function WriteBuffer(const Buffer: TValueArr; Offset, Count: integer): integer; overload;
procedure WriteBuffer(const Buffer: TBytes); overload;
Call WriteBuffer to send Count bytes from Buffer to an HTTP resource. If request data exists (WriteBuffer or WriteData has been already called), the method appends data to the end of an existing buffer.
If an application needs to set the value of the ContentLength property, the value must be set before sending data.