[753] | 1 | <!-- $Id$ --> |
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| 2 | |
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| 3 | <chapter> |
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[1187] | 4 | <title id="filter">PyKota's internals</title> |
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[865] | 5 | |
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| 6 | <para>Last modified on $Date$</para> |
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| 7 | |
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[753] | 8 | <para> |
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[1101] | 9 | To account for pages or eventually ink usage |
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| 10 | <footnote> |
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| 11 | <para> |
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| 12 | PyKota doesn't currently account for ink usage, it only accounts |
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| 13 | pages. To account for ink usage, you should use PrintBill instead. |
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| 14 | </para> |
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| 15 | </footnote> |
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| 16 | , you must plug your accounting |
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[959] | 17 | system somewhere into the printing system you use, be it either <application>CUPS</application> |
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| 18 | or <application>LPRng</application>. One way to do this without having |
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| 19 | to modify the printing system itself, is by using a <firstterm>filter</firstterm>. |
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[753] | 20 | </para> |
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[865] | 21 | |
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| 22 | <para> |
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| 23 | A filter is a computer program which takes data in one format as its input, and outputs the |
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| 24 | same data but transformed into another format. <application>CUPS</application> already |
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[1500] | 25 | contains many filters. For example there's one filter named <filename>pstops</filename> which accepts |
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[865] | 26 | PostScript data as its input, and, as its name implies, outputs PostScript data too, but after having |
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| 27 | eventually rearranged the pages to fit several pages on a single sheet of paper, or other manipulations |
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[959] | 28 | like that. |
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[865] | 29 | </para> |
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| 30 | |
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| 31 | <para> |
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[1500] | 32 | The <filename>pstops</filename> filter described above is also in charge of doing basic page |
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[865] | 33 | accounting, but <application>PyKota</application> currently doesn't use this facility since it may |
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[1168] | 34 | prove to be unreliable depending on the drivers used or if a paper jam occurs for example. |
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[865] | 35 | </para> |
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| 36 | |
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| 37 | <para> |
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[959] | 38 | <application>LPRng</application> can also use filters, one often used in combination with |
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| 39 | <application>LPRng</application> is <application>magicfilter</application> which can convert |
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| 40 | different input formats to native printers languages like PostScript or ESC/P2. |
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| 41 | </para> |
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| 42 | |
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| 43 | <para> |
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[1500] | 44 | So to do its own accounting, <application>PyKota</application> has its own filters, for <application>CUPS</application> |
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| 45 | it's named <filename>cupspykota</filename>, which is in fact a <application>CUPS</application> backends wrapper, |
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| 46 | and for <application>LPRng</application> it's named ########## TODO ########## . |
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| 47 | The procedure to plug the correct filter into your printing system is described in the |
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[865] | 48 | <xref linkend="installation" endterm="installation"> chapter. |
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| 49 | </para> |
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| 50 | |
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| 51 | <para> |
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[1500] | 52 | Currently with a <application>CUPS</application> internal accounting mechanism, the <filename>pstops</filename> |
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| 53 | filter can be bypassed. That's why <application>PyKota</application> uses its own backend. |
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| 54 | The <filename>cupspykota</filename> backend wrapper ensures that jobs can't bypass the filtering mechanism, so you can use |
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[1187] | 55 | any printer with any driver and any command line option, and you can be sure that your |
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| 56 | print job will be correctly accounted for. |
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[865] | 57 | </para> |
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| 58 | |
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| 59 | <para> |
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[959] | 60 | When used with an <application>LPRng</application> backend, the accounting filter is not defined the same way |
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| 61 | input filters are, so the problem described above doesn't exist, and <application>PyKota</application> |
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[1101] | 62 | may work with non-postscript printers, provided they can report their page counter and you know how to retrieve |
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| 63 | it. |
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[865] | 64 | </para> |
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| 65 | |
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[959] | 66 | <para> |
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[1500] | 67 | When you submit a print job, <application>PyKota</application>'s accounting mechanism is automatically launched by your printing system, |
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[959] | 68 | so it has to detect which system you are using (<application>CUPS</application> or <application>LPRng</application>) |
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| 69 | and behave like if it was specifically designed for your printing system. Fortunately there's not a lot |
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| 70 | of differences, the more important one is the exit codes used to tell the printing environment if a job |
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| 71 | has to be accepted or rejected. |
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| 72 | </para> |
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| 73 | |
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| 74 | <para> |
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[1475] | 75 | When using the <literal>hardware</literal> accounting method, |
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[1500] | 76 | the <application>cupspykota</application> CUPS backend |
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[1187] | 77 | asks the printer for its internal page counter at the start and at the end of the print job, and |
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[1500] | 78 | computes the values' difference so accounting is done immediately. |
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[959] | 79 | </para> |
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| 80 | |
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| 81 | <para> |
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[1475] | 82 | When using the <literal>software</literal> accounting method, |
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[1099] | 83 | and if the user is still allowed to print, |
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| 84 | the command you specified is launched with the job's data on its |
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| 85 | standard input. Your command must print the job's size in number of |
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| 86 | pages on a single line on its standard output. This number is then |
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[1500] | 87 | read by <application>PyKota</application> and used to update the current user's quota information. |
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[1475] | 88 | Of course checks are also done like with the <literal>hardware</literal> |
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[1101] | 89 | accounting method, to see if the current job is allowed to be printed or not. |
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[1099] | 90 | </para> |
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| 91 | |
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| 92 | <para> |
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[1500] | 93 | If a problem occurs, it is logged either to the filter's standard error or to the system logger, depending on |
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[1168] | 94 | your preferences in <application>PyKota</application>'s configuration files. Also if a print quota is reached |
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[1099] | 95 | you may choose if the administrator, the user, both or no-one will receive an email message explaining |
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[1500] | 96 | the situation and proposing a solution. You can even configure another action instead of sending email |
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| 97 | messages if you want. |
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[959] | 98 | </para> |
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| 99 | |
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[753] | 100 | </chapter> |
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| 101 | |
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| 102 | <!-- |
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| 103 | |
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| 104 | $Log$ |
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[1500] | 105 | Revision 1.11 2004/05/25 09:49:52 jalet |
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| 106 | The old pykota filter has been removed. LPRng support disabled for now. |
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| 107 | |
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[1475] | 108 | Revision 1.10 2004/05/13 13:59:28 jalet |
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| 109 | Code simplifications |
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| 110 | |
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[1386] | 111 | Revision 1.9 2004/03/03 19:35:36 jalet |
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| 112 | Spelling problem. Thanks to Jurandy Martins |
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| 113 | |
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[1187] | 114 | Revision 1.8 2003/11/15 14:59:53 jalet |
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| 115 | Documentation wrt the new CUPS backend. |
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| 116 | |
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[1168] | 117 | Revision 1.7 2003/10/14 20:26:53 jalet |
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| 118 | Better documentation. |
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| 119 | 1.15 is out ! |
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| 120 | |
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[1101] | 121 | Revision 1.6 2003/07/25 13:10:58 jalet |
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| 122 | Improved documentation |
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| 123 | |
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[1099] | 124 | Revision 1.5 2003/07/25 10:41:29 jalet |
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| 125 | Better documentation. |
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| 126 | pykotme now displays the current user's account balance. |
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| 127 | Some test changed in ldap module. |
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| 128 | |
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[982] | 129 | Revision 1.4 2003/04/30 20:00:51 jalet |
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| 130 | Typo |
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| 131 | |
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[959] | 132 | Revision 1.3 2003/04/24 21:09:47 jalet |
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| 133 | Documentation slightly improved. |
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| 134 | |
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[865] | 135 | Revision 1.2 2003/03/25 09:32:06 jalet |
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| 136 | Improved documentation. |
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| 137 | |
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[753] | 138 | Revision 1.1 2003/02/08 00:03:35 jalet |
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| 139 | Documentation skeleton added |
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| 140 | |
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| 141 | |
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| 142 | --> |
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