Internet Direct (Indy) Version 9.0.1 Beta
TIdHTTPResponseInfo.HeaderHasBeenWritten
Indicates that headers have been written in the HTTP response.

property HeaderHasBeenWritten: boolean;
Description
HeaderHasBeenWritten ia Boolean property that indicates headers have already been written in the HTTP response. HeaderHasBeenWritten is used in WriteHeader to prevent duplication of header values for the HTTP response. HeaderHasBeenWritten is also checked when a threaded connection needs to write a HTTP response in the TIdHTTPServer.OnExecute event handler.