ZLib

TDecompressionStream is the analog of the TCompressionStream class. It is a read-only, unidirectional stream; you can seek forward in the stream, but not backwards. A separate input stream provides the source data. The input stream will be a stream that was previously written to using a TCompressionStream object. The input stream is passed to the constructor, however, TDecompressionStream does not take ownership of this object. You are responsible for creating, initializing, and destroying the input stream when it is no longer needed. 

Writing to the stream will raise an exception, as will requesting the size of the stream, and attempting to perform a Seek operation backwards or relative to the current position. 

The TDecompressionStream object's OnProgress event is called when a block of data is read from the input stream. You can read the TDecompressionStream object's Position property to determine the number of raw, uncompressed bytes that have been read from the input stream so far.