MuPDF is designed to run in a variety of different environments. As such, this means input can come from many different sources. On desktop computers input may come as files on backing store. For web served files, input may be streamed over a network. For systems with DRM embedded, the data may need to be decoded on the fly.
Similarly, data can be encapsulated within different formats in different ways, with multiple layers of encoding.
Accordingly, MuPDF abstracts the idea of an ‘input stream’ to a reusable class, fz_stream. Many implementations of fz_streams are given by default in the core library, but the abstract nature of this class allows callers to provide implementations of their own to seamlessly extend the systems capabilities as required.