InputBuffer is a read-only TIdBuffer property that represents the internal storage allocated for the IOHandler. 

IOHandlers typically receive more data than they need to complete each request. InputBuffer stores this extra data for future use in other IOHandler methods. 

Values are added to InputBuffer when data is received from the source for the connection, and extracted from InputBuffer when the various read methods for the IOHandler are called. 

InputBuffer is created when the IOHandler is opened in TIdIOHandler.Open and freed in the destructor for the object instance.

TIdIOHandler.Open