…reader: &mut S) that reads the next zipfile entry from a stream by potential parsing the data descriptor

This is an alternative method to read a zip file. If possible, use the ZipArchive functions as some information will be missing when reading this manner.

This method extends the existing read_zipfile_from_stream method when the stream is seekable.

This method is superior to ZipArchive in the special case that the underlying stream implementation must buffer all seen/read data to provide seek back support and the memory consumption must be kept small. This could be the case when reading a ZipFile B.zip nested within a zip file A.zip, that is stored on disk. Since A is seekable when stored as file, A.zip can be read using ZipArchive. Be B a zip file stored in A, then we can read B's content using a decompressing reader. The problem is that the decompressing reader will not be seekable (due to decompression). When one would like to still read contents of B.zip without extracting A to disk, the file B.zip must be buffered in RAM. When using ZipArchive to read B.zip from RAM, the whole B.zip file must be buffered to RAM because the central directory of B.zip is located at the end of the file B.zip. This method will read B.zip from the start of the file and returning the first file entry found in B.zip. After the execution of this function and the ZipFile return value is dropped, the reader will be positioned at the end of the file entry. Since this function will never seek back to before the initial position of the stream when the function was called, the underlying stream implementation may discard, after dropping ZipFile, all buffered data before the current position of the stream. Summarizing: In given scenario, this method must not buffer the whole B.zip file to RAM, but only the first file entry.

# Conflicts:
#	src/read.rs

…sulate potential unsafe data

…plate T: Read in internal data structures

Added UntrustedValue and MaybeUntrusted data types

# Conflicts:
#	src/read.rs

Before: The CRC32 checksum had to be supplied before the stream is read. Though checked when EOF occurred.
Now: The CRC32 checksum can be supplied before starting to read or after finishing reading from the stream.

Signed-off-by: Chris Hennick <[email protected]>

Signed-off-by: Chris Hennick <[email protected]>

…m' into feature-read-from-seekable-stream

run cargo fmt & clippy

Signed-off-by: Chris Hennick <[email protected]>

Signed-off-by: Chris Hennick <[email protected]>

Signed-off-by: Chris Hennick <[email protected]>

Signed-off-by: Chris Hennick <[email protected]>