src/dbpage.c

   1 /*
   2 ** 2017-10-11
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 ******************************************************************************
  12 **
  13 ** This file contains an implementation of the "sqlite_dbpage" virtual table.
  14 **
  15 ** The sqlite_dbpage virtual table is used to read or write whole raw
  16 ** pages of the database file.  The pager interface is used so that
  17 ** uncommitted changes and changes recorded in the WAL file are correctly
  18 ** retrieved.
  19 **
  20 ** Usage example:
  21 **
  22 **    SELECT data FROM sqlite_dbpage('aux1') WHERE pgno=123;
  23 **
  24 ** This is an eponymous virtual table so it does not need to be created before
  25 ** use.  The optional argument to the sqlite_dbpage() table name is the
  26 ** schema for the database file that is to be read.  The default schema is
  27 ** "main".
  28 **
  29 ** The data field of sqlite_dbpage table can be updated.  The new
  30 ** value must be a BLOB which is the correct page size, otherwise the
  31 ** update fails.  Rows may not be deleted or inserted.
  32 */
  33
  34 #include "sqliteInt.h"   /* Requires access to internal data structures */
  35 #if (defined(SQLITE_ENABLE_DBPAGE_VTAB) || defined(SQLITE_TEST)) \
  36     && !defined(SQLITE_OMIT_VIRTUALTABLE)
  37
  38 typedef struct DbpageTable DbpageTable;
  39 typedef struct DbpageCursor DbpageCursor;
  40
  41 struct DbpageCursor {
  42   sqlite3_vtab_cursor base;       /* Base class.  Must be first */
  43   int pgno;                       /* Current page number */
  44   int mxPgno;                     /* Last page to visit on this scan */
  45   Pager *pPager;                  /* Pager being read/written */
  46   DbPage *pPage1;                 /* Page 1 of the database */
  47   int iDb;                        /* Index of database to analyze */
  48   int szPage;                     /* Size of each page in bytes */
  49 };
  50
  51 struct DbpageTable {
  52   sqlite3_vtab base;              /* Base class.  Must be first */
  53   sqlite3 *db;                    /* The database */
  54 };
  55
  56 /* Columns */
  57 #define DBPAGE_COLUMN_PGNO    0
  58 #define DBPAGE_COLUMN_DATA    1
  59 #define DBPAGE_COLUMN_SCHEMA  2
  60
  61
  62
  63 /*
  64 ** Connect to or create a dbpagevfs virtual table.
  65 */
  66 static int dbpageConnect(
  67   sqlite3 *db,
  68   void *pAux,
  69   int argc, const char *const*argv,
  70   sqlite3_vtab **ppVtab,
  71   char **pzErr
  72 ){
  73   DbpageTable *pTab = 0;
  74   int rc = SQLITE_OK;
  75
  76   rc = sqlite3_declare_vtab(db,
  77           "CREATE TABLE x(pgno INTEGER PRIMARY KEY, data BLOB, schema HIDDEN)");
  78   if( rc==SQLITE_OK ){
  79     pTab = (DbpageTable *)sqlite3_malloc64(sizeof(DbpageTable));
  80     if( pTab==0 ) rc = SQLITE_NOMEM_BKPT;
  81   }
  82
  83   assert( rc==SQLITE_OK || pTab==0 );
  84   if( rc==SQLITE_OK ){
  85     memset(pTab, 0, sizeof(DbpageTable));
  86     pTab->db = db;
  87   }
  88
  89   *ppVtab = (sqlite3_vtab*)pTab;
  90   return rc;
  91 }
  92
  93 /*
  94 ** Disconnect from or destroy a dbpagevfs virtual table.
  95 */
  96 static int dbpageDisconnect(sqlite3_vtab *pVtab){
  97   sqlite3_free(pVtab);
  98   return SQLITE_OK;
  99 }
 100
 101 /*
 102 ** idxNum:
 103 **
 104 **     0     schema=main, full table scan
 105 **     1     schema=main, pgno=?1
 106 **     2     schema=?1, full table scan
 107 **     3     schema=?1, pgno=?2
 108 */
 109 static int dbpageBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo){
 110   int i;
 111   int iPlan = 0;
 112
 113   /* If there is a schema= constraint, it must be honored.  Report a
 114   ** ridiculously large estimated cost if the schema= constraint is
 115   ** unavailable
 116   */
 117   for(i=0; i<pIdxInfo->nConstraint; i++){
 118     struct sqlite3_index_constraint *p = &pIdxInfo->aConstraint[i];
 119     if( p->iColumn!=DBPAGE_COLUMN_SCHEMA ) continue;
 120     if( p->op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;
 121     if( !p->usable ){
 122       /* No solution.  Use the default SQLITE_BIG_DBL cost */
 123       pIdxInfo->estimatedRows = 0x7fffffff;
 124       return SQLITE_OK;
 125     }
 126     iPlan = 2;
 127     pIdxInfo->aConstraintUsage[i].argvIndex = 1;
 128     pIdxInfo->aConstraintUsage[i].omit = 1;
 129     break;
 130   }
 131
 132   /* If we reach this point, it means that either there is no schema=
 133   ** constraint (in which case we use the "main" schema) or else the
 134   ** schema constraint was accepted.  Lower the estimated cost accordingly
 135   */
 136   pIdxInfo->estimatedCost = 1.0e6;
 137
 138   /* Check for constraints against pgno */
 139   for(i=0; i<pIdxInfo->nConstraint; i++){
 140     struct sqlite3_index_constraint *p = &pIdxInfo->aConstraint[i];
 141     if( p->usable && p->iColumn<=0 && p->op==SQLITE_INDEX_CONSTRAINT_EQ ){
 142       pIdxInfo->estimatedRows = 1;
 143       pIdxInfo->idxFlags = SQLITE_INDEX_SCAN_UNIQUE;
 144       pIdxInfo->estimatedCost = 1.0;
 145       pIdxInfo->aConstraintUsage[i].argvIndex = iPlan ? 2 : 1;
 146       pIdxInfo->aConstraintUsage[i].omit = 1;
 147       iPlan |= 1;
 148       break;
 149     }
 150   }
 151   pIdxInfo->idxNum = iPlan;
 152
 153   if( pIdxInfo->nOrderBy>=1
 154    && pIdxInfo->aOrderBy[0].iColumn<=0
 155    && pIdxInfo->aOrderBy[0].desc==0
 156   ){
 157     pIdxInfo->orderByConsumed = 1;
 158   }
 159   return SQLITE_OK;
 160 }
 161
 162 /*
 163 ** Open a new dbpagevfs cursor.
 164 */
 165 static int dbpageOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
 166   DbpageCursor *pCsr;
 167
 168   pCsr = (DbpageCursor *)sqlite3_malloc64(sizeof(DbpageCursor));
 169   if( pCsr==0 ){
 170     return SQLITE_NOMEM_BKPT;
 171   }else{
 172     memset(pCsr, 0, sizeof(DbpageCursor));
 173     pCsr->base.pVtab = pVTab;
 174     pCsr->pgno = -1;
 175   }
 176
 177   *ppCursor = (sqlite3_vtab_cursor *)pCsr;
 178   return SQLITE_OK;
 179 }
 180
 181 /*
 182 ** Close a dbpagevfs cursor.
 183 */
 184 static int dbpageClose(sqlite3_vtab_cursor *pCursor){
 185   DbpageCursor *pCsr = (DbpageCursor *)pCursor;
 186   if( pCsr->pPage1 ) sqlite3PagerUnrefPageOne(pCsr->pPage1);
 187   sqlite3_free(pCsr);
 188   return SQLITE_OK;
 189 }
 190
 191 /*
 192 ** Move a dbpagevfs cursor to the next entry in the file.
 193 */
 194 static int dbpageNext(sqlite3_vtab_cursor *pCursor){
 195   int rc = SQLITE_OK;
 196   DbpageCursor *pCsr = (DbpageCursor *)pCursor;
 197   pCsr->pgno++;
 198   return rc;
 199 }
 200
 201 static int dbpageEof(sqlite3_vtab_cursor *pCursor){
 202   DbpageCursor *pCsr = (DbpageCursor *)pCursor;
 203   return pCsr->pgno > pCsr->mxPgno;
 204 }
 205
 206 /*
 207 ** idxNum:
 208 **
 209 **     0     schema=main, full table scan
 210 **     1     schema=main, pgno=?1
 211 **     2     schema=?1, full table scan
 212 **     3     schema=?1, pgno=?2
 213 **
 214 ** idxStr is not used
 215 */
 216 static int dbpageFilter(
 217   sqlite3_vtab_cursor *pCursor,
 218   int idxNum, const char *idxStr,
 219   int argc, sqlite3_value **argv
 220 ){
 221   DbpageCursor *pCsr = (DbpageCursor *)pCursor;
 222   DbpageTable *pTab = (DbpageTable *)pCursor->pVtab;
 223   int rc;
 224   sqlite3 *db = pTab->db;
 225   Btree *pBt;
 226
 227   /* Default setting is no rows of result */
 228   pCsr->pgno = 1;
 229   pCsr->mxPgno = 0;
 230
 231   if( idxNum & 2 ){
 232     const char *zSchema;
 233     assert( argc>=1 );
 234     zSchema = (const char*)sqlite3_value_text(argv[0]);
 235     pCsr->iDb = sqlite3FindDbName(db, zSchema);
 236     if( pCsr->iDb<0 ) return SQLITE_OK;
 237   }else{
 238     pCsr->iDb = 0;
 239   }
 240   pBt = db->aDb[pCsr->iDb].pBt;
 241   if( pBt==0 ) return SQLITE_OK;
 242   pCsr->pPager = sqlite3BtreePager(pBt);
 243   pCsr->szPage = sqlite3BtreeGetPageSize(pBt);
 244   pCsr->mxPgno = sqlite3BtreeLastPage(pBt);
 245   if( idxNum & 1 ){
 246     assert( argc>(idxNum>>1) );
 247     pCsr->pgno = sqlite3_value_int(argv[idxNum>>1]);
 248     if( pCsr->pgno<1 || pCsr->pgno>pCsr->mxPgno ){
 249       pCsr->pgno = 1;
 250       pCsr->mxPgno = 0;
 251     }else{
 252       pCsr->mxPgno = pCsr->pgno;
 253     }
 254   }else{
 255     assert( pCsr->pgno==1 );
 256   }
 257   if( pCsr->pPage1 ) sqlite3PagerUnrefPageOne(pCsr->pPage1);
 258   rc = sqlite3PagerGet(pCsr->pPager, 1, &pCsr->pPage1, 0);
 259   return rc;
 260 }
 261
 262 static int dbpageColumn(
 263   sqlite3_vtab_cursor *pCursor,
 264   sqlite3_context *ctx,
 265   int i
 266 ){
 267   DbpageCursor *pCsr = (DbpageCursor *)pCursor;
 268   int rc = SQLITE_OK;
 269   switch( i ){
 270     case 0: {           /* pgno */
 271       sqlite3_result_int(ctx, pCsr->pgno);
 272       break;
 273     }
 274     case 1: {           /* data */
 275       DbPage *pDbPage = 0;
 276       rc = sqlite3PagerGet(pCsr->pPager, pCsr->pgno, (DbPage**)&pDbPage, 0);
 277       if( rc==SQLITE_OK ){
 278         sqlite3_result_blob(ctx, sqlite3PagerGetData(pDbPage), pCsr->szPage,
 279                             SQLITE_TRANSIENT);
 280       }
 281       sqlite3PagerUnref(pDbPage);
 282       break;
 283     }
 284     default: {          /* schema */
 285       sqlite3 *db = sqlite3_context_db_handle(ctx);
 286       sqlite3_result_text(ctx, db->aDb[pCsr->iDb].zDbSName, -1, SQLITE_STATIC);
 287       break;
 288     }
 289   }
 290   return SQLITE_OK;
 291 }
 292
 293 static int dbpageRowid(sqlite3_vtab_cursor *pCursor, sqlite_int64 *pRowid){
 294   DbpageCursor *pCsr = (DbpageCursor *)pCursor;
 295   *pRowid = pCsr->pgno;
 296   return SQLITE_OK;
 297 }
 298
 299 static int dbpageUpdate(
 300   sqlite3_vtab *pVtab,
 301   int argc,
 302   sqlite3_value **argv,
 303   sqlite_int64 *pRowid
 304 ){
 305   DbpageTable *pTab = (DbpageTable *)pVtab;
 306   int pgno;
 307   DbPage *pDbPage = 0;
 308   int rc = SQLITE_OK;
 309   char *zErr = 0;
 310   const char *zSchema;
 311   int iDb;
 312   Btree *pBt;
 313   Pager *pPager;
 314   int szPage;
 315
 316   if( argc==1 ){
 317     zErr = "cannot delete";
 318     goto update_fail;
 319   }
 320   pgno = sqlite3_value_int(argv[0]);
 321   if( sqlite3_value_int(argv[1])!=pgno ){
 322     zErr = "cannot insert";
 323     goto update_fail;
 324   }
 325   zSchema = (const char*)sqlite3_value_text(argv[4]);
 326   iDb = zSchema ? sqlite3FindDbName(pTab->db, zSchema) : -1;
 327   if( iDb<0 ){
 328     zErr = "no such schema";
 329     goto update_fail;
 330   }
 331   pBt = pTab->db->aDb[iDb].pBt;
 332   if( pgno<1 || pBt==0 || pgno>(int)sqlite3BtreeLastPage(pBt) ){
 333     zErr = "bad page number";
 334     goto update_fail;
 335   }
 336   szPage = sqlite3BtreeGetPageSize(pBt);
 337   if( sqlite3_value_type(argv[3])!=SQLITE_BLOB
 338    || sqlite3_value_bytes(argv[3])!=szPage
 339   ){
 340     zErr = "bad page value";
 341     goto update_fail;
 342   }
 343   pPager = sqlite3BtreePager(pBt);
 344   rc = sqlite3PagerGet(pPager, pgno, (DbPage**)&pDbPage, 0);
 345   if( rc==SQLITE_OK ){
 346     rc = sqlite3PagerWrite(pDbPage);
 347     if( rc==SQLITE_OK ){
 348       memcpy(sqlite3PagerGetData(pDbPage),
 349              sqlite3_value_blob(argv[3]),
 350              szPage);
 351     }
 352   }
 353   sqlite3PagerUnref(pDbPage);
 354   return rc;
 355
 356 update_fail:
 357   sqlite3_free(pVtab->zErrMsg);
 358   pVtab->zErrMsg = sqlite3_mprintf("%s", zErr);
 359   return SQLITE_ERROR;
 360 }
 361
 362 /* Since we do not know in advance which database files will be
 363 ** written by the sqlite_dbpage virtual table, start a write transaction
 364 ** on them all.
 365 */
 366 static int dbpageBegin(sqlite3_vtab *pVtab){
 367   DbpageTable *pTab = (DbpageTable *)pVtab;
 368   sqlite3 *db = pTab->db;
 369   int i;
 370   for(i=0; i<db->nDb; i++){
 371     Btree *pBt = db->aDb[i].pBt;
 372     if( pBt ) sqlite3BtreeBeginTrans(pBt, 1);
 373   }
 374   return SQLITE_OK;
 375 }
 376
 377
 378 /*
 379 ** Invoke this routine to register the "dbpage" virtual table module
 380 */
 381 int sqlite3DbpageRegister(sqlite3 *db){
 382   static sqlite3_module dbpage_module = {
 383     0,                            /* iVersion */
 384     dbpageConnect,                /* xCreate */
 385     dbpageConnect,                /* xConnect */
 386     dbpageBestIndex,              /* xBestIndex */
 387     dbpageDisconnect,             /* xDisconnect */
 388     dbpageDisconnect,             /* xDestroy */
 389     dbpageOpen,                   /* xOpen - open a cursor */
 390     dbpageClose,                  /* xClose - close a cursor */
 391     dbpageFilter,                 /* xFilter - configure scan constraints */
 392     dbpageNext,                   /* xNext - advance a cursor */
 393     dbpageEof,                    /* xEof - check for end of scan */
 394     dbpageColumn,                 /* xColumn - read data */
 395     dbpageRowid,                  /* xRowid - read data */
 396     dbpageUpdate,                 /* xUpdate */
 397     dbpageBegin,                  /* xBegin */
 398     0,                            /* xSync */
 399     0,                            /* xCommit */
 400     0,                            /* xRollback */
 401     0,                            /* xFindMethod */
 402     0,                            /* xRename */
 403     0,                            /* xSavepoint */
 404     0,                            /* xRelease */
 405     0,                            /* xRollbackTo */
 406   };
 407   return sqlite3_create_module(db, "sqlite_dbpage", &dbpage_module, 0);
 408 }
 409 #elif defined(SQLITE_ENABLE_DBPAGE_VTAB)
 410 int sqlite3DbpageRegister(sqlite3 *db){ return SQLITE_OK; }
 411 #endif /* SQLITE_ENABLE_DBSTAT_VTAB */