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procedure TZOracleBlob.ReadBlob;
const
  MemDelta = 1 shl 12;  // read page (2^...)
  iBufferSize = 4096;
var
  Status: integer;
  Buf: PByteArray;
  ReadNum, Offset, Cap: ub4;
  Connection: IZOracleConnection;
  atmp: integer;
  i: integer;
  ond: boolean;

{$IFDEF FPC}
  function GetSizeAtmpLast(Abuf:Pointer;SizeBuf:integer):integer;
  Var
    gi: Integer;
    chLen: LongInt;
  begin
    result := 0;
    gi:=0;
    while gi<SizeBuf do
    begin
      chLen:=UTF8CharacterLength(Pchar(Abuf));
      if chlen<=0 then
        break;
      Inc(Abuf,chLen);
      Inc(gi,chLen);
      if Pchar(Abuf)='' then break;
    End;
    result:=gi;
  End;
{$ENDIF}

begin
  if not Updated and (FLobLocator <> nil) and (BlobData = nil) and
    (not FTemporary) then
  begin
    Connection := FHandle as IZOracleConnection;

    { Opens a large object or file for read. }
    Status := FPlainDriver.LobOpen(Connection.GetContextHandle,
      Connection.GetErrorHandle, FLobLocator, OCI_LOB_READONLY);
    CheckOracleError(FPlainDriver, Connection.GetErrorHandle,
      Status, lcOther, 'Open Large Object');
    try
      { Reads data in chunks by MemDelta or more }
      Offset := 0;
      Cap := 0;
      Buf := nil;
      try     
        atmp := 0;
        Status := OCI_SUCCESS;
        ond := False;
        while (Status = OCI_NEED_DATA) or (Status = OCI_SUCCESS) do
        begin
          Cap := Cap + iBufferSize;
          ReallocMem(Buf, Cap);
          FillByte(Buf[Offset],iBufferSize,0);
          ReadNum := iBufferSize;
          Status := FPlainDriver.LobRead(Connection.GetContextHandle,
            Connection.GetErrorHandle, FLobLocator, atmp, Offset +
            1, @Buf[Offset], ReadNum, nil, nil, 0, SQLCS_IMPLICIT);
          case Status of
            OCI_NEED_DATA:
            begin
              ond := True;
              if (atmp > 0) then
                Inc(Offset, ReadNum);
            end;
            OCI_SUCCESS:
            begin
              {$IFDEF FPC}
              if ond then
                Inc(Offset,GetSizeAtmpLast(@Buf[Offset],iBufferSize))
              else
                Inc(Offset, atmp);
              {$ELSE}
              Inc(Offset, atmp);
              {$ENDIF}
              Break;
            end;
            else
              break;
          end;
        end;
        CheckOracleError(FPlainDriver, Connection.GetErrorHandle,
          Status, lcOther, 'Read Large Object');
      except
        FreeMem(Buf);
        raise;
      end;
      ReallocMem(Buf, Offset);
    finally
      { Closes large object or file. }
      Status := FPlainDriver.LobClose(Connection.GetContextHandle,
        Connection.GetErrorHandle, FLobLocator);
      CheckOracleError(FPlainDriver, Connection.GetErrorHandle,
        Status, lcOther, 'Close Large Object');
    end;
    { Assigns data }
    InternalSetData(Buf, Offset);
  end;
end;

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FillByte(Buf[Offset],iBufferSize,0);