <tr>
 759         <td>fuser-cleaning-pad</td>
 760         <td>Fuser cleaning pad</td>
 761 </tr>
 762 <tr>
 763         <td>fuser-oil</td>
 764         <td>Fuser oil</td>
 765 </tr>
 766 <tr>
 767         <td>ink</td>
 768         <td>Ink supply</td>
 769 </tr>
 770 <tr>
 771         <td>opc</td>
 772         <td>Photo conductor</td>
 773 </tr>
 774 <tr>
 775         <td>solid-wax</td>
 776         <td>Wax supply</td>
 777 </tr>
 778 <tr>
 779         <td>staples</td>
 780         <td>Staple supply</td>
 781 </tr>
 782 <tr>
 783         <td>toner</td>
 784         <td>Toner supply</td>
 785 </tr>
 786 <tr>
 787         <td>transfer-unit</td>
 788         <td>Transfer unit</td>
 789 </tr>
 790 <tr>
 791         <td>waste-ink</td>
 792         <td>Waste ink tank</td>
 793 </tr>
 794 <tr>
 795         <td>waste-toner</td>
 796         <td>Waste toner tank</td>
 797 </tr>
 798 <tr>
 799         <td>waste-wax</td>
 800         <td>Waste wax tank</td>
 801 </tr>
 802 </tbody>
 803 </table></div>
 804
 805 <br>
 806
 807 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 808 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 809 <thead>
 810 <tr>
 811         <th>Keyword</th>
 812         <th>Description</th>
 813 </tr>
 814 </thead>
 815 <tbody>
 816 <tr>
 817         <td>connecting-to-device</td>
 818         <td>Connecting to printer but not printing yet.</td>
 819 </tr>
 820 <tr>
 821         <td>cover-open</td>
 822         <td>The printer's cover is open.</td>
 823 </tr>
 824 <tr>
 825         <td>input-tray-missing</td>
 826         <td>The paper tray is missing.</td>
 827 </tr>
 828 <tr>
 829         <td>marker-supply-empty</td>
 830         <td>The printer is out of ink.</td>
 831 </tr>
 832 <tr>
 833         <td>marker-supply-low</td>
 834         <td>The printer is almost out of ink.</td>
 835 </tr>
 836 <tr>
 837         <td>marker-waste-almost-full</td>
 838         <td>The printer's waste bin is almost full.</td>
 839 </tr>
 840 <tr>
 841         <td>marker-waste-full</td>
 842         <td>The printer's waste bin is full.</td>
 843 </tr>
 844 <tr>
 845         <td>media-empty</td>
 846         <td>The paper tray (any paper tray) is empty.</td>
 847 </tr>
 848 <tr>
 849         <td>media-jam</td>
 850         <td>There is a paper jam.</td>
 851 </tr>
 852 <tr>
 853         <td>media-low</td>
 854         <td>The paper tray (any paper tray) is almost empty.</td>
 855 </tr>
 856 <tr>
 857         <td>media-needed</td>
 858         <td>The paper tray needs to be filled (for a job that is printing).</td>
 859 </tr>
 860 <tr>
 861         <td>paused</td>
 862         <td>Stop the printer.</td>
 863 </tr>
 864 <tr>
 865         <td>timed-out</td>
 866         <td>Unable to connect to printer.</td>
 867 </tr>
 868 <tr>
 869         <td>toner-empty</td>
 870         <td>The printer is out of toner.</td>
 871 </tr>
 872 <tr>
 873         <td>toner-low</td>
 874         <td>The printer is low on toner.</td>
 875 </tr>
 876 </tbody>
 877 </table></div>
 878
 879
 880 <h4><a name="ATTR_STRINGS">Reporting Attribute String Values</a></h4>
 881
 882 <p>When reporting string values using "ATTR:" messages, a filter or backend must take special care to appropriately quote those values. The scheduler uses the CUPS option parsing code for attributes, so the general syntax is:</p>
 883
 884 <pre class="example">
 885 name=simple
 886 name=simple,simple,...
 887 name='complex value'
 888 name="complex value"
 889 name='"complex value"','"complex value"',...
 890 </pre>
 891
 892 <p>Simple values are strings that do not contain spaces, quotes, backslashes, or the comma and can be placed verbatim in the "ATTR:" message, for example:</p>
 893
 894 <pre class="example">
 895 int levels[4] = { 40, 50, 60, 70 }; /* CMYK */
 896
 897 fputs("ATTR: marker-colors=#00FFFF,#FF00FF,#FFFF00,#000000\n", stderr);
 898 fputs("ATTR: marker-high-levels=100,100,100,100\n", stderr);
 899 fprintf(stderr, "ATTR: marker-levels=%d,%d,%d,%d\n", levels[0], levels[1],
 900         levels[2], levels[3], levels[4]);
 901 fputs("ATTR: marker-low-levels=5,5,5,5\n", stderr);
 902 fputs("ATTR: marker-types=toner,toner,toner,toner\n", stderr);
 903 </pre>
 904
 905 <p>Complex values that contains spaces, quotes, backslashes, or the comma must be quoted. For a single value a single set of quotes is sufficient:</p>
 906
 907 <pre class="example">
 908 fputs("ATTR: marker-message='Levels shown are approximate.'\n", stderr);
 909 </pre>
 910
 911 <p>When multiple values are reported, each value must be enclosed by a set of single and double quotes:</p>
 912
 913 <pre class="example">
 914 fputs("ATTR: marker-names='\"Cyan Toner\"','\"Magenta Toner\"',"
 915       "'\"Yellow Toner\"','\"Black Toner\"'\n", stderr);
 916 </pre>
 917
 918 <p>The IPP backend includes a <var>quote_string</var> function that may be used to properly quote a complex value in an "ATTR:" message:</p>
 919
 920 <pre class="example">
 921 static const char *                     /* O - Quoted string */
 922 quote_string(const char *s,             /* I - String */
 923              char       *q,             /* I - Quoted string buffer */
 924              size_t     qsize)          /* I - Size of quoted string buffer */
 925 {
 926   char  *qptr,                          /* Pointer into string buffer */
 927         *qend;                          /* End of string buffer */
 928
 929
 930   qptr = q;
 931   qend = q + qsize - 5;
 932
 933   if (qend &lt; q)
 934   {
 935     *q = '\0';
 936     return (q);
 937   }
 938
 939   *qptr++ = '\'';
 940   *qptr++ = '\"';
 941
 942   while (*s && qptr &lt; qend)
 943   {
 944     if (*s == '\\' || *s == '\"' || *s == '\'')
 945     {
 946       if (qptr &lt; (qend - 4))
 947       {
 948         *qptr++ = '\\';
 949         *qptr++ = '\\';
 950         *qptr++ = '\\';
 951       }
 952       else
 953         break;
 954     }
 955
 956     *qptr++ = *s++;
 957   }
 958
 959   *qptr++ = '\"';
 960   *qptr++ = '\'';
 961   *qptr   = '\0';
 962
 963   return (q);
 964 }
 965 </pre>
 966
 967
 968 <h4><a name="MANAGING_STATE">Managing Printer State in a Filter</a></h4>
 969
 970 <p>Filters are responsible for managing the state keywords they set using
 971 "STATE:" messages. Typically you will update <em>all</em> of the keywords that
 972 are used by the filter at startup, for example:</p>
 973
 974 <pre class="example">
 975 if (foo_condition != 0)
 976   fputs("STATE: +com.example.foo\n", stderr);
 977 else
 978   fputs("STATE: -com.example.foo\n", stderr);
 979
 980 if (bar_condition != 0)
 981   fputs("STATE: +com.example.bar\n", stderr);
 982 else
 983   fputs("STATE: -com.example.bar\n", stderr);
 984 </pre>
 985
 986 <p>Then as conditions change, your filter sends "STATE: +keyword" or "STATE:
 987 -keyword" messages as necessary to set or clear the corresponding keyword,
 988 respectively.</p>
 989
 990 <p>State keywords are often used to notify the user of issues that span across
 991 jobs, for example "media-empty-warning" that indicates one or more paper trays
 992 are empty. These keywords should not be cleared unless the corresponding issue
 993 no longer exists.</p>
 994
 995 <p>Filters should clear job-related keywords on startup and exit so that they
 996 do not remain set between jobs.  For example, "connecting-to-device" is a job
 997 sub-state and not an issue that applies when a job is not printing.</p>
 998
 999 <blockquote><b>Note:</b>
1000
1001 <p>"STATE:" messages often provide visible alerts to the user. For example,
1002 on OS X setting a printer-state-reason value with an "-error" or
1003 "-warning" suffix will cause the printer's dock item to bounce if the
1004 corresponding reason is localized with a cupsIPPReason keyword in the
1005 printer's PPD file.</p>
1006
1007 <p>When providing a vendor-prefixed keyword, <em>always</em> provide the
1008 corresponding standard keyword (if any) to allow clients to respond to the
1009 condition correctly. For example, if you provide a vendor-prefixed keyword
1010 for a low cyan ink condition ("com.example.cyan-ink-low") you must also set the
1011 "marker-supply-low-warning" keyword. In such cases you should also refrain
1012 from localizing the vendor-prefixed keyword in the PPD file - otherwise both
1013 the generic and vendor-specific keyword will be shown in the user
1014 interface.</p>
1015
1016 </blockquote>
1017
1018 <h4><a name="REPORTING_SUPPLIES">Reporting Supply Levels</a></h4>
1019
1020 <p>CUPS tracks several "marker-*" attributes for ink/toner supply level
1021 reporting. These attributes allow applications to display the current supply
1022 levels for a printer without printer-specific software. <a href="#TABLE3">Table 3</a> lists the marker attributes and what they represent.</p>
1023
1024 <p>Filters set marker attributes by sending "ATTR:" messages to stderr. For
1025 example, a filter supporting an inkjet printer with black and tri-color ink
1026 cartridges would use the following to initialize the supply attributes:</p>
1027
1028 <pre class="example">
1029 fputs("ATTR: marker-colors=#000000,#00FFFF#FF00FF#FFFF00\n", stderr);
1030 fputs("ATTR: marker-low-levels=5,10\n", stderr);
1031 fputs("ATTR: marker-names=Black,Tri-Color\n", stderr);
1032 fputs("ATTR: marker-types=ink,ink\n", stderr);
1033 </pre>
1034
1035 <p>Then periodically the filter queries the printer for its current supply
1036 levels and updates them with a separate "ATTR:" message:</p>
1037
1038 <pre class="example">
1039 int black_level, tri_level;
1040 ...
1041 fprintf(stderr, "ATTR: marker-levels=%d,%d\n", black_level, tri_level);
1042 </pre>
1043
1044 <div class='table'><table width='80%' summary='Table 3: Supply Level Attributes'>
1045 <caption>Table 3: <a name='TABLE3'>Supply Level Attributes</a></caption>
1046 <thead>
1047 <tr>
1048         <th>Attribute</th>
1049         <th>Description</th>
1050 </tr>
1051 </thead>
1052 <tbody>
1053 <tr>
1054         <td>marker-colors</td>
1055         <td>A list of comma-separated colors; each color is either "none" or one or
1056         more hex-encoded sRGB colors of the form "#RRGGBB".</td>
1057 </tr>
1058 <tr>
1059         <td>marker-high-levels</td>
1060         <td>A list of comma-separated "almost full" level values from 0 to 100; a
1061         value of 100 should be used for supplies that are consumed/emptied like ink
1062         cartridges.</td>
1063 </tr>
1064 <tr>
1065         <td>marker-levels</td>
1066         <td>A list of comma-separated level values for each supply. A value of -1
1067         indicates the level is unavailable, -2 indicates unknown, and -3 indicates
1068         the level is unknown but has not yet reached capacity. Values from 0 to 100
1069         indicate the corresponding percentage.</td>
1070 </tr>
1071 <tr>
1072         <td>marker-low-levels</td>
1073         <td>A list of comma-separated "almost empty" level values from 0 to 100; a
1074         value of 0 should be used for supplies that are filled like waste ink
1075         tanks.</td>
1076 </tr>
1077 <tr>
1078         <td>marker-message</td>
1079         <td>A human-readable supply status message for the user like "12 pages of
1080         ink remaining."</td>
1081 </tr>
1082 <tr>
1083         <td>marker-names</td>
1084         <td>A list of comma-separated supply names like "Cyan Ink", "Fuser",
1085         etc.</td>
1086 </tr>
1087 <tr>
1088         <td>marker-types</td>
1089         <td>A list of comma-separated supply types; the types are listed in
1090         <a href="#TABLE1">Table 1</a>.</td>
1091 </tr>
1092 </tbody>
1093 </table></div>
1094
1095 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
1096
1097 <p>Filters can communicate with the backend via the
1098 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
1099 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
1100 functions. The
1101 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
1102 reads data that has been sent back from the device and is typically used to
1103 obtain status and configuration information. For example, the following code
1104 polls the backend for back-channel data:</p>
1105
1106 <pre class="example">
1107 #include &lt;cups/cups.h&gt;
1108
1109 char buffer[8192];
1110 ssize_t bytes;
1111
1112 /* Use a timeout of 0.0 seconds to poll for back-channel data */
1113 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
1114 </pre>
1115
1116 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
1117 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
1118 when it is available.</p>
1119
1120 <p>The
1121 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
1122 function allows you to get out-of-band status information and do synchronization
1123 with the device. For example, the following code gets the current IEEE-1284
1124 device ID string from the backend:</p>
1125
1126 <pre class="example">
1127 #include &lt;cups/sidechannel.h&gt;
1128
1129 char data[2049];
1130 int datalen;
1131 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
1132
1133 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
1134    nul-termination... */
1135 datalen = sizeof(data) - 1;
1136
1137 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
1138 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
1139
1140 /* Use the returned value if OK was returned and the length is non-zero */
1141 if (status == CUPS_SC_STATUS_OK &amp;&amp; datalen > 0)
1142   data[datalen] = '\0';
1143 else
1144   data[0] = '\0';
1145 </pre>
1146
1147 <h4><a name="DRAIN_OUTPUT">Forcing All Output to a Printer</a></h4>
1148
1149 <p>The
1150 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
1151 function allows you to tell the backend to send all pending data to the printer.
1152 This is most often needed when sending query commands to the printer. For example:</p>
1153
1154 <pre class="example">
1155 #include &lt;cups/cups.h&gt;
1156 #include &lt;cups/sidechannel.h&gt;
1157
1158 char data[1024];
1159 int datalen = sizeof(data);
1160 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
1161
1162 /* Flush pending output to stdout */
1163 fflush(stdout);
1164
1165 /* Drain output to backend, waiting for up to 30 seconds */
1166 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_DRAIN_OUTPUT, data, &amp;datalen, 30.0);
1167
1168 /* Read the response if the output was sent */
1169 if (status == CUPS_SC_STATUS_OK)
1170 {
1171   ssize_t bytes;
1172
1173   /* Wait up to 10.0 seconds for back-channel data */
1174   bytes = cupsBackChannelRead(data, sizeof(data), 10.0);
1175   /* do something with the data from the printer */
1176 }
1177 </pre>
1178
1179 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
1180
1181 <p>Backends communicate with filters using the reciprocal functions
1182 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
1183 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
1184 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
1185 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
1186
1187 <pre class="example">
1188 #include &lt;cups/cups.h&gt;
1189
1190 char buffer[8192];
1191 ssize_t bytes;
1192
1193 /* Obtain data from printer/device */
1194 ...
1195
1196 /* Use a timeout of 1.0 seconds to give filters a chance to read */
1197 cupsBackChannelWrite(buffer, bytes, 1.0);
1198 </pre>
1199
1200 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
1201 function reads a side-channel command from a filter, driver, or port monitor.
1202 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
1203 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
1204 separate thread for that purpose), or use <code>select</code> or
1205 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
1206 input and output on several file descriptors at the same time.</p>
1207
1208 <p>Once a command is processed, the backend uses the
1209 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
1210 to send its response. For example, the following code shows how to poll for a
1211 side-channel command and respond to it:</p>
1212
1213 <pre class="example">
1214 #include &lt;cups/sidechannel.h&gt;
1215
1216 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
1217 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
1218 char data[2048];
1219 int datalen = sizeof(data);
1220
1221 /* Poll for a command... */
1222 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
1223 {
1224   switch (command)
1225   {
1226     /* handle supported commands, fill data/datalen/status with values as needed */
1227
1228     default :
1229         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
1230         datalen = 0;
1231         break;
1232   }
1233
1234   /* Send a response... */
1235   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
1236 }
1237 </pre>
1238
1239 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
1240
1241 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
1242 status, page counter, and supply levels from most network printers. Every
1243 piece of information is associated with an Object Identifier (OID), and
1244 every printer has a <em>community</em> name associated with it. OIDs can be
1245 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
1246
1247 <p>The two CUPS SNMP functions provide a simple API for querying network
1248 printers through the side-channel interface. Each accepts a string containing
1249 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
1250 along with a timeout for the query.</p>
1251
1252 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
1253 function queries a single OID and returns the value as a string in a buffer
1254 you supply:</p>
1255
1256 <pre class="example">
1257 #include &lt;cups/sidechannel.h&gt;
1258
1259 char data[512];
1260 int datalen = sizeof(data);
1261
1262 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
1263         == CUPS_SC_STATUS_OK)
1264 {
1265   /* Do something with the value */
1266   printf("Page counter is: %s\n", data);
1267 }
1268 </pre>
1269
1270 <p>The
1271 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
1272 function allows you to query a whole group of OIDs, calling a function of your
1273 choice for each OID that is found:</p>
1274
1275 <pre class="example">
1276 #include &lt;cups/sidechannel.h&gt;
1277
1278 void
1279 my_callback(const char *oid, const char *data, int datalen, void *context)
1280 {
1281   /* Do something with the value */
1282   printf("%s=%s\n", oid, data);
1283 }
1284
1285 ...
1286
1287 void *my_data;
1288
1289 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
1290 </pre>
1291
1292 <h2><a name="SANDBOXING">Sandboxing on OS X</a></h2>
1293
1294 <p>Starting with OS X 10.6, filters and backends are run inside a security "sandbox" which further limits (beyond the normal UNIX user/group permissions) what a filter or backend can do. This helps to both secure the printing system from malicious software and enforce the functional separation of components in the CUPS filter chain. What follows is a list of actions that are explicitly allowed for all filters and backends:</p>
1295
1296 <ol>
1297
1298         <li>Reading of files: pursuant to normal UNIX file permissions, filters and backends can read files for the current job from the <var>/private/var/spool/cups</var> directory and other files on mounted filesystems <em>except</em> for user home directories under <var>/Users</var>.</li>
1299
1300         <li>Writing of files: pursuant to normal UNIX file permissions, filters and backends can read/write files to the cache directory specified by the <code>CUPS_CACHEDIR</code> environment variable, to the state directory specified by the <code>CUPS_STATEDIR</code> environment variable, to the temporary directory specified by the <code>TMPDIR</code> environment variable, and under the <var>/private/var/db</var>, <var>/private/var/folders</var>, <var>/private/var/lib</var>, <var>/private/var/mysql</var>, <var>/private/var/run</var>, <var>/private/var/spool</var> (except <var>/private/var/spool/cups</var>), <var>/Library/Application&nbsp;Support</var>, <var>/Library/Caches</var>, <var>/Library/Logs</var>, <var>/Library/Preferences</var>, <var>/Library/WebServer</var>, and <var>/Users/Shared</var> directories.</li>
1301
1302         <li>Execution of programs: pursuant to normal UNIX file permissions, filters and backends can execute any program not located under the <var>/Users</var> directory. Child processes inherit the sandbox and are subject to the same restrictions as the parent.</li>
1303
1304         <li>Bluetooth and USB: backends can access Bluetooth and USB printers through IOKit. <em>Filters cannot access Bluetooth and USB printers directly.</em></li>
1305
1306         <li>Network: filters and backends can access UNIX domain sockets under the <var>/private/tmp</var>, <var>/private/var/run</var>, and <var>/private/var/tmp</var> directories. Backends can also create IPv4 and IPv6 TCP (outgoing) and UDP (incoming and outgoing) socket, and bind to local source ports. <em>Filters cannot directly create IPv4 and IPv6 TCP or UDP sockets.</em></li>
1307
1308         <li>Notifications: filters and backends can send notifications via the Darwin <code>notify_post()</code> API.</li>
1309
1310 </ol>
1311
1312 <blockquote><b>Note:</b> The sandbox profile used in CUPS 2.0 still allows some actions that are not listed above - these privileges will be removed over time until the profile matches the list above.</blockquote>
1313 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
1314 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/OS X 10.5&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
1315 <p class="description">Read data from the backchannel.</p>
1316 <p class="code">
1317 ssize_t cupsBackChannelRead (<br>
1318 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
1319 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1320 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1321 );</p>
1322 <h4 class="parameters">Parameters</h4>
1323 <dl>
1324 <dt>buffer</dt>
1325 <dd class="description">Buffer to read into</dd>
1326 <dt>bytes</dt>
1327 <dd class="description">Bytes to read</dd>
1328 <dt>timeout</dt>
1329 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
1330 </dl>
1331 <h4 class="returnvalue">Return Value</h4>
1332 <p class="description">Bytes read or -1 on error</p>
1333 <h4 class="discussion">Discussion</h4>
1334 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
1335 parameter controls how many seconds to wait for the data - use 0.0 to
1336 return immediately if there is no data, -1.0 to wait for data indefinitely.
1337
1338 </p>
1339 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/OS X 10.5&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
1340 <p class="description">Write data to the backchannel.</p>
1341 <p class="code">
1342 ssize_t cupsBackChannelWrite (<br>
1343 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
1344 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1345 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1346 );</p>
1347 <h4 class="parameters">Parameters</h4>
1348 <dl>
1349 <dt>buffer</dt>
1350 <dd class="description">Buffer to write</dd>
1351 <dt>bytes</dt>
1352 <dd class="description">Bytes to write</dd>
1353 <dt>timeout</dt>
1354 <dd class="description">Timeout in seconds, typically 1.0</dd>
1355 </dl>
1356 <h4 class="returnvalue">Return Value</h4>
1357 <p class="description">Bytes written or -1 on error</p>
1358 <h4 class="discussion">Discussion</h4>
1359 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
1360 controls how many seconds to wait for the data to be written - use
1361 0.0 to return immediately if the data cannot be written, -1.0 to wait
1362 indefinitely.
1363
1364 </p>
1365 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/OS X 10.5&nbsp;</span><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
1366 <p class="description">Get the device URI for a backend.</p>
1367 <p class="code">
1368 const char *cupsBackendDeviceURI (<br>
1369 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
1370 );</p>
1371 <h4 class="parameters">Parameters</h4>
1372 <dl>
1373 <dt>argv</dt>
1374 <dd class="description">Command-line arguments</dd>
1375 </dl>
1376 <h4 class="returnvalue">Return Value</h4>
1377 <p class="description">Device URI or <code>NULL</code></p>
1378 <h4 class="discussion">Discussion</h4>
1379 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
1380 function returns the device URI passed in the DEVICE_URI environment
1381 variable or the device URI passed in argv[0], whichever is found
1382 first.
1383
1384 </p>
1385 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span><a name="cupsBackendReport">cupsBackendReport</a></h3>
1386 <p class="description">Write a device line from a backend.</p>
1387 <p class="code">
1388 void cupsBackendReport (<br>
1389 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
1390 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
1391 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
1392 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
1393 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
1394 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
1395 );</p>
1396 <h4 class="parameters">Parameters</h4>
1397 <dl>
1398 <dt>device_scheme</dt>
1399 <dd class="description">device-scheme string</dd>
1400 <dt>device_uri</dt>
1401 <dd class="description">device-uri string</dd>
1402 <dt>device_make_and_model</dt>
1403 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
1404 <dt>device_info</dt>
1405 <dd class="description">device-info string or <code>NULL</code></dd>
1406 <dt>device_id</dt>
1407 <dd class="description">device-id string or <code>NULL</code></dd>
1408 <dt>device_location</dt>
1409 <dd class="description">device-location string or <code>NULL</code></dd>
1410 </dl>
1411 <h4 class="discussion">Discussion</h4>
1412 <p class="discussion">This function writes a single device line to stdout for a backend.
1413 It handles quoting of special characters in the device-make-and-model,
1414 device-info, device-id, and device-location strings.
1415
1416 </p>
1417 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/OS X 10.5&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
1418 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
1419 <p class="code">
1420 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
1421 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1422 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1423 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1424 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1425 );</p>
1426 <h4 class="parameters">Parameters</h4>
1427 <dl>
1428 <dt>command</dt>
1429 <dd class="description">Command to send</dd>
1430 <dt>data</dt>
1431 <dd class="description">Response data buffer pointer</dd>
1432 <dt>datalen</dt>
1433 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1434 <dt>timeout</dt>
1435 <dd class="description">Timeout in seconds</dd>
1436 </dl>
1437 <h4 class="returnvalue">Return Value</h4>
1438 <p class="description">Status of command</p>
1439 <h4 class="discussion">Discussion</h4>
1440 <p class="discussion">This function is normally only called by filters, drivers, or port
1441 monitors in order to communicate with the backend used by the current
1442 printer.  Programs must be prepared to handle timeout or &quot;not
1443 implemented&quot; status codes, which indicate that the backend or device
1444 do not support the specified side-channel command.<br>
1445 <br>
1446 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1447 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1448 update the value to contain the number of data bytes in the buffer.
1449
1450 </p>
1451 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/OS X 10.5&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1452 <p class="description">Read a side-channel message.</p>
1453 <p class="code">
1454 int cupsSideChannelRead (<br>
1455 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1456 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1457 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1458 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1459 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1460 );</p>
1461 <h4 class="parameters">Parameters</h4>
1462 <dl>
1463 <dt>command</dt>
1464 <dd class="description">Command code</dd>
1465 <dt>status</dt>
1466 <dd class="description">Status code</dd>
1467 <dt>data</dt>
1468 <dd class="description">Data buffer pointer</dd>
1469 <dt>datalen</dt>
1470 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1471 <dt>timeout</dt>
1472 <dd class="description">Timeout in seconds</dd>
1473 </dl>
1474 <h4 class="returnvalue">Return Value</h4>
1475 <p class="description">0 on success, -1 on error</p>
1476 <h4 class="discussion">Discussion</h4>
1477 <p class="discussion">This function is normally only called by backend programs to read
1478 commands from a filter, driver, or port monitor program.  The
1479 caller must be prepared to handle incomplete or invalid messages
1480 and return the corresponding status codes.<br>
1481 <br>
1482 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1483 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1484 update the value to contain the number of data bytes in the buffer.
1485
1486 </p>
1487 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1488 <p class="description">Query a SNMP OID's value.</p>
1489 <p class="code">
1490 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1491 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1492 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1493 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1494 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1495 );</p>
1496 <h4 class="parameters">Parameters</h4>
1497 <dl>
1498 <dt>oid</dt>
1499 <dd class="description">OID to query</dd>
1500 <dt>data</dt>
1501 <dd class="description">Buffer for OID value</dd>
1502 <dt>datalen</dt>
1503 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1504 <dt>timeout</dt>
1505 <dd class="description">Timeout in seconds</dd>
1506 </dl>
1507 <h4 class="returnvalue">Return Value</h4>
1508 <p class="description">Query status</p>
1509 <h4 class="discussion">Discussion</h4>
1510 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1511 filter, port monitor, or backend using the default community name.<br>
1512 <br>
1513 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1514 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1515 supported and must be converted to their numeric forms.<br>
1516 <br>
1517 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1518 buffer to hold the OID value as a string. HEX-String (binary) values are
1519 converted to hexadecimal strings representing the binary data, while
1520 NULL-Value and unknown OID types are returned as the empty string.
1521 The returned &quot;datalen&quot; does not include the trailing nul.
1522
1523 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1524 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1525 the printer does not respond to the SNMP query.
1526
1527 </p>
1528 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1529 <p class="description">Query multiple SNMP OID values.</p>
1530 <p class="code">
1531 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1532 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1533 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1534 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1535 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1536 );</p>
1537 <h4 class="parameters">Parameters</h4>
1538 <dl>
1539 <dt>oid</dt>
1540 <dd class="description">First numeric OID to query</dd>
1541 <dt>timeout</dt>
1542 <dd class="description">Timeout for each query in seconds</dd>
1543 <dt>cb</dt>
1544 <dd class="description">Function to call with each value</dd>
1545 <dt>context</dt>
1546 <dd class="description">Application-defined pointer to send to callback</dd>
1547 </dl>
1548 <h4 class="returnvalue">Return Value</h4>
1549 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1550 <h4 class="discussion">Discussion</h4>
1551 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1552 of the filter, port monitor, or backend using the default community name.
1553 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1554 the callback function you provide.<br>
1555 <br>
1556 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1557 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1558 supported and must be converted to their numeric forms.<br>
1559 <br>
1560 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1561 time will depend on the number of OID values found and the time required
1562 for each query.<br>
1563 <br>
1564 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1565 is an application-defined pointer that is sent to the callback function
1566 along with the OID and current data. The data passed to the callback is the
1567 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1568
1569 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1570 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1571 the printer does not respond to the first SNMP query.
1572
1573 </p>
1574 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/OS X 10.5&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1575 <p class="description">Write a side-channel message.</p>
1576 <p class="code">
1577 int cupsSideChannelWrite (<br>
1578 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1579 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1580 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1581 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1582 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1583 );</p>
1584 <h4 class="parameters">Parameters</h4>
1585 <dl>
1586 <dt>command</dt>
1587 <dd class="description">Command code</dd>
1588 <dt>status</dt>
1589 <dd class="description">Status code</dd>
1590 <dt>data</dt>
1591 <dd class="description">Data buffer pointer</dd>
1592 <dt>datalen</dt>
1593 <dd class="description">Number of bytes of data</dd>
1594 <dt>timeout</dt>
1595 <dd class="description">Timeout in seconds</dd>
1596 </dl>
1597 <h4 class="returnvalue">Return Value</h4>
1598 <p class="description">0 on success, -1 on error</p>
1599 <h4 class="discussion">Discussion</h4>
1600 <p class="discussion">This function is normally only called by backend programs to send
1601 responses to a filter, driver, or port monitor program.
1602
1603 </p>
1604 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1605 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1606 <p class="description">Backend exit codes</p>
1607 <p class="code">
1608 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1609 </p>
1610 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1611 <p class="description">Bidirectional capabilities</p>
1612 <p class="code">
1613 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1614 </p>
1615 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1616 <p class="description">Request command codes</p>
1617 <p class="code">
1618 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1619 </p>
1620 <h3 class="typedef"><a name="cups_sc_connected_t">cups_sc_connected_t</a></h3>
1621 <p class="description">Connectivity values</p>
1622 <p class="code">
1623 typedef enum <a href="#cups_sc_connected_e">cups_sc_connected_e</a> cups_sc_connected_t;
1624 </p>
1625 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1626 <p class="description">Printer state bits</p>
1627 <p class="code">
1628 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1629 </p>
1630 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1631 <p class="description">Response status codes</p>
1632 <p class="code">
1633 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1634 </p>
1635 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1636 <p class="description">SNMP walk callback</p>
1637 <p class="code">
1638 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1639 </p>
1640 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1641 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1642 <p class="description">Backend exit codes</p>
1643 <h4 class="constants">Constants</h4>
1644 <dl>
1645 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1646 <dd class="description">Job failed, authentication required</dd>
1647 <dt>CUPS_BACKEND_CANCEL </dt>
1648 <dd class="description">Job failed, cancel job</dd>
1649 <dt>CUPS_BACKEND_FAILED </dt>
1650 <dd class="description">Job failed, use error-policy</dd>
1651 <dt>CUPS_BACKEND_HOLD </dt>
1652 <dd class="description">Job failed, hold job</dd>
1653 <dt>CUPS_BACKEND_OK </dt>
1654 <dd class="description">Job completed successfully</dd>
1655 <dt>CUPS_BACKEND_RETRY </dt>
1656 <dd class="description">Job failed, retry this job later</dd>
1657 <dt>CUPS_BACKEND_RETRY_CURRENT </dt>
1658 <dd class="description">Job failed, retry this job immediately</dd>
1659 <dt>CUPS_BACKEND_STOP </dt>
1660 <dd class="description">Job failed, stop queue</dd>
1661 </dl>
1662 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1663 <p class="description">Bidirectional capability values</p>
1664 <h4 class="constants">Constants</h4>
1665 <dl>
1666 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1667 <dd class="description">Bidirectional I/O is not supported</dd>
1668 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1669 <dd class="description">Bidirectional I/O is supported</dd>
1670 </dl>
1671 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1672 <p class="description">Request command codes</p>
1673 <h4 class="constants">Constants</h4>
1674 <dl>
1675 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1676 <dd class="description">Drain all pending output</dd>
1677 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1678 <dd class="description">Return bidirectional capabilities</dd>
1679 <dt>CUPS_SC_CMD_GET_CONNECTED <span class="info">&nbsp;CUPS 1.5/OS X 10.7&nbsp;</span></dt>
1680 <dd class="description">Return whether the backend is &quot;connected&quot; to the printer </dd>
1681 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1682 <dd class="description">Return the IEEE-1284 device ID</dd>
1683 <dt>CUPS_SC_CMD_GET_STATE </dt>
1684 <dd class="description">Return the device state</dd>
1685 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span></dt>
1686 <dd class="description">Query an SNMP OID </dd>
1687 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span></dt>
1688 <dd class="description">Query the next SNMP OID </dd>
1689 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1690 <dd class="description">Do a soft reset</dd>
1691 </dl>
1692 <h3 class="enumeration"><a name="cups_sc_connected_e">cups_sc_connected_e</a></h3>
1693 <p class="description">Connectivity values</p>
1694 <h4 class="constants">Constants</h4>
1695 <dl>
1696 <dt>CUPS_SC_CONNECTED </dt>
1697 <dd class="description">Backend is &quot;connected&quot; to printer</dd>
1698 <dt>CUPS_SC_NOT_CONNECTED </dt>
1699 <dd class="description">Backend is not &quot;connected&quot; to printer</dd>
1700 </dl>
1701 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1702 <p class="description">Printer state bits</p>
1703 <h4 class="constants">Constants</h4>
1704 <dl>
1705 <dt>CUPS_SC_STATE_BUSY </dt>
1706 <dd class="description">Device is busy</dd>
1707 <dt>CUPS_SC_STATE_ERROR </dt>
1708 <dd class="description">Other error condition</dd>
1709 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1710 <dd class="description">Toner/ink out condition</dd>
1711 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1712 <dd class="description">Toner/ink low condition</dd>
1713 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1714 <dd class="description">Paper out condition</dd>
1715 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1716 <dd class="description">Paper low condition</dd>
1717 <dt>CUPS_SC_STATE_OFFLINE </dt>
1718 <dd class="description">Device is offline</dd>
1719 <dt>CUPS_SC_STATE_ONLINE </dt>
1720 <dd class="description">Device is online</dd>
1721 </dl>
1722 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1723 <p class="description">Response status codes</p>
1724 <h4 class="constants">Constants</h4>
1725 <dl>
1726 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1727 <dd class="description">The command/response message was invalid</dd>
1728 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1729 <dd class="description">An I/O error occurred</dd>
1730 <dt>CUPS_SC_STATUS_NONE </dt>
1731 <dd class="description">No status</dd>
1732 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1733 <dd class="description">Command not implemented</dd>
1734 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1735 <dd class="description">The device did not respond</dd>
1736 <dt>CUPS_SC_STATUS_OK </dt>
1737 <dd class="description">Operation succeeded</dd>
1738 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1739 <dd class="description">The backend did not respond</dd>
1740 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1741 <dd class="description">Response too big</dd>
1742 </dl>
1743 </div>
1744 </body>
1745 </html>