doc/help/api-filter.html

   1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
   2 <html>
   3 <!-- SECTION: Programming -->
   4 <head>
   5         <title>Filter and Backend Programming   </title>
   6         <meta name="keywords" content="Programming">
   7         <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
   8         <meta name="creator" content="Mini-XML v2.7">
   9 <style type="text/css"><!--
  10 BODY {
  11   font-family: lucida grande, geneva, helvetica, arial, sans-serif;
  12 }
  13
  14 H1, H2, H3, H4, H5, H6, P, TD, TH {
  15   font-family: lucida grande, geneva, helvetica, arial, sans-serif;
  16 }
  17
  18 KBD {
  19   font-family: monaco, courier, monospace;
  20   font-weight: bold;
  21 }
  22
  23 PRE {
  24   font-family: monaco, courier, monospace;
  25 }
  26
  27 PRE.command {
  28   border: dotted thin #7f7f7f;
  29   margin-left: 36pt;
  30   padding: 10px;
  31 }
  32
  33 P.compact {
  34   margin: 0;
  35 }
  36
  37 P.example {
  38   font-style: italic;
  39   margin-left: 36pt;
  40 }
  41
  42 DL.man DD {
  43   margin-left: 5em;
  44 }
  45
  46 DL.man DT {
  47   margin-left: 0;
  48 }
  49
  50 PRE.man {
  51   margin: 0;
  52 }
  53
  54 PRE.example {
  55   background: #eeeeee;
  56   border: dotted thin #999999;
  57   margin-left: 36pt;
  58   padding: 10pt;
  59 }
  60
  61 PRE.command EM, PRE.example EM {
  62   font-family: lucida grande, geneva, helvetica, arial, sans-serif;
  63 }
  64
  65 P.command {
  66   font-family: monaco, courier, monospace;
  67   margin-left: 36pt;
  68 }
  69
  70 P.formula {
  71   font-style: italic;
  72   margin-left: 36pt;
  73 }
  74
  75 BLOCKQUOTE {
  76   background: #eeeeee;
  77   border: solid thin #999999;
  78   padding: 10pt;
  79 }
  80
  81 A IMG {
  82   border: none;
  83 }
  84
  85 A:link:hover IMG {
  86   background: #f0f0f0;
  87   border-radius: 10px;
  88   -moz-border-radius: 10px;
  89 }
  90
  91 A:link, A:visited {
  92   font-weight: inherit;
  93   text-decoration: none;
  94 }
  95
  96 A:link:hover, A:visited:hover, A:active {
  97   text-decoration: underline;
  98 }
  99
 100 SUB, SUP {
 101   font-size: 50%;
 102 }
 103
 104 TR.data, TD.data, TR.data TD {
 105   margin-top: 10pt;
 106   padding: 5pt;
 107   border-bottom: solid 1pt #999999;
 108 }
 109
 110 TR.data TH {
 111   border-bottom: solid 1pt #999999;
 112   padding-top: 10pt;
 113   padding-left: 5pt;
 114   text-align: left;
 115 }
 116
 117 DIV.table TABLE {
 118   border: solid thin #999999;
 119   border-collapse: collapse;
 120   border-spacing: 0;
 121   margin-left: auto;
 122   margin-right: auto;
 123 }
 124
 125 DIV.table CAPTION {
 126   caption-side: top;
 127   font-size: 120%;
 128   font-style: italic;
 129   font-weight: bold;
 130   margin-left: auto;
 131   margin-right: auto;
 132 }
 133
 134 DIV.table TABLE TD {
 135   border: solid thin #cccccc;
 136   padding-top: 5pt;
 137 }
 138
 139 DIV.table TABLE TH {
 140   background: #cccccc;
 141   border: none;
 142   border-bottom: solid thin #999999;
 143 }
 144
 145 DIV.figure TABLE {
 146   margin-left: auto;
 147   margin-right: auto;
 148 }
 149
 150 DIV.figure CAPTION {
 151   caption-side: bottom;
 152   font-size: 120%;
 153   font-style: italic;
 154   font-weight: bold;
 155   margin-left: auto;
 156   margin-right: auto;
 157 }
 158
 159 TH.label {
 160   text-align: right;
 161   vertical-align: top;
 162 }
 163
 164 TH.sublabel {
 165   text-align: right;
 166   font-weight: normal;
 167 }
 168
 169 HR {
 170   border: solid thin;
 171 }
 172
 173 SPAN.info {
 174   background: black;
 175   border: thin solid black;
 176   color: white;
 177   font-size: 80%;
 178   font-style: italic;
 179   font-weight: bold;
 180   white-space: nowrap;
 181 }
 182
 183 H2 SPAN.info, H3 SPAN.info, H4 SPAN.info {
 184   float: right;
 185   font-size: 100%;
 186 }
 187
 188 H1.title {
 189 }
 190
 191 H2.title, H3.title {
 192   border-bottom: solid 2pt #000000;
 193 }
 194
 195 DIV.indent, TABLE.indent {
 196   margin-top: 2em;
 197   margin-left: auto;
 198   margin-right: auto;
 199   width: 90%;
 200 }
 201
 202 TABLE.indent {
 203   border-collapse: collapse;
 204 }
 205
 206 TABLE.indent TD, TABLE.indent TH {
 207   padding: 0;
 208 }
 209
 210 TABLE.list {
 211   border-collapse: collapse;
 212   margin-left: auto;
 213   margin-right: auto;
 214   width: 90%;
 215 }
 216
 217 TABLE.list TH {
 218   background: white;
 219   border-bottom: solid thin #cccccc;
 220   color: #444444;
 221   padding-top: 10pt;
 222   padding-left: 5pt;
 223   text-align: left;
 224   vertical-align: bottom;
 225   white-space: nowrap;
 226 }
 227
 228 TABLE.list TH A {
 229   color: #4444cc;
 230 }
 231
 232 TABLE.list TD {
 233   border-bottom: solid thin #eeeeee;
 234   padding-top: 5pt;
 235   padding-left: 5pt;
 236 }
 237
 238 TABLE.list TR:nth-child(even) {
 239   background: #f8f8f8;
 240 }
 241
 242 TABLE.list TR:nth-child(odd) {
 243   background: #f4f4f4;
 244 }
 245
 246 DT {
 247   margin-left: 36pt;
 248   margin-top: 12pt;
 249 }
 250
 251 DD {
 252   margin-left: 54pt;
 253 }
 254
 255 DL.category DT {
 256   font-weight: bold;
 257 }
 258
 259 P.summary {
 260   margin-left: 36pt;
 261   font-family: monaco, courier, monospace;
 262 }
 263
 264 DIV.summary TABLE {
 265   border: solid thin #999999;
 266   border-collapse: collapse;
 267   border-spacing: 0;
 268   margin: 10px;
 269 }
 270
 271 DIV.summary TABLE TD, DIV.summary TABLE TH {
 272   border: solid thin #999999;
 273   padding: 5px;
 274   text-align: left;
 275   vertical-align: top;
 276 }
 277
 278 DIV.summary TABLE THEAD TH {
 279   background: #eeeeee;
 280 }
 281
 282 /* API documentation styles... */
 283 div.body h1 {
 284   margin: 0;
 285 }
 286 div.body h2 {
 287   margin-top: 1.5em;
 288 }
 289 div.body h3, div.body h4, div.body h5 {
 290   margin-bottom: 0.5em;
 291   margin-top: 1.5em;
 292 }
 293 .class, .enumeration, .function, .struct, .typedef, .union {
 294   border-bottom: solid thin #999999;
 295   margin-bottom: 0;
 296   margin-top: 2em;
 297 }
 298 .description {
 299   margin-top: 0.5em;
 300 }
 301 code, p.code, pre, ul.code li {
 302   font-family: monaco, courier, monospace;
 303   font-size: 90%;
 304 }
 305 ul.code, ul.contents, ul.subcontents {
 306   list-style-type: none;
 307   margin: 0;
 308   padding-left: 0;
 309 }
 310 ul.code li {
 311   margin: 0;
 312 }
 313 ul.contents > li {
 314   margin-top: 1em;
 315 }
 316 ul.contents li ul.code, ul.contents li ul.subcontents {
 317   padding-left: 2em;
 318 }
 319 div.body dl {
 320   margin-left: 0;
 321   margin-top: 0;
 322 }
 323 div.body dt {
 324   font-style: italic;
 325   margin-left: 0;
 326   margin-top: 0;
 327 }
 328 div.body dd {
 329   margin-bottom: 0.5em;
 330 }
 331
 332 /* This is just for the HTML files generated with the framedhelp target */
 333 div.contents {
 334   background: #e8e8e8;
 335   border: solid thin black;
 336   padding: 10px;
 337 }
 338 div.contents h1 {
 339   font-size: 110%;
 340 }
 341 div.contents h2 {
 342   font-size: 100%;
 343 }
 344 div.contents ul.contents {
 345   font-size: 80%;
 346 }
 347 div.contents ul.subcontents li {
 348   margin-left: 1em;
 349   text-indent: -1em;
 350 }
 351 --></style>
 352 </head>
 353 <body>
 354 <div class='body'>
 355 <!--
 356   "$Id: api-filter.header 7616 2008-05-28 00:34:13Z mike $"
 357
 358   Filter and backend programming header for CUPS.
 359
 360   Copyright 2008-2014 by Apple Inc.
 361
 362   These coded instructions, statements, and computer programs are the
 363   property of Apple Inc. and are protected by Federal copyright
 364   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 365   which should have been included with this file.  If this file is
 366   file is missing or damaged, see the license at "http://www.cups.org/".
 367 -->
 368
 369 <h1 class='title'>Filter and Backend Programming</h1>
 370
 371 <div class='summary'><table summary='General Information'>
 372 <thead>
 373 <tr>
 374         <th>Headers</th>
 375         <th>cups/backend.h<br>
 376         cups/sidechannel.h</th>
 377 </tr>
 378 </thead>
 379 <tbody>
 380 <tr>
 381         <th>Library</th>
 382         <td>-lcups</td>
 383 </tr>
 384 <tr>
 385         <th>See Also</th>
 386         <td>Programming: <a href='api-overview.html' target='_top'>Introduction to CUPS Programming</a><br>
 387         Programming: <a href='api-cups.html' target='_top'>CUPS API</a><br>
 388         Programming: <a href='api-ppd.html' target='_top'>PPD API</a><br>
 389         Programming: <a href='api-raster.html' target='_top'>Raster API</a><br>
 390         Programming: <a href='postscript-driver.html' target='_top'>Developing PostScript Printer Drivers</a><br>
 391         Programming: <a href='raster-driver.html' target='_top'>Developing Raster Printer Drivers</a><br>
 392         Specifications: <a href='spec-design.html' target='_top'>CUPS Design Description</a></td>
 393 </tr>
 394 </tbody>
 395 </table></div>
 396 <h2 class="title">Contents</h2>
 397 <ul class="contents">
 398 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 399         <li><a href="#SECURITY">Security Considerations</a></li>
 400         <li><a href="#SIGNALS">Canceled Jobs and Signal Handling</a></li>
 401         <li><a href="#PERMISSIONS">File Permissions</a></li>
 402         <li><a href="#TEMPFILES">Temporary Files</a></li>
 403         <li><a href="#COPIES">Copy Generation</a></li>
 404         <li><a href="#EXITCODES">Exit Codes</a></li>
 405         <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 406         <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 407         <li><a href="#COMMUNICATING_BACKEND">Communicating with the Backend</a></li>
 408         <li><a href="#COMMUNICATING_FILTER">Communicating with Filters</a></li>
 409         <li><a href="#SNMP">Doing SNMP Queries with Network Printers</a></li>
 410 </ul></li>
 411 <li><a href="#SANDBOXING">Sandboxing on OS X</a></li>
 412 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 413         <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 414         <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 415         <li><a href="#cupsBackendDeviceURI" title="Get the device URI for a backend.">cupsBackendDeviceURI</a></li>
 416         <li><a href="#cupsBackendReport" title="Write a device line from a backend.">cupsBackendReport</a></li>
 417         <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 418         <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 419         <li><a href="#cupsSideChannelSNMPGet" title="Query a SNMP OID's value.">cupsSideChannelSNMPGet</a></li>
 420         <li><a href="#cupsSideChannelSNMPWalk" title="Query multiple SNMP OID values.">cupsSideChannelSNMPWalk</a></li>
 421         <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 422 </ul></li>
 423 <li><a href="#TYPES">Data Types</a><ul class="code">
 424         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 425         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 426         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 427         <li><a href="#cups_sc_connected_t" title="Connectivity values">cups_sc_connected_t</a></li>
 428         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 429         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 430         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 431 </ul></li>
 432 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 433         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 434         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 435         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 436         <li><a href="#cups_sc_connected_e" title="Connectivity values">cups_sc_connected_e</a></li>
 437         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 438         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 439 </ul></li>
 440 </ul>
 441 <!--
 442   "$Id: api-filter.shtml 7677 2008-06-19 23:22:19Z mike $"
 443
 444   Filter and backend programming introduction for CUPS.
 445
 446   Copyright 2007-2014 by Apple Inc.
 447   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 448
 449   These coded instructions, statements, and computer programs are the
 450   property of Apple Inc. and are protected by Federal copyright
 451   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 452   which should have been included with this file.  If this file is
 453   file is missing or damaged, see the license at "http://www.cups.org/".
 454 -->
 455
 456 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 457
 458 <p>Filters (which include printer drivers and port monitors) and backends
 459 are used to convert job files to a printable format and send that data to the
 460 printer itself. All of these programs use a common interface for processing
 461 print jobs and communicating status information to the scheduler. Each is run
 462 with a standard set of command-line arguments:<p>
 463
 464 <dl class="code">
 465
 466         <dt>argv[1]</dt>
 467         <dd>The job ID</dd>
 468
 469         <dt>argv[2]</dt>
 470         <dd>The user printing the job</dd>
 471
 472         <dt>argv[3]</dt>
 473         <dd>The job name/title</dd>
 474
 475         <dt>argv[4]</dt>
 476         <dd>The number of copies to print</dd>
 477
 478         <dt>argv[5]</dt>
 479         <dd>The options that were provided when the job was submitted</dd>
 480
 481         <dt>argv[6]</dt>
 482         <dd>The file to print (first program only)</dd>
 483 </dl>
 484
 485 <p>The scheduler runs one or more of these programs to print any given job. The
 486 first filter reads from the print file and writes to the standard output, while
 487 the remaining filters read from the standard input and write to the standard
 488 output. The backend is the last filter in the chain and writes to the
 489 device.</p>
 490
 491 <p>Filters are always run as a non-privileged user, typically "lp", with no
 492 connection to the user's desktop. Backends are run either as a non-privileged
 493 user or as root if the file permissions do not allow user or group execution.
 494 The <a href="#PERMISSIONS">file permissions</a> section talks about this in
 495 more detail.</p>
 496
 497 <h3><a name="SECURITY">Security Considerations</a></h3>
 498
 499 <p>It is always important to use security programming practices. Filters and
 500 most backends are run as a non-privileged user, so the major security
 501 consideration is resource utilization - filters should not depend on unlimited
 502 amounts of CPU, memory, or disk space, and should protect against conditions
 503 that could lead to excess usage of any resource like infinite loops and
 504 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 505 specify an arbitrary file path to a separator page, template, or other file
 506 used by the filter since that can lead to an unauthorized disclosure of
 507 information. <em>Always</em> treat input as suspect and validate it!</p>
 508
 509 <p>If you are developing a backend that runs as root, make sure to check for
 510 potential buffer overflows, integer under/overflow conditions, and file
 511 accesses since these can lead to privilege escalations. When writing files,
 512 always validate the file path and <em>never</em> allow a user to determine
 513 where to store a file.</p>
 514
 515 <blockquote><b>Note:</b>
 516
 517 <p><em>Never</em> write files to a user's home directory. Aside from the
 518 security implications, CUPS is a network print service and as such the network
 519 user may not be the same as the local user and/or there may not be a local home
 520 directory to write to.</p>
 521
 522 <p>In addition, some operating systems provide additional security mechanisms
 523 that further limit file system access, even for backends running as root. On
 524 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>
 525 </blockquote>
 526
 527 <h3><a name="SIGNALS">Canceled Jobs and Signal Handling</a></h3>
 528
 529 <p>The scheduler sends <code>SIGTERM</code> when a printing job is canceled or
 530 held. Filters, backends, and port monitors <em>must</em> catch
 531 <code>SIGTERM</code> and perform any cleanup necessary to produce a valid output
 532 file or return the printer to a known good state. The recommended behavior is to
 533 end the output on the current page, preferably on the current line or object
 534 being printed.</p>
 535
 536 <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>
 537
 538 <pre class="example">
 539 #include &lt;signal.h&gt;>
 540
 541 ...
 542
 543 int
 544 main(int argc, char *argv[])
 545 {
 546   signal(SIGPIPE, SIG_IGN);
 547
 548   ...
 549 }
 550 </pre>
 551
 552 <h3><a name="PERMISSIONS">File Permissions</a></h3>
 553
 554 <p>For security reasons, CUPS will only run filters and backends that are owned
 555 by root and do not have world or group write permissions. The recommended
 556 permissions for filters and backends are 0555 - read and execute but no write.
 557 Backends that must run as root should use permissions of 0500 - read and execute
 558 by root, no access for other users. Write permissions can be enabled for the
 559 root user only.</p>
 560
 561 <p>To avoid a warning message, the directory containing your filter(s) must also
 562 be owned by root and have world and group write disabled - permissions of 0755
 563 or 0555 are strongly encouraged.</p>
 564
 565 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 566
 567 <p>Temporary files should be created in the directory specified by the
 568 "TMPDIR" environment variable. The
 569 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 570 used to safely create temporary files in this directory.</p>
 571
 572 <h3><a name="COPIES">Copy Generation</a></h3>
 573
 574 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 575 of the input file. In general, you should only generate copies if the
 576 <em>filename</em> argument is supplied. The only exception to this are
 577 filters that produce device-independent PostScript output, since the PostScript
 578 filter <var>pstops</var> is responsible for generating copies of PostScript
 579 files.</p>
 580
 581 <h3><a name="EXITCODES">Exit Codes</a></h3>
 582
 583 <p>Filters must exit with status 0 when they successfully generate print data
 584 or 1 when they encounter an error. Backends can return any of the
 585 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 586
 587 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 588
 589 <p>The following environment variables are defined by the printing system
 590 when running print filters and backends:</p>
 591
 592 <dl class="code">
 593
 594         <dt>APPLE_LANGUAGE</dt>
 595         <dd>The Apple language identifier associated with the job
 596         (OS X only).</dd>
 597
 598         <dt>CHARSET</dt>
 599         <dd>The job character set, typically "utf-8".</dd>
 600
 601         <dt>CLASS</dt>
 602         <dd>When a job is submitted to a printer class, contains the name of
 603         the destination printer class. Otherwise this environment
 604         variable will not be set.</dd>
 605
 606         <dt>CONTENT_TYPE</dt>
 607         <dd>The MIME type associated with the file (e.g.
 608         application/postscript).</dd>
 609
 610         <dt>CUPS_CACHEDIR</dt>
 611         <dd>The directory where cache files can be stored. Cache files can be
 612         used to retain information between jobs or files in a job.</dd>
 613
 614         <dt>CUPS_DATADIR</dt>
 615         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 616
 617         <dt>CUPS_FILETYPE</dt>
 618         <dd>The type of file being printed: "job-sheet" for a banner page and
 619         "document" for a regular print file.</dd>
 620
 621         <dt>CUPS_SERVERROOT</dt>
 622         <dd>The root directory of the server.</dd>
 623
 624         <dt>DEVICE_URI</dt>
 625         <dd>The device-uri associated with the printer.</dd>
 626
 627         <dt>FINAL_CONTENT_TYPE</dt>
 628         <dd>The MIME type associated with the printer (e.g.
 629         application/vnd.cups-postscript).</dd>
 630
 631         <dt>LANG</dt>
 632         <dd>The language locale associated with the job.</dd>
 633
 634         <dt>PPD</dt>
 635         <dd>The full pathname of the PostScript Printer Description (PPD)
 636         file for this printer.</dd>
 637
 638         <dt>PRINTER</dt>
 639         <dd>The queue name of the class or printer.</dd>
 640
 641         <dt>RIP_CACHE</dt>
 642         <dd>The recommended amount of memory to use for Raster Image
 643         Processors (RIPs).</dd>
 644
 645         <dt>TMPDIR</dt>
 646         <dd>The directory where temporary files should be created.</dd>
 647
 648 </dl>
 649
 650 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 651
 652 <p>Filters and backends communicate with the scheduler by writing messages
 653 to the standard error file. The scheduler reads messages from all filters in
 654 a job and processes the message based on its prefix. For example, the following
 655 code sets the current printer state message to "Printing page 5":</p>
 656
 657 <pre class="example">
 658 int page = 5;
 659
 660 fprintf(stderr, "INFO: Printing page %d\n", page);
 661 </pre>
 662
 663 <p>Each message is a single line of text starting with one of the following
 664 prefix strings:</p>
 665
 666 <dl class="code">
 667
 668         <dt>ALERT: message</dt>
 669         <dd>Sets the printer-state-message attribute and adds the specified
 670         message to the current error log file using the "alert" log level.</dd>
 671
 672         <dt>ATTR: attribute=value [attribute=value]</dt>
 673         <dd>Sets the named printer or job attribute(s). Typically this is used
 674         to set the <code>marker-colors</code>, <code>marker-high-levels</code>,
 675         <code>marker-levels</code>, <code>marker-low-levels</code>,
 676         <code>marker-message</code>, <code>marker-names</code>,
 677         <code>marker-types</code>, <code>printer-alert</code>, and
 678         <code>printer-alert-description</code> printer attributes. Standard
 679         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 680         1</a>. String values need special handling - see <a href="#ATTR_STRINGS">Reporting Attribute String Values</a> below.</dd>
 681
 682         <dt>CRIT: message</dt>
 683         <dd>Sets the printer-state-message attribute and adds the specified
 684         message to the current error log file using the "critical" log
 685         level.</dd>
 686
 687         <dt>DEBUG: message</dt>
 688         <dd>Sets the printer-state-message attribute and adds the specified
 689         message to the current error log file using the "debug" log level.</dd>
 690
 691         <dt>DEBUG2: message</dt>
 692         <dd>Sets the printer-state-message attribute and adds the specified
 693         message to the current error log file using the "debug2" log level.</dd>
 694
 695         <dt>EMERG: message</dt>
 696         <dd>Sets the printer-state-message attribute and adds the specified
 697         message to the current error log file using the "emergency" log
 698         level.</dd>
 699
 700         <dt>ERROR: message</dt>
 701         <dd>Sets the printer-state-message attribute and adds the specified
 702         message to the current error log file using the "error" log level.
 703         Use "ERROR:" messages for non-persistent processing errors.</dd>
 704
 705         <dt>INFO: message</dt>
 706         <dd>Sets the printer-state-message attribute. If the current log level
 707         is set to "debug2", also adds the specified message to the current error
 708         log file using the "info" log level.</dd>
 709
 710         <dt>NOTICE: message</dt>
 711         <dd>Sets the printer-state-message attribute and adds the specified
 712         message to the current error log file using the "notice" log level.</dd>
 713
 714         <dt>PAGE: page-number #-copies</dt>
 715         <dt>PAGE: total #-pages</dt>
 716         <dd>Adds an entry to the current page log file. The first form adds
 717         #-copies to the job-media-sheets-completed attribute. The second
 718         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 719
 720         <dt>PPD: keyword=value [keyword=value ...]</dt>
 721         <dd>Changes or adds keywords to the printer's PPD file. Typically
 722         this is used to update installable options or default media settings
 723         based on the printer configuration.</dd>
 724
 725         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 726         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 727         <dd>Sets or clears printer-state-reason keywords for the current queue.
 728         Typically this is used to indicate persistent media, ink, toner, and
 729         configuration conditions or errors on a printer.
 730         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 731         use vendor-prefixed ("com.example.foo") keywords for custom states. See
 732         <a href="#MANAGING_STATE">Managing Printer State in a Filter</a> for more
 733         information.
 734
 735         <dt>WARNING: message</dt>
 736         <dd>Sets the printer-state-message attribute and adds the specified
 737         message to the current error log file using the "warning" log
 738         level.</dd>
 739
 740 </dl>
 741
 742 <p>Messages without one of these prefixes are treated as if they began with
 743 the "DEBUG:" prefix string.</p>
 744
 745 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 746 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 747 <thead>
 748 <tr>
 749         <th>marker-type</th>
 750         <th>Description</th>
 751 </tr>
 752 </thead>
 753 <tbody>
 754 <tr>
 755         <td>developer</td>
 756         <td>Developer unit</td>
 757 </tr>
 758 <tr>
 759         <td>fuser</td>
 760         <td>Fuser unit</td>
 761 </tr>
 762 <tr>
 763         <td>fuser-cleaning-pad</td>
 764         <td>Fuser cleaning pad</td>
 765 </tr>
 766 <tr>
 767         <td>fuser-oil</td>
 768         <td>Fuser oil</td>
 769 </tr>
 770 <tr>
 771         <td>ink</td>
 772         <td>Ink supply</td>
 773 </tr>
 774 <tr>
 775         <td>opc</td>
 776         <td>Photo conductor</td>
 777 </tr>
 778 <tr>
 779         <td>solid-wax</td>
 780         <td>Wax supply</td>
 781 </tr>
 782 <tr>
 783         <td>staples</td>
 784         <td>Staple supply</td>
 785 </tr>
 786 <tr>
 787         <td>toner</td>
 788         <td>Toner supply</td>
 789 </tr>
 790 <tr>
 791         <td>transfer-unit</td>
 792         <td>Transfer unit</td>
 793 </tr>
 794 <tr>
 795         <td>waste-ink</td>
 796         <td>Waste ink tank</td>
 797 </tr>
 798 <tr>
 799         <td>waste-toner</td>
 800         <td>Waste toner tank</td>
 801 </tr>
 802 <tr>
 803         <td>waste-wax</td>
 804         <td>Waste wax tank</td>
 805 </tr>
 806 </tbody>
 807 </table></div>
 808
 809 <br>
 810
 811 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 812 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 813 <thead>
 814 <tr>
 815         <th>Keyword</th>
 816         <th>Description</th>
 817 </tr>
 818 </thead>
 819 <tbody>
 820 <tr>
 821         <td>connecting-to-device</td>
 822         <td>Connecting to printer but not printing yet.</td>
 823 </tr>
 824 <tr>
 825         <td>cover-open</td>
 826         <td>The printer's cover is open.</td>
 827 </tr>
 828 <tr>
 829         <td>input-tray-missing</td>
 830         <td>The paper tray is missing.</td>
 831 </tr>
 832 <tr>
 833         <td>marker-supply-empty</td>
 834         <td>The printer is out of ink.</td>
 835 </tr>
 836 <tr>
 837         <td>marker-supply-low</td>
 838         <td>The printer is almost out of ink.</td>
 839 </tr>
 840 <tr>
 841         <td>marker-waste-almost-full</td>
 842         <td>The printer's waste bin is almost full.</td>
 843 </tr>
 844 <tr>
 845         <td>marker-waste-full</td>
 846         <td>The printer's waste bin is full.</td>
 847 </tr>
 848 <tr>
 849         <td>media-empty</td>
 850         <td>The paper tray (any paper tray) is empty.</td>
 851 </tr>
 852 <tr>
 853         <td>media-jam</td>
 854         <td>There is a paper jam.</td>
 855 </tr>
 856 <tr>
 857         <td>media-low</td>
 858         <td>The paper tray (any paper tray) is almost empty.</td>
 859 </tr>
 860 <tr>
 861         <td>media-needed</td>
 862         <td>The paper tray needs to be filled (for a job that is printing).</td>
 863 </tr>
 864 <tr>
 865         <td>paused</td>
 866         <td>Stop the printer.</td>
 867 </tr>
 868 <tr>
 869         <td>timed-out</td>
 870         <td>Unable to connect to printer.</td>
 871 </tr>
 872 <tr>
 873         <td>toner-empty</td>
 874         <td>The printer is out of toner.</td>
 875 </tr>
 876 <tr>
 877         <td>toner-low</td>
 878         <td>The printer is low on toner.</td>
 879 </tr>
 880 </tbody>
 881 </table></div>
 882
 883
 884 <h4><a name="ATTR_STRINGS">Reporting Attribute String Values</a></h4>
 885
 886 <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>
 887
 888 <pre class="example">
 889 name=simple
 890 name=simple,simple,...
 891 name='complex value'
 892 name="complex value"
 893 name='"complex value"','"complex value"',...
 894 </pre>
 895
 896 <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>
 897
 898 <pre class="example">
 899 int levels[4] = { 40, 50, 60, 70 }; /* CMYK */
 900
 901 fputs("ATTR: marker-colors=#00FFFF,#FF00FF,#FFFF00,#000000\n", stderr);
 902 fputs("ATTR: marker-high-levels=100,100,100,100\n", stderr);
 903 fprintf(stderr, "ATTR: marker-levels=%d,%d,%d,%d\n", levels[0], levels[1],
 904         levels[2], levels[3], levels[4]);
 905 fputs("ATTR: marker-low-levels=5,5,5,5\n", stderr);
 906 fputs("ATTR: marker-types=toner,toner,toner,toner\n", stderr);
 907 </pre>
 908
 909 <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>
 910
 911 <pre class="example">
 912 fputs("ATTR: marker-message='Levels shown are approximate.'\n", stderr);
 913 </pre>
 914
 915 <p>When multiple values are reported, each value must be enclosed by a set of single and double quotes:</p>
 916
 917 <pre class="example">
 918 fputs("ATTR: marker-names='\"Cyan Toner\"','\"Magenta Toner\"',"
 919       "'\"Yellow Toner\"','\"Black Toner\"'\n", stderr);
 920 </pre>
 921
 922 <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>
 923
 924 <pre class="example">
 925 static const char *                     /* O - Quoted string */
 926 quote_string(const char *s,             /* I - String */
 927              char       *q,             /* I - Quoted string buffer */
 928              size_t     qsize)          /* I - Size of quoted string buffer */
 929 {
 930   char  *qptr,                          /* Pointer into string buffer */
 931         *qend;                          /* End of string buffer */
 932
 933
 934   qptr = q;
 935   qend = q + qsize - 5;
 936
 937   if (qend &lt; q)
 938   {
 939     *q = '\0';
 940     return (q);
 941   }
 942
 943   *qptr++ = '\'';
 944   *qptr++ = '\"';
 945
 946   while (*s && qptr &lt; qend)
 947   {
 948     if (*s == '\\' || *s == '\"' || *s == '\'')
 949     {
 950       if (qptr &lt; (qend - 4))
 951       {
 952         *qptr++ = '\\';
 953         *qptr++ = '\\';
 954         *qptr++ = '\\';
 955       }
 956       else
 957         break;
 958     }
 959
 960     *qptr++ = *s++;
 961   }
 962
 963   *qptr++ = '\"';
 964   *qptr++ = '\'';
 965   *qptr   = '\0';
 966
 967   return (q);
 968 }
 969 </pre>
 970
 971
 972 <h4><a name="MANAGING_STATE">Managing Printer State in a Filter</a></h4>
 973
 974 <p>Filters are responsible for managing the state keywords they set using
 975 "STATE:" messages. Typically you will update <em>all</em> of the keywords that
 976 are used by the filter at startup, for example:</p>
 977
 978 <pre class="example">
 979 if (foo_condition != 0)
 980   fputs("STATE: +com.example.foo\n", stderr);
 981 else
 982   fputs("STATE: -com.example.foo\n", stderr);
 983
 984 if (bar_condition != 0)
 985   fputs("STATE: +com.example.bar\n", stderr);
 986 else
 987   fputs("STATE: -com.example.bar\n", stderr);
 988 </pre>
 989
 990 <p>Then as conditions change, your filter sends "STATE: +keyword" or "STATE:
 991 -keyword" messages as necessary to set or clear the corresponding keyword,
 992 respectively.</p>
 993
 994 <p>State keywords are often used to notify the user of issues that span across
 995 jobs, for example "media-empty-warning" that indicates one or more paper trays
 996 are empty. These keywords should not be cleared unless the corresponding issue
 997 no longer exists.</p>
 998
 999 <p>Filters should clear job-related keywords on startup and exit so that they
1000 do not remain set between jobs.  For example, "connecting-to-device" is a job
1001 sub-state and not an issue that applies when a job is not printing.</p>
1002
1003 <blockquote><b>Note:</b>
1004
1005 <p>"STATE:" messages often provide visible alerts to the user. For example,
1006 on OS X setting a printer-state-reason value with an "-error" or
1007 "-warning" suffix will cause the printer's dock item to bounce if the
1008 corresponding reason is localized with a cupsIPPReason keyword in the
1009 printer's PPD file.</p>
1010
1011 <p>When providing a vendor-prefixed keyword, <em>always</em> provide the
1012 corresponding standard keyword (if any) to allow clients to respond to the
1013 condition correctly. For example, if you provide a vendor-prefixed keyword
1014 for a low cyan ink condition ("com.example.cyan-ink-low") you must also set the
1015 "marker-supply-low-warning" keyword. In such cases you should also refrain
1016 from localizing the vendor-prefixed keyword in the PPD file - otherwise both
1017 the generic and vendor-specific keyword will be shown in the user
1018 interface.</p>
1019
1020 </blockquote>
1021
1022 <h4><a name="REPORTING_SUPPLIES">Reporting Supply Levels</a></h4>
1023
1024 <p>CUPS tracks several "marker-*" attributes for ink/toner supply level
1025 reporting. These attributes allow applications to display the current supply
1026 levels for a printer without printer-specific software. <a href="#TABLE3">Table 3</a> lists the marker attributes and what they represent.</p>
1027
1028 <p>Filters set marker attributes by sending "ATTR:" messages to stderr. For
1029 example, a filter supporting an inkjet printer with black and tri-color ink
1030 cartridges would use the following to initialize the supply attributes:</p>
1031
1032 <pre class="example">
1033 fputs("ATTR: marker-colors=#000000,#00FFFF#FF00FF#FFFF00\n", stderr);
1034 fputs("ATTR: marker-low-levels=5,10\n", stderr);
1035 fputs("ATTR: marker-names=Black,Tri-Color\n", stderr);
1036 fputs("ATTR: marker-types=ink,ink\n", stderr);
1037 </pre>
1038
1039 <p>Then periodically the filter queries the printer for its current supply
1040 levels and updates them with a separate "ATTR:" message:</p>
1041
1042 <pre class="example">
1043 int black_level, tri_level;
1044 ...
1045 fprintf(stderr, "ATTR: marker-levels=%d,%d\n", black_level, tri_level);
1046 </pre>
1047
1048 <div class='table'><table width='80%' summary='Table 3: Supply Level Attributes'>
1049 <caption>Table 3: <a name='TABLE3'>Supply Level Attributes</a></caption>
1050 <thead>
1051 <tr>
1052         <th>Attribute</th>
1053         <th>Description</th>
1054 </tr>
1055 </thead>
1056 <tbody>
1057 <tr>
1058         <td>marker-colors</td>
1059         <td>A list of comma-separated colors; each color is either "none" or one or
1060         more hex-encoded sRGB colors of the form "#RRGGBB".</td>
1061 </tr>
1062 <tr>
1063         <td>marker-high-levels</td>
1064         <td>A list of comma-separated "almost full" level values from 0 to 100; a
1065         value of 100 should be used for supplies that are consumed/emptied like ink
1066         cartridges.</td>
1067 </tr>
1068 <tr>
1069         <td>marker-levels</td>
1070         <td>A list of comma-separated level values for each supply. A value of -1
1071         indicates the level is unavailable, -2 indicates unknown, and -3 indicates
1072         the level is unknown but has not yet reached capacity. Values from 0 to 100
1073         indicate the corresponding percentage.</td>
1074 </tr>
1075 <tr>
1076         <td>marker-low-levels</td>
1077         <td>A list of comma-separated "almost empty" level values from 0 to 100; a
1078         value of 0 should be used for supplies that are filled like waste ink
1079         tanks.</td>
1080 </tr>
1081 <tr>
1082         <td>marker-message</td>
1083         <td>A human-readable supply status message for the user like "12 pages of
1084         ink remaining."</td>
1085 </tr>
1086 <tr>
1087         <td>marker-names</td>
1088         <td>A list of comma-separated supply names like "Cyan Ink", "Fuser",
1089         etc.</td>
1090 </tr>
1091 <tr>
1092         <td>marker-types</td>
1093         <td>A list of comma-separated supply types; the types are listed in
1094         <a href="#TABLE1">Table 1</a>.</td>
1095 </tr>
1096 </tbody>
1097 </table></div>
1098
1099 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
1100
1101 <p>Filters can communicate with the backend via the
1102 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
1103 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
1104 functions. The
1105 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
1106 reads data that has been sent back from the device and is typically used to
1107 obtain status and configuration information. For example, the following code
1108 polls the backend for back-channel data:</p>
1109
1110 <pre class="example">
1111 #include &lt;cups/cups.h&gt;
1112
1113 char buffer[8192];
1114 ssize_t bytes;
1115
1116 /* Use a timeout of 0.0 seconds to poll for back-channel data */
1117 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
1118 </pre>
1119
1120 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
1121 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
1122 when it is available.</p>
1123
1124 <p>The
1125 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
1126 function allows you to get out-of-band status information and do synchronization
1127 with the device. For example, the following code gets the current IEEE-1284
1128 device ID string from the backend:</p>
1129
1130 <pre class="example">
1131 #include &lt;cups/sidechannel.h&gt;
1132
1133 char data[2049];
1134 int datalen;
1135 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
1136
1137 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
1138    nul-termination... */
1139 datalen = sizeof(data) - 1;
1140
1141 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
1142 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
1143
1144 /* Use the returned value if OK was returned and the length is non-zero */
1145 if (status == CUPS_SC_STATUS_OK &amp;&amp; datalen > 0)
1146   data[datalen] = '\0';
1147 else
1148   data[0] = '\0';
1149 </pre>
1150
1151 <h4><a name="DRAIN_OUTPUT">Forcing All Output to a Printer</a></h4>
1152
1153 <p>The
1154 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
1155 function allows you to tell the backend to send all pending data to the printer.
1156 This is most often needed when sending query commands to the printer. For example:</p>
1157
1158 <pre class="example">
1159 #include &lt;cups/cups.h&gt;
1160 #include &lt;cups/sidechannel.h&gt;
1161
1162 char data[1024];
1163 int datalen = sizeof(data);
1164 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
1165
1166 /* Flush pending output to stdout */
1167 fflush(stdout);
1168
1169 /* Drain output to backend, waiting for up to 30 seconds */
1170 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_DRAIN_OUTPUT, data, &amp;datalen, 30.0);
1171
1172 /* Read the response if the output was sent */
1173 if (status == CUPS_SC_STATUS_OK)
1174 {
1175   ssize_t bytes;
1176
1177   /* Wait up to 10.0 seconds for back-channel data */
1178   bytes = cupsBackChannelRead(data, sizeof(data), 10.0);
1179   /* do something with the data from the printer */
1180 }
1181 </pre>
1182
1183 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
1184
1185 <p>Backends communicate with filters using the reciprocal functions
1186 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
1187 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
1188 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
1189 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
1190
1191 <pre class="example">
1192 #include &lt;cups/cups.h&gt;
1193
1194 char buffer[8192];
1195 ssize_t bytes;
1196
1197 /* Obtain data from printer/device */
1198 ...
1199
1200 /* Use a timeout of 1.0 seconds to give filters a chance to read */
1201 cupsBackChannelWrite(buffer, bytes, 1.0);
1202 </pre>
1203
1204 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
1205 function reads a side-channel command from a filter, driver, or port monitor.
1206 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
1207 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
1208 separate thread for that purpose), or use <code>select</code> or
1209 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
1210 input and output on several file descriptors at the same time.</p>
1211
1212 <p>Once a command is processed, the backend uses the
1213 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
1214 to send its response. For example, the following code shows how to poll for a
1215 side-channel command and respond to it:</p>
1216
1217 <pre class="example">
1218 #include &lt;cups/sidechannel.h&gt;
1219
1220 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
1221 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
1222 char data[2048];
1223 int datalen = sizeof(data);
1224
1225 /* Poll for a command... */
1226 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
1227 {
1228   switch (command)
1229   {
1230     /* handle supported commands, fill data/datalen/status with values as needed */
1231
1232     default :
1233         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
1234         datalen = 0;
1235         break;
1236   }
1237
1238   /* Send a response... */
1239   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
1240 }
1241 </pre>
1242
1243 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
1244
1245 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
1246 status, page counter, and supply levels from most network printers. Every
1247 piece of information is associated with an Object Identifier (OID), and
1248 every printer has a <em>community</em> name associated with it. OIDs can be
1249 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
1250
1251 <p>The two CUPS SNMP functions provide a simple API for querying network
1252 printers through the side-channel interface. Each accepts a string containing
1253 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
1254 along with a timeout for the query.</p>
1255
1256 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
1257 function queries a single OID and returns the value as a string in a buffer
1258 you supply:</p>
1259
1260 <pre class="example">
1261 #include &lt;cups/sidechannel.h&gt;
1262
1263 char data[512];
1264 int datalen = sizeof(data);
1265
1266 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
1267         == CUPS_SC_STATUS_OK)
1268 {
1269   /* Do something with the value */
1270   printf("Page counter is: %s\n", data);
1271 }
1272 </pre>
1273
1274 <p>The
1275 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
1276 function allows you to query a whole group of OIDs, calling a function of your
1277 choice for each OID that is found:</p>
1278
1279 <pre class="example">
1280 #include &lt;cups/sidechannel.h&gt;
1281
1282 void
1283 my_callback(const char *oid, const char *data, int datalen, void *context)
1284 {
1285   /* Do something with the value */
1286   printf("%s=%s\n", oid, data);
1287 }
1288
1289 ...
1290
1291 void *my_data;
1292
1293 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
1294 </pre>
1295
1296 <h2><a name="SANDBOXING">Sandboxing on OS X</a></h2>
1297
1298 <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>
1299
1300 <ol>
1301
1302         <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>
1303
1304         <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>
1305
1306         <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>
1307
1308         <li>Bluetooth and USB: backends can access Bluetooth and USB printers through IOKit. <em>Filters cannot access Bluetooth and USB printers directly.</em></li>
1309
1310         <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>
1311
1312         <li>Notifications: filters and backends can send notifications via the Darwin <code>notify_post()</code> API.</li>
1313
1314 </ol>
1315
1316 <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>
1317 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
1318 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/OS X 10.5&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
1319 <p class="description">Read data from the backchannel.</p>
1320 <p class="code">
1321 ssize_t cupsBackChannelRead (<br>
1322 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
1323 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1324 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1325 );</p>
1326 <h4 class="parameters">Parameters</h4>
1327 <dl>
1328 <dt>buffer</dt>
1329 <dd class="description">Buffer to read into</dd>
1330 <dt>bytes</dt>
1331 <dd class="description">Bytes to read</dd>
1332 <dt>timeout</dt>
1333 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
1334 </dl>
1335 <h4 class="returnvalue">Return Value</h4>
1336 <p class="description">Bytes read or -1 on error</p>
1337 <h4 class="discussion">Discussion</h4>
1338 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
1339 parameter controls how many seconds to wait for the data - use 0.0 to
1340 return immediately if there is no data, -1.0 to wait for data indefinitely.
1341
1342 </p>
1343 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/OS X 10.5&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
1344 <p class="description">Write data to the backchannel.</p>
1345 <p class="code">
1346 ssize_t cupsBackChannelWrite (<br>
1347 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
1348 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1349 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1350 );</p>
1351 <h4 class="parameters">Parameters</h4>
1352 <dl>
1353 <dt>buffer</dt>
1354 <dd class="description">Buffer to write</dd>
1355 <dt>bytes</dt>
1356 <dd class="description">Bytes to write</dd>
1357 <dt>timeout</dt>
1358 <dd class="description">Timeout in seconds, typically 1.0</dd>
1359 </dl>
1360 <h4 class="returnvalue">Return Value</h4>
1361 <p class="description">Bytes written or -1 on error</p>
1362 <h4 class="discussion">Discussion</h4>
1363 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
1364 controls how many seconds to wait for the data to be written - use
1365 0.0 to return immediately if the data cannot be written, -1.0 to wait
1366 indefinitely.
1367
1368 </p>
1369 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/OS X 10.5&nbsp;</span><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
1370 <p class="description">Get the device URI for a backend.</p>
1371 <p class="code">
1372 const char *cupsBackendDeviceURI (<br>
1373 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
1374 );</p>
1375 <h4 class="parameters">Parameters</h4>
1376 <dl>
1377 <dt>argv</dt>
1378 <dd class="description">Command-line arguments</dd>
1379 </dl>
1380 <h4 class="returnvalue">Return Value</h4>
1381 <p class="description">Device URI or <code>NULL</code></p>
1382 <h4 class="discussion">Discussion</h4>
1383 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
1384 function returns the device URI passed in the DEVICE_URI environment
1385 variable or the device URI passed in argv[0], whichever is found
1386 first.
1387
1388 </p>
1389 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span><a name="cupsBackendReport">cupsBackendReport</a></h3>
1390 <p class="description">Write a device line from a backend.</p>
1391 <p class="code">
1392 void cupsBackendReport (<br>
1393 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
1394 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
1395 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
1396 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
1397 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
1398 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
1399 );</p>
1400 <h4 class="parameters">Parameters</h4>
1401 <dl>
1402 <dt>device_scheme</dt>
1403 <dd class="description">device-scheme string</dd>
1404 <dt>device_uri</dt>
1405 <dd class="description">device-uri string</dd>
1406 <dt>device_make_and_model</dt>
1407 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
1408 <dt>device_info</dt>
1409 <dd class="description">device-info string or <code>NULL</code></dd>
1410 <dt>device_id</dt>
1411 <dd class="description">device-id string or <code>NULL</code></dd>
1412 <dt>device_location</dt>
1413 <dd class="description">device-location string or <code>NULL</code></dd>
1414 </dl>
1415 <h4 class="discussion">Discussion</h4>
1416 <p class="discussion">This function writes a single device line to stdout for a backend.
1417 It handles quoting of special characters in the device-make-and-model,
1418 device-info, device-id, and device-location strings.
1419
1420 </p>
1421 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/OS X 10.5&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
1422 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
1423 <p class="code">
1424 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
1425 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1426 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1427 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1428 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1429 );</p>
1430 <h4 class="parameters">Parameters</h4>
1431 <dl>
1432 <dt>command</dt>
1433 <dd class="description">Command to send</dd>
1434 <dt>data</dt>
1435 <dd class="description">Response data buffer pointer</dd>
1436 <dt>datalen</dt>
1437 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1438 <dt>timeout</dt>
1439 <dd class="description">Timeout in seconds</dd>
1440 </dl>
1441 <h4 class="returnvalue">Return Value</h4>
1442 <p class="description">Status of command</p>
1443 <h4 class="discussion">Discussion</h4>
1444 <p class="discussion">This function is normally only called by filters, drivers, or port
1445 monitors in order to communicate with the backend used by the current
1446 printer.  Programs must be prepared to handle timeout or &quot;not
1447 implemented&quot; status codes, which indicate that the backend or device
1448 do not support the specified side-channel command.<br>
1449 <br>
1450 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1451 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1452 update the value to contain the number of data bytes in the buffer.
1453
1454 </p>
1455 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/OS X 10.5&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1456 <p class="description">Read a side-channel message.</p>
1457 <p class="code">
1458 int cupsSideChannelRead (<br>
1459 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1460 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1461 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1462 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1463 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1464 );</p>
1465 <h4 class="parameters">Parameters</h4>
1466 <dl>
1467 <dt>command</dt>
1468 <dd class="description">Command code</dd>
1469 <dt>status</dt>
1470 <dd class="description">Status code</dd>
1471 <dt>data</dt>
1472 <dd class="description">Data buffer pointer</dd>
1473 <dt>datalen</dt>
1474 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1475 <dt>timeout</dt>
1476 <dd class="description">Timeout in seconds</dd>
1477 </dl>
1478 <h4 class="returnvalue">Return Value</h4>
1479 <p class="description">0 on success, -1 on error</p>
1480 <h4 class="discussion">Discussion</h4>
1481 <p class="discussion">This function is normally only called by backend programs to read
1482 commands from a filter, driver, or port monitor program.  The
1483 caller must be prepared to handle incomplete or invalid messages
1484 and return the corresponding status codes.<br>
1485 <br>
1486 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1487 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1488 update the value to contain the number of data bytes in the buffer.
1489
1490 </p>
1491 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1492 <p class="description">Query a SNMP OID's value.</p>
1493 <p class="code">
1494 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1495 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1496 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1497 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1498 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1499 );</p>
1500 <h4 class="parameters">Parameters</h4>
1501 <dl>
1502 <dt>oid</dt>
1503 <dd class="description">OID to query</dd>
1504 <dt>data</dt>
1505 <dd class="description">Buffer for OID value</dd>
1506 <dt>datalen</dt>
1507 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1508 <dt>timeout</dt>
1509 <dd class="description">Timeout in seconds</dd>
1510 </dl>
1511 <h4 class="returnvalue">Return Value</h4>
1512 <p class="description">Query status</p>
1513 <h4 class="discussion">Discussion</h4>
1514 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1515 filter, port monitor, or backend using the default community name.<br>
1516 <br>
1517 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1518 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1519 supported and must be converted to their numeric forms.<br>
1520 <br>
1521 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1522 buffer to hold the OID value as a string. HEX-String (binary) values are
1523 converted to hexadecimal strings representing the binary data, while
1524 NULL-Value and unknown OID types are returned as the empty string.
1525 The returned &quot;datalen&quot; does not include the trailing nul.
1526
1527 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1528 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1529 the printer does not respond to the SNMP query.
1530
1531 </p>
1532 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1533 <p class="description">Query multiple SNMP OID values.</p>
1534 <p class="code">
1535 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1536 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1537 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1538 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1539 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1540 );</p>
1541 <h4 class="parameters">Parameters</h4>
1542 <dl>
1543 <dt>oid</dt>
1544 <dd class="description">First numeric OID to query</dd>
1545 <dt>timeout</dt>
1546 <dd class="description">Timeout for each query in seconds</dd>
1547 <dt>cb</dt>
1548 <dd class="description">Function to call with each value</dd>
1549 <dt>context</dt>
1550 <dd class="description">Application-defined pointer to send to callback</dd>
1551 </dl>
1552 <h4 class="returnvalue">Return Value</h4>
1553 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1554 <h4 class="discussion">Discussion</h4>
1555 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1556 of the filter, port monitor, or backend using the default community name.
1557 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1558 the callback function you provide.<br>
1559 <br>
1560 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1561 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1562 supported and must be converted to their numeric forms.<br>
1563 <br>
1564 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1565 time will depend on the number of OID values found and the time required
1566 for each query.<br>
1567 <br>
1568 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1569 is an application-defined pointer that is sent to the callback function
1570 along with the OID and current data. The data passed to the callback is the
1571 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1572
1573 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1574 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1575 the printer does not respond to the first SNMP query.
1576
1577 </p>
1578 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/OS X 10.5&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1579 <p class="description">Write a side-channel message.</p>
1580 <p class="code">
1581 int cupsSideChannelWrite (<br>
1582 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1583 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1584 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1585 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1586 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1587 );</p>
1588 <h4 class="parameters">Parameters</h4>
1589 <dl>
1590 <dt>command</dt>
1591 <dd class="description">Command code</dd>
1592 <dt>status</dt>
1593 <dd class="description">Status code</dd>
1594 <dt>data</dt>
1595 <dd class="description">Data buffer pointer</dd>
1596 <dt>datalen</dt>
1597 <dd class="description">Number of bytes of data</dd>
1598 <dt>timeout</dt>
1599 <dd class="description">Timeout in seconds</dd>
1600 </dl>
1601 <h4 class="returnvalue">Return Value</h4>
1602 <p class="description">0 on success, -1 on error</p>
1603 <h4 class="discussion">Discussion</h4>
1604 <p class="discussion">This function is normally only called by backend programs to send
1605 responses to a filter, driver, or port monitor program.
1606
1607 </p>
1608 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1609 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1610 <p class="description">Backend exit codes</p>
1611 <p class="code">
1612 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1613 </p>
1614 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1615 <p class="description">Bidirectional capabilities</p>
1616 <p class="code">
1617 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1618 </p>
1619 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1620 <p class="description">Request command codes</p>
1621 <p class="code">
1622 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1623 </p>
1624 <h3 class="typedef"><a name="cups_sc_connected_t">cups_sc_connected_t</a></h3>
1625 <p class="description">Connectivity values</p>
1626 <p class="code">
1627 typedef enum <a href="#cups_sc_connected_e">cups_sc_connected_e</a> cups_sc_connected_t;
1628 </p>
1629 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1630 <p class="description">Printer state bits</p>
1631 <p class="code">
1632 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1633 </p>
1634 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1635 <p class="description">Response status codes</p>
1636 <p class="code">
1637 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1638 </p>
1639 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1640 <p class="description">SNMP walk callback</p>
1641 <p class="code">
1642 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1643 </p>
1644 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1645 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1646 <p class="description">Backend exit codes</p>
1647 <h4 class="constants">Constants</h4>
1648 <dl>
1649 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1650 <dd class="description">Job failed, authentication required</dd>
1651 <dt>CUPS_BACKEND_CANCEL </dt>
1652 <dd class="description">Job failed, cancel job</dd>
1653 <dt>CUPS_BACKEND_FAILED </dt>
1654 <dd class="description">Job failed, use error-policy</dd>
1655 <dt>CUPS_BACKEND_HOLD </dt>
1656 <dd class="description">Job failed, hold job</dd>
1657 <dt>CUPS_BACKEND_OK </dt>
1658 <dd class="description">Job completed successfully</dd>
1659 <dt>CUPS_BACKEND_RETRY </dt>
1660 <dd class="description">Job failed, retry this job later</dd>
1661 <dt>CUPS_BACKEND_RETRY_CURRENT </dt>
1662 <dd class="description">Job failed, retry this job immediately</dd>
1663 <dt>CUPS_BACKEND_STOP </dt>
1664 <dd class="description">Job failed, stop queue</dd>
1665 </dl>
1666 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1667 <p class="description">Bidirectional capability values</p>
1668 <h4 class="constants">Constants</h4>
1669 <dl>
1670 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1671 <dd class="description">Bidirectional I/O is not supported</dd>
1672 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1673 <dd class="description">Bidirectional I/O is supported</dd>
1674 </dl>
1675 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1676 <p class="description">Request command codes</p>
1677 <h4 class="constants">Constants</h4>
1678 <dl>
1679 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1680 <dd class="description">Drain all pending output</dd>
1681 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1682 <dd class="description">Return bidirectional capabilities</dd>
1683 <dt>CUPS_SC_CMD_GET_CONNECTED <span class="info">&nbsp;CUPS 1.5/OS X 10.7&nbsp;</span></dt>
1684 <dd class="description">Return whether the backend is &quot;connected&quot; to the printer </dd>
1685 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1686 <dd class="description">Return the IEEE-1284 device ID</dd>
1687 <dt>CUPS_SC_CMD_GET_STATE </dt>
1688 <dd class="description">Return the device state</dd>
1689 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span></dt>
1690 <dd class="description">Query an SNMP OID </dd>
1691 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4/OS X 10.6&nbsp;</span></dt>
1692 <dd class="description">Query the next SNMP OID </dd>
1693 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1694 <dd class="description">Do a soft reset</dd>
1695 </dl>
1696 <h3 class="enumeration"><a name="cups_sc_connected_e">cups_sc_connected_e</a></h3>
1697 <p class="description">Connectivity values</p>
1698 <h4 class="constants">Constants</h4>
1699 <dl>
1700 <dt>CUPS_SC_CONNECTED </dt>
1701 <dd class="description">Backend is &quot;connected&quot; to printer</dd>
1702 <dt>CUPS_SC_NOT_CONNECTED </dt>
1703 <dd class="description">Backend is not &quot;connected&quot; to printer</dd>
1704 </dl>
1705 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1706 <p class="description">Printer state bits</p>
1707 <h4 class="constants">Constants</h4>
1708 <dl>
1709 <dt>CUPS_SC_STATE_BUSY </dt>
1710 <dd class="description">Device is busy</dd>
1711 <dt>CUPS_SC_STATE_ERROR </dt>
1712 <dd class="description">Other error condition</dd>
1713 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1714 <dd class="description">Toner/ink out condition</dd>
1715 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1716 <dd class="description">Toner/ink low condition</dd>
1717 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1718 <dd class="description">Paper out condition</dd>
1719 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1720 <dd class="description">Paper low condition</dd>
1721 <dt>CUPS_SC_STATE_OFFLINE </dt>
1722 <dd class="description">Device is offline</dd>
1723 <dt>CUPS_SC_STATE_ONLINE </dt>
1724 <dd class="description">Device is online</dd>
1725 </dl>
1726 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1727 <p class="description">Response status codes</p>
1728 <h4 class="constants">Constants</h4>
1729 <dl>
1730 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1731 <dd class="description">The command/response message was invalid</dd>
1732 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1733 <dd class="description">An I/O error occurred</dd>
1734 <dt>CUPS_SC_STATUS_NONE </dt>
1735 <dd class="description">No status</dd>
1736 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1737 <dd class="description">Command not implemented</dd>
1738 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1739 <dd class="description">The device did not respond</dd>
1740 <dt>CUPS_SC_STATUS_OK </dt>
1741 <dd class="description">Operation succeeded</dd>
1742 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1743 <dd class="description">The backend did not respond</dd>
1744 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1745 <dd class="description">Response too big</dd>
1746 </dl>
1747 </div>
1748 </body>
1749 </html>