SQLite

# 2014 August 30
#
# 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.
#
#***********************************************************************
#

set testdir [file join [file dirname $argv0] .. .. test]
source $testdir/tester.tcl
set ::testprefix ota1


# Create a simple OTA database. That expects to write to a table:
#
#   CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c);
#
proc create_ota1 {filename} {
  forcedelete $filename
  sqlite3 ota1 $filename  
  ota1 eval {
    CREATE TABLE data_t1(a, b, c, ota_control);
    INSERT INTO data_t1 VALUES(1, 2, 3, 0);
    INSERT INTO data_t1 VALUES(2, 'two', 'three', 0);
    INSERT INTO data_t1 VALUES(3, NULL, 8.2, 0);
  }
  ota1 close
  return $filename
}

# Create an empty target database suitable for the OTA created by 
# [create_ota1].
#
#   CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c);
#
proc create_target1 {filename} {
  forcedelete $filename
  sqlite3 target1 $filename  
  target1 eval { CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c) }
  target1 close
  return $filename
}

# Run the OTA in file $ota on target database $target until completion.
#
proc run_ota {target ota} {
  sqlite3ota ota $target $ota
  while { [ota step]=="SQLITE_OK" } {}
  ota close
}

proc step_ota {target ota} {
  while 1 {
    sqlite3ota ota $target $ota
    set rc [ota step]
    ota close
    if {$rc != "SQLITE_OK"} break
  }
  set rc
}

foreach {tn2 cmd} {1 step_ota 2 run_ota} {
  foreach {tn schema} {
    1 {
      CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c);
    }
    2 { 
      CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c);
      CREATE INDEX i1 ON t1(b);
    }
    3 { 
      CREATE TABLE t1(a PRIMARY KEY, b, c) WITHOUT ROWID;
    }
    4 { 
      CREATE TABLE t1(a PRIMARY KEY, b, c) WITHOUT ROWID;
      CREATE INDEX i1 ON t1(b);
    }
    5 { 
      CREATE TABLE t1(a, b, c, PRIMARY KEY(a, c)) WITHOUT ROWID;
      CREATE INDEX i1 ON t1(b);
    }
    6 { 
      CREATE TABLE t1(a, b, c, PRIMARY KEY(c)) WITHOUT ROWID;
      CREATE INDEX i1 ON t1(b, a);
    }
    7 { 
      CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c);
      CREATE INDEX i1 ON t1(b, c);
      CREATE INDEX i2 ON t1(c, b);
      CREATE INDEX i3 ON t1(a, b, c, a, b, c);
    }
  } {
    reset_db
    execsql $schema
  
    do_test 1.$tn2.$tn.1 {
      create_ota1 ota.db
      $cmd test.db ota.db
    } {SQLITE_DONE}
    
    do_execsql_test 1.$tn2.$tn.2 {
      SELECT * FROM t1 ORDER BY a ASC;
    } {
      1 2 3 
      2 two three 
      3 {} 8.2
    }
  
    do_execsql_test 1.$tn2.$tn.3 { PRAGMA integrity_check } ok
  }
}

#-------------------------------------------------------------------------
# Check that an OTA cannot be applied to a table that has no PK.
#
reset_db
create_ota1 ota.db
do_execsql_test 2.1 { CREATE TABLE t1(a, b, c) }
do_test 2.2 {
  sqlite3ota ota test.db ota.db
  ota step
} {SQLITE_ERROR}
do_test 2.3 {
  list [catch { ota close } msg] $msg
} {1 {SQLITE_ERROR - table t1 has no PRIMARY KEY}}

reset_db
do_execsql_test 2.4 { CREATE TABLE t1(a PRIMARY KEY, b, c) }
do_test 2.5 {
  sqlite3ota ota test.db ota.db
  ota step
} {SQLITE_ERROR}
do_test 2.6 {
  list [catch { ota close } msg] $msg
} {1 {SQLITE_ERROR - table t1 has no PRIMARY KEY}}

#-------------------------------------------------------------------------
# Check that if a UNIQUE constraint is violated the current and all 
# subsequent [ota step] calls return SQLITE_CONSTRAINT. And that the OTA 
# transaction is rolled back by the [ota close] that deletes the ota 
# handle.
#
foreach {tn errcode errmsg schema} {
  1 SQLITE_CONSTRAINT "UNIQUE constraint failed: t1.a" {
    CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c);
    INSERT INTO t1 VALUES(3, 2, 1);
  } 

  2 SQLITE_CONSTRAINT "UNIQUE constraint failed: t1.c" {
    CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c UNIQUE);
    INSERT INTO t1 VALUES(4, 2, 'three');
  } 

} {
  reset_db
  execsql $schema
  set cksum [dbcksum db main]

  do_test 3.$tn.1 {
    create_ota1 ota.db
    sqlite3ota ota test.db ota.db
    while {[set res [ota step]]=="SQLITE_OK"} {}
    set res
  } $errcode

  do_test 3.$tn.2 { ota step } $errcode

  do_test 3.$tn.3 { 
    list [catch { ota close } msg] $msg
  } [list 1 "$errcode - $errmsg"]

  do_test 3.$tn.4 { dbcksum db main } $cksum
}


finish_test

# 2014 August 30
#
# 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.
#
#***********************************************************************
#

set testdir [file join [file dirname $argv0] .. .. test]
source $testdir/tester.tcl
set ::testprefix ota2


do_execsql_test 1.0 {
  PRAGMA ota_mode = 1;
  PRAGMA journal_mode = wal;
  CREATE TABLE t1(a, b);
  BEGIN;
    INSERT INTO t1 VALUES(1, 2);
} {wal}

do_test 1.1 {
  set state [sqlite3_transaction_save db]
  db close
  file exists test.db-wal
} {1}

do_test 1.2 {
  sqlite3 db test.db
  db eval {SELECT * FROM t1}
} {}

do_test 1.3 {
  execsql {BEGIN IMMEDIATE}
  sqlite3_transaction_restore db $::state
  db eval {SELECT * FROM t1}
} {1 2}

do_test 1.4 {
  execsql {
    INSERT INTO t1 VALUES(3, 4);
    COMMIT;
    SELECT * FROM t1;
  }
} {1 2 3 4}

do_test 1.5 {
  db close
  file exists test.db-wal
} {0}

do_test 1.5 {
  sqlite3 db test.db
  db eval {SELECT * FROM t1}
} {1 2 3 4}

finish_test

/*
** 2014 August 30
**
** 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.
**
*************************************************************************
*/

#include <assert.h>
#include <string.h>

#include "sqlite3.h"
#include "sqlite3ota.h"


/*
** The ota_state table is used to save the state of a partially applied
** update so that it can be resumed later. The table contains at most a
** single row:
**
**   "wal_state" -> Blob to use with sqlite3_transaction_restore().
**
**   "tbl"       -> Table currently being written (target database names).
**
**   "idx"       -> Index currently being written (target database names).
**                  Or, if the main table is being written, a NULL value.
**
**   "row"       -> Last rowid processed from ota database table (i.e. data_%).
**
**   "progress"  -> total number of key/value b-tree operations performed
**                  so far as part of this ota update.
*/
#define OTA_CREATE_STATE "CREATE TABLE IF NOT EXISTS ota_state"        \
                             "(wal_state, tbl, idx, row, progress)"

typedef struct OtaTblIter OtaTblIter;
typedef struct OtaIdxIter OtaIdxIter;

/*
** Iterator used to iterate through all data tables in the OTA. As follows:
**
**   OtaTblIter iter;
**   for(rc=tblIterFirst(db, &iter); 
**       rc==SQLITE_OK && iter.zTarget; 
**       rc=tblIterNext(&iter)
**   ){
**   }
*/
struct OtaTblIter {
  sqlite3_stmt *pTblIter;         /* Iterate through tables */
  int iEntry;                     /* Index of current entry (from 1) */

  /* Output varibles. zTarget==0 implies EOF. */
  const char *zTarget;            /* Name of target table */
  const char *zSource;            /* Name of source table */

  /* Useful things populated by a call to tblIterPrepareAll() */
  int nCol;                       /* Number of columns in this table */
  char **azCol;                   /* Array of quoted column names */
  sqlite3_stmt *pSelect;          /* PK b-tree SELECT statement */
  sqlite3_stmt *pInsert;          /* PK b-tree INSERT statement */
};

/*
** API is:
**
**     idxIterFirst()
**     idxIterNext()
**     idxIterFinalize()
**     idxIterPrepareAll()
*/
struct OtaIdxIter {
  sqlite3_stmt *pIdxIter;         /* Iterate through indexes */
  int iEntry;                     /* Index of current entry (from 1) */

  /* Output varibles. zTarget==0 implies EOF. */
  const char *zIndex;             /* Name of index */

  int nCol;                       /* Number of columns in index */
  int *aiCol;                     /* Array of column indexes */
  sqlite3_stmt *pWriter;          /* Index writer */
  sqlite3_stmt *pSelect;          /* Select to read values in index order */
};


struct sqlite3ota {
  sqlite3 *dbDest;                /* Target db */
  sqlite3 *dbOta;                 /* Ota db */

  int rc;                         /* Value returned by last ota_step() call */
  char *zErrmsg;                  /* Error message if rc!=SQLITE_OK */

  OtaTblIter tbliter;             /* Used to iterate through tables */
  OtaIdxIter idxiter;             /* Used to iterate through indexes */
};

static int prepareAndCollectError(
  sqlite3 *db, 
  const char *zSql, 
  sqlite3_stmt **ppStmt,
  char **pzErrmsg
){
  int rc = sqlite3_prepare_v2(db, zSql, -1, ppStmt, 0);
  if( rc!=SQLITE_OK ){
    *pzErrmsg = sqlite3_mprintf("%s", sqlite3_errmsg(db));
    *ppStmt = 0;
  }
  return rc;
}

/*
** Unless it is NULL, argument zSql points to a buffer allocated using
** sqlite3_malloc containing an SQL statement. This function prepares the SQL
** statement against database db and frees the buffer. If statement 
** compilation is successful, *ppStmt is set to point to the new statement 
** handle and SQLITE_OK is returned. 
**
** Otherwise, if an error occurs, *ppStmt is set to NULL and an error code
** returned. In this case, *pzErrmsg may also be set to point to an error
** message. It is the responsibility of the caller to free this error message
** buffer using sqlite3_free().
**
** If argument zSql is NULL, this function assumes that an OOM has occurred.
** In this case SQLITE_NOMEM is returned and *ppStmt set to NULL.
*/
static int prepareFreeAndCollectError(
  sqlite3 *db, 
  char *zSql, 
  sqlite3_stmt **ppStmt,
  char **pzErrmsg
){
  int rc;
  assert( *pzErrmsg==0 );
  if( zSql==0 ){
    rc = SQLITE_NOMEM;
    *ppStmt = 0;
  }else{
    rc = prepareAndCollectError(db, zSql, ppStmt, pzErrmsg);
    sqlite3_free(zSql);
  }
  return rc;
}

static char *quoteSqlName(const char *zName){
  int nName = strlen(zName);
  char *zRet = sqlite3_malloc(nName * 2 + 2 + 1);
  if( zRet ){
    int i;
    char *p = zRet;
    *p++ = '"';
    for(i=0; i<nName; i++){
      if( zName[i]=='"' ) *p++ = '"';
      *p++ = zName[i];
    }
    *p++ = '"';
    *p++ = '\0';
  }
  return zRet;
}

static int tblIterPrepareAll(sqlite3ota *p){
  OtaTblIter *pIter = &p->tbliter;
  int rc = SQLITE_OK;
  char *zCol = 0;
  char *zBindings = 0;
  char *zSql;
  sqlite3_stmt *pPragma = 0;
  int i;
  int bSeenPk = 0;                /* Set to true once PK column seen */

  /* Allocate and populate the azCol[] array */
  zSql = sqlite3_mprintf("PRAGMA main.table_info(%Q)", pIter->zTarget);
  rc = prepareFreeAndCollectError(p->dbDest, zSql, &pPragma, &p->zErrmsg);
  pIter->nCol = 0;
  if( rc==SQLITE_OK ){
    while( SQLITE_ROW==sqlite3_step(pPragma) ){
      const char *zName = (const char*)sqlite3_column_text(pPragma, 1);
      if( (pIter->nCol % 4)==0 ){
        int nByte = sizeof(char*) * (pIter->nCol+4);
        char **azNew = (char**)sqlite3_realloc(pIter->azCol, nByte);
        if( azNew==0 ){
          rc = SQLITE_NOMEM;
          break;
        }
        pIter->azCol = azNew;
      }
      pIter->azCol[pIter->nCol] = quoteSqlName(zName);
      if( pIter->azCol[pIter->nCol]==0 ){
        rc = SQLITE_NOMEM;
        break;
      }
      pIter->nCol++;
      if( sqlite3_column_int(pPragma, 5) ) bSeenPk = 1;
    }
    if( rc==SQLITE_OK ){
      rc = sqlite3_finalize(pPragma);
    }else{
      sqlite3_finalize(pPragma);
    }
  }

  /* If the table has no PRIMARY KEY, throw an exception. */
  if( bSeenPk==0 ){
    p->zErrmsg = sqlite3_mprintf("table %s has no PRIMARY KEY", pIter->zTarget);
    rc = SQLITE_ERROR;
  }

  /* Populate the zCol variable */
  for(i=0; rc==SQLITE_OK && i<pIter->nCol; i++){
    zCol = sqlite3_mprintf("%z%s%s", zCol, (i==0?"":", "), pIter->azCol[i]);
    if( zCol==0 ){
      rc = SQLITE_NOMEM;
    }
  }

  /* Allocate and populate zBindings */
  if( rc==SQLITE_OK ){
    zBindings = (char*)sqlite3_malloc(pIter->nCol * 2);
    if( zBindings==0 ){
      rc = SQLITE_NOMEM;
    }else{
      int i;
      for(i=0; i<pIter->nCol; i++){
        zBindings[i*2] = '?';
        zBindings[i*2+1] = ',';
      }
      zBindings[pIter->nCol*2-1] = '\0';
    }
  }

  /* Create OtaTblIter.pSelect */
  if( rc==SQLITE_OK ){
    zSql = sqlite3_mprintf("SELECT rowid, %s FROM %Q", zCol, pIter->zSource);
    rc = prepareFreeAndCollectError(p->dbOta,zSql,&pIter->pSelect, &p->zErrmsg);
  }

  /* Create OtaTblIter.pInsert */
  if( rc==SQLITE_OK ){
    zSql = sqlite3_mprintf("INSERT INTO %Q(%s) VALUES(%s)", 
        pIter->zTarget, zCol, zBindings
    );
    rc = prepareFreeAndCollectError(p->dbDest,zSql,&pIter->pInsert,&p->zErrmsg);
  }

  sqlite3_free(zCol);
  sqlite3_free(zBindings);
  return rc;
}

static void tblIterFreeAll(OtaTblIter *pIter){
  int i;

  sqlite3_finalize(pIter->pSelect);
  sqlite3_finalize(pIter->pInsert);
  for(i=0; i<pIter->nCol; i++) sqlite3_free(pIter->azCol[i]);
  sqlite3_free(pIter->azCol);
  pIter->azCol = 0;
  pIter->pSelect = 0;
  pIter->pInsert = 0;
  pIter->nCol = 0;
}

static int tblIterNext(OtaTblIter *pIter){
  int rc;

  tblIterFreeAll(pIter);
  assert( pIter->pTblIter );
  rc = sqlite3_step(pIter->pTblIter);
  if( rc==SQLITE_ROW ){
    pIter->zSource = (const char*)sqlite3_column_text(pIter->pTblIter, 0);
    pIter->zTarget = &pIter->zSource[5]; assert( 5==strlen("data_") );
    pIter->iEntry++;
  }else{
    pIter->zSource = 0;
    pIter->zTarget = 0;
  }

  if( rc==SQLITE_ROW || rc==SQLITE_DONE ) rc = SQLITE_OK;
  return rc;
}

static int tblIterFirst(sqlite3 *db, OtaTblIter *pIter){
  int rc;                         /* return code */
  memset(pIter, 0, sizeof(OtaTblIter));
  rc = sqlite3_prepare_v2(db, 
      "SELECT name FROM sqlite_master "
      "WHERE type='table' AND name LIKE 'data_%'", -1, &pIter->pTblIter, 0
  );
  if( rc==SQLITE_OK ){
    rc = tblIterNext(pIter);
  }
  return rc;
}


static void tblIterFinalize(OtaTblIter *pIter){
  tblIterFreeAll(pIter);
  sqlite3_finalize(pIter->pTblIter);
  memset(pIter, 0, sizeof(OtaTblIter));
}

static void idxIterFreeAll(OtaIdxIter *pIter){
  sqlite3_finalize(pIter->pWriter);
  sqlite3_finalize(pIter->pSelect);
  pIter->pWriter = 0;
  pIter->pSelect = 0;
  pIter->aiCol = 0;
  pIter->nCol = 0;
}

static int idxIterPrepareAll(sqlite3ota *p){
  int rc;
  int i;                          /* Iterator variable */
  char *zSql = 0;
  char *zCols = 0;                /* Columns list */
  OtaIdxIter *pIter = &p->idxiter;

  /* Prepare the writer statement to write (insert) entries into the index. */
  rc = sqlite3_index_writer(
      p->dbDest, 0, pIter->zIndex, &pIter->pWriter, &pIter->aiCol, &pIter->nCol
  );

  /* Prepare a SELECT statement to read values from the source table in 
  ** the same order as they are stored in the current index. The statement 
  ** is:
  **
  **     SELECT rowid, <cols> FROM data_<tbl> ORDER BY <cols>
  */
  for(i=0; rc==SQLITE_OK && i<pIter->nCol; i++){
    const char *zQuoted = p->tbliter.azCol[ pIter->aiCol[i] ];
    zCols = sqlite3_mprintf("%z%s%s", zCols, zCols?", ":"", zQuoted);
    if( !zCols ){
      rc = SQLITE_NOMEM;
    }
  }
  if( rc==SQLITE_OK ){
    const char *zFmt = "SELECT rowid, %s FROM %Q ORDER BY %s";
    zSql = sqlite3_mprintf(zFmt, zCols, p->tbliter.zSource, zCols);
    if( zSql ){
      sqlite3_stmt **pp = &p->idxiter.pSelect;
      rc = prepareFreeAndCollectError(p->dbOta, zSql, pp, &p->zErrmsg);
    }else{
      rc = SQLITE_NOMEM;
    }
  }

  sqlite3_free(zCols);
  return rc;
}

static int idxIterNext(OtaIdxIter *pIter){
  int rc;

  idxIterFreeAll(pIter);
  assert( pIter->pIdxIter );
  rc = sqlite3_step(pIter->pIdxIter);
  if( rc==SQLITE_ROW ){
    pIter->zIndex = (const char*)sqlite3_column_text(pIter->pIdxIter, 0);
    pIter->iEntry++;
  }else{
    pIter->zIndex = 0;
    rc = sqlite3_finalize(pIter->pIdxIter);
    pIter->pIdxIter = 0;
  }

  if( rc==SQLITE_ROW ) rc = SQLITE_OK;
  return rc;
}

static int idxIterFirst(sqlite3 *db, const char *zTable, OtaIdxIter *pIter){
  int rc;                         /* return code */
  memset(pIter, 0, sizeof(OtaIdxIter));
  rc = sqlite3_prepare_v2(db, 
      "SELECT name FROM sqlite_master "
      "WHERE type='index' AND tbl_name = ?", -1, &pIter->pIdxIter, 0
  );
  if( rc==SQLITE_OK ){
    rc = sqlite3_bind_text(pIter->pIdxIter, 1, zTable, -1, SQLITE_TRANSIENT);
  }
  if( rc==SQLITE_OK ){
    rc = idxIterNext(pIter);
  }
  return rc;
}

static void idxIterFinalize(OtaIdxIter *pIter){
  idxIterFreeAll(pIter);
  sqlite3_finalize(pIter->pIdxIter);
  memset(pIter, 0, sizeof(OtaIdxIter));
}

/*
** Call sqlite3_reset() on the SQL statement passed as the second argument.
** If it returns anything other than SQLITE_OK, store the error code and
** error message in the OTA handle.
*/
static void otaResetStatement(sqlite3ota *p, sqlite3_stmt *pStmt){
  assert( p->rc==SQLITE_OK );
  assert( p->zErrmsg==0 );
  p->rc = sqlite3_reset(pStmt);
  if( p->rc!=SQLITE_OK ){
    sqlite3 *db = sqlite3_db_handle(pStmt);
    p->zErrmsg = sqlite3_mprintf("%s", sqlite3_errmsg(db));
  }
}

/* 
** Check that all SQL statements required to process the current 
** table and index have been prepared. If not, prepare them. If
** an error occurs, store the error code and message in the OTA
** handle before returning.
*/
static int otaPrepareAll(sqlite3ota *p){
  assert( p->rc==SQLITE_OK );
  assert( p->zErrmsg==0 );
  assert( p->tbliter.zTarget );

  if( p->tbliter.pSelect==0 ){
    p->rc = tblIterPrepareAll(p);
  }
  if( p->rc==SQLITE_OK && p->idxiter.zIndex && 0==p->idxiter.pSelect ){
    p->rc = idxIterPrepareAll(p);
  }
  return p->rc;
}

int sqlite3ota_step(sqlite3ota *p){
  if( p ){
    while( p && p->rc==SQLITE_OK && p->tbliter.zTarget ){
      sqlite3_stmt *pSelect;
      int i;

      otaPrepareAll(p);
      pSelect = (p->idxiter.zIndex ? p->idxiter.pSelect : p->tbliter.pSelect);

      /* Advance to the next input row. */
      if( p->rc==SQLITE_OK ){
        int rc = sqlite3_step(pSelect);
        if( rc!=SQLITE_ROW ){
          otaResetStatement(p, pSelect);

          /* Go to the next index. */
          if( p->rc==SQLITE_OK ){
            if( p->idxiter.zIndex ){
              p->rc = idxIterNext(&p->idxiter);
            }else{
              p->rc = idxIterFirst(p->dbDest, p->tbliter.zTarget, &p->idxiter);
            }
          }

          /* If there is no next index, go to the next table. */
          if( p->rc==SQLITE_OK && p->idxiter.zIndex==0 ){
            p->rc = tblIterNext(&p->tbliter);
          }
          continue;
        }
      }

      /* Update the target database PK table according to the row that 
      ** tbliter.pSelect currently points to. 
      **
      ** todo: For now, we assume all rows are INSERT commands - this will 
      ** change.  */
      if( p->rc==SQLITE_OK ){
        sqlite3_stmt *pInsert;
        int nCol;
        if( p->idxiter.zIndex ){
          pInsert = p->idxiter.pWriter;
          nCol = p->idxiter.nCol;
        }else{
          pInsert = p->tbliter.pInsert;
          nCol = p->tbliter.nCol;
        }

        for(i=0; i<nCol; i++){
          sqlite3_value *pVal = sqlite3_column_value(pSelect, i+1);
          sqlite3_bind_value(pInsert, i+1, pVal);
        }

        sqlite3_step(pInsert);
        otaResetStatement(p, pInsert);
      }
      
      break;
    }

    if( p->rc==SQLITE_OK && p->tbliter.zTarget==0 ) p->rc = SQLITE_DONE;
  }

  return (p ? p->rc : SQLITE_NOMEM);
}

static void otaOpenDatabase(sqlite3ota *p, sqlite3 **pDb, const char *zFile){
  if( p->rc==SQLITE_OK ){
    p->rc = sqlite3_open(zFile, pDb);
    if( p->rc ){
      const char *zErr = sqlite3_errmsg(*pDb);
      p->zErrmsg = sqlite3_mprintf("sqlite3_open(): %s", zErr);
    }
  }
}

static void otaSaveTransactionState(sqlite3ota *p){
  sqlite3_stmt *pStmt = 0;
  void *pWalState = 0;
  int nWalState = 0;
  int rc;

  const char *zInsert = 
    "INSERT INTO ota_state(wal_state, tbl, idx, row, progress)"
    "VALUES(:wal_state, :tbl, :idx, :row, :progress)";

  rc = sqlite3_transaction_save(p->dbDest, &pWalState, &nWalState);
  if( rc==SQLITE_OK ){
    rc = sqlite3_exec(p->dbOta, "DELETE FROM ota_state", 0, 0, 0);
  }
  if( rc==SQLITE_OK ){
    rc = prepareAndCollectError(p->dbOta, zInsert, &pStmt, &p->zErrmsg);
  }
  if( rc==SQLITE_OK ){
    sqlite3_stmt *pSelect;
    pSelect = (p->idxiter.zIndex ? p->idxiter.pSelect : p->tbliter.pSelect);
    sqlite3_bind_blob(pStmt, 1, pWalState, nWalState, SQLITE_STATIC);
    sqlite3_bind_text(pStmt, 2, p->tbliter.zTarget, -1, SQLITE_STATIC);
    if( p->idxiter.zIndex ){
      sqlite3_bind_text(pStmt, 3, p->idxiter.zIndex, -1, SQLITE_STATIC);
    }
    sqlite3_bind_int64(pStmt, 4, sqlite3_column_int64(pSelect, 0));
    sqlite3_step(pStmt);
    rc = sqlite3_finalize(pStmt);
    if( rc==SQLITE_OK ){
      rc = sqlite3_exec(p->dbOta, "COMMIT", 0, 0, 0);
    }
    if( rc!=SQLITE_OK ){
      p->zErrmsg = sqlite3_mprintf("%s", sqlite3_errmsg(p->dbOta));
    }
  }
  sqlite3_free(pWalState);
  assert( p->rc==SQLITE_OK );
  p->rc = rc;
}

static void otaLoadTransactionState(sqlite3ota *p){
  sqlite3_stmt *pStmt = 0;
  int rc;

  const char *zSelect = 
    "SELECT wal_state, tbl, idx, row, progress FROM ota_state";

  rc = prepareAndCollectError(p->dbOta, zSelect, &pStmt, &p->zErrmsg);
  if( rc==SQLITE_OK ){
    if( SQLITE_ROW==sqlite3_step(pStmt) ){
      const void *pWalState = 0;
      int nWalState = 0;
      const char *zTbl;
      const char *zIdx;
      sqlite3_int64 iRowid;

      pWalState = sqlite3_column_blob(pStmt, 0);
      nWalState = sqlite3_column_bytes(pStmt, 0);
      zTbl = (const char*)sqlite3_column_text(pStmt, 1);
      zIdx = (const char*)sqlite3_column_text(pStmt, 2);
      iRowid = sqlite3_column_int64(pStmt, 3);
      rc = sqlite3_transaction_restore(p->dbDest, pWalState, nWalState);

      while( rc==SQLITE_OK 
          && p->tbliter.zTarget 
          && sqlite3_stricmp(p->tbliter.zTarget, zTbl) 
      ){
        rc = tblIterNext(&p->tbliter);
      }
      if( rc==SQLITE_OK && !p->tbliter.zTarget ){
        rc = SQLITE_ERROR;
        p->zErrmsg = sqlite3_mprintf("ota_state mismatch error");
      }

      if( rc==SQLITE_OK && zIdx ){
        rc = idxIterFirst(p->dbDest, p->tbliter.zTarget, &p->idxiter);
        while( rc==SQLITE_OK 
            && p->idxiter.zIndex 
            && sqlite3_stricmp(p->idxiter.zIndex, zIdx) 
        ){
          rc = idxIterNext(&p->idxiter);
        }
        if( rc==SQLITE_OK && !p->idxiter.zIndex ){
          rc = SQLITE_ERROR;
          p->zErrmsg = sqlite3_mprintf("ota_state mismatch error");
        }
      }

      if( rc==SQLITE_OK ){
        rc = otaPrepareAll(p);
      }

      if( rc==SQLITE_OK ){
        sqlite3_stmt *pSelect;
        pSelect = (p->idxiter.zIndex ? p->idxiter.pSelect : p->tbliter.pSelect);
        while( sqlite3_column_int64(pSelect, 0)!=iRowid ){
          rc = sqlite3_step(pSelect);
          if( rc!=SQLITE_ROW ) break;
        }
        if( rc==SQLITE_ROW ){
          rc = SQLITE_OK;
        }else{
          rc = SQLITE_ERROR;
          p->zErrmsg = sqlite3_mprintf("ota_state mismatch error");
        }
      }
    }
    if( rc==SQLITE_OK ){
      rc = sqlite3_finalize(pStmt);
    }else{
      sqlite3_finalize(pStmt);
    }
  }
  p->rc = rc;
}


/*
** Open and return a new OTA handle. 
*/
sqlite3ota *sqlite3ota_open(const char *zTarget, const char *zOta){
  sqlite3ota *p;

  p = (sqlite3ota*)sqlite3_malloc(sizeof(sqlite3ota));
  if( p ){

    /* Open the target database */
    memset(p, 0, sizeof(sqlite3ota));
    otaOpenDatabase(p, &p->dbDest, zTarget);
    otaOpenDatabase(p, &p->dbOta, zOta);

    /* If it has not already been created, create the ota_state table */
    if( p->rc==SQLITE_OK ){
      p->rc = sqlite3_exec(p->dbOta, OTA_CREATE_STATE, 0, 0, &p->zErrmsg);
    }

    if( p->rc==SQLITE_OK ){
      const char *zScript = 
        "PRAGMA ota_mode=1;"
        "PRAGMA journal_mode=wal;"
        "BEGIN IMMEDIATE;"
      ;
      p->rc = sqlite3_exec(p->dbDest, zScript, 0, 0, &p->zErrmsg);
    }

    if( p->rc==SQLITE_OK ){
      const char *zScript = "BEGIN IMMEDIATE";
      p->rc = sqlite3_exec(p->dbOta, zScript, 0, 0, &p->zErrmsg);
    }

    /* Point the table iterator at the first table */
    if( p->rc==SQLITE_OK ){
      p->rc = tblIterFirst(p->dbOta, &p->tbliter);
    }

    if( p->rc==SQLITE_OK ){
      otaLoadTransactionState(p);
    }
  }

  return p;
}

static void otaCloseHandle(sqlite3 *db){
  int rc = sqlite3_close(db);
  assert( rc==SQLITE_OK );
}

int sqlite3ota_close(sqlite3ota *p, char **pzErrmsg){
  int rc;
  if( p ){

    /* If the update has not been fully applied, save the state in 
    ** the ota db. If successful, this call also commits the open 
    ** transaction on the ota db. */
    assert( p->rc!=SQLITE_ROW );
    if( p->rc==SQLITE_OK ){
      assert( p->zErrmsg==0 );
      otaSaveTransactionState(p);
    }

    /* Close all open statement handles. */
    tblIterFinalize(&p->tbliter);
    idxIterFinalize(&p->idxiter);

    /* If the ota update has been fully applied, commit the transaction
    ** on the target database. */
    if( p->rc==SQLITE_DONE ){
      rc = sqlite3_exec(p->dbDest, "COMMIT", 0, 0, &p->zErrmsg);
      if( rc!=SQLITE_OK ) p->rc = rc;
    }

    rc = p->rc;
    *pzErrmsg = p->zErrmsg;
    otaCloseHandle(p->dbDest);
    otaCloseHandle(p->dbOta);
    sqlite3_free(p);
  }else{
    rc = SQLITE_NOMEM;
    *pzErrmsg = 0;
  }
  return rc;
}


/**************************************************************************/

#ifdef SQLITE_TEST 

#include <tcl.h>

/* From main.c (apparently...) */
extern const char *sqlite3ErrName(int);

static int test_sqlite3ota_cmd(
  ClientData clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int ret = TCL_OK;
  sqlite3ota *pOta = (sqlite3ota*)clientData;
  const char *azMethod[] = { "step", "close", 0 };
  int iMethod;

  if( objc!=2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "METHOD");
    return TCL_ERROR;
  }
  if( Tcl_GetIndexFromObj(interp, objv[1], azMethod, "method", 0, &iMethod) ){
    return TCL_ERROR;
  }

  switch( iMethod ){
    case 0: /* step */ {
      int rc = sqlite3ota_step(pOta);
      Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
      break;
    }

    case 1: /* close */ {
      char *zErrmsg = 0;
      int rc;
      Tcl_DeleteCommand(interp, Tcl_GetString(objv[0]));
      rc = sqlite3ota_close(pOta, &zErrmsg);
      if( rc==SQLITE_OK || rc==SQLITE_DONE ){
        Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
        assert( zErrmsg==0 );
      }else{
        Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
        if( zErrmsg ){
          Tcl_AppendResult(interp, " - ", zErrmsg, 0);
          sqlite3_free(zErrmsg);
        }
        ret = TCL_ERROR;
      }
      break;
    }

    default: /* seems unlikely */
      assert( !"cannot happen" );
      break;
  }

  return ret;
}

/*
** Tclcmd: sqlite3ota CMD <target-db> <ota-db>
*/
static int test_sqlite3ota(
  ClientData clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  sqlite3ota *pOta = 0;
  const char *zCmd;
  const char *zTarget;
  const char *zOta;

  if( objc!=4 ){
    Tcl_WrongNumArgs(interp, 1, objv, "NAME TARGET-DB OTA-DB");
    return TCL_ERROR;
  }
  zCmd = Tcl_GetString(objv[1]);
  zTarget = Tcl_GetString(objv[2]);
  zOta = Tcl_GetString(objv[3]);

  pOta = sqlite3ota_open(zTarget, zOta);
  Tcl_CreateObjCommand(interp, zCmd, test_sqlite3ota_cmd, (ClientData)pOta, 0);
  Tcl_SetObjResult(interp, objv[1]);
  return TCL_OK;
}

int SqliteOta_Init(Tcl_Interp *interp){ 
  Tcl_CreateObjCommand(interp, "sqlite3ota", test_sqlite3ota, 0, 0);
  return TCL_OK;
}

#endif                  /* ifdef SQLITE_TEST */

/*
** 2014 August 30
**
** 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 the public interface for the OTA extension. 
*/

/*
** SUMMARY
**
** Writing a transaction containing a large number of operations on 
** b-tree indexes that are collectively larger than the available cache
** memory can be very inefficient. 
**
** The problem is that in order to update a b-tree, the leaf page (at least)
** containing the entry being inserted or deleted must be modified. If the
** working set of leaves is larger than the available cache memory, then a 
** single leaf that is modified more than once as part of the transaction 
** may be loaded from or written to the persistent media more than once. 
** Additionally, because the index updates are likely to be applied in
** random order, access to pages within the databse is also likely to be in 
** random order, which is itself quite inefficient.
**
** One way to improve the situation is to sort the operations on each index
** by index key before applying them to the b-tree. This leads to an IO
** pattern that resembles a single linear scan through the index b-tree,
** and all but guarantees each modified leaf page is loaded and stored 
** exactly once. SQLite uses this trick to improve the performance of
** CREATE INDEX commands. This extension allows it to be used to improve
** the performance of large transactions on existing databases.
**
** Additionally, this extension allows the work involved in writing the 
** large transaction to be broken down into sub-transactions performed 
** sequentially by separate processes. This is useful if the system cannot 
** guarantee that a single update process may run for long enough to apply 
** the entire update, for example because the update is running on a mobile
** device that is frequently rebooted. Even after the writer process has 
** committed one or more sub-transactions, other database clients continue
** to read from the original database snapshot. In other words, partially 
** applied transactions are not visible to other clients. 
**
** "OTA" stands for "Over The Air" update. As in a large database update
** transmitted via a wireless network to a mobile device. A transaction
** applied using this extension is hence refered to as an "OTA update".
**
**
** LIMITATIONS
**
** An "OTA update" transaction is subject to the following limitations:
**
**   * The transaction must consist of INSERT, UPDATE and DELETE operations
**     only.
**
**   * INSERT statements may not use any default values.
**
**   * UPDATE and DELETE statements must identify their target rows by
**     real PRIMARY KEY values - i.e. INTEGER PRIMARY KEY columns or 
**     by the PRIMARY KEY columns of WITHOUT ROWID tables.
**
**   * UPDATE statements may not modify real PRIMARY KEY columns.
**
**   * No triggers will be fired.
**
**   * No foreign key violations are detected or reported.
**
**   * No constraint handling mode except for "OR ROLLBACK" is supported.
**
**
** PREPARATION
**
** An "OTA update" is stored as a separate SQLite database. A database
** containing an OTA update is an "OTA database". For each table in the 
** target database to be updated, the OTA database should contain a table
** named "data_<target name>" containing the same set of columns as the
** target table, and one more - "ota_control". The data_% table should 
** have no PRIMARY KEY or UNIQUE constraints, but each column should have
** the same type as the corresponding column in the target database.
** The "ota_control" column should have no type at all. For example, if
** the target database contains:
**
**   CREATE TABLE t1(a INTEGER PRIMARY KEY, b TEXT, c UNIQUE);
**
** Then the OTA database should contain:
**
**   CREATE TABLE data_t1(a INTEGER, b TEXT, c, ota_control);
**
** The order of the columns in the data_% table does not matter.
**
** For each row to INSERT into the target database as part of the OTA 
** update, the corresponding data_% table should contain a single record
** with the "ota_control" column set to contain integer value 0. The
** other columns should be set to the values that make up the new record 
** to insert.
**
** For each row to DELETE from the target database as part of the OTA 
** update, the corresponding data_% table should contain a single record
** with the "ota_control" column set to contain integer value 1. The
** real primary key values of the row to delete should be stored in the
** corresponding columns of the data_% table. The values stored in the
** other columns are not used.
**
** For each row to DELETE from the target database as part of the OTA 
** update, the corresponding data_% table should contain a single record
** with the "ota_control" column set to contain a value of type text.
** The real primary key values identifying the row to update should be 
** stored in the corresponding columns of the data_% table row, as should
** the new values of all columns being update. The text value in the 
** "ota_control" column must contain the same number of characters as
** there are column in the target database table, and must consist entirely
** of "x" and "." characters. For each column that is being updated,
** the corresponding character is set to "x". For those that remain as
** they are, the corresponding character of the ota_control value should
** be set to ".". For example, given the tables above, the update 
** statement:
**
**   UPDATE t1 SET c = 'usa' WHERE a = 4;
**
** is represented by the data_t1 row created by:
**
**   INSERT INTO data_t1(a, b, c, ota_control) VALUES(4, NULL, 'usa', '..x');
**
**
** USAGE
**
** The API declared below allows an application to apply an OTA update 
** stored on disk to an existing target database. Essentially, the 
** application:
**
**     1) Opens an OTA handle using the sqlite3ota_open() function.
**
**     2) Calls the sqlite3ota_step() function one or more times on
**        the new handle. Each call to sqlite3ota_step() performs a single
**        b-tree operation, so thousands of calls may be required to apply 
**        a complete update.
**
**     3) Calls sqlite3ota_close() to close the OTA update handle. If
**        sqlite3ota_step() has been called enough times to completely
**        apply the update to the target database, then it is committed
**        and made visible to other database clients at this point. 
**        Otherwise, the state of the OTA update application is saved
**        in the OTA database for later resumption.
**
** See comments below for more detail on APIs.
**
** If an update is only partially applied to the target database by the
** time sqlite3ota_close() is called, various state information is saved 
** within the OTA database. This allows subsequent processes to automatically
** resume the OTA update from where it left off.
**
** To remove all OTA extension state information, returning an OTA database 
** to its original contents, it is sufficient to drop all tables that begin
** with the prefix "ota_"
*/

#ifndef _SQLITE3OTA_H
#define _SQLITE3OTA_H

typedef struct sqlite3ota sqlite3ota;

/*
** Open an OTA handle.
**
** Argument zTarget is the path to the target database. Argument zOta is
** the path to the OTA database. Each call to this function must be matched
** by a call to sqlite3ota_close().
*/
sqlite3ota *sqlite3ota_open(const char *zTarget, const char *zOta);

/*
** Do some work towards applying the OTA update to the target db. 
**
** Return SQLITE_DONE if the update has been completely applied, or 
** SQLITE_OK if no error occurs but there remains work to do to apply
** the OTA update. If an error does occur, some other error code is 
** returned. 
**
** Once a call to sqlite3ota_step() has returned a value other than
** SQLITE_OK, all subsequent calls on the same OTA handle are no-ops
** that immediately return the same value.
*/
int sqlite3ota_step(sqlite3ota *pOta);

/*
** Close an OTA handle. 
**
** If the OTA update has been completely applied, commit it to the target 
** database. Otherwise, assuming no error has occurred, save the current 
** state of the OTA update appliation to the OTA database.
**
** If an error has already occurred as part of an sqlite3ota_step()
** or sqlite3ota_open() call, or if one occurs within this function, an
** SQLite error code is returned. Additionally, *pzErrmsg may be set to
** point to a buffer containing a utf-8 formatted English language error
** message. It is the responsibility of the caller to eventually free any 
** such buffer using sqlite3_free().
**
** Otherwise, if no error occurs, this function returns SQLITE_OK if the
** update has been partially applied, or SQLITE_DONE if it has been 
** completely applied.
*/
int sqlite3ota_close(sqlite3ota *pOta, char **pzErrmsg);

#endif /* _SQLITE3OTA_H */

  $(TOP)/src/where.c \
  parse.c \
  $(TOP)/ext/fts3/fts3.c \
  $(TOP)/ext/fts3/fts3_aux.c \
  $(TOP)/ext/fts3/fts3_expr.c \
  $(TOP)/ext/fts3/fts3_tokenizer.c \
  $(TOP)/ext/fts3/fts3_write.c \
  $(TOP)/ext/async/sqlite3async.c \
  $(TOP)/ext/ota/sqlite3ota.c

# Header files used by all library source files.
#
HDR = \
   $(TOP)/src/btree.h \
   $(TOP)/src/btreeInt.h \
   $(TOP)/src/hash.h \

  Pgno iTab = 0;
  BtLock *pLock;

  /* If this database is not shareable, or if the client is reading
  ** and has the read-uncommitted flag set, then no lock is required. 
  ** Return true immediately.
  */
  if( (pBtree->db->flags & SQLITE_OtaMode)
   || (pBtree->sharable==0)
   || (eLockType==READ_LOCK && (pBtree->db->flags & SQLITE_ReadUncommitted))
  ){
    return 1;
  }

  /* If the client is reading  or writing an index and the schema is
  ** not loaded, then it is too difficult to actually check to see if

  }
#endif
  *ppBtree = p;

btree_open_out:
  if( rc!=SQLITE_OK ){
    if( pBt && pBt->pPager ){
      sqlite3PagerClose(pBt->pPager, 0);
    }
    sqlite3_free(pBt);
    sqlite3_free(p);
    *ppBtree = 0;
  }else{
    /* If the B-Tree was successfully opened, set the pager-cache size to the
    ** default value. Except, when opening on an existing shared pager-cache,

  if( !p->sharable || removeFromSharingList(pBt) ){
    /* The pBt is no longer on the sharing list, so we can access
    ** it without having to hold the mutex.
    **
    ** Clean out and delete the BtShared object.
    */
    assert( !pBt->pCursor );
    sqlite3PagerClose(pBt->pPager, (p->db->flags & SQLITE_OtaMode)!=0);
    if( pBt->xFreeSchema && pBt->pSchema ){
      pBt->xFreeSchema(pBt->pSchema);
    }
    sqlite3DbFree(0, pBt->pSchema);
    freeTempSpace(pBt);
    sqlite3_free(pBt);
  }

  ** WITHOUT ROWID table.
  */
  for(ix=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, ix++){
    int regIdx;          /* Range of registers hold conent for pIdx */
    int regR;            /* Range of registers holding conflicting PK */
    int iThisCur;        /* Cursor for this UNIQUE index */
    int addrUniqueOk;    /* Jump here if the UNIQUE constraint is satisfied */

    /* If the "ota_mode" flag is set, ignore all indexes except the PK 
    ** index of WITHOUT ROWID tables.  */
    if( (db->flags & SQLITE_OtaMode) && pIdx!=pPk) continue;

    if( aRegIdx[ix]==0 ) continue;  /* Skip indices that do not change */
    if( bAffinityDone==0 ){
      sqlite3TableAffinity(v, pTab, regNewData+1);
      bAffinityDone = 1;
    }
    iThisCur = iIdxCur+ix;

  u8 bAffinityDone = 0; /* True if OP_Affinity has been run already */

  v = sqlite3GetVdbe(pParse);
  assert( v!=0 );
  assert( pTab->pSelect==0 );  /* This table is not a VIEW */
  for(i=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, i++){
    if( aRegIdx[i]==0 ) continue;

    /* If the "ota_mode" flag is set, ignore all indexes except the PK 
    ** index of WITHOUT ROWID tables.  */
    if( (pParse->db->flags & SQLITE_OtaMode) 
     && (pTab->iPKey>=0 || pIdx->idxType!=SQLITE_IDXTYPE_PRIMARYKEY) 
    ){
      continue;
    }

    bAffinityDone = 1;
    if( pIdx->pPartIdxWhere ){
      sqlite3VdbeAddOp2(v, OP_IsNull, aRegIdx[i], sqlite3VdbeCurrentAddr(v)+2);
      VdbeCoverage(v);
    }
    sqlite3VdbeAddOp2(v, OP_IdxInsert, iIdxCur+i, aRegIdx[i]);
    pik_flags = 0;

** Return 1 if database is read-only or 0 if read/write.  Return -1 if
** no such database exists.
*/
int sqlite3_db_readonly(sqlite3 *db, const char *zDbName){
  Btree *pBt = sqlite3DbNameToBtree(db, zDbName);
  return pBt ? sqlite3BtreeIsReadonly(pBt) : -1;
}

int sqlite3_transaction_save(sqlite3 *db, void **ppState, int *pnState){
  Pager *pPager = sqlite3BtreePager(db->aDb[0].pBt);
  return sqlite3PagerSaveState(pPager, ppState, pnState);
}

int sqlite3_transaction_restore(sqlite3 *db, const void *pState, int nState){
  Pager *pPager = sqlite3BtreePager(db->aDb[0].pBt);
  return sqlite3PagerRestoreState(pPager, pState, nState);
}

** result in a coredump.
**
** This function always succeeds. If a transaction is active an attempt
** is made to roll it back. If an error occurs during the rollback 
** a hot journal may be left in the filesystem but no error is returned
** to the caller.
*/
int sqlite3PagerClose(Pager *pPager, int bOtaMode){
  u8 *pTmp = (u8 *)pPager->pTmpSpace;

  assert( assert_pager_state(pPager) );
  disable_simulated_io_errors();
  sqlite3BeginBenignMalloc();
  pagerFreeMapHdrs(pPager);
  /* pPager->errCode = 0; */
  pPager->exclusiveMode = 0;
#ifndef SQLITE_OMIT_WAL
  sqlite3WalClose(
      pPager->pWal, pPager->ckptSyncFlags, pPager->pageSize, (bOtaMode?0:pTmp)
  );
  pPager->pWal = 0;
#endif
  pager_reset(pPager);
  if( MEMDB ){
    pager_unlock(pPager);
  }else{
    /* If it is open, sync the journal file before calling UnlockAndRollback.

    if( rc==SQLITE_OK ){
      rc = sqlite3WalClose(pPager->pWal, pPager->ckptSyncFlags,
                           pPager->pageSize, (u8*)pPager->pTmpSpace);
      pPager->pWal = 0;
      pagerFixMaplimit(pPager);
    }
  }
  return rc;
}

int sqlite3PagerSaveState(Pager *pPager, void **ppState, int *pnState){
  int rc = SQLITE_OK;
  *ppState = 0;
  *pnState = 0;
  if( pPager->pWal==0 || pPager->eState<PAGER_WRITER_LOCKED ){
    rc = SQLITE_ERROR;
  }else{
    /* Flush all dirty pages to the wal. */
    PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);
    rc = sqlite3WalFrames(pPager->pWal, 
        pPager->pageSize, pList, 0, 0, pPager->walSyncFlags
    );
    if( rc==SQLITE_OK ){
      rc = sqlite3WalSaveState(pPager->pWal, ppState, pnState);
    }
  }
  return rc;
}

int sqlite3PagerRestoreState(Pager *pPager, const void *pState, int nState){
  int rc = SQLITE_OK;
  if( pPager->pWal==0 
   || pPager->eState<PAGER_WRITER_LOCKED 
   || sqlite3PcacheDirtyList(pPager->pPCache)
  ){
    rc = SQLITE_ERROR;
  }else{
    sqlite3PcacheTruncate(pPager->pPCache, 1);
    rc = sqlite3WalRestoreState(pPager->pWal, pState, nState);
    pPager->eState = PAGER_WRITER_CACHEMOD;
  }

  return rc;
}

#endif /* !SQLITE_OMIT_WAL */

#ifdef SQLITE_ENABLE_ZIPVFS
/*

  Pager **ppPager,
  const char*,
  int,
  int,
  int,
  void(*)(DbPage*)
);
int sqlite3PagerClose(Pager *pPager, int);
int sqlite3PagerReadFileheader(Pager*, int, unsigned char*);

/* Functions used to configure a Pager object. */
void sqlite3PagerSetBusyhandler(Pager*, int(*)(void *), void *);
int sqlite3PagerSetPagesize(Pager*, u32*, int);
int sqlite3PagerMaxPageCount(Pager*, int);
void sqlite3PagerSetCachesize(Pager*, int);

  void disable_simulated_io_errors(void);
  void enable_simulated_io_errors(void);
#else
# define disable_simulated_io_errors()
# define enable_simulated_io_errors()
#endif

int sqlite3PagerSaveState(Pager *pPager, void **ppState, int *pnState);
int sqlite3PagerRestoreState(Pager *pPager, const void *pState, int nState);

#endif /* _PAGER_H_ */

    /* ePragTyp:  */ PragTyp_PAGE_COUNT,
    /* ePragFlag: */ PragFlag_NeedSchema,
    /* iArg:      */ 0 },
  { /* zName:     */ "mmap_size",
    /* ePragTyp:  */ PragTyp_MMAP_SIZE,
    /* ePragFlag: */ 0,
    /* iArg:      */ 0 },
#endif
  { /* zName:     */ "ota_mode",
    /* ePragTyp:  */ PragTyp_FLAG,
    /* ePragFlag: */ 0,
    /* iArg:      */ SQLITE_OtaMode },
#if !defined(SQLITE_OMIT_PAGER_PRAGMAS)
  { /* zName:     */ "page_count",
    /* ePragTyp:  */ PragTyp_PAGE_COUNT,
    /* ePragFlag: */ PragFlag_NeedSchema,
    /* iArg:      */ 0 },
  { /* zName:     */ "page_size",
    /* ePragTyp:  */ PragTyp_PAGE_SIZE,
    /* ePragFlag: */ 0,

          sqlite3VdbeAddOp2(v, OP_Null, 0, 5);
        }
        if( (pCol->colFlags & COLFLAG_PRIMKEY)==0 ){
          k = 0;
        }else if( pPk==0 ){
          k = 1;
        }else{
          if( (db->flags & SQLITE_OtaMode) && HasRowid(pTab) ){
            k = 0;
          }else{
            for(k=1; ALWAYS(k<=pTab->nCol) && pPk->aiColumn[k-1]!=i; k++){}
          }
        }
        sqlite3VdbeAddOp2(v, OP_Integer, k, 6);
        sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 6);
      }
    }
  }
  break;

  const char **pzTail       /* OUT: End of parsed string */
){
  int rc;
  rc = sqlite3LockAndPrepare(db,zSql,nBytes,1,0,ppStmt,pzTail);
  assert( rc==SQLITE_OK || ppStmt==0 || *ppStmt==0 );  /* VERIFY: F13021 */
  return rc;
}


#ifndef SQLITE_OMIT_UTF16
/*
** Compile the UTF-16 encoded SQL statement zSql into a statement handle.
*/
static int sqlite3Prepare16(
  sqlite3 *db,              /* Database handle. */ 

*/
#define SQLITE_ROLLBACK 1
/* #define SQLITE_IGNORE 2 // Also used by sqlite3_authorizer() callback */
#define SQLITE_FAIL     3
/* #define SQLITE_ABORT 4  // Also an error code */
#define SQLITE_REPLACE  5

/*
** Allocate a statement handle that may be used to write directly to an
** index b-tree. This allows the user to create a corrupt database. Once
** the statement handle is allocated, it may be used with the same APIs
** as any statement handle created with sqlite3_prepare().
**
** The statement writes to the index specified by parameter zIndex, which
** must be in the "main" database. If argument bDelete is false, then each
** time the statement is sqlite3_step()ed, an entry is inserted into the
** b-tree index. If it is true, then an entry may be deleted (or may not, if 
** the specified key is not found) each time the statement is 
** sqlite3_step()ed.
**
** If statement compilation is successful, *ppStmt is set to point to the 
** new statement handle and SQLITE_OK is returned. Otherwise, if an error
** occurs, *ppStmt is set to NULL and an error code returned. An error
** message may be left in the database handle in this case.
**
** If statement compilation succeeds, output variable *pnCol is set to the
** total number of columns in the index, including the primary key columns
** at the end. Variable *paiCol is set to point to an array *pnCol entries 
** in size. Each entry is the table column index, numbered from zero from left 
** to right, of the corresponding index column. For example, if:
**
**       CREATE TABLE t1(a, b, c, d);
**       CREATE INDEX i1 ON t1(b, c);
**
** then *pnCol is 3 and *paiCol points to an array containing {1, 2, -1}.
** If table t1 had an explicit INTEGER PRIMARY KEY, then the "-1" in the
** *paiCol array would be replaced by its column index. Or if:
**
**       CREATE TABLE t2(a, b, c, d, PRIMARY KEY(d, c)) WITHOUT ROWID;
**       CREATE INDEX i2 ON t2(a);
**
** then (*pnCol) is 3 and *paiCol points to an array containing {0, 3, 2}.
**
** The lifetime of the array is the same as that of the statement handle -
** it is automatically freed when the statement handle is passed to
** sqlite3_finalize().
**
** The statement has (*pnCol) SQL variables that values may be bound to.
** They correspond to the values used to create the index key that is
** inserted or deleted when the statement is stepped.
**
** If the index is a UNIQUE index, the usual checking and error codes apply
** to insert operations.
*/
int sqlite3_index_writer(
  sqlite3 *db, 
  int bDelete,                    /* Zero for insert, non-zero for delete */
  const char *zIndex,             /* Index to write to */
  sqlite3_stmt**,                 /* OUT: New statement handle */
  int **paiCol, int *pnCol        /* OUT: See above */
);

/*
** This function is used to save the state of an ongoing WAL mode write 
** transaction on the "main" database of the supplied database handle.
**
** If successful, SQLITE_OK is returned and output variable (*ppState)
** is set to point to a buffer containing the transaction state data. 
** (*pnState) is set to the size of that buffer in bytes. Otherwise, if
** an error occurs, an SQLite error code is returned and both output
** variables are zeroed.
**
** A transaction state may be saved if: 
**
**   * the transaction does not contain any schema modifications.
**   * there are no open sub-transactions.
*/
int sqlite3_transaction_save(sqlite3 *db, void **ppState, int *pnState);

int sqlite3_transaction_restore(sqlite3 *db, const void *pState, int nState);

/*
** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double

#define SQLITE_PreferBuiltin  0x00200000  /* Preference to built-in funcs */
#define SQLITE_LoadExtension  0x00400000  /* Enable load_extension */
#define SQLITE_EnableTrigger  0x00800000  /* True to enable triggers */
#define SQLITE_DeferFKs       0x01000000  /* Defer all FK constraints */
#define SQLITE_QueryOnly      0x02000000  /* Disable database changes */
#define SQLITE_VdbeEQP        0x04000000  /* Debug EXPLAIN QUERY PLAN */

#define SQLITE_OtaMode        0x08000000  /* True in "ota mode" */


/*
** Bits of the sqlite3.dbOptFlags field that are used by the
** sqlite3_test_control(SQLITE_TESTCTRL_OPTIMIZATIONS,...) interface to
** selectively disable various optimizations.
*/
#define SQLITE_QueryFlattener 0x0001   /* Query flattening */

# define sqlite3MemdebugNoType(X,Y)   1
#endif
#define MEMTYPE_HEAP       0x01  /* General heap allocations */
#define MEMTYPE_LOOKASIDE  0x02  /* Might have been lookaside memory */
#define MEMTYPE_SCRATCH    0x04  /* Scratch allocations */
#define MEMTYPE_PCACHE     0x08  /* Page cache allocations */
#define MEMTYPE_DB         0x10  /* Uses sqlite3DbMalloc, not sqlite_malloc */


/*
** Threading interface
*/
#if SQLITE_MAX_WORKER_THREADS>0
int sqlite3ThreadCreate(SQLiteThread**,void*(*)(void*),void*);
int sqlite3ThreadJoin(SQLiteThread*, void**);
#endif

#endif /* _SQLITEINT_H_ */

    extern int Sqlitetestintarray_Init(Tcl_Interp*);
    extern int Sqlitetestvfs_Init(Tcl_Interp *);
    extern int Sqlitetestrtree_Init(Tcl_Interp*);
    extern int Sqlitequota_Init(Tcl_Interp*);
    extern int Sqlitemultiplex_Init(Tcl_Interp*);
    extern int SqliteSuperlock_Init(Tcl_Interp*);
    extern int SqlitetestSyscall_Init(Tcl_Interp*);

    extern int SqliteOta_Init(Tcl_Interp*);

#if defined(SQLITE_ENABLE_FTS3) || defined(SQLITE_ENABLE_FTS4)
    extern int Sqlitetestfts3_Init(Tcl_Interp *interp);
#endif

#ifdef SQLITE_ENABLE_ZIPVFS
    extern int Zipvfs_Init(Tcl_Interp*);

    Sqlitetestintarray_Init(interp);
    Sqlitetestvfs_Init(interp);
    Sqlitetestrtree_Init(interp);
    Sqlitequota_Init(interp);
    Sqlitemultiplex_Init(interp);
    SqliteSuperlock_Init(interp);
    SqlitetestSyscall_Init(interp);
    SqliteOta_Init(interp);

#if defined(SQLITE_ENABLE_FTS3) || defined(SQLITE_ENABLE_FTS4)
    Sqlitetestfts3_Init(interp);
#endif

    Tcl_CreateObjCommand(
        interp, "load_testfixture_extensions", init_all_cmd, 0, 0

  return TCL_OK;
 sql_error:
  Tcl_AppendResult(interp, "sql error: ", sqlite3_errmsg(db), 0);
  return TCL_ERROR;
}


/*
** tclcmd: sqlite3_transaction_save DB
*/
static int testTransactionSave(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  void *pState;
  int nState;
  sqlite3 *db;
  int rc;

  if( objc!=2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB");
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;

  rc = sqlite3_transaction_save(db, &pState, &nState);
  if( rc==SQLITE_OK ){
    Tcl_SetObjResult(interp, Tcl_NewByteArrayObj(pState, nState));
  }else{
    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
    return TCL_ERROR;
  }

  sqlite3_free(pState);
  return TCL_OK;
}

/*
** tclcmd: sqlite3_transaction_restore DB BLOB
*/
static int testTransactionRestore(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  void *pState;
  int nState;
  sqlite3 *db;
  int rc;

  if( objc!=3 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB BLOB");
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
  pState = (void*)Tcl_GetByteArrayFromObj(objv[2], &nState);

  rc = sqlite3_transaction_restore(db, pState, nState);
  if( rc==SQLITE_OK ){
    Tcl_ResetResult(interp);
  }else{
    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
    return TCL_ERROR;
  }

  return TCL_OK;
}

/*
** Register commands with the TCL interpreter.
*/
int Sqlitetest1_Init(Tcl_Interp *interp){
  extern int sqlite3_search_count;
  extern int sqlite3_found_count;

     { "sqlite3_test_control", test_test_control },
#if SQLITE_OS_UNIX
     { "getrusage", test_getrusage },
#endif
     { "load_static_extension", tclLoadStaticExtensionCmd },
     { "sorter_test_fakeheap", sorter_test_fakeheap },
     { "sorter_test_sort4_helper", sorter_test_sort4_helper },
     { "sqlite3_transaction_save",    testTransactionSave },
     { "sqlite3_transaction_restore", testTransactionRestore },
  };
  static int bitmask_size = sizeof(Bitmask)*8;
  int i;
  extern int sqlite3_sync_count, sqlite3_fullsync_count;
  extern int sqlite3_opentemp_count;
  extern int sqlite3_like_count;
  extern int sqlite3_xferopt_count;

  int rc;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  pPager = sqlite3TestTextToPtr(argv[1]);
  rc = sqlite3PagerClose(pPager, 0);
  if( rc!=SQLITE_OK ){
    Tcl_AppendResult(interp, sqlite3ErrName(rc), 0);
    return TCL_ERROR;
  }
  return TCL_OK;
}

  }

  rc = sqlite3ApiExit(db, rc);
  assert( rc==SQLITE_OK || p->pStmt==0 );
  sqlite3_mutex_leave(db->mutex);
  return rc;
}

int sqlite3_index_writer(
  sqlite3 *db, 
  int bDelete,
  const char *zIndex, 
  sqlite3_stmt **ppStmt,
  int **paiCol, int *pnCol
){
  int rc = SQLITE_OK;
  Parse *pParse = 0;
  Index *pIdx = 0;                /* The index to write to */
  Table *pTab;
  int i;                          /* Used to iterate through index columns */
  Vdbe *v = 0;
  int regRec;                     /* Register to assemble record in */
  int *aiCol = 0;

  sqlite3_mutex_enter(db->mutex);
  sqlite3BtreeEnterAll(db);

  /* Allocate the parse context */
  pParse = sqlite3StackAllocRaw(db, sizeof(*pParse));
  if( !pParse ) goto index_writer_out;
  memset(pParse, 0, sizeof(Parse));
  pParse->db = db;

  /* Allocate the Vdbe */
  v = sqlite3GetVdbe(pParse);
  if( v==0 ) goto index_writer_out;

  /* Find the index to write to */
  pIdx = sqlite3FindIndex(db, zIndex, "main");
  if( pIdx==0 ){
    sqlite3ErrorMsg(pParse, "no such index: %s", zIndex);
    goto index_writer_out;
  }
  pTab = pIdx->pTable;

  /* Populate the two output variables, *pnCol and *pnAiCol. */
  *pnCol = pIdx->nColumn;
  *paiCol = aiCol = sqlite3DbMallocZero(db, sizeof(int) * pIdx->nColumn);
  if( aiCol==0 ){
    rc = SQLITE_NOMEM;
    goto index_writer_out;
  }
  for(i=0; i<pIdx->nKeyCol; i++){
    aiCol[i] = pIdx->aiColumn[i];
  }
  if( !HasRowid(pTab) ){
    Index *pPk = sqlite3PrimaryKeyIndex(pIdx->pTable);
    assert( pIdx->nColumn==pIdx->nKeyCol+pPk->nKeyCol );
    if( pPk==pIdx ){
      rc = SQLITE_ERROR;
      goto index_writer_out;
    }
    for(i=0; i<pPk->nKeyCol; i++){
      aiCol[pIdx->nKeyCol+i] = pPk->aiColumn[i];
    }
  }else{
    assert( pIdx->nColumn==pIdx->nKeyCol+1 );
    aiCol[i] = pTab->iPKey;
  }

  /* Add an OP_Noop to the VDBE program. Then store a pointer to the 
  ** output array *paiCol as its P4 value. This is so that the array
  ** is automatically deleted when the user finalizes the statement. The
  ** OP_Noop serves no other purpose. */
  sqlite3VdbeAddOp0(v, OP_Noop);
  sqlite3VdbeChangeP4(v, -1, (const char*)aiCol, P4_INTARRAY);

  sqlite3BeginWriteOperation(pParse, 0, 0);

  /* Open a write cursor on the index */
  pParse->nTab = 1;
  sqlite3VdbeAddOp3(v, OP_OpenWrite, 0, pIdx->tnum, 0);
  sqlite3VdbeSetP4KeyInfo(pParse, pIdx);

  /* Create the record to insert into the index. Store it in register regRec. */
  pParse->nVar = pIdx->nColumn;
  pParse->nMem = pIdx->nColumn;
  for(i=1; i<=pIdx->nColumn; i++){
    sqlite3VdbeAddOp2(v, OP_Variable, i, i);
  }
  regRec = ++pParse->nMem;
  sqlite3VdbeAddOp3(v, OP_MakeRecord, 1, pIdx->nColumn, regRec);

  /* If this is a UNIQUE index, check the constraint. */
  if( pIdx->onError ){
    int addr = sqlite3VdbeAddOp4Int(v, OP_NoConflict, 0, 0, 1, pIdx->nKeyCol);
    sqlite3UniqueConstraint(pParse, SQLITE_ABORT, pIdx);
    sqlite3VdbeJumpHere(v, addr);
  }

  /* Code the IdxInsert to write to the b-tree index. */
  sqlite3VdbeAddOp2(v, OP_IdxInsert, 0, regRec);
  sqlite3FinishCoding(pParse);

index_writer_out:
  if( rc==SQLITE_OK && db->mallocFailed==0 ){
    *ppStmt = (sqlite3_stmt*)v;
  }else{
    *ppStmt = 0;
    if( v ) sqlite3VdbeFinalize(v);
  }

  sqlite3ParserReset(pParse);
  sqlite3StackFree(db, pParse);
  sqlite3BtreeLeaveAll(db);
  rc = sqlite3ApiExit(db, rc);
  sqlite3_mutex_leave(db->mutex);
  return rc;
}

#endif /* #ifndef SQLITE_OMIT_INCRBLOB */

#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
  }


  return rc;
}

static int walFileReadHdr(Wal *pWal, int *pbValid){
  u8 aBuf[WAL_HDRSIZE];           /* Buffer to load WAL header into */
  int rc;                         /* Return code */
  u32 magic;                      /* Magic value read from WAL header */
  int szPage;                     /* Page size according to the log */
  u32 version;                    /* Magic value read from WAL header */

  *pbValid = 0;

  /* Read in the WAL header. */
  rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0);
  if( rc!=SQLITE_OK ){
    return rc;
  }

  /* If the database page size is not a power of two, or is greater than
  ** SQLITE_MAX_PAGE_SIZE, conclude that the WAL file contains no valid 
  ** data. Similarly, if the 'magic' value is invalid, ignore the whole
  ** WAL file.
  */
  magic = sqlite3Get4byte(&aBuf[0]);
  szPage = sqlite3Get4byte(&aBuf[8]);
  if( (magic&0xFFFFFFFE)!=WAL_MAGIC 
      || szPage&(szPage-1) 
      || szPage>SQLITE_MAX_PAGE_SIZE 
      || szPage<512 
  ){
    return SQLITE_OK;
  }

  pWal->hdr.bigEndCksum = (u8)(magic&0x00000001);
  pWal->szPage = szPage;
  pWal->nCkpt = sqlite3Get4byte(&aBuf[12]);
  memcpy(&pWal->hdr.aSalt, &aBuf[16], 8);

  /* Verify that the WAL header checksum is correct */
  walChecksumBytes(pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN, 
      aBuf, WAL_HDRSIZE-2*4, 0, pWal->hdr.aFrameCksum
  );
  if( pWal->hdr.aFrameCksum[0]!=sqlite3Get4byte(&aBuf[24])
      || pWal->hdr.aFrameCksum[1]!=sqlite3Get4byte(&aBuf[28])
  ){
    return SQLITE_OK;
  }

  /* Verify that the version number on the WAL format is one that
  ** are able to understand */
  version = sqlite3Get4byte(&aBuf[4]);
  if( version!=WAL_MAX_VERSION ){
    return SQLITE_CANTOPEN_BKPT;
  }

  *pbValid = 1;
  return SQLITE_OK;
}


/*
** Recover the wal-index by reading the write-ahead log file. 
**
** This routine first tries to establish an exclusive lock on the
** wal-index to prevent other threads/processes from doing anything
** with the WAL or wal-index while recovery is running.  The

  rc = sqlite3OsFileSize(pWal->pWalFd, &nSize);
  if( rc!=SQLITE_OK ){
    goto recovery_error;
  }

  if( nSize>WAL_HDRSIZE ){

    u8 *aFrame = 0;               /* Malloc'd buffer to load entire frame */
    int szFrame;                  /* Number of bytes in buffer aFrame[] */
    u8 *aData;                    /* Pointer to data part of aFrame buffer */
    int iFrame;                   /* Index of last frame read */
    i64 iOffset;                  /* Next offset to read from log file */
    int szPage;                   /* Page size according to the log */


    int isValid;                  /* True if this frame is valid */

    rc = walFileReadHdr(pWal, &isValid);

    if( rc!=SQLITE_OK ) goto recovery_error;















    if( isValid==0 ) goto finished;


    szPage = pWal->szPage;





















    /* Malloc a buffer to read frames into. */
    szFrame = szPage + WAL_FRAME_HDRSIZE;
    aFrame = (u8 *)sqlite3_malloc(szFrame);
    if( !aFrame ){
      rc = SQLITE_NOMEM;
      goto recovery_error;

    ** ordinary, rollback-mode locking methods, this guarantees that the
    ** connection associated with this log file is the only connection to
    ** the database. In this case checkpoint the database and unlink both
    ** the wal and wal-index files.
    **
    ** The EXCLUSIVE lock is not released before returning.
    */
    if( zBuf ){
      rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE);
      if( rc==SQLITE_OK ){
        if( pWal->exclusiveMode==WAL_NORMAL_MODE ){
          pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
        }
        rc = sqlite3WalCheckpoint(
            pWal, SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0
        );
        if( rc==SQLITE_OK ){
          int bPersist = -1;
          sqlite3OsFileControlHint(
              pWal->pDbFd, SQLITE_FCNTL_PERSIST_WAL, &bPersist
          );
          if( bPersist!=1 ){
            /* Try to delete the WAL file if the checkpoint completed and
            ** fsyned (rc==SQLITE_OK) and if we are not in persistent-wal
            ** mode (!bPersist) */
            isDelete = 1;
          }else if( pWal->mxWalSize>=0 ){
            /* Try to truncate the WAL file to zero bytes if the checkpoint
            ** completed and fsynced (rc==SQLITE_OK) and we are in persistent
            ** WAL mode (bPersist) and if the PRAGMA journal_size_limit is a
            ** non-negative value (pWal->mxWalSize>=0).  Note that we truncate
            ** to zero bytes as truncating to the journal_size_limit might
            ** leave a corrupt WAL file on disk. */
            walLimitSize(pWal, 0);
          }
        }
      }
    }

    walIndexClose(pWal, isDelete);
    sqlite3OsClose(pWal->pWalFd);
    if( isDelete ){

** Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
int sqlite3WalHeapMemory(Wal *pWal){
  return (pWal && pWal->exclusiveMode==WAL_HEAPMEMORY_MODE );
}

/*
** Save current transaction state.
**
** The transaction state consists of a series of 32-bit big-endian integers:
**
**     * initial number of frames in WAL file.
**     * initial checksum values (2 integers).
**     * current number of frames.
**     * current checksum values (2 integers).
*/
int sqlite3WalSaveState(Wal *pWal, void **ppState, int *pnState){
  int rc = SQLITE_OK;

  *ppState = 0;
  *pnState = 0;
  if( pWal->writeLock==0 ){
    /* Must be in a write transaction to call this function. */
    rc = SQLITE_ERROR;
  }else{
    WalIndexHdr *pOrig = (WalIndexHdr*)walIndexHdr(pWal);
    int nBuf = 6 * 4;             /* Bytes of space to allocate */
    u8 *aBuf;

    aBuf = sqlite3_malloc(nBuf);
    if( aBuf==0 ){
      rc = SQLITE_NOMEM;
    }else{
      sqlite3Put4byte(&aBuf[0], pOrig->mxFrame);
      sqlite3Put4byte(&aBuf[4], pOrig->aFrameCksum[0]);
      sqlite3Put4byte(&aBuf[8], pOrig->aFrameCksum[1]);
      sqlite3Put4byte(&aBuf[12], pWal->hdr.mxFrame);
      sqlite3Put4byte(&aBuf[16], pWal->hdr.aFrameCksum[0]);
      sqlite3Put4byte(&aBuf[20], pWal->hdr.aFrameCksum[1]);
      *ppState = (void*)aBuf;
      *pnState = nBuf;
    }
  }

  return rc;
}

static int walUndoNoop(void *pUndoCtx, Pgno pgno){
  UNUSED_PARAMETER(pUndoCtx);
  UNUSED_PARAMETER(pgno);
  return SQLITE_OK;
}

/*
** If possible, restore the state of the curent transaction to that 
** described by the second and third arguments.
*/
int sqlite3WalRestoreState(Wal *pWal, const void *pState, int nState){
  int rc = SQLITE_OK;

  if( pWal->writeLock==0 ){
    /* Must have opened a write transaction to call this */
    rc = SQLITE_ERROR;
  }else{
    u8 *aBuf = (u8*)pState;
    int szFrame;                    /* Size of each frame in WAL file */
    u8 *aFrame = 0;                 /* Buffer to read data into */
    u8 *aData;                      /* Data part of aFrame[] buffer */
    u32 mxFrame;                    /* Maximum frame following restoration */
    int i;                          /* Iterator variable */

    WalIndexHdr *pOrig = (WalIndexHdr*)walIndexHdr(pWal);

    /* Check that no dirty pages have been written to the WAL file since
    ** the current transaction was opened.  */
    if( pOrig->mxFrame!=pWal->hdr.mxFrame 
     || pOrig->aFrameCksum[0]!=pWal->hdr.aFrameCksum[0] 
     || pOrig->aFrameCksum[1]!=pWal->hdr.aFrameCksum[1] 
    ){
      rc = SQLITE_ERROR;
    }

    /* Check that the WAL file is in the same state that it was when the
    ** transaction was saved. If not, return SQLITE_MISMATCH - cannot 
    ** resume this transaction  */
    if( rc==SQLITE_OK && (
          pWal->hdr.mxFrame!=sqlite3Get4byte(&aBuf[0])
       || pWal->hdr.aFrameCksum[0]!=sqlite3Get4byte(&aBuf[4])
       || pWal->hdr.aFrameCksum[1]!=sqlite3Get4byte(&aBuf[8])
    )){
      rc = SQLITE_MISMATCH;
    }

    if( rc==SQLITE_OK && pWal->readLock==0 ){
      int cnt = 0;
      walUnlockShared(pWal, WAL_READ_LOCK(0));
      pWal->readLock = -1;
      do{
        int notUsed;
        rc = walTryBeginRead(pWal, &notUsed, 1, ++cnt);
      }while( rc==WAL_RETRY );
      
      if( rc==SQLITE_OK ){
        int bValid;
        rc = walFileReadHdr(pWal, &bValid);
        if( rc==SQLITE_OK && bValid==0 ) rc = SQLITE_MISMATCH;
        pWal->hdr.szPage = (u16)((pWal->szPage&0xff00) | (pWal->szPage>>16));
      }
    }

    /* Malloc a buffer to read frames into. */
    if( rc==SQLITE_OK ){
      szFrame = pWal->szPage + WAL_FRAME_HDRSIZE;
      aFrame = (u8*)sqlite3_malloc(szFrame);
      if( !aFrame ){
        rc = SQLITE_NOMEM;
      }else{
        aData = &aFrame[WAL_FRAME_HDRSIZE];
      }
    }

    mxFrame = sqlite3Get4byte(&aBuf[12]);
    for(i=pWal->hdr.mxFrame+1; rc==SQLITE_OK && i<=mxFrame; i++){
      sqlite3_int64 iOff = walFrameOffset(i, pWal->szPage);
      rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOff);
      if( rc==SQLITE_OK ){
        u32 iPg;
        u32 dummy;
        if( 0==walDecodeFrame(pWal, &iPg, &dummy, aData, aFrame) ){
          rc = SQLITE_MISMATCH;
        }else{
          rc = walIndexAppend(pWal, i, iPg);
          if( iPg>pWal->hdr.nPage ) pWal->hdr.nPage = iPg;
        }
        pWal->hdr.mxFrame = i;
      }
    }
    sqlite3_free(aFrame);

    if( rc==SQLITE_OK ){
      assert( pWal->hdr.mxFrame==mxFrame );
      if( pWal->hdr.aFrameCksum[0]!=sqlite3Get4byte(&aBuf[16])
       || pWal->hdr.aFrameCksum[1]!=sqlite3Get4byte(&aBuf[20])
      ){
        rc = SQLITE_MISMATCH;
      }
    }


    if( rc!=SQLITE_OK ){
      sqlite3WalUndo(pWal, walUndoNoop, 0);
    }
  }

  return rc;
}

#ifdef SQLITE_ENABLE_ZIPVFS
/*
** If the argument is not NULL, it points to a Wal object that holds a
** read-lock. This function returns the database page-size if it is known,
** or zero if it is not (or if pWal is NULL).
*/

/* Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
int sqlite3WalHeapMemory(Wal *pWal);

int sqlite3WalSaveState(Wal *pWal, void **ppState, int *pnState);
int sqlite3WalRestoreState(Wal *pWal, const void *pState, int nState);

#ifdef SQLITE_ENABLE_ZIPVFS
/* If the WAL file is not empty, return the number of bytes of content
** stored in each frame (i.e. the db page-size when the WAL was created).
*/
int sqlite3WalFramesize(Wal *pWal);
#endif