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+/*
+** 2017-10-11
+**
+** The author disclaims copyright to this source code. In place of
+** a legal notice, here is a blessing:
+**
+** May you do good and not evil.
+** May you find forgiveness for yourself and forgive others.
+** May you share freely, never taking more than you give.
+**
+******************************************************************************
+**
+** This file contains an implementation of the "sqlite_dbpage" virtual table.
+**
+** The sqlite_dbpage virtual table is used to read or write whole raw
+** pages of the database file. The pager interface is used so that
+** uncommitted changes and changes recorded in the WAL file are correctly
+** retrieved.
+**
+** Usage example:
+**
+** SELECT data FROM sqlite_dbpage('aux1') WHERE pgno=123;
+**
+** This is an eponymous virtual table so it does not need to be created before
+** use. The optional argument to the sqlite_dbpage() table name is the
+** schema for the database file that is to be read. The default schema is
+** "main".
+**
+** The data field of sqlite_dbpage table can be updated. The new
+** value must be a BLOB which is the correct page size, otherwise the
+** update fails. Rows may not be deleted or inserted.
+*/
+
+#include "sqliteInt.h" /* Requires access to internal data structures */
+#if (defined(SQLITE_ENABLE_DBPAGE_VTAB) || defined(SQLITE_TEST)) \
+ && !defined(SQLITE_OMIT_VIRTUALTABLE)
+
+typedef struct DbpageTable DbpageTable;
+typedef struct DbpageCursor DbpageCursor;
+
+struct DbpageCursor {
+ sqlite3_vtab_cursor base; /* Base class. Must be first */
+ int pgno; /* Current page number */
+ int mxPgno; /* Last page to visit on this scan */
+ Pager *pPager; /* Pager being read/written */
+ DbPage *pPage1; /* Page 1 of the database */
+ int iDb; /* Index of database to analyze */
+ int szPage; /* Size of each page in bytes */
+};
+
+struct DbpageTable {
+ sqlite3_vtab base; /* Base class. Must be first */
+ sqlite3 *db; /* The database */
+};
+
+/* Columns */
+#define DBPAGE_COLUMN_PGNO 0
+#define DBPAGE_COLUMN_DATA 1
+#define DBPAGE_COLUMN_SCHEMA 2
+
+
+
+/*
+** Connect to or create a dbpagevfs virtual table.
+*/
+static int dbpageConnect(
+ sqlite3 *db,
+ void *pAux,
+ int argc, const char *const*argv,
+ sqlite3_vtab **ppVtab,
+ char **pzErr
+){
+ DbpageTable *pTab = 0;
+ int rc = SQLITE_OK;
+
+ sqlite3_vtab_config(db, SQLITE_VTAB_DIRECTONLY);
+ rc = sqlite3_declare_vtab(db,
+ "CREATE TABLE x(pgno INTEGER PRIMARY KEY, data BLOB, schema HIDDEN)");
+ if( rc==SQLITE_OK ){
+ pTab = (DbpageTable *)sqlite3_malloc64(sizeof(DbpageTable));
+ if( pTab==0 ) rc = SQLITE_NOMEM_BKPT;
+ }
+
+ assert( rc==SQLITE_OK || pTab==0 );
+ if( rc==SQLITE_OK ){
+ memset(pTab, 0, sizeof(DbpageTable));
+ pTab->db = db;
+ }
+
+ *ppVtab = (sqlite3_vtab*)pTab;
+ return rc;
+}
+
+/*
+** Disconnect from or destroy a dbpagevfs virtual table.
+*/
+static int dbpageDisconnect(sqlite3_vtab *pVtab){
+ sqlite3_free(pVtab);
+ return SQLITE_OK;
+}
+
+/*
+** idxNum:
+**
+** 0 schema=main, full table scan
+** 1 schema=main, pgno=?1
+** 2 schema=?1, full table scan
+** 3 schema=?1, pgno=?2
+*/
+static int dbpageBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo){
+ int i;
+ int iPlan = 0;
+
+ /* If there is a schema= constraint, it must be honored. Report a
+ ** ridiculously large estimated cost if the schema= constraint is
+ ** unavailable
+ */
+ for(i=0; i<pIdxInfo->nConstraint; i++){
+ struct sqlite3_index_constraint *p = &pIdxInfo->aConstraint[i];
+ if( p->iColumn!=DBPAGE_COLUMN_SCHEMA ) continue;
+ if( p->op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;
+ if( !p->usable ){
+ /* No solution. */
+ return SQLITE_CONSTRAINT;
+ }
+ iPlan = 2;
+ pIdxInfo->aConstraintUsage[i].argvIndex = 1;
+ pIdxInfo->aConstraintUsage[i].omit = 1;
+ break;
+ }
+
+ /* If we reach this point, it means that either there is no schema=
+ ** constraint (in which case we use the "main" schema) or else the
+ ** schema constraint was accepted. Lower the estimated cost accordingly
+ */
+ pIdxInfo->estimatedCost = 1.0e6;
+
+ /* Check for constraints against pgno */
+ for(i=0; i<pIdxInfo->nConstraint; i++){
+ struct sqlite3_index_constraint *p = &pIdxInfo->aConstraint[i];
+ if( p->usable && p->iColumn<=0 && p->op==SQLITE_INDEX_CONSTRAINT_EQ ){
+ pIdxInfo->estimatedRows = 1;
+ pIdxInfo->idxFlags = SQLITE_INDEX_SCAN_UNIQUE;
+ pIdxInfo->estimatedCost = 1.0;
+ pIdxInfo->aConstraintUsage[i].argvIndex = iPlan ? 2 : 1;
+ pIdxInfo->aConstraintUsage[i].omit = 1;
+ iPlan |= 1;
+ break;
+ }
+ }
+ pIdxInfo->idxNum = iPlan;
+
+ if( pIdxInfo->nOrderBy>=1
+ && pIdxInfo->aOrderBy[0].iColumn<=0
+ && pIdxInfo->aOrderBy[0].desc==0
+ ){
+ pIdxInfo->orderByConsumed = 1;
+ }
+ sqlite3VtabUsesAllSchemas(pIdxInfo);
+ return SQLITE_OK;
+}
+
+/*
+** Open a new dbpagevfs cursor.
+*/
+static int dbpageOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
+ DbpageCursor *pCsr;
+
+ pCsr = (DbpageCursor *)sqlite3_malloc64(sizeof(DbpageCursor));
+ if( pCsr==0 ){
+ return SQLITE_NOMEM_BKPT;
+ }else{
+ memset(pCsr, 0, sizeof(DbpageCursor));
+ pCsr->base.pVtab = pVTab;
+ pCsr->pgno = -1;
+ }
+
+ *ppCursor = (sqlite3_vtab_cursor *)pCsr;
+ return SQLITE_OK;
+}
+
+/*
+** Close a dbpagevfs cursor.
+*/
+static int dbpageClose(sqlite3_vtab_cursor *pCursor){
+ DbpageCursor *pCsr = (DbpageCursor *)pCursor;
+ if( pCsr->pPage1 ) sqlite3PagerUnrefPageOne(pCsr->pPage1);
+ sqlite3_free(pCsr);
+ return SQLITE_OK;
+}
+
+/*
+** Move a dbpagevfs cursor to the next entry in the file.
+*/
+static int dbpageNext(sqlite3_vtab_cursor *pCursor){
+ int rc = SQLITE_OK;
+ DbpageCursor *pCsr = (DbpageCursor *)pCursor;
+ pCsr->pgno++;
+ return rc;
+}
+
+static int dbpageEof(sqlite3_vtab_cursor *pCursor){
+ DbpageCursor *pCsr = (DbpageCursor *)pCursor;
+ return pCsr->pgno > pCsr->mxPgno;
+}
+
+/*
+** idxNum:
+**
+** 0 schema=main, full table scan
+** 1 schema=main, pgno=?1
+** 2 schema=?1, full table scan
+** 3 schema=?1, pgno=?2
+**
+** idxStr is not used
+*/
+static int dbpageFilter(
+ sqlite3_vtab_cursor *pCursor,
+ int idxNum, const char *idxStr,
+ int argc, sqlite3_value **argv
+){
+ DbpageCursor *pCsr = (DbpageCursor *)pCursor;
+ DbpageTable *pTab = (DbpageTable *)pCursor->pVtab;
+ int rc;
+ sqlite3 *db = pTab->db;
+ Btree *pBt;
+
+ /* Default setting is no rows of result */
+ pCsr->pgno = 1;
+ pCsr->mxPgno = 0;
+
+ if( idxNum & 2 ){
+ const char *zSchema;
+ assert( argc>=1 );
+ zSchema = (const char*)sqlite3_value_text(argv[0]);
+ pCsr->iDb = sqlite3FindDbName(db, zSchema);
+ if( pCsr->iDb<0 ) return SQLITE_OK;
+ }else{
+ pCsr->iDb = 0;
+ }
+ pBt = db->aDb[pCsr->iDb].pBt;
+ if( pBt==0 ) return SQLITE_OK;
+ pCsr->pPager = sqlite3BtreePager(pBt);
+ pCsr->szPage = sqlite3BtreeGetPageSize(pBt);
+ pCsr->mxPgno = sqlite3BtreeLastPage(pBt);
+ if( idxNum & 1 ){
+ assert( argc>(idxNum>>1) );
+ pCsr->pgno = sqlite3_value_int(argv[idxNum>>1]);
+ if( pCsr->pgno<1 || pCsr->pgno>pCsr->mxPgno ){
+ pCsr->pgno = 1;
+ pCsr->mxPgno = 0;
+ }else{
+ pCsr->mxPgno = pCsr->pgno;
+ }
+ }else{
+ assert( pCsr->pgno==1 );
+ }
+ if( pCsr->pPage1 ) sqlite3PagerUnrefPageOne(pCsr->pPage1);
+ rc = sqlite3PagerGet(pCsr->pPager, 1, &pCsr->pPage1, 0);
+ return rc;
+}
+
+static int dbpageColumn(
+ sqlite3_vtab_cursor *pCursor,
+ sqlite3_context *ctx,
+ int i
+){
+ DbpageCursor *pCsr = (DbpageCursor *)pCursor;
+ int rc = SQLITE_OK;
+ switch( i ){
+ case 0: { /* pgno */
+ sqlite3_result_int(ctx, pCsr->pgno);
+ break;
+ }
+ case 1: { /* data */
+ DbPage *pDbPage = 0;
+ if( pCsr->pgno==((PENDING_BYTE/pCsr->szPage)+1) ){
+ /* The pending byte page. Assume it is zeroed out. Attempting to
+ ** request this page from the page is an SQLITE_CORRUPT error. */
+ sqlite3_result_zeroblob(ctx, pCsr->szPage);
+ }else{
+ rc = sqlite3PagerGet(pCsr->pPager, pCsr->pgno, (DbPage**)&pDbPage, 0);
+ if( rc==SQLITE_OK ){
+ sqlite3_result_blob(ctx, sqlite3PagerGetData(pDbPage), pCsr->szPage,
+ SQLITE_TRANSIENT);
+ }
+ sqlite3PagerUnref(pDbPage);
+ }
+ break;
+ }
+ default: { /* schema */
+ sqlite3 *db = sqlite3_context_db_handle(ctx);
+ sqlite3_result_text(ctx, db->aDb[pCsr->iDb].zDbSName, -1, SQLITE_STATIC);
+ break;
+ }
+ }
+ return rc;
+}
+
+static int dbpageRowid(sqlite3_vtab_cursor *pCursor, sqlite_int64 *pRowid){
+ DbpageCursor *pCsr = (DbpageCursor *)pCursor;
+ *pRowid = pCsr->pgno;
+ return SQLITE_OK;
+}
+
+static int dbpageUpdate(
+ sqlite3_vtab *pVtab,
+ int argc,
+ sqlite3_value **argv,
+ sqlite_int64 *pRowid
+){
+ DbpageTable *pTab = (DbpageTable *)pVtab;
+ Pgno pgno;
+ DbPage *pDbPage = 0;
+ int rc = SQLITE_OK;
+ char *zErr = 0;
+ const char *zSchema;
+ int iDb;
+ Btree *pBt;
+ Pager *pPager;
+ int szPage;
+
+ if( pTab->db->flags & SQLITE_Defensive ){
+ zErr = "read-only";
+ goto update_fail;
+ }
+ if( argc==1 ){
+ zErr = "cannot delete";
+ goto update_fail;
+ }
+ pgno = sqlite3_value_int(argv[0]);
+ if( (Pgno)sqlite3_value_int(argv[1])!=pgno ){
+ zErr = "cannot insert";
+ goto update_fail;
+ }
+ zSchema = (const char*)sqlite3_value_text(argv[4]);
+ iDb = zSchema ? sqlite3FindDbName(pTab->db, zSchema) : -1;
+ if( iDb<0 ){
+ zErr = "no such schema";
+ goto update_fail;
+ }
+ pBt = pTab->db->aDb[iDb].pBt;
+ if( pgno<1 || pBt==0 || pgno>sqlite3BtreeLastPage(pBt) ){
+ zErr = "bad page number";
+ goto update_fail;
+ }
+ szPage = sqlite3BtreeGetPageSize(pBt);
+ if( sqlite3_value_type(argv[3])!=SQLITE_BLOB
+ || sqlite3_value_bytes(argv[3])!=szPage
+ ){
+ zErr = "bad page value";
+ goto update_fail;
+ }
+ pPager = sqlite3BtreePager(pBt);
+ rc = sqlite3PagerGet(pPager, pgno, (DbPage**)&pDbPage, 0);
+ if( rc==SQLITE_OK ){
+ const void *pData = sqlite3_value_blob(argv[3]);
+ assert( pData!=0 || pTab->db->mallocFailed );
+ if( pData
+ && (rc = sqlite3PagerWrite(pDbPage))==SQLITE_OK
+ ){
+ memcpy(sqlite3PagerGetData(pDbPage), pData, szPage);
+ }
+ }
+ sqlite3PagerUnref(pDbPage);
+ return rc;
+
+update_fail:
+ sqlite3_free(pVtab->zErrMsg);
+ pVtab->zErrMsg = sqlite3_mprintf("%s", zErr);
+ return SQLITE_ERROR;
+}
+
+/* Since we do not know in advance which database files will be
+** written by the sqlite_dbpage virtual table, start a write transaction
+** on them all.
+*/
+static int dbpageBegin(sqlite3_vtab *pVtab){
+ DbpageTable *pTab = (DbpageTable *)pVtab;
+ sqlite3 *db = pTab->db;
+ int i;
+ int rc = SQLITE_OK;
+ for(i=0; rc==SQLITE_OK && i<db->nDb; i++){
+ Btree *pBt = db->aDb[i].pBt;
+ if( pBt ) rc = sqlite3BtreeBeginTrans(pBt, 1, 0);
+ }
+ return rc;
+}
+
+
+/*
+** Invoke this routine to register the "dbpage" virtual table module
+*/
+int sqlite3DbpageRegister(sqlite3 *db){
+ static sqlite3_module dbpage_module = {
+ 0, /* iVersion */
+ dbpageConnect, /* xCreate */
+ dbpageConnect, /* xConnect */
+ dbpageBestIndex, /* xBestIndex */
+ dbpageDisconnect, /* xDisconnect */
+ dbpageDisconnect, /* xDestroy */
+ dbpageOpen, /* xOpen - open a cursor */
+ dbpageClose, /* xClose - close a cursor */
+ dbpageFilter, /* xFilter - configure scan constraints */
+ dbpageNext, /* xNext - advance a cursor */
+ dbpageEof, /* xEof - check for end of scan */
+ dbpageColumn, /* xColumn - read data */
+ dbpageRowid, /* xRowid - read data */
+ dbpageUpdate, /* xUpdate */
+ dbpageBegin, /* xBegin */
+ 0, /* xSync */
+ 0, /* xCommit */
+ 0, /* xRollback */
+ 0, /* xFindMethod */
+ 0, /* xRename */
+ 0, /* xSavepoint */
+ 0, /* xRelease */
+ 0, /* xRollbackTo */
+ 0 /* xShadowName */
+ };
+ return sqlite3_create_module(db, "sqlite_dbpage", &dbpage_module, 0);
+}
+#elif defined(SQLITE_ENABLE_DBPAGE_VTAB)
+int sqlite3DbpageRegister(sqlite3 *db){ return SQLITE_OK; }
+#endif /* SQLITE_ENABLE_DBSTAT_VTAB */