Extended SharpCompress.Common.ExtractionOptions with a delegate to write symbolic links. If not is null, and a symbolic link is encountered, an exception is thrown.
Removed Mono.Posix.NETStandard from the library, but added to the .NET Core 2.1 test application.
Extended the test to implement the delegate.
Extracts linkname from the tar header, and exposes this on IEntry as the LinkTarget (string) property. If an entry is not a symlink, then that property is null.
Uses Mono.Posix.NETStandard nuget to create a symlink. However, this is only applicable to .NET standard 2.0+. So far, unable to find a nuget that works for older versions.
Also, not sure what to do on Windows.
From Microsoft docs: “In a class derived from Stream that doesn't
support writing, Flush is typically implemented as an empty method to
ensure full compatibility with other Stream types since it's valid to
flush a read-only stream.”
Update the sub-stream classes to all inherit from `NonDisposingStream`.
This allows them to correctly implement the `Dispose` pattern, and delegate
the actual disposal to `NonDisposingStream`.
In doing so, we need to remove some redundant overrides from
`NonDisposingStream`, otherwise `BufferedSubStream` would use the
overrides inherited from `NonDisposingStream` instead of the ones
inherited from `Stream` (i.e. delegate `ReadByte` to `Read`).
`ReaderFactory.Open()` calls `ZipArchive.IsZipFile()` to determine if
the `Stream` is a zip archive, which calls into
`ZipHeaderFactory.ReadHeader()`, which throws a `NotSupportedException`
when the `Stream` is not a zip archive.
To be clear, this exception is caught and `IsZipFile()` returns `false`,
but when called in a hot-path, these exceptions can become expensive.
To address this issue, `ReadHeader` now returns `null` in the default
cause instead of throwing. All callsites were already checking for and
handling `null`, so no behavior changes.
