TScBeforeSendDataEvent = procedure (Sender: TObject; Offset, Count: Int64; var Cancel: boolean) of object;
property BeforeSendData: TScBeforeSendDataEvent;
The BeforeSendData event occurs before sending each block of request data to the web server. The data blocks are divided into pieces specified in the SendBlockSize property.
BeforeSendData occurs for content data and not for the headers.
Offset is the number of bytes of data that has been already sent to the Internet resource.
Count is the common number of bytes of data to be sent to the Internet resource. Count is the same as the ContentLength property.
You can set the Cancel parameter to True to cancel request sending, in which case the OperationCanceledException will be raised.