property ContentLength: Int64; default -1;
Gets or sets the Content-length HTTP header. The ContentLength value is the number of bytes of data to send to the Internet resource. The default is -1, which indicates the property has not been set and that there is no request data to send.
The ContentLength property contains the value to send as the Content-length HTTP header with the request. Any value other than -1 in the ContentLength property indicates that the request uploads data and that only methods that upload data are allowed to be set in the Method property.