doc/help/api-filter.html

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 252 <!--
 253   "$Id: api-cups.header 7279 2008-01-31 01:50:44Z mike $"
 254
 255   Filter and backend programming header for the Common UNIX Printing System
 256   (CUPS).
 257
 258   Copyright 2008 by Apple Inc.
 259
 260   These coded instructions, statements, and computer programs are the
 261   property of Apple Inc. and are protected by Federal copyright
 262   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 263   which should have been included with this file.  If this file is
 264   file is missing or damaged, see the license at "http://www.cups.org/".
 265 -->
 266
 267 <h1 class="title">Filter and Backend Programming</h1>
 268
 269 <div class='summary'><table summary='General Information'>
 270 <thead>
 271 <tr>
 272         <th>Header</th>
 273         <th>cups/backend.h<br>
 274         cups/sidechannel.h</th>
 275 </tr>
 276 </thead>
 277 <tbody>
 278 <tr>
 279         <th>Library</th>
 280         <td>-lcups</td>
 281 </tr>
 282 <tr>
 283         <th>See Also</th>
 284         <td>Programming: <a href='api-overview.html' target='_top'>Introduction to CUPS Programming</a><br>
 285         Programming: <a href='api-cups.html' target='_top'>CUPS API</a><br>
 286         Programming: <a href='api-ppd.html' target='_top'>PPD API</a><br>
 287         Programming: <a href='api-raster.html' target='_top'>Raster API</a></td>
 288 </tr>
 289 </tbody>
 290 </table></div>
 291 <h2 class="title">Contents</h2>
 292 <ul class="contents">
 293 </li>
 294 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 295 <li><a href="#EXITCODES">Exit Codes</a></li>
 296 <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 297 <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 298 <li><a href="#COMMUNICATING">Communicating with the Backend</a></li>
 299 </ul></li>
 300 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 301 <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 302 <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 303 <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 304 <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 305 <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 306 </ul>
 307 <li><a href="#TYPES">Data Types</a><ul class="code">
 308         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 309         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 310         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 311         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 312         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 313 </ul></li>
 314 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 315         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 316         <li><a href="#cups_sc_bidi_e" title="Bidirectional capabilities">cups_sc_bidi_e</a></li>
 317         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 318         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 319         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 320 </ul></li>
 321 </ul>
 322 <!--
 323   "$Id: api-filter.shtml 6649 2007-07-11 21:46:42Z mike $"
 324
 325   Filter and backend programming introduction for the Common UNIX Printing
 326   System (CUPS).
 327
 328   Copyright 2007-2008 by Apple Inc.
 329   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 330
 331   These coded instructions, statements, and computer programs are the
 332   property of Apple Inc. and are protected by Federal copyright
 333   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 334   which should have been included with this file.  If this file is
 335   file is missing or damaged, see the license at "http://www.cups.org/".
 336 -->
 337
 338 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 339
 340 <p>Filters, printer drivers, port monitors, and backends use a common interface
 341 for processing print jobs and communicating status information to the scheduler.
 342 Each filter is run with a standard set of command-line arguments:<p>
 343
 344 <dl class="code">
 345
 346         <dt>argv[1]</dt>
 347         <dd>The job ID</dd>
 348
 349         <dt>argv[2]</dt>
 350         <dd>The user printing the job</dd>
 351
 352         <dt>argv[3]</dt>
 353         <dd>The job name/title</dd>
 354
 355         <dt>argv[4]</dt>
 356         <dd>The number of copies to print</dd>
 357
 358         <dt>argv[5]</dt>
 359         <dd>The options that were provided when the job was submitted</dd>
 360
 361         <dt>argv[6]</dt>
 362         <dd>The file to print (first filter only)</dd>
 363 </dl>
 364
 365 <p>The scheduler runs one or more of these programs to print any given job. The
 366 first filter reads from the print file and writes to the standard output, while
 367 the remaining filters read from the standard input and write to the standard
 368 output. The backend is the last filter in the chain and writes to the
 369 device.</p>
 370
 371 <h3><a name="EXITCODES">Exit Codes</a></h3>
 372
 373 <p>Filters must exit with status 0 when they successfully generate print data
 374 or 1 when they encounter an error. Backends can return any of the
 375 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 376
 377 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 378
 379 <p>The following environment variables are defined by the printing system:</p>
 380
 381 <dl class="code">
 382
 383         <dt>APPLE_LANGUAGES</dt>
 384         <dd>The Apple language identifier associated with the job
 385         (Mac OS X only).</dd>
 386
 387         <dt>CHARSET</dt>
 388         <dd>The job character set, typically "utf-8".</dd>
 389
 390         <dt>CLASS</dt>
 391         <dd>When a job is submitted to a printer class, contains the name of
 392         the destination printer class. Otherwise this environment
 393         variable will not be set.</dd>
 394
 395         <dt>CONTENT_TYPE</dt>
 396         <dd>The MIME type associated with the file (e.g.
 397         application/postscript).</dd>
 398
 399         <dt>CUPS_CACHEDIR</dt>
 400         <dd>The directory where cache files can be stored.</dd>
 401
 402         <dt>CUPS_DATADIR</dt>
 403         <dd>The directory where data files can be found.</dd>
 404
 405         <dt>CUPS_SERVERROOT</dt>
 406         <dd>The root directory of the server.</dd>
 407
 408         <dt>DEVICE_URI</dt>
 409         <dd>The device-uri associated with the printer.</dd>
 410
 411         <dt>FINAL_CONTENT_TYPE</dt>
 412         <dd>The MIME type associated with the printer (e.g.
 413         application/vnd.cups-postscript).</dd>
 414
 415         <dt>LANG</dt>
 416         <dd>The language locale associated with the job.</dd>
 417
 418         <dt>PPD</dt>
 419         <dd>The full pathname of the PostScript Printer Description (PPD)
 420         file for this printer.</dd>
 421
 422         <dt>PRINTER</dt>
 423         <dd>The name of the printer.</dd>
 424
 425         <dt>RIP_CACHE</dt>
 426         <dd>The recommended amount of memory to use for Raster Image
 427         Processors (RIPs).</dd>
 428
 429 </dl>
 430
 431 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 432
 433 <p>Filters and backends communicate wih the scheduler by writing messages
 434 to the standard error file. For example, the following code sets the current
 435 printer state message to "Printing page 5":</p>
 436
 437 <pre class="example">
 438 int page = 5;
 439
 440 fprintf(stderr, "INFO: Printing page %d\n", page);
 441 </pre>
 442
 443 <p>Each message is a single line of text starting with one of the following
 444 prefix strings:</p>
 445
 446 <dl class="code">
 447
 448         <dt>ALERT: message</dt>
 449         <dd>Sets the printer-state-message attribute and adds the specified
 450         message to the current error log file using the "alert" log level.</dd>
 451
 452         <dt>ATTR: attribute=value [attribute=value]</dt>
 453         <dd>Sets the named printer or job attribute(s). Typically this is used
 454         to set the <code>marker-colors</code>, <code>marker-levels</code>,
 455         <code>marker-names</code>, <code>marker-types</code>,
 456         <code>printer-alert</code>, and <code>printer-alert-description</code>
 457         printer attributes.</dd>
 458
 459         <dt>CRIT: message</dt>
 460         <dd>Sets the printer-state-message attribute and adds the specified
 461         message to the current error log file using the "critical" log
 462         level.</dd>
 463
 464         <dt>DEBUG: message</dt>
 465         <dd>Sets the printer-state-message attribute and adds the specified
 466         message to the current error log file using the "debug" log level.</dd>
 467
 468         <dt>DEBUG2: message</dt>
 469         <dd>Sets the printer-state-message attribute and adds the specified
 470         message to the current error log file using the "debug2" log level.</dd>
 471
 472         <dt>EMERG: message</dt>
 473         <dd>Sets the printer-state-message attribute and adds the specified
 474         message to the current error log file using the "emergency" log
 475         level.</dd>
 476
 477         <dt>ERROR: message</dt>
 478         <dd>Sets the printer-state-message attribute and adds the specified
 479         message to the current error log file using the "error" log level.</dd>
 480
 481         <dt>INFO: message</dt>
 482         <dd>Sets the printer-state-message attribute. If the current log level
 483         is set to "debug2", also adds the specified message to the current error
 484         log file using the "info" log level.</dd>
 485
 486         <dt>NOTICE: message</dt>
 487         <dd>Sets the printer-state-message attribute and adds the specified
 488         message to the current error log file using the "notice" log level.</dd>
 489
 490         <dt>PAGE: page-number #-copies</dt>
 491         <dt>PAGE: total #-pages</dt>
 492         <dd>Adds an entry to the current page log file. The first form adds
 493         #-copies to the job-media-sheets-completed attribute. The second
 494         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 495
 496         <dt>STATE: printer-state-reason [printer-state-reason ...]</dt>
 497         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 498         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 499         <dd>Sets, adds, or removes printer-state-reason keywords to the
 500         current queue. Typically this is used to indicate media, ink, and
 501         toner conditions on a printer.</dd>
 502
 503         <dt>WARNING: message</dt>
 504         <dd>Sets the printer-state-message attribute and adds the specified
 505         message to the current error log file using the "warning" log
 506         level.</dd>
 507
 508 </dl>
 509
 510 <p>Messages without one of these prefixes are treated as if they began with
 511 the "DEBUG:" prefix string.</p>
 512
 513 <h3><a name="COMMUNICATING">Communicating with the Backend</a></h3>
 514
 515 <p>Filters can communicate with the backend via the
 516 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
 517 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 518 functions. The
 519 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
 520 reads data that has been sent back from the device and is typically used to
 521 obtain status and configuration information. For example, the following code
 522 polls the backend for back-channel data:</p>
 523
 524 <pre class="example">
 525 #include &lt;cups/cups.h&gt;
 526
 527 char buffer[8192];
 528 ssize_t bytes;
 529
 530 /* Use a timeout of 0.0 seconds to poll for back-channel data */
 531 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
 532 </pre>
 533
 534 The
 535 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 536 function allows you to get out-of-band status information and do synchronization
 537 with the device. For example, the following code gets the current IEEE-1284
 538 device ID string from the backend:</p>
 539
 540 <pre class="example">
 541 #include &lt;cups/sidechannel.h&gt;
 542
 543 char data[2049];
 544 int datalen;
 545 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 546
 547 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for nul-termination... */
 548 datalen = sizeof(data) - 1;
 549
 550 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
 551 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
 552
 553 /* Use the returned value if OK was returned and the length is non-zero */
 554 if (status == CUPS_SC_STATUS_OK && datalen > 0)
 555   data[datalen] = '\0';
 556 else
 557   data[0] = '\0';
 558 </pre>
 559
 560 <p>Backends communicate with filters using the reciprocal functions
 561 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
 562 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
 563 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
 564 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
 565
 566 <pre class="example">
 567 #include &lt;cups/cups.h&gt;
 568
 569 char buffer[8192];
 570 ssize_t bytes;
 571
 572 /* Use a timeout of 1.0 seconds to give filters a chance to read */
 573 cupsBackChannelWrite(buffer, bytes, 1.0);
 574 </pre>
 575
 576 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
 577 function reads a side-channel command from a filter, driver, or port monitor.
 578 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
 579 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
 580 separate thread for that purpose), or use <code>select</code> or
 581 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
 582 input and output on several file descriptors at the same time. Backends can pass
 583 <code>NULL</code> for the <code>data</code> and <code>datalen</code> parameters
 584 since none of the commands sent by upstream filters contain any data at this
 585 time.</p>
 586
 587 <p>Once a command is processed, the backend uses the
 588 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
 589 to send its response. For example, the following code shows how to poll for a
 590 side-channel command and respond to it:</p>
 591
 592 <pre class="example">
 593 #include &lt;cups/sidechannel.h&gt;
 594
 595 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
 596 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 597
 598 /* Poll for a command... */
 599 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, NULL, NULL, 0.0))
 600 {
 601   char data[2048];
 602   int datalen;
 603
 604   switch (command)
 605   {
 606     /* handle supported commands, file data/datalen/status with values as needed */
 607
 608     default :
 609         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
 610         datalen = 0;
 611         break;
 612   }
 613
 614   /* Send a response... */
 615   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
 616 }
 617 </pre>
 618 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
 619 <h3 class="function"><span class="info">&nbsp;CUPS 1.2&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
 620 <p class="description">Read data from the backchannel.</p>
 621 <p class="code">
 622 ssize_t cupsBackChannelRead (<br>
 623 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
 624 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
 625 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
 626 );</p>
 627 <h4 class="parameters">Parameters</h4>
 628 <dl>
 629 <dt>buffer</dt>
 630 <dd class="description">Buffer to read</dd>
 631 <dt>bytes</dt>
 632 <dd class="description">Bytes to read</dd>
 633 <dt>timeout</dt>
 634 <dd class="description">Timeout in seconds</dd>
 635 </dl>
 636 <h4 class="returnvalue">Return Value</h4>
 637 <p class="description">Bytes read or -1 on error</p>
 638 <h4 class="discussion">Discussion</h4>
 639 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel. The &quot;timeout&quot;
 640 parameter controls how many seconds to wait for the data - use
 641 0.0 to return immediately if there is no data, -1.0 to wait
 642 for data indefinitely.
 643
 644 </p>
 645 <h3 class="function"><span class="info">&nbsp;CUPS 1.2&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
 646 <p class="description">Write data to the backchannel.</p>
 647 <p class="code">
 648 ssize_t cupsBackChannelWrite (<br>
 649 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
 650 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
 651 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
 652 );</p>
 653 <h4 class="parameters">Parameters</h4>
 654 <dl>
 655 <dt>buffer</dt>
 656 <dd class="description">Buffer to write</dd>
 657 <dt>bytes</dt>
 658 <dd class="description">Bytes to write</dd>
 659 <dt>timeout</dt>
 660 <dd class="description">Timeout in seconds</dd>
 661 </dl>
 662 <h4 class="returnvalue">Return Value</h4>
 663 <p class="description">Bytes written or -1 on error</p>
 664 <h4 class="discussion">Discussion</h4>
 665 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel. The &quot;timeout&quot; parameter
 666 controls how many seconds to wait for the data to be written - use
 667 0.0 to return immediately if the data cannot be written, -1.0 to wait
 668 indefinitely.
 669
 670 </p>
 671 <h3 class="function"><span class="info">&nbsp;CUPS 1.3&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
 672 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
 673 <p class="code">
 674 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
 675 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
 676 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
 677 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
 678 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
 679 );</p>
 680 <h4 class="parameters">Parameters</h4>
 681 <dl>
 682 <dt>command</dt>
 683 <dd class="description">Command to send</dd>
 684 <dt>data</dt>
 685 <dd class="description">Response data buffer pointer</dd>
 686 <dt>datalen</dt>
 687 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
 688 <dt>timeout</dt>
 689 <dd class="description">Timeout in seconds</dd>
 690 </dl>
 691 <h4 class="returnvalue">Return Value</h4>
 692 <p class="description">Status of command</p>
 693 <h4 class="discussion">Discussion</h4>
 694 <p class="discussion">This function is normally only called by filters, drivers, or port
 695 monitors in order to communicate with the backend used by the current
 696 printer.  Programs must be prepared to handle timeout or &quot;not
 697 implemented&quot; status codes, which indicate that the backend or device
 698 do not support the specified side-channel command.<br>
 699 <br>
 700 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
 701 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
 702 update the value to contain the number of data bytes in the buffer.
 703
 704 </p>
 705 <h3 class="function"><span class="info">&nbsp;CUPS 1.3&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
 706 <p class="description">Read a side-channel message.</p>
 707 <p class="code">
 708 int cupsSideChannelRead (<br>
 709 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
 710 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
 711 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
 712 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
 713 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
 714 );</p>
 715 <h4 class="parameters">Parameters</h4>
 716 <dl>
 717 <dt>command</dt>
 718 <dd class="description">Command code</dd>
 719 <dt>status</dt>
 720 <dd class="description">Status code</dd>
 721 <dt>data</dt>
 722 <dd class="description">Data buffer pointer</dd>
 723 <dt>datalen</dt>
 724 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
 725 <dt>timeout</dt>
 726 <dd class="description">Timeout in seconds</dd>
 727 </dl>
 728 <h4 class="returnvalue">Return Value</h4>
 729 <p class="description">0 on success, -1 on error</p>
 730 <h4 class="discussion">Discussion</h4>
 731 <p class="discussion">This function is normally only called by backend programs to read
 732 commands from a filter, driver, or port monitor program.  The
 733 caller must be prepared to handle incomplete or invalid messages
 734 and return the corresponding status codes.<br>
 735 <br>
 736 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
 737 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
 738 update the value to contain the number of data bytes in the buffer.
 739
 740 </p>
 741 <h3 class="function"><span class="info">&nbsp;CUPS 1.3&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
 742 <p class="description">Write a side-channel message.</p>
 743 <p class="code">
 744 int cupsSideChannelWrite (<br>
 745 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
 746 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
 747 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
 748 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
 749 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
 750 );</p>
 751 <h4 class="parameters">Parameters</h4>
 752 <dl>
 753 <dt>command</dt>
 754 <dd class="description">Command code</dd>
 755 <dt>status</dt>
 756 <dd class="description">Status code</dd>
 757 <dt>data</dt>
 758 <dd class="description">Data buffer pointer</dd>
 759 <dt>datalen</dt>
 760 <dd class="description">Number of bytes of data</dd>
 761 <dt>timeout</dt>
 762 <dd class="description">Timeout in seconds</dd>
 763 </dl>
 764 <h4 class="returnvalue">Return Value</h4>
 765 <p class="description">0 on success, -1 on error</p>
 766 <h4 class="discussion">Discussion</h4>
 767 <p class="discussion">This function is normally only called by backend programs to send
 768 responses to a filter, driver, or port monitor program.
 769
 770 </p>
 771 <h2 class="title"><a name="TYPES">Data Types</a></h2>
 772 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
 773 <p class="description">Backend exit codes</p>
 774 <p class="code">
 775 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
 776 </p>
 777 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
 778 <p class="description">Bidirectional capabilities</p>
 779 <p class="code">
 780 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
 781 </p>
 782 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
 783 <p class="description">Request command codes</p>
 784 <p class="code">
 785 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
 786 </p>
 787 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
 788 <p class="description">Printer state bits</p>
 789 <p class="code">
 790 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
 791 </p>
 792 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
 793 <p class="description">Response status codes</p>
 794 <p class="code">
 795 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
 796 </p>
 797 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
 798 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
 799 <p class="description">Backend exit codes</p>
 800 <h4 class="constants">Constants</h4>
 801 <dl>
 802 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
 803 <dd class="description">Job failed, authentication required</dd>
 804 <dt>CUPS_BACKEND_CANCEL </dt>
 805 <dd class="description">Job failed, cancel job</dd>
 806 <dt>CUPS_BACKEND_FAILED </dt>
 807 <dd class="description">Job failed, use error-policy</dd>
 808 <dt>CUPS_BACKEND_HOLD </dt>
 809 <dd class="description">Job failed, hold job</dd>
 810 <dt>CUPS_BACKEND_OK </dt>
 811 <dd class="description">Job completed successfully</dd>
 812 <dt>CUPS_BACKEND_STOP </dt>
 813 <dd class="description">Job failed, stop queue</dd>
 814 </dl>
 815 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
 816 <p class="description">Bidirectional capabilities</p>
 817 <h4 class="constants">Constants</h4>
 818 <dl>
 819 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
 820 <dd class="description">Bidirectional I/O is not supported</dd>
 821 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
 822 <dd class="description">Bidirectional I/O is supported</dd>
 823 </dl>
 824 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
 825 <p class="description">Request command codes</p>
 826 <h4 class="constants">Constants</h4>
 827 <dl>
 828 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
 829 <dd class="description">Drain all pending output</dd>
 830 <dt>CUPS_SC_CMD_GET_BIDI </dt>
 831 <dd class="description">Return bidirectional capabilities</dd>
 832 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
 833 <dd class="description">Return the IEEE-1284 device ID</dd>
 834 <dt>CUPS_SC_CMD_GET_STATE </dt>
 835 <dd class="description">Return the device state</dd>
 836 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
 837 <dd class="description">Do a soft reset</dd>
 838 </dl>
 839 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
 840 <p class="description">Printer state bits</p>
 841 <h4 class="constants">Constants</h4>
 842 <dl>
 843 <dt>CUPS_SC_STATE_BUSY </dt>
 844 <dd class="description">Device is busy</dd>
 845 <dt>CUPS_SC_STATE_ERROR </dt>
 846 <dd class="description">Other error condition</dd>
 847 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
 848 <dd class="description">Toner/ink out condition</dd>
 849 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
 850 <dd class="description">Toner/ink low condition</dd>
 851 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
 852 <dd class="description">Paper out condition</dd>
 853 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
 854 <dd class="description">Paper low condition</dd>
 855 <dt>CUPS_SC_STATE_OFFLINE </dt>
 856 <dd class="description">Device is off-line</dd>
 857 <dt>CUPS_SC_STATE_ONLINE </dt>
 858 <dd class="description">Device is on-line</dd>
 859 </dl>
 860 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
 861 <p class="description">Response status codes</p>
 862 <h4 class="constants">Constants</h4>
 863 <dl>
 864 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
 865 <dd class="description">The command/response message was invalid</dd>
 866 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
 867 <dd class="description">An I/O error occurred</dd>
 868 <dt>CUPS_SC_STATUS_NONE </dt>
 869 <dd class="description">No status</dd>
 870 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
 871 <dd class="description">Command not implemented</dd>
 872 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
 873 <dd class="description">The device did not respond</dd>
 874 <dt>CUPS_SC_STATUS_OK </dt>
 875 <dd class="description">Operation succeeded</dd>
 876 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
 877 <dd class="description">The backend did not respond</dd>
 878 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
 879 <dd class="description">Response too big</dd>
 880 </dl>
 881 </div>
 882 </body>
 883 </html>