<!--
- "$Id: api-filter.shtml 6649 2007-07-11 21:46:42Z mike $"
+ "$Id: api-filter.shtml 7677 2008-06-19 23:22:19Z mike $"
Filter and backend programming introduction for the Common UNIX Printing
System (CUPS).
<h2 class='title'><a name="OVERVIEW">Overview</a></h2>
-<p>Filters, printer drivers, port monitors, and backends use a common interface
-for processing print jobs and communicating status information to the scheduler.
-Each filter is run with a standard set of command-line arguments:<p>
+<p>Filters (which include printer drivers and port monitors) and backends
+are used to convert job files to a printable format and send that data to the
+printer itself. All of these programs use a common interface for processing
+print jobs and communicating status information to the scheduler. Each is run
+with a standard set of command-line arguments:<p>
<dl class="code">
<dd>The options that were provided when the job was submitted</dd>
<dt>argv[6]</dt>
- <dd>The file to print (first filter only)</dd>
+ <dd>The file to print (first program only)</dd>
</dl>
<p>The scheduler runs one or more of these programs to print any given job. The
<h3><a name="ENVIRONMENT">Environment Variables</a></h3>
-<p>The following environment variables are defined by the printing system:</p>
+<p>The following environment variables are defined by the printing system
+when running print filters and backends:</p>
<dl class="code">
application/postscript).</dd>
<dt>CUPS_CACHEDIR</dt>
- <dd>The directory where cache files can be stored.</dd>
+ <dd>The directory where cache files can be stored. Cache files can be
+ used to retain information between jobs or files in a job.</dd>
<dt>CUPS_DATADIR</dt>
- <dd>The directory where data files can be found.</dd>
+ <dd>The directory where (read-only) CUPS data files can be found.</dd>
<dt>CUPS_SERVERROOT</dt>
<dd>The root directory of the server.</dd>
file for this printer.</dd>
<dt>PRINTER</dt>
- <dd>The name of the printer.</dd>
+ <dd>The queue name of the class or printer.</dd>
<dt>RIP_CACHE</dt>
<dd>The recommended amount of memory to use for Raster Image
Processors (RIPs).</dd>
+ <dt>TMPDIR</dt>
+ <dd>The directory where temporary files should be created.</dd>
+
</dl>
<h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
-<p>Filters and backends communicate wih the scheduler by writing messages
-to the standard error file. For example, the following code sets the current
-printer state message to "Printing page 5":</p>
+<p>Filters and backends communicate with the scheduler by writing messages
+to the standard error file. The scheduler reads messages from all filters in
+a job and processes the message based on its prefix. For example, the following
+code sets the current printer state message to "Printing page 5":</p>
<pre class="example">
int page = 5;
<dt>ATTR: attribute=value [attribute=value]</dt>
<dd>Sets the named printer or job attribute(s). Typically this is used
to set the <code>marker-colors</code>, <code>marker-levels</code>,
- <code>marker-names</code>, <code>marker-types</code>,
- <code>printer-alert</code>, and <code>printer-alert-description</code>
- printer attributes.</dd>
+ <code>marker-message</code>, <code>marker-names</code>,
+ <code>marker-types</code>, <code>printer-alert</code>, and
+ <code>printer-alert-description</code> printer attributes. Standard
+ <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
+ 1</a>.</dd>
<dt>CRIT: message</dt>
<dd>Sets the printer-state-message attribute and adds the specified
<dt>ERROR: message</dt>
<dd>Sets the printer-state-message attribute and adds the specified
- message to the current error log file using the "error" log level.</dd>
+ message to the current error log file using the "error" log level.
+ Use "ERROR:" messages for non-persistent processing errors.</dd>
<dt>INFO: message</dt>
<dd>Sets the printer-state-message attribute. If the current log level
#-copies to the job-media-sheets-completed attribute. The second
form sets the job-media-sheets-completed attribute to #-pages.</dd>
+ <dt>PPD: keyword=value [keyword=value ...]</dt>
+ <dd>Changes or adds keywords to the printer's PPD file. Typically
+ this is used to update installable options or default media settings
+ based on the printer configuration.</dd>
+
<dt>STATE: printer-state-reason [printer-state-reason ...]</dt>
<dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
<dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
<dd>Sets, adds, or removes printer-state-reason keywords to the
- current queue. Typically this is used to indicate media, ink, and
- toner conditions on a printer.</dd>
+ current queue. Typically this is used to indicate persistent media,
+ ink, toner, and configuration conditions or errors on a printer.
+ <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
+ use vendor-prefixed ("com.acme.foo") keywords for custom states.</dd>
<dt>WARNING: message</dt>
<dd>Sets the printer-state-message attribute and adds the specified
<p>Messages without one of these prefixes are treated as if they began with
the "DEBUG:" prefix string.</p>
-<h3><a name="COMMUNICATING">Communicating with the Backend</a></h3>
+
+<div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
+<caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
+<thead>
+<tr>
+ <th>marker-type</th>
+ <th>Description</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+ <td>developer</td>
+ <td>Developer unit</td>
+</tr>
+<tr>
+ <td>fuser</td>
+ <td>Fuser unit</td>
+</tr>
+<tr>
+ <td>fuserCleaningPad</td>
+ <td>Fuser cleaning pad</td>
+</tr>
+<tr>
+ <td>fuserOil</td>
+ <td>Fuser oil</td>
+</tr>
+<tr>
+ <td>ink</td>
+ <td>Ink supply</td>
+</tr>
+<tr>
+ <td>opc</td>
+ <td>Photo conductor</td>
+</tr>
+<tr>
+ <td>solidWax</td>
+ <td>Wax supply</td>
+</tr>
+<tr>
+ <td>staples</td>
+ <td>Staple supply</td>
+</tr>
+<tr>
+ <td>toner</td>
+ <td>Toner supply</td>
+</tr>
+<tr>
+ <td>transferUnit</td>
+ <td>Transfer unit</td>
+</tr>
+<tr>
+ <td>wasteInk</td>
+ <td>Waste ink tank</td>
+</tr>
+<tr>
+ <td>wasteToner</td>
+ <td>Waste toner tank</td>
+</tr>
+<tr>
+ <td>wasteWax</td>
+ <td>Waste wax tank</td>
+</tr>
+</tbody>
+</table></div>
+
+<br>
+
+<div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
+<caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
+<thead>
+<tr>
+ <th>Keyword</th>
+ <th>Description</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+ <td>connecting-to-device</td>
+ <td>Connecting to printer but not printing yet</td>
+</tr>
+<tr>
+ <td>cover-open</td>
+ <td>A cover is open on the printer</td>
+</tr>
+<tr>
+ <td>input-tray-missing</td>
+ <td>An input tray is missing from the printer</td>
+</tr>
+<tr>
+ <td>marker-supply-empty</td>
+ <td>Out of ink</td>
+</tr>
+<tr>
+ <td>marker-supply-low</td>
+ <td>Low on ink</td>
+</tr>
+<tr>
+ <td>marker-waste-almost-full</td>
+ <td>Waste tank almost full</td>
+</tr>
+<tr>
+ <td>marker-waste-full</td>
+ <td>Waste tank full</td>
+</tr>
+<tr>
+ <td>media-empty</td>
+ <td>Out of media</td>
+</tr>
+<tr>
+ <td>media-jam</td>
+ <td>Media is jammed in the printer</td>
+</tr>
+<tr>
+ <td>media-low</td>
+ <td>Low on media</td>
+</tr>
+<tr>
+ <td>paused</td>
+ <td>Stop the printer</td>
+</tr>
+<tr>
+ <td>timed-out</td>
+ <td>Unable to connect to printer</td>
+</tr>
+<tr>
+ <td>toner-empty</td>
+ <td>Out of toner</td>
+</tr>
+<tr>
+ <td>toner-low</td>
+ <td>Low on toner</td>
+</tr>
+</tbody>
+</table></div>
+
+<h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
<p>Filters can communicate with the backend via the
<a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
</pre>
-The
+<p>Filters can also use <code>select()</code> or <code>poll()</code> on the
+back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
+when it is available.</p>
+
+<p>The
<a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
function allows you to get out-of-band status information and do synchronization
with the device. For example, the following code gets the current IEEE-1284
int datalen;
<a href="#cups_sc_status_t">cups_sc_status_t</a> status;
-/* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for nul-termination... */
+/* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
+ nul-termination... */
datalen = sizeof(data) - 1;
/* Get the IEEE-1284 device ID, waiting for up to 1 second */
data[0] = '\0';
</pre>
+<h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
+
<p>Backends communicate with filters using the reciprocal functions
<a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
<a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
char buffer[8192];
ssize_t bytes;
+/* Obtain data from printer/device */
+...
+
/* Use a timeout of 1.0 seconds to give filters a chance to read */
cupsBackChannelWrite(buffer, bytes, 1.0);
</pre>
indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
separate thread for that purpose), or use <code>select</code> or
<code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
-input and output on several file descriptors at the same time. Backends can pass
-<code>NULL</code> for the <code>data</code> and <code>datalen</code> parameters
-since none of the commands sent by upstream filters contain any data at this
-time.</p>
+input and output on several file descriptors at the same time.</p>
<p>Once a command is processed, the backend uses the
<a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
<a href="#cups_sc_command_t">cups_sc_command_t</a> command;
<a href="#cups_sc_status_t">cups_sc_status_t</a> status;
+char data[2048];
+int datalen = sizeof(data);
/* Poll for a command... */
-if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&command, &status, NULL, NULL, 0.0))
+if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&command, &status, data, &datalen, 0.0))
{
- char data[2048];
- int datalen;
-
switch (command)
{
- /* handle supported commands, file data/datalen/status with values as needed */
+ /* handle supported commands, fill data/datalen/status with values as needed */
default :
status = CUPS_SC_STATUS_NOT_IMPLEMENTED;
<h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
-<p>Re-write for side-channel-based SNMP queries.</p>
-
-<!--
<p>The Simple Network Management Protocol (SNMP) allows you to get the current
status, page counter, and supply levels from most network printers. Every
piece of information is associated with an Object Identifier (OID), and
every printer has a <em>community</em> name associated with it. OIDs can be
queried directly or by "walking" over a range of OIDs with a common prefix.</p>
-<p>The CUPS SNMP functions provide a simple API for querying network printers.
-Queries are made using a datagram socket that is created using
-<a href="#cupsSNMPOpen"><code>cupsSNMPOpen</code></a> and destroyed using
-<a href="#cupsSNMPClose"><code>cupsSNMPClose</code></a>:</p>
-
-<pre class="example">
-#include <cups/snmp.h>
-
-int snmp = <a href="#cupsSNMPOpen">cupsSNMPOpen</a>(AF_INET);
-
-/* do some queries */
-
-<a href="#cupsSNMPClose">cupsSNMPClose</a>(snmp);
-</pre>
+<p>The two CUPS SNMP functions provide a simple API for querying network
+printers through the side-channel interface. Each accepts a string containing
+an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
+along with a timeout for the query.</p>
-<p>OIDs are simple C arrays of integers, terminated by a value of -1. For
-example, the page counter OID .1.3.6.1.2.1.43.10.2.1.4.1.1 would be:</p>
+<p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
+function queries a single OID and returns the value as a string in a buffer
+you supply:</p>
<pre class="example">
-int page_counter_oid[] = { 1, 3, 6, 1, 2, 1, 43, 10, 2, 1, 4, 1, 1, -1 };
-</pre>
-
-<p>You send a query using
-<a href="#cupsSNMPWrite"><code>cupsSNMPWrite</code></a> and read the value back
-using <a href="#cupsSNMPRead"><code>cupsSNMPRead</code></a>. The value is read
-into a structure called <a href="#cups_snmp_t"><code>cups_snmp_t</code></a>:</p>
-
-<pre class="example">
-#include <cups/snmp.h>
+#include <cups/sidechannel.h>
-int page_counter_oid[] = { 1, 3, 6, 1, 2, 1, 43, 10, 2, 1, 4, 1, 1, -1 };
-http_addrlist_t *host = httpAddrGetList("myprinter", AF_UNSPEC, "161");
-int snmp = <a href="#cupsSNMPOpen">cupsSNMPOpen</a>(host->addr.addr.sa_family);
-<a href="#cups_snmp_t">cups_snmp_t</a> packet;
+char data[512];
+int datalen = sizeof(data);
-<a href="#cupsSNMPWrite">cupsSNMPWrite</a>(snmp, &(host->addr), CUPS_SNMP_VERSION_1,
- <a href="#cupsSNMPDefaultCommunity">cupsSNMPDefaultCommunity</a>(), CUPS_ASN1_GET_REQUEST, 1,
- page_counter_oid);
-if (<a href="#cupsSNMPRead">cupsSNMPRead</a>(snmp, &packet, 5000))
+if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &datalen, 5.0)
+ == CUPS_SC_STATUS_OK)
{
/* Do something with the value */
- printf("Page counter is: %d\n", packet.object_value.integer);
+ printf("Page counter is: %s\n", data);
}
</pre>
-<p>The <a href="#cupsSNMPWalk"><code>cupsSNMPWalk</code></a> function allows you
-to query a whole group of OIDs, calling a function of your choice for each OID
-that is found:</p>
+<p>The
+<a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
+function allows you to query a whole group of OIDs, calling a function of your
+choice for each OID that is found:</p>
<pre class="example">
-#include <cups/snmp.h>
+#include <cups/sidechannel.h>
void
-my_callback(<a href="#cups_snmp_t">cups_snmp_t</a> *packet, void *data)
+my_callback(const char *oid, const char *data, int datalen, void *context)
{
/* Do something with the value */
+ printf("%s=%s\n", oid, data);
}
-int printer_mib_oid[] = { 1, 3, 6, 1, 2, 1, 43, -1 };
-http_addrlist_t *host = httpAddrGetList("myprinter", AF_UNSPEC, "161");
-int snmp = <a href="#cupsSNMPOpen">cupsSNMPOpen</a>(host->addr.addr.sa_family);
+...
+
void *my_data;
-<a href="#cupsSNMPWalk">cupsSNMPWalk</a>(snmp, &(host->addr), CUPS_SNMP_VERSION_1,
- <a href="#cupsSNMPDefaultCommunity">cupsSNMPDefaultCommunity</a>(), printer_mib_oid, my_callback, my_data);
+<a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
</pre>
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