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