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ef416fc2 | 1 | <!-- |
75bd9771 | 2 | "$Id: api-filter.shtml 7677 2008-06-19 23:22:19Z mike $" |
ef416fc2 | 3 | |
5a738aea MS |
4 | Filter and backend programming introduction for the Common UNIX Printing |
5 | System (CUPS). | |
ef416fc2 | 6 | |
5a738aea | 7 | Copyright 2007-2008 by Apple Inc. |
bc44d920 | 8 | Copyright 1997-2006 by Easy Software Products, all rights reserved. |
ef416fc2 | 9 | |
10 | These coded instructions, statements, and computer programs are the | |
bc44d920 | 11 | property of Apple Inc. and are protected by Federal copyright |
12 | law. Distribution and use rights are outlined in the file "LICENSE.txt" | |
13 | which should have been included with this file. If this file is | |
14 | file is missing or damaged, see the license at "http://www.cups.org/". | |
ef416fc2 | 15 | --> |
16 | ||
5a738aea | 17 | <h2 class='title'><a name="OVERVIEW">Overview</a></h2> |
ef416fc2 | 18 | |
79e1d494 MS |
19 | <p>Filters (which include printer drivers and port monitors) and backends |
20 | are used to convert job files to a printable format and send that data to the | |
21 | printer itself. All of these programs use a common interface for processing | |
22 | print jobs and communicating status information to the scheduler. Each is run | |
23 | with a standard set of command-line arguments:<p> | |
ef416fc2 | 24 | |
5a738aea | 25 | <dl class="code"> |
ef416fc2 | 26 | |
5a738aea MS |
27 | <dt>argv[1]</dt> |
28 | <dd>The job ID</dd> | |
ef416fc2 | 29 | |
5a738aea MS |
30 | <dt>argv[2]</dt> |
31 | <dd>The user printing the job</dd> | |
f7deaa1a | 32 | |
5a738aea MS |
33 | <dt>argv[3]</dt> |
34 | <dd>The job name/title</dd> | |
ef416fc2 | 35 | |
5a738aea MS |
36 | <dt>argv[4]</dt> |
37 | <dd>The number of copies to print</dd> | |
ef416fc2 | 38 | |
5a738aea MS |
39 | <dt>argv[5]</dt> |
40 | <dd>The options that were provided when the job was submitted</dd> | |
f7deaa1a | 41 | |
5a738aea | 42 | <dt>argv[6]</dt> |
79e1d494 | 43 | <dd>The file to print (first program only)</dd> |
5a738aea | 44 | </dl> |
ef416fc2 | 45 | |
5a738aea MS |
46 | <p>The scheduler runs one or more of these programs to print any given job. The |
47 | first filter reads from the print file and writes to the standard output, while | |
48 | the remaining filters read from the standard input and write to the standard | |
49 | output. The backend is the last filter in the chain and writes to the | |
50 | device.</p> | |
f7deaa1a | 51 | |
ac884b6a MS |
52 | <h3><a name="SECURITY">Security Considerations</a></h3> |
53 | ||
54 | <p>It is always important to use security programming practices. Filters and | |
55 | most backends are run as a non-priviledged user, so the major security | |
56 | consideration is resource utilization - filters should not depend on unlimited | |
57 | amounts of CPU, memory, or disk space, and should protect against conditions | |
58 | that could lead to excess usage of any resource like infinite loops and | |
59 | unbounded recursion. In addition, filters must <em>never</em> allow the user to | |
60 | specify an arbitrary file path to a separator page, template, or other file | |
61 | used by the filter since that can lead to an unauthorized disclosure of | |
62 | information. <em>Always</em> treat input as suspect and validate it!</p> | |
63 | ||
64 | <p>If you are developing a backend that runs as root, make sure to check for | |
65 | potential buffer overflows, integer under/overflow conditions, and file | |
66 | accesses since these can lead to privilege escalations. When writing files, | |
67 | always validate the file path and <em>never</em> allow a user to determine | |
68 | where to store a file.</p> | |
69 | ||
70 | <blockquote><b>Note:</b> | |
71 | ||
72 | <p><em>Never</em> write files to a user's home directory. Aside from the | |
73 | security implications, CUPS is a network print service and as such the network | |
74 | user may not be the same as the local user and/or there may not be a local home | |
75 | directory to write to.</p> | |
76 | ||
77 | <p>In addition, some operating systems provide additional security mechanisms | |
78 | that further limit file system access, even for backends running as root. On | |
79 | Mac OS X, for example, no backend may write to a user's home directory.</p> | |
80 | </blockquote> | |
81 | ||
82 | <h3><a name="TEMPFILES">Temporary Files</a></h3> | |
83 | ||
84 | <p>Temporary files should be created in the directory specified by the | |
85 | "TMPDIR" environment variable. The | |
86 | <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be | |
87 | used to safely create temporary files in this directory.</p> | |
88 | ||
89 | <h3><a name="COPIES">Copy Generation</a></h3> | |
90 | ||
91 | <p>The <code>argv[4]</code> argument specifies the number of copies to produce | |
92 | of the input file. In general, you should only generate copies if the | |
93 | <em>filename</em> argument is supplied. The only exception to this are | |
94 | filters that produce device-independent PostScript output, since the PostScript | |
95 | filter <var>pstops</var> is responsible for generating copies of PostScript | |
96 | files.</p> | |
97 | ||
5a738aea | 98 | <h3><a name="EXITCODES">Exit Codes</a></h3> |
f7deaa1a | 99 | |
5a738aea MS |
100 | <p>Filters must exit with status 0 when they successfully generate print data |
101 | or 1 when they encounter an error. Backends can return any of the | |
102 | <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p> | |
f7deaa1a | 103 | |
5a738aea | 104 | <h3><a name="ENVIRONMENT">Environment Variables</a></h3> |
f7deaa1a | 105 | |
79e1d494 MS |
106 | <p>The following environment variables are defined by the printing system |
107 | when running print filters and backends:</p> | |
f7deaa1a | 108 | |
5a738aea | 109 | <dl class="code"> |
f7deaa1a | 110 | |
5a738aea MS |
111 | <dt>APPLE_LANGUAGES</dt> |
112 | <dd>The Apple language identifier associated with the job | |
113 | (Mac OS X only).</dd> | |
f7deaa1a | 114 | |
5a738aea MS |
115 | <dt>CHARSET</dt> |
116 | <dd>The job character set, typically "utf-8".</dd> | |
f7deaa1a | 117 | |
5a738aea MS |
118 | <dt>CLASS</dt> |
119 | <dd>When a job is submitted to a printer class, contains the name of | |
120 | the destination printer class. Otherwise this environment | |
121 | variable will not be set.</dd> | |
f7deaa1a | 122 | |
5a738aea MS |
123 | <dt>CONTENT_TYPE</dt> |
124 | <dd>The MIME type associated with the file (e.g. | |
125 | application/postscript).</dd> | |
f7deaa1a | 126 | |
5a738aea | 127 | <dt>CUPS_CACHEDIR</dt> |
79e1d494 MS |
128 | <dd>The directory where cache files can be stored. Cache files can be |
129 | used to retain information between jobs or files in a job.</dd> | |
f7deaa1a | 130 | |
5a738aea | 131 | <dt>CUPS_DATADIR</dt> |
79e1d494 | 132 | <dd>The directory where (read-only) CUPS data files can be found.</dd> |
f7deaa1a | 133 | |
0af14961 MS |
134 | <dt>CUPS_FILETYPE</dt> |
135 | <dd>The type of file being printed: "job-sheet" for a banner page and | |
136 | "document" for a regular print file.</dd> | |
137 | ||
5a738aea MS |
138 | <dt>CUPS_SERVERROOT</dt> |
139 | <dd>The root directory of the server.</dd> | |
f7deaa1a | 140 | |
5a738aea MS |
141 | <dt>DEVICE_URI</dt> |
142 | <dd>The device-uri associated with the printer.</dd> | |
f7deaa1a | 143 | |
5a738aea MS |
144 | <dt>FINAL_CONTENT_TYPE</dt> |
145 | <dd>The MIME type associated with the printer (e.g. | |
146 | application/vnd.cups-postscript).</dd> | |
f7deaa1a | 147 | |
5a738aea MS |
148 | <dt>LANG</dt> |
149 | <dd>The language locale associated with the job.</dd> | |
f7deaa1a | 150 | |
5a738aea MS |
151 | <dt>PPD</dt> |
152 | <dd>The full pathname of the PostScript Printer Description (PPD) | |
153 | file for this printer.</dd> | |
f7deaa1a | 154 | |
5a738aea | 155 | <dt>PRINTER</dt> |
79e1d494 | 156 | <dd>The queue name of the class or printer.</dd> |
f7deaa1a | 157 | |
5a738aea MS |
158 | <dt>RIP_CACHE</dt> |
159 | <dd>The recommended amount of memory to use for Raster Image | |
160 | Processors (RIPs).</dd> | |
f7deaa1a | 161 | |
79e1d494 MS |
162 | <dt>TMPDIR</dt> |
163 | <dd>The directory where temporary files should be created.</dd> | |
164 | ||
5a738aea | 165 | </dl> |
f7deaa1a | 166 | |
5a738aea | 167 | <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3> |
f7deaa1a | 168 | |
79e1d494 MS |
169 | <p>Filters and backends communicate with the scheduler by writing messages |
170 | to the standard error file. The scheduler reads messages from all filters in | |
171 | a job and processes the message based on its prefix. For example, the following | |
172 | code sets the current printer state message to "Printing page 5":</p> | |
f7deaa1a | 173 | |
5a738aea MS |
174 | <pre class="example"> |
175 | int page = 5; | |
f7deaa1a | 176 | |
5a738aea MS |
177 | fprintf(stderr, "INFO: Printing page %d\n", page); |
178 | </pre> | |
f7deaa1a | 179 | |
5a738aea MS |
180 | <p>Each message is a single line of text starting with one of the following |
181 | prefix strings:</p> | |
182 | ||
183 | <dl class="code"> | |
184 | ||
185 | <dt>ALERT: message</dt> | |
186 | <dd>Sets the printer-state-message attribute and adds the specified | |
187 | message to the current error log file using the "alert" log level.</dd> | |
188 | ||
189 | <dt>ATTR: attribute=value [attribute=value]</dt> | |
190 | <dd>Sets the named printer or job attribute(s). Typically this is used | |
191 | to set the <code>marker-colors</code>, <code>marker-levels</code>, | |
75bd9771 MS |
192 | <code>marker-message</code>, <code>marker-names</code>, |
193 | <code>marker-types</code>, <code>printer-alert</code>, and | |
194 | <code>printer-alert-description</code> printer attributes. Standard | |
195 | <code>marker-types</code> values are listed in <a href='#TABLE1'>Table | |
196 | 1</a>.</dd> | |
5a738aea MS |
197 | |
198 | <dt>CRIT: message</dt> | |
199 | <dd>Sets the printer-state-message attribute and adds the specified | |
200 | message to the current error log file using the "critical" log | |
201 | level.</dd> | |
202 | ||
203 | <dt>DEBUG: message</dt> | |
204 | <dd>Sets the printer-state-message attribute and adds the specified | |
205 | message to the current error log file using the "debug" log level.</dd> | |
206 | ||
207 | <dt>DEBUG2: message</dt> | |
208 | <dd>Sets the printer-state-message attribute and adds the specified | |
209 | message to the current error log file using the "debug2" log level.</dd> | |
210 | ||
211 | <dt>EMERG: message</dt> | |
212 | <dd>Sets the printer-state-message attribute and adds the specified | |
213 | message to the current error log file using the "emergency" log | |
214 | level.</dd> | |
215 | ||
216 | <dt>ERROR: message</dt> | |
217 | <dd>Sets the printer-state-message attribute and adds the specified | |
79e1d494 MS |
218 | message to the current error log file using the "error" log level. |
219 | Use "ERROR:" messages for non-persistent processing errors.</dd> | |
5a738aea MS |
220 | |
221 | <dt>INFO: message</dt> | |
222 | <dd>Sets the printer-state-message attribute. If the current log level | |
223 | is set to "debug2", also adds the specified message to the current error | |
224 | log file using the "info" log level.</dd> | |
225 | ||
226 | <dt>NOTICE: message</dt> | |
227 | <dd>Sets the printer-state-message attribute and adds the specified | |
228 | message to the current error log file using the "notice" log level.</dd> | |
229 | ||
230 | <dt>PAGE: page-number #-copies</dt> | |
231 | <dt>PAGE: total #-pages</dt> | |
232 | <dd>Adds an entry to the current page log file. The first form adds | |
233 | #-copies to the job-media-sheets-completed attribute. The second | |
234 | form sets the job-media-sheets-completed attribute to #-pages.</dd> | |
235 | ||
20fbc903 MS |
236 | <dt>PPD: keyword=value [keyword=value ...]</dt> |
237 | <dd>Changes or adds keywords to the printer's PPD file. Typically | |
238 | this is used to update installable options or default media settings | |
239 | based on the printer configuration.</dd> | |
240 | ||
5a738aea MS |
241 | <dt>STATE: printer-state-reason [printer-state-reason ...]</dt> |
242 | <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt> | |
243 | <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt> | |
244 | <dd>Sets, adds, or removes printer-state-reason keywords to the | |
79e1d494 MS |
245 | current queue. Typically this is used to indicate persistent media, |
246 | ink, toner, and configuration conditions or errors on a printer. | |
247 | <a href='#TABLE2'>Table 2</a> lists the standard state keywords - | |
248 | use vendor-prefixed ("com.acme.foo") keywords for custom states.</dd> | |
5a738aea MS |
249 | |
250 | <dt>WARNING: message</dt> | |
251 | <dd>Sets the printer-state-message attribute and adds the specified | |
252 | message to the current error log file using the "warning" log | |
253 | level.</dd> | |
254 | ||
255 | </dl> | |
256 | ||
257 | <p>Messages without one of these prefixes are treated as if they began with | |
258 | the "DEBUG:" prefix string.</p> | |
259 | ||
79e1d494 MS |
260 | |
261 | <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'> | |
262 | <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption> | |
263 | <thead> | |
264 | <tr> | |
265 | <th>marker-type</th> | |
266 | <th>Description</th> | |
267 | </tr> | |
268 | </thead> | |
269 | <tbody> | |
270 | <tr> | |
271 | <td>developer</td> | |
272 | <td>Developer unit</td> | |
273 | </tr> | |
274 | <tr> | |
275 | <td>fuser</td> | |
276 | <td>Fuser unit</td> | |
277 | </tr> | |
278 | <tr> | |
279 | <td>fuserCleaningPad</td> | |
280 | <td>Fuser cleaning pad</td> | |
281 | </tr> | |
282 | <tr> | |
283 | <td>fuserOil</td> | |
284 | <td>Fuser oil</td> | |
285 | </tr> | |
286 | <tr> | |
287 | <td>ink</td> | |
288 | <td>Ink supply</td> | |
289 | </tr> | |
290 | <tr> | |
291 | <td>opc</td> | |
292 | <td>Photo conductor</td> | |
293 | </tr> | |
294 | <tr> | |
295 | <td>solidWax</td> | |
296 | <td>Wax supply</td> | |
297 | </tr> | |
298 | <tr> | |
299 | <td>staples</td> | |
300 | <td>Staple supply</td> | |
301 | </tr> | |
302 | <tr> | |
303 | <td>toner</td> | |
304 | <td>Toner supply</td> | |
305 | </tr> | |
306 | <tr> | |
307 | <td>transferUnit</td> | |
308 | <td>Transfer unit</td> | |
309 | </tr> | |
310 | <tr> | |
311 | <td>wasteInk</td> | |
312 | <td>Waste ink tank</td> | |
313 | </tr> | |
314 | <tr> | |
315 | <td>wasteToner</td> | |
316 | <td>Waste toner tank</td> | |
317 | </tr> | |
318 | <tr> | |
319 | <td>wasteWax</td> | |
320 | <td>Waste wax tank</td> | |
321 | </tr> | |
322 | </tbody> | |
323 | </table></div> | |
324 | ||
325 | <br> | |
326 | ||
327 | <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'> | |
328 | <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption> | |
329 | <thead> | |
330 | <tr> | |
331 | <th>Keyword</th> | |
332 | <th>Description</th> | |
333 | </tr> | |
334 | </thead> | |
335 | <tbody> | |
336 | <tr> | |
337 | <td>connecting-to-device</td> | |
338 | <td>Connecting to printer but not printing yet</td> | |
339 | </tr> | |
340 | <tr> | |
341 | <td>cover-open</td> | |
342 | <td>A cover is open on the printer</td> | |
343 | </tr> | |
344 | <tr> | |
345 | <td>input-tray-missing</td> | |
346 | <td>An input tray is missing from the printer</td> | |
347 | </tr> | |
348 | <tr> | |
349 | <td>marker-supply-empty</td> | |
350 | <td>Out of ink</td> | |
351 | </tr> | |
352 | <tr> | |
353 | <td>marker-supply-low</td> | |
354 | <td>Low on ink</td> | |
355 | </tr> | |
356 | <tr> | |
357 | <td>marker-waste-almost-full</td> | |
358 | <td>Waste tank almost full</td> | |
359 | </tr> | |
360 | <tr> | |
361 | <td>marker-waste-full</td> | |
362 | <td>Waste tank full</td> | |
363 | </tr> | |
364 | <tr> | |
365 | <td>media-empty</td> | |
366 | <td>Out of media</td> | |
367 | </tr> | |
368 | <tr> | |
369 | <td>media-jam</td> | |
370 | <td>Media is jammed in the printer</td> | |
371 | </tr> | |
372 | <tr> | |
373 | <td>media-low</td> | |
374 | <td>Low on media</td> | |
375 | </tr> | |
376 | <tr> | |
377 | <td>paused</td> | |
378 | <td>Stop the printer</td> | |
379 | </tr> | |
380 | <tr> | |
381 | <td>timed-out</td> | |
382 | <td>Unable to connect to printer</td> | |
383 | </tr> | |
384 | <tr> | |
385 | <td>toner-empty</td> | |
386 | <td>Out of toner</td> | |
387 | </tr> | |
388 | <tr> | |
389 | <td>toner-low</td> | |
390 | <td>Low on toner</td> | |
391 | </tr> | |
392 | </tbody> | |
393 | </table></div> | |
394 | ||
20fbc903 | 395 | <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3> |
5a738aea MS |
396 | |
397 | <p>Filters can communicate with the backend via the | |
398 | <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and | |
399 | <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a> | |
400 | functions. The | |
401 | <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function | |
402 | reads data that has been sent back from the device and is typically used to | |
403 | obtain status and configuration information. For example, the following code | |
404 | polls the backend for back-channel data:</p> | |
405 | ||
406 | <pre class="example"> | |
407 | #include <cups/cups.h> | |
f7deaa1a | 408 | |
5a738aea MS |
409 | char buffer[8192]; |
410 | ssize_t bytes; | |
f7deaa1a | 411 | |
5a738aea MS |
412 | /* Use a timeout of 0.0 seconds to poll for back-channel data */ |
413 | bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0); | |
f7deaa1a | 414 | </pre> |
415 | ||
79e1d494 MS |
416 | <p>Filters can also use <code>select()</code> or <code>poll()</code> on the |
417 | back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only | |
418 | when it is available.</p> | |
419 | ||
420 | <p>The | |
5a738aea MS |
421 | <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a> |
422 | function allows you to get out-of-band status information and do synchronization | |
423 | with the device. For example, the following code gets the current IEEE-1284 | |
424 | device ID string from the backend:</p> | |
f7deaa1a | 425 | |
5a738aea | 426 | <pre class="example"> |
f7deaa1a | 427 | #include <cups/sidechannel.h> |
428 | ||
429 | char data[2049]; | |
430 | int datalen; | |
5a738aea | 431 | <a href="#cups_sc_status_t">cups_sc_status_t</a> status; |
f7deaa1a | 432 | |
79e1d494 MS |
433 | /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for |
434 | nul-termination... */ | |
f7deaa1a | 435 | datalen = sizeof(data) - 1; |
436 | ||
437 | /* Get the IEEE-1284 device ID, waiting for up to 1 second */ | |
5a738aea | 438 | status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &datalen, 1.0); |
f7deaa1a | 439 | |
440 | /* Use the returned value if OK was returned and the length is non-zero */ | |
441 | if (status == CUPS_SC_STATUS_OK && datalen > 0) | |
442 | data[datalen] = '\0'; | |
443 | else | |
444 | data[0] = '\0'; | |
445 | </pre> | |
446 | ||
20fbc903 MS |
447 | <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3> |
448 | ||
5a738aea MS |
449 | <p>Backends communicate with filters using the reciprocal functions |
450 | <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>, | |
451 | <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and | |
452 | <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We | |
453 | recommend writing back-channel data using a timeout of 1.0 seconds:</p> | |
f7deaa1a | 454 | |
5a738aea MS |
455 | <pre class="example"> |
456 | #include <cups/cups.h> | |
f7deaa1a | 457 | |
5a738aea MS |
458 | char buffer[8192]; |
459 | ssize_t bytes; | |
f7deaa1a | 460 | |
79e1d494 MS |
461 | /* Obtain data from printer/device */ |
462 | ... | |
463 | ||
5a738aea MS |
464 | /* Use a timeout of 1.0 seconds to give filters a chance to read */ |
465 | cupsBackChannelWrite(buffer, bytes, 1.0); | |
f7deaa1a | 466 | </pre> |
467 | ||
5a738aea MS |
468 | <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a> |
469 | function reads a side-channel command from a filter, driver, or port monitor. | |
470 | Backends can either poll for commands using a <code>timeout</code> of 0.0, wait | |
471 | indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a | |
472 | separate thread for that purpose), or use <code>select</code> or | |
473 | <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle | |
20fbc903 | 474 | input and output on several file descriptors at the same time.</p> |
5a738aea MS |
475 | |
476 | <p>Once a command is processed, the backend uses the | |
477 | <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function | |
478 | to send its response. For example, the following code shows how to poll for a | |
479 | side-channel command and respond to it:</p> | |
480 | ||
481 | <pre class="example"> | |
f7deaa1a | 482 | #include <cups/sidechannel.h> |
483 | ||
5a738aea MS |
484 | <a href="#cups_sc_command_t">cups_sc_command_t</a> command; |
485 | <a href="#cups_sc_status_t">cups_sc_status_t</a> status; | |
20fbc903 MS |
486 | char data[2048]; |
487 | int datalen = sizeof(data); | |
f7deaa1a | 488 | |
489 | /* Poll for a command... */ | |
20fbc903 | 490 | if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&command, &status, data, &datalen, 0.0)) |
f7deaa1a | 491 | { |
f7deaa1a | 492 | switch (command) |
493 | { | |
20fbc903 | 494 | /* handle supported commands, fill data/datalen/status with values as needed */ |
f7deaa1a | 495 | |
496 | default : | |
497 | status = CUPS_SC_STATUS_NOT_IMPLEMENTED; | |
498 | datalen = 0; | |
499 | break; | |
500 | } | |
501 | ||
502 | /* Send a response... */ | |
5a738aea | 503 | <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0); |
f7deaa1a | 504 | } |
505 | </pre> | |
ac884b6a MS |
506 | |
507 | <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3> | |
508 | ||
509 | <p>The Simple Network Management Protocol (SNMP) allows you to get the current | |
510 | status, page counter, and supply levels from most network printers. Every | |
511 | piece of information is associated with an Object Identifier (OID), and | |
512 | every printer has a <em>community</em> name associated with it. OIDs can be | |
513 | queried directly or by "walking" over a range of OIDs with a common prefix.</p> | |
514 | ||
20fbc903 MS |
515 | <p>The two CUPS SNMP functions provide a simple API for querying network |
516 | printers through the side-channel interface. Each accepts a string containing | |
517 | an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID) | |
518 | along with a timeout for the query.</p> | |
ac884b6a | 519 | |
20fbc903 MS |
520 | <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a> |
521 | function queries a single OID and returns the value as a string in a buffer | |
522 | you supply:</p> | |
ac884b6a MS |
523 | |
524 | <pre class="example"> | |
20fbc903 | 525 | #include <cups/sidechannel.h> |
ac884b6a | 526 | |
20fbc903 MS |
527 | char data[512]; |
528 | int datalen = sizeof(data); | |
ac884b6a | 529 | |
20fbc903 MS |
530 | if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &datalen, 5.0) |
531 | == CUPS_SC_STATUS_OK) | |
ac884b6a MS |
532 | { |
533 | /* Do something with the value */ | |
20fbc903 | 534 | printf("Page counter is: %s\n", data); |
ac884b6a MS |
535 | } |
536 | </pre> | |
537 | ||
20fbc903 MS |
538 | <p>The |
539 | <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a> | |
540 | function allows you to query a whole group of OIDs, calling a function of your | |
541 | choice for each OID that is found:</p> | |
ac884b6a MS |
542 | |
543 | <pre class="example"> | |
20fbc903 | 544 | #include <cups/sidechannel.h> |
ac884b6a MS |
545 | |
546 | void | |
20fbc903 | 547 | my_callback(const char *oid, const char *data, int datalen, void *context) |
ac884b6a MS |
548 | { |
549 | /* Do something with the value */ | |
20fbc903 | 550 | printf("%s=%s\n", oid, data); |
ac884b6a MS |
551 | } |
552 | ||
20fbc903 MS |
553 | ... |
554 | ||
ac884b6a MS |
555 | void *my_data; |
556 | ||
20fbc903 | 557 | <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data); |
ac884b6a | 558 | </pre> |