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ef416fc2 | 1 | <!-- |
75bd9771 | 2 | "$Id: api-filter.shtml 7677 2008-06-19 23:22:19Z mike $" |
ef416fc2 | 3 | |
22c9029b | 4 | Filter and backend programming introduction for CUPS. |
ef416fc2 | 5 | |
f3c17241 | 6 | Copyright 2007-2012 by Apple Inc. |
bc44d920 | 7 | Copyright 1997-2006 by Easy Software Products, all rights reserved. |
ef416fc2 | 8 | |
9 | These coded instructions, statements, and computer programs are the | |
bc44d920 | 10 | property of Apple Inc. and are protected by Federal copyright |
11 | law. Distribution and use rights are outlined in the file "LICENSE.txt" | |
12 | which should have been included with this file. If this file is | |
13 | file is missing or damaged, see the license at "http://www.cups.org/". | |
ef416fc2 | 14 | --> |
15 | ||
5a738aea | 16 | <h2 class='title'><a name="OVERVIEW">Overview</a></h2> |
ef416fc2 | 17 | |
79e1d494 MS |
18 | <p>Filters (which include printer drivers and port monitors) and backends |
19 | are used to convert job files to a printable format and send that data to the | |
20 | printer itself. All of these programs use a common interface for processing | |
21 | print jobs and communicating status information to the scheduler. Each is run | |
22 | with a standard set of command-line arguments:<p> | |
ef416fc2 | 23 | |
5a738aea | 24 | <dl class="code"> |
ef416fc2 | 25 | |
5a738aea MS |
26 | <dt>argv[1]</dt> |
27 | <dd>The job ID</dd> | |
ef416fc2 | 28 | |
5a738aea MS |
29 | <dt>argv[2]</dt> |
30 | <dd>The user printing the job</dd> | |
f7deaa1a | 31 | |
5a738aea MS |
32 | <dt>argv[3]</dt> |
33 | <dd>The job name/title</dd> | |
ef416fc2 | 34 | |
5a738aea MS |
35 | <dt>argv[4]</dt> |
36 | <dd>The number of copies to print</dd> | |
ef416fc2 | 37 | |
5a738aea MS |
38 | <dt>argv[5]</dt> |
39 | <dd>The options that were provided when the job was submitted</dd> | |
f7deaa1a | 40 | |
5a738aea | 41 | <dt>argv[6]</dt> |
79e1d494 | 42 | <dd>The file to print (first program only)</dd> |
5a738aea | 43 | </dl> |
ef416fc2 | 44 | |
5a738aea MS |
45 | <p>The scheduler runs one or more of these programs to print any given job. The |
46 | first filter reads from the print file and writes to the standard output, while | |
47 | the remaining filters read from the standard input and write to the standard | |
48 | output. The backend is the last filter in the chain and writes to the | |
49 | device.</p> | |
f7deaa1a | 50 | |
178cb736 MS |
51 | <p>Filters are always run as a non-privileged user, typically "lp", with no |
52 | connection to the user's desktop. Backends are run either as a non-privileged | |
53 | user or as root if the file permissions do not allow user or group execution. | |
54 | The <a href="#PERMISSIONS">file permissions</a> section talks about this in | |
55 | more detail.</p> | |
56 | ||
ac884b6a MS |
57 | <h3><a name="SECURITY">Security Considerations</a></h3> |
58 | ||
59 | <p>It is always important to use security programming practices. Filters and | |
eac3a0a0 | 60 | most backends are run as a non-privileged user, so the major security |
ac884b6a MS |
61 | consideration is resource utilization - filters should not depend on unlimited |
62 | amounts of CPU, memory, or disk space, and should protect against conditions | |
63 | that could lead to excess usage of any resource like infinite loops and | |
64 | unbounded recursion. In addition, filters must <em>never</em> allow the user to | |
65 | specify an arbitrary file path to a separator page, template, or other file | |
66 | used by the filter since that can lead to an unauthorized disclosure of | |
67 | information. <em>Always</em> treat input as suspect and validate it!</p> | |
68 | ||
4d301e69 | 69 | <p>If you are developing a backend that runs as root, make sure to check for |
ac884b6a MS |
70 | potential buffer overflows, integer under/overflow conditions, and file |
71 | accesses since these can lead to privilege escalations. When writing files, | |
72 | always validate the file path and <em>never</em> allow a user to determine | |
73 | where to store a file.</p> | |
74 | ||
75 | <blockquote><b>Note:</b> | |
76 | ||
77 | <p><em>Never</em> write files to a user's home directory. Aside from the | |
78 | security implications, CUPS is a network print service and as such the network | |
79 | user may not be the same as the local user and/or there may not be a local home | |
80 | directory to write to.</p> | |
81 | ||
82 | <p>In addition, some operating systems provide additional security mechanisms | |
178cb736 | 83 | that further limit file system access, even for backends running as root. On |
f3c17241 | 84 | OS X, for example, no backend may write to a user's home directory.</p> |
ac884b6a MS |
85 | </blockquote> |
86 | ||
f228370c | 87 | <h3><a name="SIGNALS">Canceled Jobs and Signal Handling</a></h3> |
22c9029b MS |
88 | |
89 | <p>The scheduler sends <code>SIGTERM</code> when a printing job is canceled or | |
90 | held. Filters, backends, and port monitors <em>must</em> catch | |
91 | <code>SIGTERM</code> and perform any cleanup necessary to produce a valid output | |
92 | file or return the printer to a known good state. The recommended behavior is to | |
88f9aafc MS |
93 | end the output on the current page, preferably on the current line or object |
94 | being printed.</p> | |
22c9029b | 95 | |
88f9aafc | 96 | <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> |
eac3a0a0 MS |
97 | |
98 | <pre class="example"> | |
99 | #include <signal.h>> | |
100 | ||
101 | ... | |
102 | ||
103 | int | |
104 | main(int argc, char *argv[]) | |
105 | { | |
106 | signal(SIGPIPE, SIG_IGN); | |
107 | ||
108 | ... | |
109 | } | |
110 | </pre> | |
111 | ||
178cb736 MS |
112 | <h3><a name="PERMISSIONS">File Permissions</a></h3> |
113 | ||
114 | <p>For security reasons, CUPS will only run filters and backends that are owned | |
4d301e69 MS |
115 | by root and do not have world or group write permissions. The recommended |
116 | permissions for filters and backends are 0555 - read and execute but no write. | |
117 | Backends that must run as root should use permissions of 0500 - read and execute | |
118 | by root, no access for other users. Write permissions can be enabled for the | |
119 | root user only.</p> | |
178cb736 MS |
120 | |
121 | <p>To avoid a warning message, the directory containing your filter(s) must also | |
4d301e69 MS |
122 | be owned by root and have world and group write disabled - permissions of 0755 |
123 | or 0555 are strongly encouraged.</p> | |
178cb736 | 124 | |
ac884b6a MS |
125 | <h3><a name="TEMPFILES">Temporary Files</a></h3> |
126 | ||
127 | <p>Temporary files should be created in the directory specified by the | |
128 | "TMPDIR" environment variable. The | |
129 | <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be | |
130 | used to safely create temporary files in this directory.</p> | |
131 | ||
132 | <h3><a name="COPIES">Copy Generation</a></h3> | |
133 | ||
134 | <p>The <code>argv[4]</code> argument specifies the number of copies to produce | |
135 | of the input file. In general, you should only generate copies if the | |
136 | <em>filename</em> argument is supplied. The only exception to this are | |
137 | filters that produce device-independent PostScript output, since the PostScript | |
138 | filter <var>pstops</var> is responsible for generating copies of PostScript | |
139 | files.</p> | |
140 | ||
5a738aea | 141 | <h3><a name="EXITCODES">Exit Codes</a></h3> |
f7deaa1a | 142 | |
5a738aea MS |
143 | <p>Filters must exit with status 0 when they successfully generate print data |
144 | or 1 when they encounter an error. Backends can return any of the | |
145 | <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p> | |
f7deaa1a | 146 | |
5a738aea | 147 | <h3><a name="ENVIRONMENT">Environment Variables</a></h3> |
f7deaa1a | 148 | |
79e1d494 MS |
149 | <p>The following environment variables are defined by the printing system |
150 | when running print filters and backends:</p> | |
f7deaa1a | 151 | |
5a738aea | 152 | <dl class="code"> |
f7deaa1a | 153 | |
acb056cb | 154 | <dt>APPLE_LANGUAGE</dt> |
5a738aea | 155 | <dd>The Apple language identifier associated with the job |
f3c17241 | 156 | (OS X only).</dd> |
f7deaa1a | 157 | |
5a738aea MS |
158 | <dt>CHARSET</dt> |
159 | <dd>The job character set, typically "utf-8".</dd> | |
f7deaa1a | 160 | |
5a738aea MS |
161 | <dt>CLASS</dt> |
162 | <dd>When a job is submitted to a printer class, contains the name of | |
163 | the destination printer class. Otherwise this environment | |
164 | variable will not be set.</dd> | |
f7deaa1a | 165 | |
5a738aea MS |
166 | <dt>CONTENT_TYPE</dt> |
167 | <dd>The MIME type associated with the file (e.g. | |
168 | application/postscript).</dd> | |
f7deaa1a | 169 | |
5a738aea | 170 | <dt>CUPS_CACHEDIR</dt> |
79e1d494 MS |
171 | <dd>The directory where cache files can be stored. Cache files can be |
172 | used to retain information between jobs or files in a job.</dd> | |
f7deaa1a | 173 | |
5a738aea | 174 | <dt>CUPS_DATADIR</dt> |
79e1d494 | 175 | <dd>The directory where (read-only) CUPS data files can be found.</dd> |
f7deaa1a | 176 | |
0af14961 MS |
177 | <dt>CUPS_FILETYPE</dt> |
178 | <dd>The type of file being printed: "job-sheet" for a banner page and | |
179 | "document" for a regular print file.</dd> | |
180 | ||
5a738aea MS |
181 | <dt>CUPS_SERVERROOT</dt> |
182 | <dd>The root directory of the server.</dd> | |
f7deaa1a | 183 | |
5a738aea MS |
184 | <dt>DEVICE_URI</dt> |
185 | <dd>The device-uri associated with the printer.</dd> | |
f7deaa1a | 186 | |
5a738aea MS |
187 | <dt>FINAL_CONTENT_TYPE</dt> |
188 | <dd>The MIME type associated with the printer (e.g. | |
189 | application/vnd.cups-postscript).</dd> | |
f7deaa1a | 190 | |
5a738aea MS |
191 | <dt>LANG</dt> |
192 | <dd>The language locale associated with the job.</dd> | |
f7deaa1a | 193 | |
5a738aea MS |
194 | <dt>PPD</dt> |
195 | <dd>The full pathname of the PostScript Printer Description (PPD) | |
196 | file for this printer.</dd> | |
f7deaa1a | 197 | |
5a738aea | 198 | <dt>PRINTER</dt> |
79e1d494 | 199 | <dd>The queue name of the class or printer.</dd> |
f7deaa1a | 200 | |
5a738aea MS |
201 | <dt>RIP_CACHE</dt> |
202 | <dd>The recommended amount of memory to use for Raster Image | |
203 | Processors (RIPs).</dd> | |
f7deaa1a | 204 | |
79e1d494 MS |
205 | <dt>TMPDIR</dt> |
206 | <dd>The directory where temporary files should be created.</dd> | |
207 | ||
5a738aea | 208 | </dl> |
f7deaa1a | 209 | |
5a738aea | 210 | <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3> |
f7deaa1a | 211 | |
79e1d494 MS |
212 | <p>Filters and backends communicate with the scheduler by writing messages |
213 | to the standard error file. The scheduler reads messages from all filters in | |
214 | a job and processes the message based on its prefix. For example, the following | |
215 | code sets the current printer state message to "Printing page 5":</p> | |
f7deaa1a | 216 | |
5a738aea MS |
217 | <pre class="example"> |
218 | int page = 5; | |
f7deaa1a | 219 | |
5a738aea MS |
220 | fprintf(stderr, "INFO: Printing page %d\n", page); |
221 | </pre> | |
f7deaa1a | 222 | |
5a738aea MS |
223 | <p>Each message is a single line of text starting with one of the following |
224 | prefix strings:</p> | |
225 | ||
226 | <dl class="code"> | |
227 | ||
228 | <dt>ALERT: message</dt> | |
229 | <dd>Sets the printer-state-message attribute and adds the specified | |
230 | message to the current error log file using the "alert" log level.</dd> | |
231 | ||
232 | <dt>ATTR: attribute=value [attribute=value]</dt> | |
233 | <dd>Sets the named printer or job attribute(s). Typically this is used | |
88f9aafc MS |
234 | to set the <code>marker-colors</code>, <code>marker-high-levels</code>, |
235 | <code>marker-levels</code>, <code>marker-low-levels</code>, | |
75bd9771 MS |
236 | <code>marker-message</code>, <code>marker-names</code>, |
237 | <code>marker-types</code>, <code>printer-alert</code>, and | |
238 | <code>printer-alert-description</code> printer attributes. Standard | |
239 | <code>marker-types</code> values are listed in <a href='#TABLE1'>Table | |
240 | 1</a>.</dd> | |
5a738aea MS |
241 | |
242 | <dt>CRIT: message</dt> | |
243 | <dd>Sets the printer-state-message attribute and adds the specified | |
244 | message to the current error log file using the "critical" log | |
245 | level.</dd> | |
246 | ||
247 | <dt>DEBUG: message</dt> | |
248 | <dd>Sets the printer-state-message attribute and adds the specified | |
249 | message to the current error log file using the "debug" log level.</dd> | |
250 | ||
251 | <dt>DEBUG2: message</dt> | |
252 | <dd>Sets the printer-state-message attribute and adds the specified | |
253 | message to the current error log file using the "debug2" log level.</dd> | |
254 | ||
255 | <dt>EMERG: message</dt> | |
256 | <dd>Sets the printer-state-message attribute and adds the specified | |
257 | message to the current error log file using the "emergency" log | |
258 | level.</dd> | |
259 | ||
260 | <dt>ERROR: message</dt> | |
261 | <dd>Sets the printer-state-message attribute and adds the specified | |
79e1d494 MS |
262 | message to the current error log file using the "error" log level. |
263 | Use "ERROR:" messages for non-persistent processing errors.</dd> | |
5a738aea MS |
264 | |
265 | <dt>INFO: message</dt> | |
266 | <dd>Sets the printer-state-message attribute. If the current log level | |
267 | is set to "debug2", also adds the specified message to the current error | |
268 | log file using the "info" log level.</dd> | |
269 | ||
270 | <dt>NOTICE: message</dt> | |
271 | <dd>Sets the printer-state-message attribute and adds the specified | |
272 | message to the current error log file using the "notice" log level.</dd> | |
273 | ||
274 | <dt>PAGE: page-number #-copies</dt> | |
275 | <dt>PAGE: total #-pages</dt> | |
276 | <dd>Adds an entry to the current page log file. The first form adds | |
277 | #-copies to the job-media-sheets-completed attribute. The second | |
278 | form sets the job-media-sheets-completed attribute to #-pages.</dd> | |
279 | ||
20fbc903 MS |
280 | <dt>PPD: keyword=value [keyword=value ...]</dt> |
281 | <dd>Changes or adds keywords to the printer's PPD file. Typically | |
282 | this is used to update installable options or default media settings | |
283 | based on the printer configuration.</dd> | |
284 | ||
5a738aea MS |
285 | <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt> |
286 | <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt> | |
88f9aafc MS |
287 | <dd>Sets or clears printer-state-reason keywords for the current queue. |
288 | Typically this is used to indicate persistent media, ink, toner, and | |
289 | configuration conditions or errors on a printer. | |
79e1d494 | 290 | <a href='#TABLE2'>Table 2</a> lists the standard state keywords - |
88f9aafc MS |
291 | use vendor-prefixed ("com.example.foo") keywords for custom states. See |
292 | <a href="#MANAGING_STATE">Managing Printer State in a Filter</a> for more | |
293 | information. | |
5a738aea MS |
294 | |
295 | <dt>WARNING: message</dt> | |
296 | <dd>Sets the printer-state-message attribute and adds the specified | |
297 | message to the current error log file using the "warning" log | |
298 | level.</dd> | |
299 | ||
300 | </dl> | |
301 | ||
302 | <p>Messages without one of these prefixes are treated as if they began with | |
303 | the "DEBUG:" prefix string.</p> | |
304 | ||
79e1d494 MS |
305 | <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'> |
306 | <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption> | |
307 | <thead> | |
308 | <tr> | |
309 | <th>marker-type</th> | |
310 | <th>Description</th> | |
311 | </tr> | |
312 | </thead> | |
313 | <tbody> | |
314 | <tr> | |
315 | <td>developer</td> | |
316 | <td>Developer unit</td> | |
317 | </tr> | |
318 | <tr> | |
319 | <td>fuser</td> | |
320 | <td>Fuser unit</td> | |
321 | </tr> | |
322 | <tr> | |
323 | <td>fuserCleaningPad</td> | |
324 | <td>Fuser cleaning pad</td> | |
325 | </tr> | |
326 | <tr> | |
327 | <td>fuserOil</td> | |
328 | <td>Fuser oil</td> | |
329 | </tr> | |
330 | <tr> | |
331 | <td>ink</td> | |
332 | <td>Ink supply</td> | |
333 | </tr> | |
334 | <tr> | |
335 | <td>opc</td> | |
336 | <td>Photo conductor</td> | |
337 | </tr> | |
338 | <tr> | |
339 | <td>solidWax</td> | |
340 | <td>Wax supply</td> | |
341 | </tr> | |
342 | <tr> | |
343 | <td>staples</td> | |
344 | <td>Staple supply</td> | |
345 | </tr> | |
346 | <tr> | |
347 | <td>toner</td> | |
348 | <td>Toner supply</td> | |
349 | </tr> | |
350 | <tr> | |
351 | <td>transferUnit</td> | |
352 | <td>Transfer unit</td> | |
353 | </tr> | |
354 | <tr> | |
355 | <td>wasteInk</td> | |
356 | <td>Waste ink tank</td> | |
357 | </tr> | |
358 | <tr> | |
359 | <td>wasteToner</td> | |
360 | <td>Waste toner tank</td> | |
361 | </tr> | |
362 | <tr> | |
363 | <td>wasteWax</td> | |
364 | <td>Waste wax tank</td> | |
365 | </tr> | |
366 | </tbody> | |
367 | </table></div> | |
368 | ||
369 | <br> | |
370 | ||
371 | <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'> | |
372 | <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption> | |
373 | <thead> | |
374 | <tr> | |
375 | <th>Keyword</th> | |
376 | <th>Description</th> | |
377 | </tr> | |
378 | </thead> | |
379 | <tbody> | |
380 | <tr> | |
381 | <td>connecting-to-device</td> | |
88f9aafc | 382 | <td>Connecting to printer but not printing yet.</td> |
79e1d494 MS |
383 | </tr> |
384 | <tr> | |
385 | <td>cover-open</td> | |
88f9aafc | 386 | <td>The printer's cover is open.</td> |
79e1d494 MS |
387 | </tr> |
388 | <tr> | |
389 | <td>input-tray-missing</td> | |
88f9aafc | 390 | <td>The paper tray is missing.</td> |
79e1d494 MS |
391 | </tr> |
392 | <tr> | |
393 | <td>marker-supply-empty</td> | |
88f9aafc | 394 | <td>The printer is out of ink.</td> |
79e1d494 MS |
395 | </tr> |
396 | <tr> | |
397 | <td>marker-supply-low</td> | |
88f9aafc | 398 | <td>The printer is almost out of ink.</td> |
79e1d494 MS |
399 | </tr> |
400 | <tr> | |
401 | <td>marker-waste-almost-full</td> | |
88f9aafc | 402 | <td>The printer's waste bin is almost full.</td> |
79e1d494 MS |
403 | </tr> |
404 | <tr> | |
405 | <td>marker-waste-full</td> | |
88f9aafc | 406 | <td>The printer's waste bin is full.</td> |
79e1d494 MS |
407 | </tr> |
408 | <tr> | |
409 | <td>media-empty</td> | |
88f9aafc | 410 | <td>The paper tray (any paper tray) is empty.</td> |
79e1d494 MS |
411 | </tr> |
412 | <tr> | |
413 | <td>media-jam</td> | |
88f9aafc | 414 | <td>There is a paper jam.</td> |
79e1d494 MS |
415 | </tr> |
416 | <tr> | |
417 | <td>media-low</td> | |
88f9aafc MS |
418 | <td>The paper tray (any paper tray) is almost empty.</td> |
419 | </tr> | |
420 | <tr> | |
421 | <td>media-needed</td> | |
422 | <td>The paper tray needs to be filled (for a job that is printing).</td> | |
79e1d494 MS |
423 | </tr> |
424 | <tr> | |
425 | <td>paused</td> | |
88f9aafc | 426 | <td>Stop the printer.</td> |
79e1d494 MS |
427 | </tr> |
428 | <tr> | |
429 | <td>timed-out</td> | |
88f9aafc | 430 | <td>Unable to connect to printer.</td> |
79e1d494 MS |
431 | </tr> |
432 | <tr> | |
433 | <td>toner-empty</td> | |
88f9aafc | 434 | <td>The printer is out of toner.</td> |
79e1d494 MS |
435 | </tr> |
436 | <tr> | |
437 | <td>toner-low</td> | |
88f9aafc MS |
438 | <td>The printer is low on toner.</td> |
439 | </tr> | |
440 | </tbody> | |
441 | </table></div> | |
442 | ||
443 | <h4><a name="MANAGING_STATE">Managing Printer State in a Filter</a></h4> | |
444 | ||
445 | <p>Filters are responsible for managing the state keywords they set using | |
446 | "STATE:" messages. Typically you will update <em>all</em> of the keywords that | |
447 | are used by the filter at startup, for example:</p> | |
448 | ||
449 | <pre class="example"> | |
450 | if (foo_condition != 0) | |
451 | fputs("STATE: +com.example.foo\n", stderr); | |
452 | else | |
453 | fputs("STATE: -com.example.foo\n", stderr); | |
454 | ||
455 | if (bar_condition != 0) | |
456 | fputs("STATE: +com.example.bar\n", stderr); | |
457 | else | |
458 | fputs("STATE: -com.example.bar\n", stderr); | |
459 | </pre> | |
460 | ||
461 | <p>Then as conditions change, your filter sends "STATE: +keyword" or "STATE: | |
462 | -keyword" messages as necessary to set or clear the corresponding keyword, | |
463 | respectively.</p> | |
464 | ||
465 | <p>State keywords are often used to notify the user of issues that span across | |
466 | jobs, for example "media-empty-warning" that indicates one or more paper trays | |
467 | are empty. These keywords should not be cleared unless the corresponding issue | |
468 | no longer exists.</p> | |
469 | ||
470 | <p>Filters should clear job-related keywords on startup and exit so that they | |
471 | do not remain set between jobs. For example, "connecting-to-device" is a job | |
472 | sub-state and not an issue that applies when a job is not printing.</p> | |
473 | ||
474 | <blockquote><b>Note:</b> | |
475 | ||
476 | <p>"STATE:" messages often provide visible alerts to the user. For example, | |
f3c17241 | 477 | on OS X setting a printer-state-reason value with an "-error" or |
88f9aafc MS |
478 | "-warning" suffix will cause the printer's dock item to bounce if the |
479 | corresponding reason is localized with a cupsIPPReason keyword in the | |
480 | printer's PPD file.</p> | |
481 | ||
482 | <p>When providing a vendor-prefixed keyword, <em>always</em> provide the | |
483 | corresponding standard keyword (if any) to allow clients to respond to the | |
484 | condition correctly. For example, if you provide a vendor-prefixed keyword | |
485 | for a low cyan ink condition ("com.example.cyan-ink-low") you must also set the | |
486 | "marker-supply-low-warning" keyword. In such cases you should also refrain | |
487 | from localizing the vendor-prefixed keyword in the PPD file - otherwise both | |
488 | the generic and vendor-specific keyword will be shown in the user | |
489 | interface.</p> | |
490 | ||
491 | </blockquote></dd> | |
492 | ||
493 | <h4><a name="REPORTING_SUPPLIES">Reporting Supply Levels</a></h4> | |
494 | ||
495 | <p>CUPS tracks several "marker-*" attributes for ink/toner supply level | |
496 | reporting. These attributes allow applications to display the current supply | |
497 | levels for a printer without printer-specific software. <a href="#TABLE3">Table 3</a> lists the marker attributes and what they represent.</p> | |
498 | ||
499 | <p>Filters set marker attributes by sending "ATTR:" messages to stderr. For | |
500 | example, a filter supporting an inkjet printer with black and tri-color ink | |
501 | cartridges would use the following to initialize the supply attributes:</p> | |
502 | ||
503 | <pre class="example"> | |
504 | fputs("ATTR: marker-colors=#000000,#00FFFF#FF00FF#FFFF00\n", stderr); | |
505 | fputs("ATTR: marker-low-levels=5,10\n", stderr); | |
506 | fputs("ATTR: marker-names=Black,Tri-Color\n", stderr); | |
507 | fputs("ATTR: marker-types=ink,ink\n", stderr); | |
508 | </pre> | |
509 | ||
510 | <p>Then periodically the filter queries the printer for its current supply | |
511 | levels and updates them with a separate "ATTR:" message:</p> | |
512 | ||
513 | <pre class="example"> | |
514 | int black_level, tri_level; | |
515 | ... | |
516 | fprintf(stderr, "ATTR: marker-levels=%d,%d\n", black_level, tri_level); | |
517 | </pre> | |
518 | ||
519 | <div class='table'><table width='80%' summary='Table 3: Supply Level Attributes'> | |
520 | <caption>Table 3: <a name='TABLE3'>Supply Level Attributes</a></caption> | |
521 | <thead> | |
522 | <tr> | |
523 | <th>Attribute</th> | |
524 | <th>Description</th> | |
525 | </tr> | |
526 | </thead> | |
527 | <tbody> | |
528 | <tr> | |
529 | <td>marker-colors</td> | |
530 | <td>A list of comma-separated colors; each color is either "none" or one or | |
531 | more hex-encoded sRGB colors of the form "#RRGGBB".</td> | |
532 | </tr> | |
533 | <tr> | |
534 | <td>marker-high-levels</td> | |
535 | <td>A list of comma-separated "almost full" level values from 0 to 100; a | |
536 | value of 100 should be used for supplies that are consumed/emptied like ink | |
537 | cartridges.</td> | |
538 | </tr> | |
539 | <tr> | |
540 | <td>marker-levels</td> | |
541 | <td>A list of comma-separated level values for each supply. A value of -1 | |
542 | indicates the level is unavailable, -2 indicates unknown, and -3 indicates | |
543 | the level is unknown but has not yet reached capacity. Values from 0 to 100 | |
544 | indicate the corresponding percentage.</td> | |
545 | </tr> | |
546 | <tr> | |
547 | <td>marker-low-levels</td> | |
548 | <td>A list of comma-separated "almost empty" level values from 0 to 100; a | |
549 | value of 0 should be used for supplies that are filled like waste ink | |
550 | tanks.</td> | |
551 | </tr> | |
552 | <tr> | |
553 | <td>marker-message</td> | |
554 | <td>A human-readable supply status message for the user like "12 pages of | |
555 | ink remaining."</td> | |
556 | </tr> | |
557 | <tr> | |
558 | <td>marker-names</td> | |
559 | <td>A list of comma-separated supply names like "Cyan Ink", "Fuser", | |
560 | etc.</td> | |
561 | </tr> | |
562 | <tr> | |
563 | <td>marker-types</td> | |
564 | <td>A list of comma-separated supply types; the types are listed in | |
565 | <a href="#TABLE1">Table 1</a>.</td> | |
79e1d494 MS |
566 | </tr> |
567 | </tbody> | |
568 | </table></div> | |
569 | ||
20fbc903 | 570 | <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3> |
5a738aea MS |
571 | |
572 | <p>Filters can communicate with the backend via the | |
573 | <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and | |
574 | <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a> | |
22c9029b | 575 | functions. The |
5a738aea MS |
576 | <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function |
577 | reads data that has been sent back from the device and is typically used to | |
578 | obtain status and configuration information. For example, the following code | |
579 | polls the backend for back-channel data:</p> | |
580 | ||
581 | <pre class="example"> | |
582 | #include <cups/cups.h> | |
f7deaa1a | 583 | |
5a738aea MS |
584 | char buffer[8192]; |
585 | ssize_t bytes; | |
f7deaa1a | 586 | |
5a738aea MS |
587 | /* Use a timeout of 0.0 seconds to poll for back-channel data */ |
588 | bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0); | |
f7deaa1a | 589 | </pre> |
590 | ||
79e1d494 MS |
591 | <p>Filters can also use <code>select()</code> or <code>poll()</code> on the |
592 | back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only | |
593 | when it is available.</p> | |
594 | ||
595 | <p>The | |
5a738aea MS |
596 | <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a> |
597 | function allows you to get out-of-band status information and do synchronization | |
598 | with the device. For example, the following code gets the current IEEE-1284 | |
599 | device ID string from the backend:</p> | |
f7deaa1a | 600 | |
5a738aea | 601 | <pre class="example"> |
f7deaa1a | 602 | #include <cups/sidechannel.h> |
603 | ||
604 | char data[2049]; | |
605 | int datalen; | |
5a738aea | 606 | <a href="#cups_sc_status_t">cups_sc_status_t</a> status; |
f7deaa1a | 607 | |
79e1d494 MS |
608 | /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for |
609 | nul-termination... */ | |
f7deaa1a | 610 | datalen = sizeof(data) - 1; |
611 | ||
612 | /* Get the IEEE-1284 device ID, waiting for up to 1 second */ | |
5a738aea | 613 | status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &datalen, 1.0); |
f7deaa1a | 614 | |
615 | /* Use the returned value if OK was returned and the length is non-zero */ | |
616 | if (status == CUPS_SC_STATUS_OK && datalen > 0) | |
617 | data[datalen] = '\0'; | |
618 | else | |
619 | data[0] = '\0'; | |
620 | </pre> | |
621 | ||
88f9aafc MS |
622 | <h4><a name="DRAIN_OUTPUT">Forcing All Output to a Printer</a></h4> |
623 | ||
624 | <p>The | |
625 | <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a> | |
626 | function allows you to tell the backend to send all pending data to the printer. | |
627 | This is most often needed when sending query commands to the printer. For example:</p> | |
628 | ||
629 | <pre class="example"> | |
630 | #include <cups/cups.h> | |
631 | #include <cups/sidechannel.h> | |
632 | ||
633 | char data[1024]; | |
634 | int datalen = sizeof(data); | |
635 | <a href="#cups_sc_status_t">cups_sc_status_t</a> status; | |
636 | ||
637 | /* Flush pending output to stdout */ | |
638 | fflush(stdout); | |
639 | ||
640 | /* Drain output to backend, waiting for up to 30 seconds */ | |
641 | status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_DRAIN_OUTPUT, data, &datalen, 30.0); | |
642 | ||
643 | /* Read the response if the output was sent */ | |
644 | if (status == CUPS_SC_STATUS_OK) | |
645 | { | |
646 | ssize_t bytes; | |
647 | ||
648 | /* Wait up to 10.0 seconds for back-channel data */ | |
649 | bytes = cupsBackChannelRead(data, sizeof(data), 10.0); | |
650 | /* do something with the data from the printer */ | |
651 | } | |
652 | </pre> | |
653 | ||
20fbc903 MS |
654 | <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3> |
655 | ||
5a738aea MS |
656 | <p>Backends communicate with filters using the reciprocal functions |
657 | <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>, | |
658 | <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and | |
659 | <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We | |
660 | recommend writing back-channel data using a timeout of 1.0 seconds:</p> | |
f7deaa1a | 661 | |
5a738aea MS |
662 | <pre class="example"> |
663 | #include <cups/cups.h> | |
f7deaa1a | 664 | |
5a738aea MS |
665 | char buffer[8192]; |
666 | ssize_t bytes; | |
f7deaa1a | 667 | |
79e1d494 MS |
668 | /* Obtain data from printer/device */ |
669 | ... | |
670 | ||
5a738aea MS |
671 | /* Use a timeout of 1.0 seconds to give filters a chance to read */ |
672 | cupsBackChannelWrite(buffer, bytes, 1.0); | |
f7deaa1a | 673 | </pre> |
674 | ||
5a738aea MS |
675 | <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a> |
676 | function reads a side-channel command from a filter, driver, or port monitor. | |
677 | Backends can either poll for commands using a <code>timeout</code> of 0.0, wait | |
678 | indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a | |
679 | separate thread for that purpose), or use <code>select</code> or | |
680 | <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle | |
20fbc903 | 681 | input and output on several file descriptors at the same time.</p> |
5a738aea MS |
682 | |
683 | <p>Once a command is processed, the backend uses the | |
684 | <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function | |
685 | to send its response. For example, the following code shows how to poll for a | |
686 | side-channel command and respond to it:</p> | |
687 | ||
688 | <pre class="example"> | |
f7deaa1a | 689 | #include <cups/sidechannel.h> |
690 | ||
5a738aea MS |
691 | <a href="#cups_sc_command_t">cups_sc_command_t</a> command; |
692 | <a href="#cups_sc_status_t">cups_sc_status_t</a> status; | |
20fbc903 MS |
693 | char data[2048]; |
694 | int datalen = sizeof(data); | |
f7deaa1a | 695 | |
696 | /* Poll for a command... */ | |
20fbc903 | 697 | if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&command, &status, data, &datalen, 0.0)) |
f7deaa1a | 698 | { |
f7deaa1a | 699 | switch (command) |
700 | { | |
20fbc903 | 701 | /* handle supported commands, fill data/datalen/status with values as needed */ |
f7deaa1a | 702 | |
703 | default : | |
704 | status = CUPS_SC_STATUS_NOT_IMPLEMENTED; | |
705 | datalen = 0; | |
706 | break; | |
707 | } | |
708 | ||
709 | /* Send a response... */ | |
5a738aea | 710 | <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0); |
f7deaa1a | 711 | } |
712 | </pre> | |
ac884b6a MS |
713 | |
714 | <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3> | |
715 | ||
716 | <p>The Simple Network Management Protocol (SNMP) allows you to get the current | |
717 | status, page counter, and supply levels from most network printers. Every | |
718 | piece of information is associated with an Object Identifier (OID), and | |
719 | every printer has a <em>community</em> name associated with it. OIDs can be | |
720 | queried directly or by "walking" over a range of OIDs with a common prefix.</p> | |
721 | ||
20fbc903 MS |
722 | <p>The two CUPS SNMP functions provide a simple API for querying network |
723 | printers through the side-channel interface. Each accepts a string containing | |
724 | an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID) | |
725 | along with a timeout for the query.</p> | |
ac884b6a | 726 | |
20fbc903 MS |
727 | <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a> |
728 | function queries a single OID and returns the value as a string in a buffer | |
729 | you supply:</p> | |
ac884b6a MS |
730 | |
731 | <pre class="example"> | |
20fbc903 | 732 | #include <cups/sidechannel.h> |
ac884b6a | 733 | |
20fbc903 MS |
734 | char data[512]; |
735 | int datalen = sizeof(data); | |
ac884b6a | 736 | |
20fbc903 MS |
737 | if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &datalen, 5.0) |
738 | == CUPS_SC_STATUS_OK) | |
ac884b6a MS |
739 | { |
740 | /* Do something with the value */ | |
20fbc903 | 741 | printf("Page counter is: %s\n", data); |
ac884b6a MS |
742 | } |
743 | </pre> | |
744 | ||
20fbc903 MS |
745 | <p>The |
746 | <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a> | |
747 | function allows you to query a whole group of OIDs, calling a function of your | |
748 | choice for each OID that is found:</p> | |
ac884b6a MS |
749 | |
750 | <pre class="example"> | |
20fbc903 | 751 | #include <cups/sidechannel.h> |
ac884b6a MS |
752 | |
753 | void | |
20fbc903 | 754 | my_callback(const char *oid, const char *data, int datalen, void *context) |
ac884b6a MS |
755 | { |
756 | /* Do something with the value */ | |
20fbc903 | 757 | printf("%s=%s\n", oid, data); |
ac884b6a MS |
758 | } |
759 | ||
20fbc903 MS |
760 | ... |
761 | ||
ac884b6a MS |
762 | void *my_data; |
763 | ||
20fbc903 | 764 | <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data); |
ac884b6a | 765 | </pre> |