XZStream doesn't support non-seekable streams

[montoner0]

XZStream tries to get a position from a stream and this isn't supported for non-seekable streams.

A simple repro:

using System.Net.Http;
using SharpCompress.Compressors.Xz;

new XZStream(await new HttpClient()
    .GetStreamAsync("https://deb.debian.org/debian/dists/bookworm/main/binary-amd64/Packages.xz"))
        .ReadByte();

will throw

System.NotSupportedException: Specified method is not supported.
   at System.Net.Http.HttpBaseStream.get_Position()
   at SharpCompress.Compressors.Xz.XZBlock..ctor(Stream stream, CheckType checkType, Int32 checkSize)
   at SharpCompress.Compressors.Xz.XZStream.NextBlock()
   at SharpCompress.Compressors.Xz.XZStream.ReadBlocks(Byte[] buffer, Int32 offset, Int32 count)
   at SharpCompress.Compressors.Xz.XZStream.Read(Byte[] buffer, Int32 offset, Int32 count)
   at System.IO.Stream.ReadByte()
   at Program.<<Initialize>>d__0.MoveNext() in :line 5

[Nanook]

I'll look at this

[adamhathcock]

I think this was fixed by #930

[montoner0]

I don't think so. v0.41.0 still crashes

[adamhathcock]

If you wrap the HttpResponseStream in a SharpCompressStream.Create it works. This new stream class handles some of the random access needed by certain compressions

[montoner0]

Then I guess it should be documented somehow. It's quite not obvious.

And strictly speaking the issue is still valid since XZStream doesn't support such streams even though there's a workaround.

[adamhathcock]

I'm not saying it isn't an issue, it's just not documented as the way to do things is with the Reader/Writer/Archive interfaces.

From a basic search, XZ itself doesn't support forward only access in all scenarios.