SQLite

  char *zDb;                      /* Name of database session is attached to */
  int bEnable;                    /* True if currently recording */
  int bIndirect;                  /* True if all changes are indirect */
  int bAutoAttach;                /* True to auto-attach tables */
  int rc;                         /* Non-zero if an error has occurred */
  void *pFilterCtx;               /* First argument to pass to xTableFilter */
  int (*xTableFilter)(void *pCtx, const char *zTab);
  sqlite3_value *pZeroBlob;       /* Value containing X'' */
  sqlite3_session *pNext;         /* Next session object on same db. */
  SessionTable *pTable;           /* List of attached tables */
  SessionHook hook;               /* APIs to grab new and old data with */
};

/*
** Instances of this structure are used to build strings or binary records.

        rc = pSession->hook.xNew(pSession->hook.pCtx, i, &pVal);
      }else{
        rc = pSession->hook.xOld(pSession->hook.pCtx, i, &pVal);
      }
      if( rc!=SQLITE_OK ) return rc;

      eType = sqlite3_value_type(pVal);



      h = sessionHashAppendType(h, eType);
      if( eType==SQLITE_INTEGER || eType==SQLITE_FLOAT ){
        i64 iVal;
        if( eType==SQLITE_INTEGER ){
          iVal = sqlite3_value_int64(pVal);
        }else{
          double rVal = sqlite3_value_double(pVal);
          assert( sizeof(iVal)==8 && sizeof(rVal)==8 );
          memcpy(&iVal, &rVal, 8);
        }
        h = sessionHashAppendI64(h, iVal);
      }else if( eType==SQLITE_TEXT || eType==SQLITE_BLOB ){
        const u8 *z;
        int n;
        if( eType==SQLITE_TEXT ){
          z = (const u8 *)sqlite3_value_text(pVal);
        }else{
          z = (const u8 *)sqlite3_value_blob(pVal);
        }
        n = sqlite3_value_bytes(pVal);
        if( !z && (eType!=SQLITE_BLOB || n>0) ) return SQLITE_NOMEM;
        h = sessionHashAppendBlob(h, n, z);
      }else{
        assert( eType==SQLITE_NULL );
        assert( pTab->bStat1==0 || i!=1 );
        *pbNullPK = 1;

      }
    }
  }

  *piHash = (h % pTab->nChange);
  return SQLITE_OK;
}

    /* It is not possible for eType to be SQLITE_NULL here. The session 
    ** module does not record changes for rows with NULL values stored in
    ** primary key columns. */
    assert( eType==SQLITE_INTEGER || eType==SQLITE_FLOAT 
         || eType==SQLITE_TEXT || eType==SQLITE_BLOB 
         || eType==SQLITE_NULL || eType==0 
    );
    assert( !isPK || (eType!=0 && eType!=SQLITE_NULL) );

    if( isPK ){
      a++;
      h = sessionHashAppendType(h, eType);
      if( eType==SQLITE_INTEGER || eType==SQLITE_FLOAT ){
        h = sessionHashAppendI64(h, sessionGetI64(a));
        a += 8;
      }else{
        int n; 
        a += sessionVarintGet(a, &n);
        h = sessionHashAppendBlob(h, n, a);
        a += n;
      }
    }else{
      a += sessionSerialLen(a);

  for(iCol=0; iCol<pTab->nCol; iCol++){
    if( !pTab->abPK[iCol] ){
      a += sessionSerialLen(a);
    }else{
      sqlite3_value *pVal;        /* Value returned by preupdate_new/old */
      int rc;                     /* Error code from preupdate_new/old */
      int eType = *a++;           /* Type of value from change record */


      /* The following calls to preupdate_new() and preupdate_old() can not
      ** fail. This is because they cache their return values, and by the
      ** time control flows to here they have already been called once from
      ** within sessionPreupdateHash(). The first two asserts below verify
      ** this (that the method has already been called). */
      if( op==SQLITE_INSERT ){
        /* assert( db->pPreUpdate->pNewUnpacked || db->pPreUpdate->aNew ); */
        rc = pSession->hook.xNew(pSession->hook.pCtx, iCol, &pVal);
      }else{
        /* assert( db->pPreUpdate->pUnpacked ); */
        rc = pSession->hook.xOld(pSession->hook.pCtx, iCol, &pVal);
      }
      assert( rc==SQLITE_OK );
      if( sqlite3_value_type(pVal)!=eType ) return 0;








      /* A SessionChange object never has a NULL value in a PK column */
      assert( eType==SQLITE_INTEGER || eType==SQLITE_FLOAT
           || eType==SQLITE_BLOB    || eType==SQLITE_TEXT
      );

      if( eType==SQLITE_INTEGER || eType==SQLITE_FLOAT ){

      if( 0==sqlite3_stricmp("sqlite_stat1", pTab->zName) ){
        pTab->bStat1 = 1;
      }
    }
  }
  return (pSession->rc || pTab->abPK==0);
}

/*
** Versions of the four methods in object SessionHook for use with the
** sqlite_stat1 table. The purpose of this is to substitute a zero-length
** blob each time a NULL value is read from the "idx" column of the
** sqlite_stat1 table.
*/
typedef struct SessionStat1Ctx SessionStat1Ctx;
struct SessionStat1Ctx {
  SessionHook hook;
  sqlite3_session *pSession;
};
static int sessionStat1Old(void *pCtx, int iCol, sqlite3_value **ppVal){
  SessionStat1Ctx *p = (SessionStat1Ctx*)pCtx;
  sqlite3_value *pVal = 0;
  int rc = p->hook.xOld(p->hook.pCtx, iCol, &pVal);
  if( rc==SQLITE_OK && iCol==1 && sqlite3_value_type(pVal)==SQLITE_NULL ){
    pVal = p->pSession->pZeroBlob;
  }
  *ppVal = pVal;
  return rc;
}
static int sessionStat1New(void *pCtx, int iCol, sqlite3_value **ppVal){
  SessionStat1Ctx *p = (SessionStat1Ctx*)pCtx;
  sqlite3_value *pVal = 0;
  int rc = p->hook.xNew(p->hook.pCtx, iCol, &pVal);
  if( rc==SQLITE_OK && iCol==1 && sqlite3_value_type(pVal)==SQLITE_NULL ){
    pVal = p->pSession->pZeroBlob;
  }
  *ppVal = pVal;
  return rc;
}
static int sessionStat1Count(void *pCtx){
  SessionStat1Ctx *p = (SessionStat1Ctx*)pCtx;
  return p->hook.xCount(p->hook.pCtx);
}
static int sessionStat1Depth(void *pCtx){
  SessionStat1Ctx *p = (SessionStat1Ctx*)pCtx;
  return p->hook.xDepth(p->hook.pCtx);
}


/*
** This function is only called from with a pre-update-hook reporting a 
** change on table pTab (attached to session pSession). The type of change
** (UPDATE, INSERT, DELETE) is specified by the first argument.
**
** Unless one is already present or an error occurs, an entry is added
** to the changed-rows hash table associated with table pTab.
*/
static void sessionPreupdateOneChange(
  int op,                         /* One of SQLITE_UPDATE, INSERT, DELETE */
  sqlite3_session *pSession,      /* Session object pTab is attached to */
  SessionTable *pTab              /* Table that change applies to */
){
  int iHash; 
  int bNull = 0; 
  int rc = SQLITE_OK;
  SessionStat1Ctx stat1;

  if( pSession->rc ) return;

  /* Load table details if required */
  if( sessionInitTable(pSession, pTab) ) return;

  /* Check the number of columns in this xPreUpdate call matches the 
  ** number of columns in the table.  */
  if( pTab->nCol!=pSession->hook.xCount(pSession->hook.pCtx) ){
    pSession->rc = SQLITE_SCHEMA;
    return;
  }

  /* Grow the hash table if required */
  if( sessionGrowHash(0, pTab) ){
    pSession->rc = SQLITE_NOMEM;
    return;
  }

  if( pTab->bStat1 ){
    stat1.hook = pSession->hook;
    stat1.pSession = pSession;
    pSession->hook.pCtx = (void*)&stat1;
    pSession->hook.xNew = sessionStat1New;
    pSession->hook.xOld = sessionStat1Old;
    pSession->hook.xCount = sessionStat1Count;
    pSession->hook.xDepth = sessionStat1Depth;
    if( pSession->pZeroBlob==0 ){
      sqlite3_value *p = sqlite3ValueNew(0);
      if( p==0 ){
        rc = SQLITE_NOMEM;
        goto error_out;
      }
      sqlite3ValueSetStr(p, 0, "", 0, SQLITE_STATIC);
      pSession->pZeroBlob = p;
    }
  }

  /* Calculate the hash-key for this change. If the primary key of the row
  ** includes a NULL value, exit early. Such changes are ignored by the
  ** session module. */
  rc = sessionPreupdateHash(pSession, pTab, op==SQLITE_INSERT, &iHash, &bNull);
  if( rc!=SQLITE_OK ) goto error_out;

  if( bNull==0 ){
    /* Search the hash table for an existing record for this row. */
    SessionChange *pC;
    for(pC=pTab->apChange[iHash]; pC; pC=pC->pNext){
      if( sessionPreupdateEqual(pSession, pTab, pC, op) ) break;
    }

    if( pC==0 ){

        }

        /* This may fail if SQLite value p contains a utf-16 string that must
        ** be converted to utf-8 and an OOM error occurs while doing so. */
        rc = sessionSerializeValue(0, p, &nByte);
        if( rc!=SQLITE_OK ) goto error_out;
      }

  
      /* Allocate the change object */
      pChange = (SessionChange *)sqlite3_malloc(nByte);
      if( !pChange ){
        rc = SQLITE_NOMEM;
        goto error_out;
      }else{

      for(i=0; i<pTab->nCol; i++){
        sqlite3_value *p = 0;
        if( op!=SQLITE_INSERT ){
          pSession->hook.xOld(pSession->hook.pCtx, i, &p);
        }else if( pTab->abPK[i] ){
          pSession->hook.xNew(pSession->hook.pCtx, i, &p);
        }




        sessionSerializeValue(&pChange->aRecord[nByte], p, &nByte);

      }

      /* Add the change to the hash-table */
      if( pSession->bIndirect || pSession->hook.xDepth(pSession->hook.pCtx) ){
        pChange->bIndirect = 1;
      }
      pChange->nRecord = nByte;

        pC->bIndirect = 0;
      }
    }
  }

  /* If an error has occurred, mark the session object as failed. */
 error_out:
  if( pTab->bStat1 ){
    pSession->hook = stat1.hook;
  }
  if( rc!=SQLITE_OK ){
    pSession->rc = rc;
  }
}

static int sessionFindTable(
  sqlite3_session *pSession, 

    if( (*pp)==pSession ){
      *pp = (*pp)->pNext;
      if( pHead ) sqlite3_preupdate_hook(db, xPreUpdate, (void*)pHead);
      break;
    }
  }
  sqlite3_mutex_leave(sqlite3_db_mutex(db));
  sqlite3ValueFree(pSession->pZeroBlob);

  /* Delete all attached table objects. And the contents of their 
  ** associated hash-tables. */
  sessionDeleteTable(pSession->pTable);

  /* Free the session object itself. */
  sqlite3_free(pSession);

  for(i=0; i<nCol && rc==SQLITE_OK; i++){
    int eType = *a++;

    switch( eType ){
      case 0:
      case SQLITE_NULL:
        assert( abPK[i]==0 );
        break;

      case SQLITE_INTEGER: {
        if( abPK[i] ){
          i64 iVal = sessionGetI64(a);
          rc = sqlite3_bind_int64(pSelect, i+1, iVal);
        }