src/vdbeblob.c

   1 /*
   2 ** 2007 May 1
   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 code used to implement incremental BLOB I/O.
  14 */
  15
  16 #include "sqliteInt.h"
  17 #include "vdbeInt.h"
  18
  19 #ifndef SQLITE_OMIT_INCRBLOB
  20
  21 /*
  22 ** Valid sqlite3_blob* handles point to Incrblob structures.
  23 */
  24 typedef struct Incrblob Incrblob;
  25 struct Incrblob {
  26   int nByte;              /* Size of open blob, in bytes */
  27   int iOffset;            /* Byte offset of blob in cursor data */
  28   u16 iCol;               /* Table column this handle is open on */
  29   BtCursor *pCsr;         /* Cursor pointing at blob row */
  30   sqlite3_stmt *pStmt;    /* Statement holding cursor open */
  31   sqlite3 *db;            /* The associated database */
  32   char *zDb;              /* Database name */
  33   Table *pTab;            /* Table object */
  34 };
  35
  36
  37 /*
  38 ** This function is used by both blob_open() and blob_reopen(). It seeks
  39 ** the b-tree cursor associated with blob handle p to point to row iRow.
  40 ** If successful, SQLITE_OK is returned and subsequent calls to
  41 ** sqlite3_blob_read() or sqlite3_blob_write() access the specified row.
  42 **
  43 ** If an error occurs, or if the specified row does not exist or does not
  44 ** contain a value of type TEXT or BLOB in the column nominated when the
  45 ** blob handle was opened, then an error code is returned and *pzErr may
  46 ** be set to point to a buffer containing an error message. It is the
  47 ** responsibility of the caller to free the error message buffer using
  48 ** sqlite3DbFree().
  49 **
  50 ** If an error does occur, then the b-tree cursor is closed. All subsequent
  51 ** calls to sqlite3_blob_read(), blob_write() or blob_reopen() will
  52 ** immediately return SQLITE_ABORT.
  53 */
  54 static int blobSeekToRow(Incrblob *p, sqlite3_int64 iRow, char **pzErr){
  55   int rc;                         /* Error code */
  56   char *zErr = 0;                 /* Error message */
  57   Vdbe *v = (Vdbe *)p->pStmt;
  58
  59   /* Set the value of register r[1] in the SQL statement to integer iRow.
  60   ** This is done directly as a performance optimization
  61   */
  62   v->aMem[1].flags = MEM_Int;
  63   v->aMem[1].u.i = iRow;
  64
  65   /* If the statement has been run before (and is paused at the OP_ResultRow)
  66   ** then back it up to the point where it does the OP_NotExists.  This could
  67   ** have been down with an extra OP_Goto, but simply setting the program
  68   ** counter is faster. */
  69   if( v->pc>4 ){
  70     v->pc = 4;
  71     assert( v->aOp[v->pc].opcode==OP_NotExists );
  72     rc = sqlite3VdbeExec(v);
  73   }else{
  74     rc = sqlite3_step(p->pStmt);
  75   }
  76   if( rc==SQLITE_ROW ){
  77     VdbeCursor *pC = v->apCsr[0];
  78     u32 type = pC->nHdrParsed>p->iCol ? pC->aType[p->iCol] : 0;
  79     testcase( pC->nHdrParsed==p->iCol );
  80     testcase( pC->nHdrParsed==p->iCol+1 );
  81     if( type<12 ){
  82       zErr = sqlite3MPrintf(p->db, "cannot open value of type %s",
  83           type==0?"null": type==7?"real": "integer"
  84       );
  85       rc = SQLITE_ERROR;
  86       sqlite3_finalize(p->pStmt);
  87       p->pStmt = 0;
  88     }else{
  89       p->iOffset = pC->aType[p->iCol + pC->nField];
  90       p->nByte = sqlite3VdbeSerialTypeLen(type);
  91       p->pCsr =  pC->uc.pCursor;
  92       sqlite3BtreeIncrblobCursor(p->pCsr);
  93     }
  94   }
  95
  96   if( rc==SQLITE_ROW ){
  97     rc = SQLITE_OK;
  98   }else if( p->pStmt ){
  99     rc = sqlite3_finalize(p->pStmt);
 100     p->pStmt = 0;
 101     if( rc==SQLITE_OK ){
 102       zErr = sqlite3MPrintf(p->db, "no such rowid: %lld", iRow);
 103       rc = SQLITE_ERROR;
 104     }else{
 105       zErr = sqlite3MPrintf(p->db, "%s", sqlite3_errmsg(p->db));
 106     }
 107   }
 108
 109   assert( rc!=SQLITE_OK || zErr==0 );
 110   assert( rc!=SQLITE_ROW && rc!=SQLITE_DONE );
 111
 112   *pzErr = zErr;
 113   return rc;
 114 }
 115
 116 /*
 117 ** Open a blob handle.
 118 */
 119 int sqlite3_blob_open(
 120   sqlite3* db,            /* The database connection */
 121   const char *zDb,        /* The attached database containing the blob */
 122   const char *zTable,     /* The table containing the blob */
 123   const char *zColumn,    /* The column containing the blob */
 124   sqlite_int64 iRow,      /* The row containing the glob */
 125   int wrFlag,             /* True -> read/write access, false -> read-only */
 126   sqlite3_blob **ppBlob   /* Handle for accessing the blob returned here */
 127 ){
 128   int nAttempt = 0;
 129   int iCol;               /* Index of zColumn in row-record */
 130   int rc = SQLITE_OK;
 131   char *zErr = 0;
 132   Table *pTab;
 133   Incrblob *pBlob = 0;
 134   Parse sParse;
 135
 136 #ifdef SQLITE_ENABLE_API_ARMOR
 137   if( ppBlob==0 ){
 138     return SQLITE_MISUSE_BKPT;
 139   }
 140 #endif
 141   *ppBlob = 0;
 142 #ifdef SQLITE_ENABLE_API_ARMOR
 143   if( !sqlite3SafetyCheckOk(db) || zTable==0 ){
 144     return SQLITE_MISUSE_BKPT;
 145   }
 146 #endif
 147   wrFlag = !!wrFlag;                /* wrFlag = (wrFlag ? 1 : 0); */
 148
 149   sqlite3_mutex_enter(db->mutex);
 150
 151   pBlob = (Incrblob *)sqlite3DbMallocZero(db, sizeof(Incrblob));
 152   do {
 153     memset(&sParse, 0, sizeof(Parse));
 154     if( !pBlob ) goto blob_open_out;
 155     sParse.db = db;
 156     sqlite3DbFree(db, zErr);
 157     zErr = 0;
 158
 159     sqlite3BtreeEnterAll(db);
 160     pTab = sqlite3LocateTable(&sParse, 0, zTable, zDb);
 161     if( pTab && IsVirtual(pTab) ){
 162       pTab = 0;
 163       sqlite3ErrorMsg(&sParse, "cannot open virtual table: %s", zTable);
 164     }
 165     if( pTab && !HasRowid(pTab) ){
 166       pTab = 0;
 167       sqlite3ErrorMsg(&sParse, "cannot open table without rowid: %s", zTable);
 168     }
 169 #ifndef SQLITE_OMIT_VIEW
 170     if( pTab && pTab->pSelect ){
 171       pTab = 0;
 172       sqlite3ErrorMsg(&sParse, "cannot open view: %s", zTable);
 173     }
 174 #endif
 175     if( !pTab ){
 176       if( sParse.zErrMsg ){
 177         sqlite3DbFree(db, zErr);
 178         zErr = sParse.zErrMsg;
 179         sParse.zErrMsg = 0;
 180       }
 181       rc = SQLITE_ERROR;
 182       sqlite3BtreeLeaveAll(db);
 183       goto blob_open_out;
 184     }
 185     pBlob->pTab = pTab;
 186     pBlob->zDb = db->aDb[sqlite3SchemaToIndex(db, pTab->pSchema)].zDbSName;
 187
 188     /* Now search pTab for the exact column. */
 189     for(iCol=0; iCol<pTab->nCol; iCol++) {
 190       if( sqlite3StrICmp(pTab->aCol[iCol].zName, zColumn)==0 ){
 191         break;
 192       }
 193     }
 194     if( iCol==pTab->nCol ){
 195       sqlite3DbFree(db, zErr);
 196       zErr = sqlite3MPrintf(db, "no such column: \"%s\"", zColumn);
 197       rc = SQLITE_ERROR;
 198       sqlite3BtreeLeaveAll(db);
 199       goto blob_open_out;
 200     }
 201
 202     /* If the value is being opened for writing, check that the
 203     ** column is not indexed, and that it is not part of a foreign key.
 204     */
 205     if( wrFlag ){
 206       const char *zFault = 0;
 207       Index *pIdx;
 208 #ifndef SQLITE_OMIT_FOREIGN_KEY
 209       if( db->flags&SQLITE_ForeignKeys ){
 210         /* Check that the column is not part of an FK child key definition. It
 211         ** is not necessary to check if it is part of a parent key, as parent
 212         ** key columns must be indexed. The check below will pick up this
 213         ** case.  */
 214         FKey *pFKey;
 215         for(pFKey=pTab->pFKey; pFKey; pFKey=pFKey->pNextFrom){
 216           int j;
 217           for(j=0; j<pFKey->nCol; j++){
 218             if( pFKey->aCol[j].iFrom==iCol ){
 219               zFault = "foreign key";
 220             }
 221           }
 222         }
 223       }
 224 #endif
 225       for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
 226         int j;
 227         for(j=0; j<pIdx->nKeyCol; j++){
 228           /* FIXME: Be smarter about indexes that use expressions */
 229           if( pIdx->aiColumn[j]==iCol || pIdx->aiColumn[j]==XN_EXPR ){
 230             zFault = "indexed";
 231           }
 232         }
 233       }
 234       if( zFault ){
 235         sqlite3DbFree(db, zErr);
 236         zErr = sqlite3MPrintf(db, "cannot open %s column for writing", zFault);
 237         rc = SQLITE_ERROR;
 238         sqlite3BtreeLeaveAll(db);
 239         goto blob_open_out;
 240       }
 241     }
 242
 243     pBlob->pStmt = (sqlite3_stmt *)sqlite3VdbeCreate(&sParse);
 244     assert( pBlob->pStmt || db->mallocFailed );
 245     if( pBlob->pStmt ){
 246
 247       /* This VDBE program seeks a btree cursor to the identified
 248       ** db/table/row entry. The reason for using a vdbe program instead
 249       ** of writing code to use the b-tree layer directly is that the
 250       ** vdbe program will take advantage of the various transaction,
 251       ** locking and error handling infrastructure built into the vdbe.
 252       **
 253       ** After seeking the cursor, the vdbe executes an OP_ResultRow.
 254       ** Code external to the Vdbe then "borrows" the b-tree cursor and
 255       ** uses it to implement the blob_read(), blob_write() and
 256       ** blob_bytes() functions.
 257       **
 258       ** The sqlite3_blob_close() function finalizes the vdbe program,
 259       ** which closes the b-tree cursor and (possibly) commits the
 260       ** transaction.
 261       */
 262       static const int iLn = VDBE_OFFSET_LINENO(2);
 263       static const VdbeOpList openBlob[] = {
 264         {OP_TableLock,      0, 0, 0},  /* 0: Acquire a read or write lock */
 265         {OP_OpenRead,       0, 0, 0},  /* 1: Open a cursor */
 266         /* blobSeekToRow() will initialize r[1] to the desired rowid */
 267         {OP_NotExists,      0, 5, 1},  /* 2: Seek the cursor to rowid=r[1] */
 268         {OP_Column,         0, 0, 1},  /* 3  */
 269         {OP_ResultRow,      1, 0, 0},  /* 4  */
 270         {OP_Halt,           0, 0, 0},  /* 5  */
 271       };
 272       Vdbe *v = (Vdbe *)pBlob->pStmt;
 273       int iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
 274       VdbeOp *aOp;
 275
 276       sqlite3VdbeAddOp4Int(v, OP_Transaction, iDb, wrFlag,
 277                            pTab->pSchema->schema_cookie,
 278                            pTab->pSchema->iGeneration);
 279       sqlite3VdbeChangeP5(v, 1);
 280       assert( sqlite3VdbeCurrentAddr(v)==2 || db->mallocFailed );
 281       aOp = sqlite3VdbeAddOpList(v, ArraySize(openBlob), openBlob, iLn);
 282
 283       /* Make sure a mutex is held on the table to be accessed */
 284       sqlite3VdbeUsesBtree(v, iDb);
 285
 286       if( db->mallocFailed==0 ){
 287         assert( aOp!=0 );
 288         /* Configure the OP_TableLock instruction */
 289 #ifdef SQLITE_OMIT_SHARED_CACHE
 290         aOp[0].opcode = OP_Noop;
 291 #else
 292         aOp[0].p1 = iDb;
 293         aOp[0].p2 = pTab->tnum;
 294         aOp[0].p3 = wrFlag;
 295         sqlite3VdbeChangeP4(v, 2, pTab->zName, P4_TRANSIENT);
 296       }
 297       if( db->mallocFailed==0 ){
 298 #endif
 299
 300         /* Remove either the OP_OpenWrite or OpenRead. Set the P2
 301         ** parameter of the other to pTab->tnum.  */
 302         if( wrFlag ) aOp[1].opcode = OP_OpenWrite;
 303         aOp[1].p2 = pTab->tnum;
 304         aOp[1].p3 = iDb;
 305
 306         /* Configure the number of columns. Configure the cursor to
 307         ** think that the table has one more column than it really
 308         ** does. An OP_Column to retrieve this imaginary column will
 309         ** always return an SQL NULL. This is useful because it means
 310         ** we can invoke OP_Column to fill in the vdbe cursors type
 311         ** and offset cache without causing any IO.
 312         */
 313         aOp[1].p4type = P4_INT32;
 314         aOp[1].p4.i = pTab->nCol+1;
 315         aOp[3].p2 = pTab->nCol;
 316
 317         sParse.nVar = 0;
 318         sParse.nMem = 1;
 319         sParse.nTab = 1;
 320         sqlite3VdbeMakeReady(v, &sParse);
 321       }
 322     }
 323
 324     pBlob->iCol = iCol;
 325     pBlob->db = db;
 326     sqlite3BtreeLeaveAll(db);
 327     if( db->mallocFailed ){
 328       goto blob_open_out;
 329     }
 330     rc = blobSeekToRow(pBlob, iRow, &zErr);
 331   } while( (++nAttempt)<SQLITE_MAX_SCHEMA_RETRY && rc==SQLITE_SCHEMA );
 332
 333 blob_open_out:
 334   if( rc==SQLITE_OK && db->mallocFailed==0 ){
 335     *ppBlob = (sqlite3_blob *)pBlob;
 336   }else{
 337     if( pBlob && pBlob->pStmt ) sqlite3VdbeFinalize((Vdbe *)pBlob->pStmt);
 338     sqlite3DbFree(db, pBlob);
 339   }
 340   sqlite3ErrorWithMsg(db, rc, (zErr ? "%s" : 0), zErr);
 341   sqlite3DbFree(db, zErr);
 342   sqlite3ParserReset(&sParse);
 343   rc = sqlite3ApiExit(db, rc);
 344   sqlite3_mutex_leave(db->mutex);
 345   return rc;
 346 }
 347
 348 /*
 349 ** Close a blob handle that was previously created using
 350 ** sqlite3_blob_open().
 351 */
 352 int sqlite3_blob_close(sqlite3_blob *pBlob){
 353   Incrblob *p = (Incrblob *)pBlob;
 354   int rc;
 355   sqlite3 *db;
 356
 357   if( p ){
 358     db = p->db;
 359     sqlite3_mutex_enter(db->mutex);
 360     rc = sqlite3_finalize(p->pStmt);
 361     sqlite3DbFree(db, p);
 362     sqlite3_mutex_leave(db->mutex);
 363   }else{
 364     rc = SQLITE_OK;
 365   }
 366   return rc;
 367 }
 368
 369 /*
 370 ** Perform a read or write operation on a blob
 371 */
 372 static int blobReadWrite(
 373   sqlite3_blob *pBlob,
 374   void *z,
 375   int n,
 376   int iOffset,
 377   int (*xCall)(BtCursor*, u32, u32, void*)
 378 ){
 379   int rc;
 380   Incrblob *p = (Incrblob *)pBlob;
 381   Vdbe *v;
 382   sqlite3 *db;
 383
 384   if( p==0 ) return SQLITE_MISUSE_BKPT;
 385   db = p->db;
 386   sqlite3_mutex_enter(db->mutex);
 387   v = (Vdbe*)p->pStmt;
 388
 389   if( n<0 || iOffset<0 || ((sqlite3_int64)iOffset+n)>p->nByte ){
 390     /* Request is out of range. Return a transient error. */
 391     rc = SQLITE_ERROR;
 392   }else if( v==0 ){
 393     /* If there is no statement handle, then the blob-handle has
 394     ** already been invalidated. Return SQLITE_ABORT in this case.
 395     */
 396     rc = SQLITE_ABORT;
 397   }else{
 398     /* Call either BtreeData() or BtreePutData(). If SQLITE_ABORT is
 399     ** returned, clean-up the statement handle.
 400     */
 401     assert( db == v->db );
 402     sqlite3BtreeEnterCursor(p->pCsr);
 403
 404 #ifdef SQLITE_ENABLE_PREUPDATE_HOOK
 405     if( xCall==sqlite3BtreePutData && db->xPreUpdateCallback ){
 406       /* If a pre-update hook is registered and this is a write cursor,
 407       ** invoke it here.
 408       **
 409       ** TODO: The preupdate-hook is passed SQLITE_DELETE, even though this
 410       ** operation should really be an SQLITE_UPDATE. This is probably
 411       ** incorrect, but is convenient because at this point the new.* values
 412       ** are not easily obtainable. And for the sessions module, an
 413       ** SQLITE_UPDATE where the PK columns do not change is handled in the
 414       ** same way as an SQLITE_DELETE (the SQLITE_DELETE code is actually
 415       ** slightly more efficient). Since you cannot write to a PK column
 416       ** using the incremental-blob API, this works. For the sessions module
 417       ** anyhow.
 418       */
 419       sqlite3_int64 iKey;
 420       iKey = sqlite3BtreeIntegerKey(p->pCsr);
 421       sqlite3VdbePreUpdateHook(
 422           v, v->apCsr[0], SQLITE_DELETE, p->zDb, p->pTab, iKey, -1
 423       );
 424     }
 425 #endif
 426
 427     rc = xCall(p->pCsr, iOffset+p->iOffset, n, z);
 428     sqlite3BtreeLeaveCursor(p->pCsr);
 429     if( rc==SQLITE_ABORT ){
 430       sqlite3VdbeFinalize(v);
 431       p->pStmt = 0;
 432     }else{
 433       v->rc = rc;
 434     }
 435   }
 436   sqlite3Error(db, rc);
 437   rc = sqlite3ApiExit(db, rc);
 438   sqlite3_mutex_leave(db->mutex);
 439   return rc;
 440 }
 441
 442 /*
 443 ** Read data from a blob handle.
 444 */
 445 int sqlite3_blob_read(sqlite3_blob *pBlob, void *z, int n, int iOffset){
 446   return blobReadWrite(pBlob, z, n, iOffset, sqlite3BtreePayloadChecked);
 447 }
 448
 449 /*
 450 ** Write data to a blob handle.
 451 */
 452 int sqlite3_blob_write(sqlite3_blob *pBlob, const void *z, int n, int iOffset){
 453   return blobReadWrite(pBlob, (void *)z, n, iOffset, sqlite3BtreePutData);
 454 }
 455
 456 /*
 457 ** Query a blob handle for the size of the data.
 458 **
 459 ** The Incrblob.nByte field is fixed for the lifetime of the Incrblob
 460 ** so no mutex is required for access.
 461 */
 462 int sqlite3_blob_bytes(sqlite3_blob *pBlob){
 463   Incrblob *p = (Incrblob *)pBlob;
 464   return (p && p->pStmt) ? p->nByte : 0;
 465 }
 466
 467 /*
 468 ** Move an existing blob handle to point to a different row of the same
 469 ** database table.
 470 **
 471 ** If an error occurs, or if the specified row does not exist or does not
 472 ** contain a blob or text value, then an error code is returned and the
 473 ** database handle error code and message set. If this happens, then all
 474 ** subsequent calls to sqlite3_blob_xxx() functions (except blob_close())
 475 ** immediately return SQLITE_ABORT.
 476 */
 477 int sqlite3_blob_reopen(sqlite3_blob *pBlob, sqlite3_int64 iRow){
 478   int rc;
 479   Incrblob *p = (Incrblob *)pBlob;
 480   sqlite3 *db;
 481
 482   if( p==0 ) return SQLITE_MISUSE_BKPT;
 483   db = p->db;
 484   sqlite3_mutex_enter(db->mutex);
 485
 486   if( p->pStmt==0 ){
 487     /* If there is no statement handle, then the blob-handle has
 488     ** already been invalidated. Return SQLITE_ABORT in this case.
 489     */
 490     rc = SQLITE_ABORT;
 491   }else{
 492     char *zErr;
 493     rc = blobSeekToRow(p, iRow, &zErr);
 494     if( rc!=SQLITE_OK ){
 495       sqlite3ErrorWithMsg(db, rc, (zErr ? "%s" : 0), zErr);
 496       sqlite3DbFree(db, zErr);
 497     }
 498     assert( rc!=SQLITE_SCHEMA );
 499   }
 500
 501   rc = sqlite3ApiExit(db, rc);
 502   assert( rc==SQLITE_OK || p->pStmt==0 );
 503   sqlite3_mutex_leave(db->mutex);
 504   return rc;
 505 }
 506
 507 #endif /* #ifndef SQLITE_OMIT_INCRBLOB */