/*
** Open the database handle and attach the RBU database as "rbu". If an
** error occurs, leave an error code and message in the RBU handle.
*/
static void rbuOpenDatabase(sqlite3rbu *p){
  assert( p->rc==SQLITE_OK );
  assert( p->dbMain==0 && p->dbRbu==0 );


  /* Open the RBU database */
  p->dbRbu = rbuOpenDbhandle(p, p->zRbu);

  /* If using separate RBU and state databases, attach the state database to
  ** the RBU db handle now.  */
  if( p->zState ){
................................................................................
      }
    }
    if( bOpen ) p->dbMain = rbuOpenDbhandle(p, p->zRbu);
  }

  p->eStage = 0;
  if( p->dbMain==0 ){
    if( p->zTarget ){
      p->dbMain = rbuOpenDbhandle(p, p->zTarget);
    }else{
      char *zTarget = sqlite3_mprintf("%s-vacuum", p->zRbu);
      if( zTarget==0 ){
        p->rc = SQLITE_NOMEM;
        return;
      }
      p->dbMain = rbuOpenDbhandle(p, zTarget);
      sqlite3_free(zTarget);





    }
  }

  if( p->rc==SQLITE_OK ){
    p->rc = sqlite3_create_function(p->dbMain, 
        "rbu_tmp_insert", -1, SQLITE_UTF8, (void*)p, rbuTmpInsertFunc, 0, 0
    );
................................................................................
** on the database file. This proc moves the *-oal file to the *-wal path,
** then reopens the database file (this time in vanilla, non-oal, WAL mode).
** If an error occurs, leave an error code and error message in the rbu 
** handle.
*/
static void rbuMoveOalFile(sqlite3rbu *p){
  const char *zBase = sqlite3_db_filename(p->dbMain, "main");
  char *zOal = sqlite3_mprintf("%s-oal", zBase);

  char *zWal;

  if( rbuIsVacuum(p) ){
    zWal = sqlite3_mprintf("%s-wal", sqlite3_db_filename(p->dbRbu, "main"));
  }else{
    zWal = sqlite3_mprintf("%s-wal", zBase);
  }

  assert( p->eStage==RBU_STAGE_MOVE );
  assert( p->rc==SQLITE_OK && p->zErrmsg==0 );
  if( zWal==0 || zOal==0 ){
    p->rc = SQLITE_NOMEM;
  }else{
    /* Move the *-oal file to *-wal. At this point connection p->db is
................................................................................
    }
  }
  return p->rc;
}

/*
** Increment the schema cookie of the main database opened by p->dbMain.




*/
static void rbuIncrSchemaCookie(sqlite3rbu *p){
  if( p->rc==SQLITE_OK ){

    int iCookie = 1000000;
    sqlite3_stmt *pStmt;

    p->rc = prepareAndCollectError(p->dbMain, &pStmt, &p->zErrmsg, 
        "PRAGMA schema_version"
    );
    if( p->rc==SQLITE_OK ){
      /* Coverage: it may be that this sqlite3_step() cannot fail. There
      ** is already a transaction open, so the prepared statement cannot
      ** throw an SQLITE_SCHEMA exception. The only database page the
      ** statement reads is page 1, which is guaranteed to be in the cache.
................................................................................
      }else if( p->eStage==RBU_STAGE_MOVE ){
        p->eStage = RBU_STAGE_CKPT;
        p->nStep = 0;
      }
    }

    if( p->rc==SQLITE_OK

     && (p->eStage==RBU_STAGE_OAL || p->eStage==RBU_STAGE_MOVE)
     && pState->eStage!=0 && p->pTargetFd->iCookie!=pState->iCookie
    ){   
      /* At this point (pTargetFd->iCookie) contains the value of the
      ** change-counter cookie (the thing that gets incremented when a 
      ** transaction is committed in rollback mode) currently stored on 
      ** page 1 of the database file. */
................................................................................
     && (p->openFlags & SQLITE_OPEN_WAL) 
     && iOfst>=pRbu->iOalSz 
    ){
      rc = SQLITE_OK;
      memset(zBuf, 0, iAmt);
    }else{
      rc = p->pReal->pMethods->xRead(p->pReal, zBuf, iAmt, iOfst);
      /* If this is being called to read the first page of the target 
      ** database as part of an rbu vacuum operation, synthesize the 
      ** contents of the first page if it does not yet exist. Otherwise,
      ** SQLite will not check for a *-wal file.  */
      if( p->pRbu && rbuIsVacuum(p->pRbu) 
       && rc==SQLITE_IOERR_SHORT_READ && iOfst==0
       && (p->openFlags & SQLITE_OPEN_MAIN_DB)
      ){
        sqlite3_file *pFd = 0;
        rc = sqlite3_file_control(
            p->pRbu->dbRbu, "main", SQLITE_FCNTL_FILE_POINTER, (void*)&pFd
        );
        if( rc==SQLITE_OK ){
          rc = pFd->pMethods->xRead(pFd, zBuf, iAmt, iOfst);
        }
        if( rc==SQLITE_OK ){
          rbuPutU32(&zBuf[52], 0);          /* largest root page number */
          rbuPutU32(&zBuf[36], 0);          /* number of free pages */
          rbuPutU32(&zBuf[32], 0);          /* first page on free list trunk */
          rbuPutU32(&zBuf[28], 1);          /* size of db file in pages */

          if( iAmt>100 ){
            assert( iAmt>=101 );
            memset(&zBuf[101], 0, iAmt-101);
            rbuPutU16(&zBuf[105], iAmt & 0xFFFF);
          }
        }
      }
    }
    if( rc==SQLITE_OK && iOfst==0 && (p->openFlags & SQLITE_OPEN_MAIN_DB) ){
      /* These look like magic numbers. But they are stable, as they are part
       ** of the definition of the SQLite file format, which may not change. */
      u8 *pBuf = (u8*)zBuf;
      p->iCookie = rbuGetU32(&pBuf[24]);
      p->iWriteVer = pBuf[19];







    }
  }
  return rc;
}

/*
** Write data to an rbuVfs-file.
................................................................................
}

/*
** Return the current file-size of an rbuVfs-file.
*/
static int rbuVfsFileSize(sqlite3_file *pFile, sqlite_int64 *pSize){
  rbu_file *p = (rbu_file *)pFile;
  int rc;
  rc = p->pReal->pMethods->xFileSize(p->pReal, pSize);

  /* If this is an RBU vacuum operation and this is the target database,
  ** pretend that it has at least one page. Otherwise, SQLite will not
  ** check for the existance of a *-wal file. rbuVfsRead() contains 
  ** similar logic.  */
  if( rc==SQLITE_OK && *pSize==0 
   && p->pRbu && rbuIsVacuum(p->pRbu) 
   && (p->openFlags & SQLITE_OPEN_MAIN_DB)
  ){
    *pSize = 1024;
  }
  return rc;
}

/*
** Lock an rbuVfs-file.
*/
static int rbuVfsLock(sqlite3_file *pFile, int eLock){
  rbu_file *p = (rbu_file*)pFile;
................................................................................
static rbu_file *rbuFindMaindb(rbu_vfs *pRbuVfs, const char *zWal){
  rbu_file *pDb;
  sqlite3_mutex_enter(pRbuVfs->mutex);
  for(pDb=pRbuVfs->pMain; pDb && pDb->zWal!=zWal; pDb=pDb->pMainNext){}
  sqlite3_mutex_leave(pRbuVfs->mutex);
  return pDb;
}




























/*
** Open an rbu file handle.
*/
static int rbuVfsOpen(
  sqlite3_vfs *pVfs,
  const char *zName,
................................................................................
    0, 0                          /* xFetch, xUnfetch */
  };
  rbu_vfs *pRbuVfs = (rbu_vfs*)pVfs;
  sqlite3_vfs *pRealVfs = pRbuVfs->pRealVfs;
  rbu_file *pFd = (rbu_file *)pFile;
  int rc = SQLITE_OK;
  const char *zOpen = zName;


  memset(pFd, 0, sizeof(rbu_file));
  pFd->pReal = (sqlite3_file*)&pFd[1];
  pFd->pRbuVfs = pRbuVfs;
  pFd->openFlags = flags;
  if( zName ){
    if( flags & SQLITE_OPEN_MAIN_DB ){
      /* A main database has just been opened. The following block sets
      ** (pFd->zWal) to point to a buffer owned by SQLite that contains
      ** the name of the *-wal file this db connection will use. SQLite
      ** happens to pass a pointer to this buffer when using xAccess()
      ** or xOpen() to operate on the *-wal file.  */
      int n = (int)strlen(zName);
      const char *z = &zName[n];
      if( flags & SQLITE_OPEN_URI ){
        int odd = 0;
        while( 1 ){
          if( z[0]==0 ){
            odd = 1 - odd;
            if( odd && z[1]==0 ) break;
          }
          z++;
        }
        z += 2;
      }else{
        while( *z==0 ) z++;
      }
      z += (n + 8 + 1);
      pFd->zWal = z;
    }
    else if( flags & SQLITE_OPEN_WAL ){
      rbu_file *pDb = rbuFindMaindb(pRbuVfs, zName);
      if( pDb ){
        if( pDb->pRbu && pDb->pRbu->eStage==RBU_STAGE_OAL ){
          /* This call is to open a *-wal file. Intead, open the *-oal. This
          ** code ensures that the string passed to xOpen() is terminated by a
          ** pair of '\0' bytes in case the VFS attempts to extract a URI 
          ** parameter from it.  */







          size_t nCopy = strlen(zName);
          char *zCopy = sqlite3_malloc64(nCopy+2);
          if( zCopy ){
            memcpy(zCopy, zName, nCopy);
            zCopy[nCopy-3] = 'o';
            zCopy[nCopy] = '\0';
            zCopy[nCopy+1] = '\0';
            zOpen = (const char*)(pFd->zDel = zCopy);
          }else{
            rc = SQLITE_NOMEM;
          }
          pFd->pRbu = pDb->pRbu;
        }
        pDb->pWalFd = pFd;
      }
    }
  }










  if( rc==SQLITE_OK ){
    rc = pRealVfs->xOpen(pRealVfs, zOpen, pFd->pReal, flags, pOutFlags);
  }
  if( pFd->pReal->pMethods ){
    /* The xOpen() operation has succeeded. Set the sqlite3_file.pMethods
    ** pointer and, if the file is a main database file, link it into the
    ** mutex protected linked list of all such files.  */
    pFile->pMethods = &rbuvfs_io_methods;
    if( flags & SQLITE_OPEN_MAIN_DB ){

/*
** Open the database handle and attach the RBU database as "rbu". If an
** error occurs, leave an error code and message in the RBU handle.
*/
static void rbuOpenDatabase(sqlite3rbu *p){
  assert( p->rc==SQLITE_OK );
  assert( p->dbMain==0 && p->dbRbu==0 );
  assert( rbuIsVacuum(p) || p->zTarget!=0 );

  /* Open the RBU database */
  p->dbRbu = rbuOpenDbhandle(p, p->zRbu);

  /* If using separate RBU and state databases, attach the state database to
  ** the RBU db handle now.  */
  if( p->zState ){
................................................................................
      }
    }
    if( bOpen ) p->dbMain = rbuOpenDbhandle(p, p->zRbu);
  }

  p->eStage = 0;
  if( p->dbMain==0 ){
    if( !rbuIsVacuum(p) ){
      p->dbMain = rbuOpenDbhandle(p, p->zTarget);
    }else{
      char *zTarget = sqlite3_mprintf("file:%s-vacuum?rbu_memory=1", p->zRbu);
      if( zTarget==0 ){
        p->rc = SQLITE_NOMEM;
        return;
      }
      p->dbMain = rbuOpenDbhandle(p, zTarget);
      sqlite3_free(zTarget);
      if( p->rc==SQLITE_OK ){
        p->rc = sqlite3_exec(p->dbMain, 
            "PRAGMA journal_mode=off; BEGIN EXCLUSIVE; COMMIT;", 0, 0, 0
        );
      }
    }
  }

  if( p->rc==SQLITE_OK ){
    p->rc = sqlite3_create_function(p->dbMain, 
        "rbu_tmp_insert", -1, SQLITE_UTF8, (void*)p, rbuTmpInsertFunc, 0, 0
    );
................................................................................
** on the database file. This proc moves the *-oal file to the *-wal path,
** then reopens the database file (this time in vanilla, non-oal, WAL mode).
** If an error occurs, leave an error code and error message in the rbu 
** handle.
*/
static void rbuMoveOalFile(sqlite3rbu *p){
  const char *zBase = sqlite3_db_filename(p->dbMain, "main");
  const char *zMove = zBase;
  char *zOal;
  char *zWal;

  if( rbuIsVacuum(p) ){
    zMove = sqlite3_db_filename(p->dbRbu, "main");
  }
  zOal = sqlite3_mprintf("%s-oal", zMove);
  zWal = sqlite3_mprintf("%s-wal", zMove);

  assert( p->eStage==RBU_STAGE_MOVE );
  assert( p->rc==SQLITE_OK && p->zErrmsg==0 );
  if( zWal==0 || zOal==0 ){
    p->rc = SQLITE_NOMEM;
  }else{
    /* Move the *-oal file to *-wal. At this point connection p->db is
................................................................................
    }
  }
  return p->rc;
}

/*
** Increment the schema cookie of the main database opened by p->dbMain.
**
** Or, if this is an RBU vacuum, set the schema cookie of the main db
** opened by p->dbMain to one more than the schema cookie of the main
** db opened by p->dbRbu.
*/
static void rbuIncrSchemaCookie(sqlite3rbu *p){
  if( p->rc==SQLITE_OK ){
    sqlite3 *dbread = (rbuIsVacuum(p) ? p->dbRbu : p->dbMain);
    int iCookie = 1000000;
    sqlite3_stmt *pStmt;

    p->rc = prepareAndCollectError(dbread, &pStmt, &p->zErrmsg, 
        "PRAGMA schema_version"
    );
    if( p->rc==SQLITE_OK ){
      /* Coverage: it may be that this sqlite3_step() cannot fail. There
      ** is already a transaction open, so the prepared statement cannot
      ** throw an SQLITE_SCHEMA exception. The only database page the
      ** statement reads is page 1, which is guaranteed to be in the cache.
................................................................................
      }else if( p->eStage==RBU_STAGE_MOVE ){
        p->eStage = RBU_STAGE_CKPT;
        p->nStep = 0;
      }
    }

    if( p->rc==SQLITE_OK
     && !rbuIsVacuum(p)
     && (p->eStage==RBU_STAGE_OAL || p->eStage==RBU_STAGE_MOVE)
     && pState->eStage!=0 && p->pTargetFd->iCookie!=pState->iCookie
    ){   
      /* At this point (pTargetFd->iCookie) contains the value of the
      ** change-counter cookie (the thing that gets incremented when a 
      ** transaction is committed in rollback mode) currently stored on 
      ** page 1 of the database file. */
................................................................................
     && (p->openFlags & SQLITE_OPEN_WAL) 
     && iOfst>=pRbu->iOalSz 
    ){
      rc = SQLITE_OK;
      memset(zBuf, 0, iAmt);
    }else{
      rc = p->pReal->pMethods->xRead(p->pReal, zBuf, iAmt, iOfst);




























    }
    if( rc==SQLITE_OK && iOfst==0 && (p->openFlags & SQLITE_OPEN_MAIN_DB) ){
      /* These look like magic numbers. But they are stable, as they are part
       ** of the definition of the SQLite file format, which may not change. */
      u8 *pBuf = (u8*)zBuf;
      p->iCookie = rbuGetU32(&pBuf[24]);
      p->iWriteVer = pBuf[19];
      if( pRbu && rbuIsVacuum(p->pRbu) ){
        rbu_file *pRbuFd = 0;
        sqlite3_file_control(pRbu->dbRbu, "main", 
            SQLITE_FCNTL_FILE_POINTER, (void*)&pRbuFd
        );
        rbuPutU32(&pBuf[24], pRbuFd->iCookie+1);
      }
    }
  }
  return rc;
}

/*
** Write data to an rbuVfs-file.
................................................................................
}

/*
** Return the current file-size of an rbuVfs-file.
*/
static int rbuVfsFileSize(sqlite3_file *pFile, sqlite_int64 *pSize){
  rbu_file *p = (rbu_file *)pFile;

  return p->pReal->pMethods->xFileSize(p->pReal, pSize);












}

/*
** Lock an rbuVfs-file.
*/
static int rbuVfsLock(sqlite3_file *pFile, int eLock){
  rbu_file *p = (rbu_file*)pFile;
................................................................................
static rbu_file *rbuFindMaindb(rbu_vfs *pRbuVfs, const char *zWal){
  rbu_file *pDb;
  sqlite3_mutex_enter(pRbuVfs->mutex);
  for(pDb=pRbuVfs->pMain; pDb && pDb->zWal!=zWal; pDb=pDb->pMainNext){}
  sqlite3_mutex_leave(pRbuVfs->mutex);
  return pDb;
}

/* 
** A main database named zName has just been opened. The following 
** function returns a pointer to a buffer owned by SQLite that contains
** the name of the *-wal file this db connection will use. SQLite
** happens to pass a pointer to this buffer when using xAccess()
** or xOpen() to operate on the *-wal file.  
*/
static const char *rbuMainToWal(const char *zName, int flags){
  int n = (int)strlen(zName);
  const char *z = &zName[n];
  if( flags & SQLITE_OPEN_URI ){
    int odd = 0;
    while( 1 ){
      if( z[0]==0 ){
        odd = 1 - odd;
        if( odd && z[1]==0 ) break;
      }
      z++;
    }
    z += 2;
  }else{
    while( *z==0 ) z++;
  }
  z += (n + 8 + 1);
  return z;
}

/*
** Open an rbu file handle.
*/
static int rbuVfsOpen(
  sqlite3_vfs *pVfs,
  const char *zName,
................................................................................
    0, 0                          /* xFetch, xUnfetch */
  };
  rbu_vfs *pRbuVfs = (rbu_vfs*)pVfs;
  sqlite3_vfs *pRealVfs = pRbuVfs->pRealVfs;
  rbu_file *pFd = (rbu_file *)pFile;
  int rc = SQLITE_OK;
  const char *zOpen = zName;
  int oflags = flags;

  memset(pFd, 0, sizeof(rbu_file));
  pFd->pReal = (sqlite3_file*)&pFd[1];
  pFd->pRbuVfs = pRbuVfs;
  pFd->openFlags = flags;
  if( zName ){
    if( flags & SQLITE_OPEN_MAIN_DB ){
      /* A main database has just been opened. The following block sets
      ** (pFd->zWal) to point to a buffer owned by SQLite that contains
      ** the name of the *-wal file this db connection will use. SQLite
      ** happens to pass a pointer to this buffer when using xAccess()
      ** or xOpen() to operate on the *-wal file.  */
















      pFd->zWal = rbuMainToWal(zName, flags);
    }
    else if( flags & SQLITE_OPEN_WAL ){
      rbu_file *pDb = rbuFindMaindb(pRbuVfs, zName);
      if( pDb ){
        if( pDb->pRbu && pDb->pRbu->eStage==RBU_STAGE_OAL ){
          /* This call is to open a *-wal file. Intead, open the *-oal. This
          ** code ensures that the string passed to xOpen() is terminated by a
          ** pair of '\0' bytes in case the VFS attempts to extract a URI 
          ** parameter from it.  */
          const char *zBase = zName;
          size_t nCopy;
          char *zCopy;
          if( rbuIsVacuum(pDb->pRbu) ){
            zBase = sqlite3_db_filename(pDb->pRbu->dbRbu, "main");
            zBase = rbuMainToWal(zBase, SQLITE_OPEN_URI);
          }
          nCopy = strlen(zBase);
          zCopy = sqlite3_malloc64(nCopy+2);
          if( zCopy ){
            memcpy(zCopy, zBase, nCopy);
            zCopy[nCopy-3] = 'o';
            zCopy[nCopy] = '\0';
            zCopy[nCopy+1] = '\0';
            zOpen = (const char*)(pFd->zDel = zCopy);
          }else{
            rc = SQLITE_NOMEM;
          }
          pFd->pRbu = pDb->pRbu;
        }
        pDb->pWalFd = pFd;
      }
    }
  }

  if( oflags & SQLITE_OPEN_MAIN_DB 
   && sqlite3_uri_boolean(zName, "rbu_memory", 0) 
  ){
    assert( oflags & SQLITE_OPEN_MAIN_DB );
    oflags =  SQLITE_OPEN_TEMP_DB | SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE |
              SQLITE_OPEN_EXCLUSIVE | SQLITE_OPEN_DELETEONCLOSE;
    zOpen = 0;
  }

  if( rc==SQLITE_OK ){
    rc = pRealVfs->xOpen(pRealVfs, zOpen, pFd->pReal, oflags, pOutFlags);
  }
  if( pFd->pReal->pMethods ){
    /* The xOpen() operation has succeeded. Set the sqlite3_file.pMethods
    ** pointer and, if the file is a main database file, link it into the
    ** mutex protected linked list of all such files.  */
    pFile->pMethods = &rbuvfs_io_methods;
    if( flags & SQLITE_OPEN_MAIN_DB ){