dbscripts/dupetrigger/dupetrigger.c

   1 //
   2 //
   3 // This File contructs a PostgreSQL trigger.
   4 // The trigger is fired BEFORE an INSERT or UPDATE of an article
   5 // or comment. It first calculates a CRC32 checksum of the row to be
   6 // inserted or updated and checks whether there exists already another
   7 // row with the same checksum and the same content. In this case,
   8 // the trigger returns NULL and thus, aborts the SQL command.
   9 //
  10 // Author: Matthias Jordan <mjordan@code-fu.de>
  11 //
  12
  13
  14 #include "executor/spi.h"
  15 #include "commands/trigger.h"
  16 #include "string.h"
  17
  18 extern Datum dupecheck(PG_FUNCTION_ARGS);
  19
  20 PG_FUNCTION_INFO_V1(dupecheck);
  21
  22
  23
  24
  25 //
  26 //
  27 // CRC32 stuff
  28 //
  29
  30 // crc32 table based on the following polynom
  31 #define CRC32_POLY 0x04c11db7     /* AUTODIN II, Ethernet, & FDDI */
  32
  33 u_long crc32_table[256] =
  34         {0x0000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9, 0x130476dc, 0x17c56b6b,
  35         0x1a864db2, 0x1e475005, 0x2608edb8, 0x22c9f00f, 0x2f8ad6d6, 0x2b4bcb61,
  36         0x350c9b64, 0x31cd86d3, 0x3c8ea00a, 0x384fbdbd, 0x4c11db70, 0x48d0c6c7,
  37         0x4593e01e, 0x4152fda9, 0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75,
  38         0x6a1936c8, 0x6ed82b7f, 0x639b0da6, 0x675a1011, 0x791d4014, 0x7ddc5da3,
  39         0x709f7b7a, 0x745e66cd, 0x9823b6e0, 0x9ce2ab57, 0x91a18d8e, 0x95609039,
  40         0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5, 0xbe2b5b58, 0xbaea46ef,
  41         0xb7a96036, 0xb3687d81, 0xad2f2d84, 0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d,
  42         0xd4326d90, 0xd0f37027, 0xddb056fe, 0xd9714b49, 0xc7361b4c, 0xc3f706fb,
  43         0xceb42022, 0xca753d95, 0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1,
  44         0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d, 0x34867077, 0x30476dc0,
  45         0x3d044b19, 0x39c556ae, 0x278206ab, 0x23431b1c, 0x2e003dc5, 0x2ac12072,
  46         0x128e9dcf, 0x164f8078, 0x1b0ca6a1, 0x1fcdbb16, 0x018aeb13, 0x54bf6a4,
  47         0x0808d07d, 0x0cc9cdca, 0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde,
  48         0x6b93dddb, 0x6f52c06c, 0x6211e6b5, 0x66d0fb02, 0x5e9f46bf, 0x5a5e5b08,
  49         0x571d7dd1, 0x53dc6066, 0x4d9b3063, 0x495a2dd4, 0x44190b0d, 0x40d816ba,
  50         0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e, 0xbfa1b04b, 0xbb60adfc,
  51         0xb6238b25, 0xb2e29692, 0x8aad2b2f, 0x8e6c3698, 0x832f1041, 0x87ee0df6,
  52         0x99a95df3, 0x9d684044, 0x902b669d, 0x94ea7b2a, 0xe0b41de7, 0xe4750050,
  53         0xe9362689, 0xedf73b3e, 0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
  54         0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686, 0xd5b88683, 0xd1799b34,
  55         0xdc3abded, 0xd8fba05a, 0x690ce0ee, 0x6dcdfd59, 0x608edb80, 0x644fc637,
  56         0x7a089632, 0x7ec98b85, 0x738aad5c, 0x774bb0eb, 0x4f040d56, 0x4bc510e1,
  57         0x46863638, 0x42472b8f, 0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53,
  58         0x251d3b9e, 0x21dc2629, 0x2c9f00f0, 0x285e1d47, 0x36194d42, 0x32d850f5,
  59         0x3f9b762c, 0x3b5a6b9b, 0x0315d626, 0x07d4cb91, 0x0a97ed48, 0xe56f0ff,
  60         0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623, 0xf12f560e, 0xf5ee4bb9,
  61         0xf8ad6d60, 0xfc6c70d7, 0xe22b20d2, 0xe6ea3d65, 0xeba91bbc, 0xef68060b,
  62         0xd727bbb6, 0xd3e6a601, 0xdea580d8, 0xda649d6f, 0xc423cd6a, 0xc0e2d0dd,
  63         0xcda1f604, 0xc960ebb3, 0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7,
  64         0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b, 0x9b3660c6, 0x9ff77d71,
  65         0x92b45ba8, 0x9675461f, 0x8832161a, 0x8cf30bad, 0x81b02d74, 0x857130c3,
  66         0x5d8a9099, 0x594b8d2e, 0x5408abf7, 0x50c9b640, 0x4e8ee645, 0x4a4ffbf2,
  67         0x470cdd2b, 0x43cdc09c, 0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8,
  68         0x68860bfd, 0x6c47164a, 0x61043093, 0x65c52d24, 0x119b4be9, 0x155a565e,
  69         0x18197087, 0x1cd86d30, 0x029f3d35, 0x065e2082, 0x0b1d065b, 0xfdc1bec,
  70         0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088, 0x2497d08d, 0x2056cd3a,
  71         0x2d15ebe3, 0x29d4f654, 0xc5a92679, 0xc1683bce, 0xcc2b1d17, 0xc8ea00a0,
  72         0xd6ad50a5, 0xd26c4d12, 0xdf2f6bcb, 0xdbee767c, 0xe3a1cbc1, 0xe760d676,
  73         0xea23f0af, 0xeee2ed18, 0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
  74         0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0, 0x9abc8bd5, 0x9e7d9662,
  75         0x933eb0bb, 0x97ffad0c, 0xafb010b1, 0xab710d06, 0xa6322bdf, 0xa2f33668,
  76         0xbcb4666d, 0xb8757bda, 0xb5365d03, 0xb1f740b4};
  77
  78
  79 static u_long crc32(u_char *buf, unsigned len)
  80 {
  81         u_char *p;
  82         u_long  crc;
  83
  84         crc = 0xffffffff;       /* preload shift register, per CRC-32 spec */
  85         for (p = buf; len > 0; ++p, --len)
  86         {
  87                 crc = (crc << 8) ^ crc32_table[(crc >> 24) ^ *p];
  88         }
  89         return ~crc;            /* transmit complement, per CRC-32 spec */
  90 } /* crc32 */
  91
  92
  93
  94
  95
  96 //
  97 //
  98 // Trigger stuff
  99 //
 100
 101
 102
 103
 104 Datum dupecheck(PG_FUNCTION_ARGS)
 105 {
 106         TriggerData *trigdata = (TriggerData *) fcinfo->context;
 107         TupleDesc       tupdesc;
 108         HeapTuple       rettuple;
 109         bool            isnull;
 110         int                     ret = 0, i, fnumber;
 111         long rowstrlen = 0,
 112                 crc;
 113         int maxitems = 3,
 114                 num;
 115         char *items[maxitems],
 116                 *rowstring,
 117                 *query;
 118
 119
 120         /* Make sure trigdata is pointing at what I expect */
 121         if (!CALLED_AS_TRIGGER(fcinfo))
 122                 elog(ERROR, "dupecheck: not fired by trigger manager");
 123
 124         /* tuple to return to Executor */
 125         if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
 126                 rettuple = trigdata->tg_newtuple;
 127         else
 128                 rettuple = trigdata->tg_trigtuple;
 129
 130         if (TRIGGER_FIRED_BY_DELETE(trigdata->tg_event))
 131                 return PointerGetDatum(NULL);
 132
 133         tupdesc = trigdata->tg_relation->rd_att;
 134
 135         /* Connect to SPI manager */
 136         if ((ret = SPI_connect()) < 0)
 137         ret = SPI_connect();
 138         elog(NOTICE, "dupecheck: SPI_connect returned %d", ret);
 139
 140         // Now we are connected to the database's SPI manager
 141         // We will now construct a string of some important row values.
 142         // First, we determine how long the string will be to allocate memory
 143         // To include an additional item, add another SPI_getvalue line and
 144         // increase maxitems above by 1
 145
 146         items[0] = SPI_getvalue(rettuple, tupdesc, SPI_fnumber(tupdesc, "creator"));
 147         items[1] = SPI_getvalue(rettuple, tupdesc, SPI_fnumber(tupdesc, "title"));
 148         items[2] = SPI_getvalue(rettuple, tupdesc, SPI_fnumber(tupdesc, "description"));
 149
 150         for (i=0; (i < maxitems); i++)
 151         {
 152                 rowstrlen += strlen(items[i]);
 153         }
 154         rowstrlen++; // add space for 0-terminator
 155
 156         rowstring = malloc(rowstrlen);
 157         if (rowstring == NULL)
 158         {
 159                 // Big problem.
 160                 return PointerGetDatum(NULL);
 161         }
 162
 163         *rowstring = 0;
 164         for (i=0; (i < maxitems); i++)
 165         {
 166                 strcat(rowstring, items[i]);
 167         }
 168
 169         // rowstring now contains the data of the maxitems important
 170         // items of the table record. Now we calculate the CRC-32 checksum
 171         // of the rowstring
 172
 173         crc = crc32(rowstring, rowstrlen - 1);
 174
 175         // Now we allocate some space and construct the SQL query
 176         query = malloc(47 + 11 + 2 + 1); // SELECT part + crc32 + "';" + 0-term
 177         if (query == NULL)
 178         {
 179                 // Big problem
 180                 return PointerGetDatum(NULL);
 181         }
 182
 183         sprintf(query, "SELECT count(*) FROM comment WHERE checksum='%ld';", crc);
 184         ret = SPI_exec(query, 2);
 185         num = SPI_getbinval(SPI_tuptable->vals[0], SPI_tuptable->tupdesc, 1, &isnull);
 186
 187         if ((ret == SPI_OK_SELECT) && (num > 0))
 188         {
 189                 elog(NOTICE, "dupecheck: UBD prevented (dupe dropped)");
 190                 return PointerGetDatum(NULL);
 191         }
 192         else
 193         {
 194                 // The checksum wasn't found. So we modify the tuple to be
 195                 // inserted and add the fresh checksum.
 196                 int attnum;
 197                 Datum value;
 198                 char nulls = 0;
 199
 200                 elog(NOTICE, "dupecheck: Adding checksum to INSERT");
 201                 attnum = SPI_fnumber(tupdesc, "checksum");
 202                 value = (Datum) crc;
 203                 rettuple = SPI_modifytuple(trigdata->tg_relation, rettuple, 1, &attnum, &value, &nulls);
 204         }
 205
 206         SPI_finish();
 207         return PointerGetDatum(rettuple);
 208 }
 209