Fix XZStream to support non-seekable streams

Co-authored-by: adamhathcock <527620+adamhathcock@users.noreply.github.com>

src/SharpCompress/Compressors/Xz/XZStream.cs

@@ -5,6 +5,7 @@ using System.IO;
 using System.Threading;
 using System.Threading.Tasks;
 using SharpCompress.Common;
+using SharpCompress.IO;
 
 namespace SharpCompress.Compressors.Xz;
 
@@ -12,9 +13,21 @@ namespace SharpCompress.Compressors.Xz;
 public sealed partial class XZStream : XZReadOnlyStream
 {
     public XZStream(Stream baseStream)
-        : base(baseStream)
+        : base(WrapIfNeeded(baseStream))
     {
-        _baseStream = baseStream;
+        _baseStream = BaseStream;
+    }
+
+    private static Stream WrapIfNeeded(Stream stream)
+    {
+        // XZ format requires position tracking for padding calculations.
+        // For non-seekable streams, wrap with SharpCompressStream which provides
+        // limited backward seeking via a ring buffer.
+        if (!stream.CanSeek)
+        {
+            return SharpCompressStream.Create(stream);
+        }
+        return stream;
     }
 
     protected override void Dispose(bool disposing)

tests/SharpCompress.Test/Xz/XZStreamAsyncTests.cs

@@ -34,4 +34,24 @@ public class XzStreamAsyncTests : XzTestsBase
         var uncompressed = await sr.ReadToEndAsync().ConfigureAwait(false);
         Assert.Equal(OriginalIndexed, uncompressed);
     }
+
+    [Fact]
+    public async ValueTask CanReadNonSeekableStreamAsync()
+    {
+        var nonSeekable = new ForwardOnlyStream(new MemoryStream(Compressed));
+        var xz = new XZStream(nonSeekable);
+        using var sr = new StreamReader(new AsyncOnlyStream(xz));
+        var uncompressed = await sr.ReadToEndAsync().ConfigureAwait(false);
+        Assert.Equal(Original, uncompressed);
+    }
+
+    [Fact]
+    public async ValueTask CanReadNonSeekableEmptyStreamAsync()
+    {
+        var nonSeekable = new ForwardOnlyStream(new MemoryStream(CompressedEmpty));
+        var xz = new XZStream(nonSeekable);
+        using var sr = new StreamReader(new AsyncOnlyStream(xz));
+        var uncompressed = await sr.ReadToEndAsync().ConfigureAwait(false);
+        Assert.Equal(OriginalEmpty, uncompressed);
+    }
 }

tests/SharpCompress.Test/Xz/XZStreamTests.cs

@@ -1,5 +1,6 @@
 using System.IO;
 using SharpCompress.Compressors.Xz;
+using SharpCompress.Test.Mocks;
 using Xunit;
 
 namespace SharpCompress.Test.Xz;
@@ -32,4 +33,24 @@ public class XzStreamTests : XzTestsBase
         var uncompressed = sr.ReadToEnd();
         Assert.Equal(OriginalIndexed, uncompressed);
     }
+
+    [Fact]
+    public void CanReadNonSeekableStream()
+    {
+        var nonSeekable = new ForwardOnlyStream(new MemoryStream(Compressed));
+        var xz = new XZStream(nonSeekable);
+        using var sr = new StreamReader(xz);
+        var uncompressed = sr.ReadToEnd();
+        Assert.Equal(Original, uncompressed);
+    }
+
+    [Fact]
+    public void CanReadNonSeekableEmptyStream()
+    {
+        var nonSeekable = new ForwardOnlyStream(new MemoryStream(CompressedEmpty));
+        var xz = new XZStream(nonSeekable);
+        using var sr = new StreamReader(xz);
+        var uncompressed = sr.ReadToEnd();
+        Assert.Equal(OriginalEmpty, uncompressed);
+    }
 }