SQLite

    }
  }

  *paOut = aOut;
  return 1;
}

/*
** This function is only called from within a pre-update-hook callback.
** It determines if the current pre-update-hook change affects the same row
** as the change stored in argument pChange. If so, it returns true. Otherwise
** if the pre-update-hook does not affect the same row as pChange, it returns
** false.
*/
static int sessionPreupdateEqual(
  sqlite3 *db,                    /* Database handle */
  SessionTable *pTab,             /* Table associated with change */
  SessionChange *pChange,         /* Change to compare to */
  int op                          /* Current pre-update operation */

){
  int iCol;                       /* Used to iterate through columns */
  u8 *a = pChange->aRecord;       /* Cursor used to scan change record */


  assert( op==SQLITE_INSERT || op==SQLITE_UPDATE || op==SQLITE_DELETE );
  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 = sqlite3_preupdate_new(db, iCol, &pVal);
      }else{
        assert( db->pPreUpdate->pUnpacked );
        rc = sqlite3_preupdate_old(db, 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 ){
        i64 iVal = sessionGetI64(a);
        a += 8;
        if( eType==SQLITE_INTEGER ){
          if( sqlite3_value_int64(pVal)!=iVal ) return 0;
        }else{
          double rVal;
          assert( sizeof(iVal)==8 && sizeof(rVal)==8 );
          memcpy(&rVal, &iVal, 8);
          if( sqlite3_value_double(pVal)!=rVal ) return 0;
        }
      }else{
        int n;
        const u8 *z;
        a += sessionVarintGet(a, &n);
        if( sqlite3_value_bytes(pVal)!=n ) return 0;
        if( eType==SQLITE_TEXT ){
          z = sqlite3_value_text(pVal);
        }else{
          z = sqlite3_value_blob(pVal);
        }
        if( memcmp(a, z, n) ) return 0;
        a += n;
        break;
      }
    }
  }


  return 1;
}

/*
** If required, grow the hash table used to store changes on table pTab 
** (part of the session pSession). If a fatal OOM error occurs, set the
** session object to failed and return SQLITE_ERROR. Otherwise, return
** SQLITE_OK.

/*
** This function queries the database for the names of the columns of table
** zThis, in schema zDb. It is expected that the table has nCol columns. If
** not, SQLITE_SCHEMA is returned and none of the output variables are
** populated.
**
** Otherwise, if they are not NULL, variable *pnCol is set to the number
** of columns in the database table and variable *pzTab is set to point to a
** nul-terminated copy of the table name. *pazCol (if not NULL) is set to
** point to an array of pointers to column names. And *pabPK (again, if not
** NULL) is set to point to an array of booleans - true if the corresponding
** column is part of the primary key.
**
** For example, if the table is declared as:
**
**     CREATE TABLE tbl1(w, x, y, z, PRIMARY KEY(w, z));
**
** Then the four output variables are populated as follows:
**
**     *pnCol  = 4
**     *pzTab  = "tbl1"
**     *pazCol = {"w", "x", "y", "z"}
**     *pabPK  = {1, 0, 0, 1}
**
** All returned buffers are part of the same single allocation, which must
** be freed using sqlite3_free() by the caller. If pazCol was not NULL, then
** pointer *pazCol should be freed to release all memory. Otherwise, pointer

   && pTab->nCol!=sqlite3_preupdate_count(pSession->db) 
  ){
    pSession->rc = SQLITE_SCHEMA;
  }
  return pSession->rc;
}

/*
** 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 */
){
  sqlite3 *db = pSession->db;
  int iHash; 
  int bNullPk = 0; 
  int rc = SQLITE_OK;

  if( pSession->rc ) return;

  rc = sessionPreupdateHash(db, pTab, op==SQLITE_INSERT, &iHash, &bNullPk);
  if( rc!=SQLITE_OK ) goto error_out;

  if( bNullPk==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(db, pTab, pC, op) ) break;

    }

    if( pC==0 ){
      /* Create a new change object containing all the old values (if
      ** this is an SQLITE_UPDATE or SQLITE_DELETE), or just the PK
      ** values (if this is an INSERT). */
      SessionChange *pChange; /* New change object */

  pNew->pNext = pOld;
  sqlite3_mutex_leave(sqlite3_db_mutex(db));

  *ppSession = pNew;
  return SQLITE_OK;
}

/*
** Free the list of table objects passed as the first argument. The contents
** of the changed-rows hash tables are also deleted.
*/
void sessionDeleteTable(SessionTable *pList){
  SessionTable *pNext;
  SessionTable *pTab;

  for(pTab=pList; pTab; pTab=pNext){
    int i;
    pNext = pTab->pNext;

    sessionAppendBlob(pBuf, buf2.aBuf, buf2.nBuf, &rc);
  }
  sqlite3_free(buf2.aBuf);

  return rc;
}

/*
** Formulate and prepare a SELECT statement to retrieve a row from table
** zTab in database zDb based on its primary key. i.e.
**
**   SELECT * FROM zDb.zTab WHERE pk1 = ? AND pk2 = ? AND ...
*/
static int sessionSelectStmt(
  sqlite3 *db,                    /* Database handle */
  const char *zDb,                /* Database name */
  const char *zTab,               /* Table name */
  int nCol,                       /* Number of columns in table */
  const char **azCol,             /* Names of table columns */
  u8 *abPK,                       /* PRIMARY KEY  array */
  sqlite3_stmt **ppStmt           /* OUT: Prepared SELECT statement */
){
  int rc = SQLITE_OK;
  int i;
  const char *zSep = "";
  SessionBuffer buf = {0, 0, 0};

  sessionAppendStr(&buf, "SELECT * FROM ", &rc);

  if( rc==SQLITE_OK ){
    rc = sqlite3_prepare_v2(db, (char *)buf.aBuf, buf.nBuf, ppStmt, 0);
  }
  sqlite3_free(buf.aBuf);
  return rc;
}

/*
** Bind the PRIMARY KEY values from the change passed in argument pChange
** to the SELECT statement passed as the first argument. The SELECT statement
** is as prepared by function sessionSelectStmt().
**
** Return SQLITE_OK if all PK values are successfully bound, or an SQLite
** error code (e.g. SQLITE_NOMEM) otherwise.
*/
static int sessionSelectBind(
  sqlite3_stmt *pSelect,          /* SELECT from sessionSelectStmt() */
  int nCol,                       /* Number of columns in table */
  u8 *abPK,                       /* PRIMARY KEY array */
  SessionChange *pChange          /* Change structure */
){
  int i;
  int rc = SQLITE_OK;
  u8 *a = pChange->aRecord;

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

      }
    }
  }

  return rc;
}

/*
** This function is a no-op if *pRc is set to other than SQLITE_OK when it
** is called. Otherwise, append a serialized table header (part of the binary 
** changeset format) to buffer *pBuf. If an error occurs, set *pRc to an
** SQLite error code before returning.
*/
static void sessionAppendTableHdr(
  SessionBuffer *pBuf, 
  SessionTable *pTab, 
  int *pRc
){
  /* Write a table header */
  sessionAppendByte(pBuf, 'T', pRc);

    }
  }

  *paChange = aRec;
  return SQLITE_OK;
}

/*
** Advance the changeset iterator to the next change.
**
** If both paRec and pnRec are NULL, then this function works like the public
** API sqlite3changeset_next(). If SQLITE_ROW is returned, then the
** sqlite3changeset_new() and old() APIs may be used to query for values.
**
** Otherwise, if paRec and pnRec are not NULL, then a pointer to the change
** record is written to *paRec before returning and the number of bytes in
** the record to *pnRec.
**
** Either way, this function returns SQLITE_ROW if the iterator is 
** successfully advanced to the next change in the changeset, an SQLite 
** error code if an error occurs, or SQLITE_DONE if there are no further 
** changes in the changeset.
*/
static int sessionChangesetNext(
  sqlite3_changeset_iter *p,      /* Changeset iterator */
  u8 **paRec,                     /* If non-NULL, store record pointer here */
  int *pnRec                      /* If non-NULL, store size of record here */
){
  u8 *aChange;
  int i;

  assert( (paRec==0 && pnRec==0) || (paRec && pnRec) );

  /* If the iterator is in the error-state, return immediately. */

*/
int sqlite3changeset_next(sqlite3_changeset_iter *p){
  return sessionChangesetNext(p, 0, 0);
}

/*
** The following function extracts information on the current change
** from a changeset iterator. It may only be called after changeset_next()
** has returned SQLITE_ROW.
*/
int sqlite3changeset_op(
  sqlite3_changeset_iter *pIter,  /* Iterator handle */
  const char **pzTab,             /* OUT: Pointer to table name */
  int *pnCol,                     /* OUT: Number of columns in table */
  int *pOp,                       /* OUT: SQLITE_INSERT, DELETE or UPDATE */
  int *pbIndirect                 /* OUT: True if change is indirect */
){
  *pOp = pIter->op;
  *pnCol = pIter->nCol;
  *pzTab = pIter->zTab;
  if( pbIndirect ) *pbIndirect = pIter->bIndirect;
  return SQLITE_OK;
}

/*
** Return information regarding the PRIMARY KEY and number of columns in
** the database table affected by the change that pIter currently points
** to. This function may only be called after changeset_next() returns
** SQLITE_ROW.
*/
int sqlite3changeset_pk(
  sqlite3_changeset_iter *pIter,  /* Iterator object */
  unsigned char **pabPK,          /* OUT: Array of boolean - true for PK cols */
  int *pnCol                      /* OUT: Number of entries in output array */
){
  *pabPK = pIter->abPK;
  if( pnCol ) *pnCol = pIter->nCol;

  sqlite3_finalize(sApply.pUpdate);
  sqlite3_finalize(sApply.pSelect);
  sqlite3_free((char*)sApply.azCol);  /* cast works around VC++ bug */
  sqlite3_mutex_leave(sqlite3_db_mutex(db));
  return rc;
}

/*
** This function is called to merge two changes to the same row together as
** part of an sqlite3changeset_concat() operation. A new change object is
** allocated and a pointer to it stored in *ppNew.
*/
static int sessionChangeMerge(
  SessionTable *pTab,             /* Table structure */
  SessionChange *pExist,          /* Existing change */
  int op2,                        /* Second change operation */
  int bIndirect,                  /* True if second change is indirect */
  u8 *aRec,                       /* Second change record */
  int nRec,                       /* Number of bytes in aRec */
  SessionChange **ppNew           /* OUT: Merged change */
){
  SessionChange *pNew = 0;

  if( !pExist ){
    pNew = (SessionChange *)sqlite3_malloc(sizeof(SessionChange));
    if( !pNew ){
      return SQLITE_NOMEM;

    }
  }

  *ppNew = pNew;
  return SQLITE_OK;
}

/*
** Add all changes in the changeset passed via the first two arguments to
** hash tables.
*/
int sessionConcatChangeset(
  int nChangeset,                 /* Number of bytes in pChangeset */
  void *pChangeset,               /* Changeset buffer */
  SessionTable **ppTabList        /* IN/OUT: List of table objects */
){
  u8 *aRec;
  int nRec;
  sqlite3_changeset_iter *pIter;
  int rc;
  SessionTable *pTab = 0;