From e89fb211cec3d10b39b5b01159a2610f08032e37 Mon Sep 17 00:00:00 2001
From: Adam Hathcock <adam@hathcock.uk>
Date: Sun, 25 Jan 2026 15:03:51 +0000
Subject: [PATCH] gzipwriter async

---
 .../Writers/AbstractWriter.Async.cs           | 20 +++---------
 .../Writers/GZip/GZipWriter.Async.cs          | 31 +++++++++++++++++++
 2 files changed, 35 insertions(+), 16 deletions(-)
 create mode 100644 src/SharpCompress/Writers/GZip/GZipWriter.Async.cs

diff --git a/src/SharpCompress/Writers/AbstractWriter.Async.cs b/src/SharpCompress/Writers/AbstractWriter.Async.cs
index e2960ab9..c0d94de7 100644
--- a/src/SharpCompress/Writers/AbstractWriter.Async.cs
+++ b/src/SharpCompress/Writers/AbstractWriter.Async.cs
@@ -8,30 +8,18 @@ namespace SharpCompress.Writers;
 
 public abstract partial class AbstractWriter
 {
-    public virtual async ValueTask WriteAsync(
+    public abstract ValueTask WriteAsync(
         string filename,
         Stream source,
         DateTime? modificationTime,
         CancellationToken cancellationToken = default
-    )
-    {
-        // Default implementation calls synchronous version
-        // Derived classes should override for true async behavior
-        Write(filename, source, modificationTime);
-        await Task.CompletedTask.ConfigureAwait(false);
-    }
+    );
 
-    public virtual async ValueTask WriteDirectoryAsync(
+    public abstract ValueTask WriteDirectoryAsync(
         string directoryName,
         DateTime? modificationTime,
         CancellationToken cancellationToken = default
-    )
-    {
-        // Default implementation calls synchronous version
-        // Derived classes should override for true async behavior
-        WriteDirectory(directoryName, modificationTime);
-        await Task.CompletedTask.ConfigureAwait(false);
-    }
+    );
 
     public ValueTask DisposeAsync()
     {
diff --git a/src/SharpCompress/Writers/GZip/GZipWriter.Async.cs b/src/SharpCompress/Writers/GZip/GZipWriter.Async.cs
new file mode 100644
index 00000000..5471deaa
--- /dev/null
+++ b/src/SharpCompress/Writers/GZip/GZipWriter.Async.cs
@@ -0,0 +1,31 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using SharpCompress.Compressors.Deflate;
+
+namespace SharpCompress.Writers.GZip;
+
+public partial class GZipWriter
+{
+    public override async ValueTask WriteAsync(string filename, Stream source, DateTime? modificationTime, CancellationToken cancellationToken = default)
+    {
+        if (_wroteToStream)
+        {
+            throw new ArgumentException("Can only write a single stream to a GZip file.");
+        }
+        var stream = (GZipStream)OutputStream;
+        stream.FileName = filename;
+        stream.LastModified = modificationTime;
+        var progressStream = WrapWithProgress(source, filename);
+#if LEGACY_DOTNET
+        await progressStream.CopyToAsync(stream);
+        #else
+        await progressStream.CopyToAsync(stream, cancellationToken);
+#endif
+        _wroteToStream = true;
+    }
+
+    public override ValueTask WriteDirectoryAsync(string directoryName, DateTime? modificationTime, CancellationToken cancellationToken = default) =>
+        throw new NotSupportedException("GZip archives do not support directory entries.");
+}