From c9a68593ea9ce2b0880e53203b640b501e212aae Mon Sep 17 00:00:00 2001
From: Adam Hathcock <adam@hathcock.uk>
Date: Thu, 23 Apr 2026 11:19:09 +0100
Subject: [PATCH] add writable checks

---
 .../StreamValidationExtensions.cs             | 12 +++++++
 .../Writers/GZip/GZipWriter.Factory.cs        |  2 +-
 .../SevenZip/SevenZipWriter.Factory.cs        |  2 +-
 .../Writers/Tar/TarWriter.Factory.cs          |  2 +-
 src/SharpCompress/Writers/WriterFactory.cs    |  4 +++
 .../Writers/Zip/ZipWriter.Factory.cs          |  2 +-
 .../SharpCompress.Test/WriterFactoryTests.cs  | 34 +++++++++++++++++++
 7 files changed, 54 insertions(+), 4 deletions(-)
 create mode 100644 tests/SharpCompress.Test/WriterFactoryTests.cs

diff --git a/src/SharpCompress/StreamValidationExtensions.cs b/src/SharpCompress/StreamValidationExtensions.cs
index 7420bcec..8c2b87db 100644
--- a/src/SharpCompress/StreamValidationExtensions.cs
+++ b/src/SharpCompress/StreamValidationExtensions.cs
@@ -31,6 +31,18 @@ internal static class StreamValidationExtensions
         return stream;
     }
 
+    internal static Stream RequireWritable(this Stream stream)
+    {
+        stream.NotNull(nameof(stream));
+
+        if (!stream.CanWrite)
+        {
+            throw new ArgumentException("Stream must be writable", nameof(stream));
+        }
+
+        return stream;
+    }
+
     internal static IReadOnlyList<Stream> RequireSeekable(this IReadOnlyList<Stream> streams)
     {
         streams.NotNull(nameof(streams));
diff --git a/src/SharpCompress/Writers/GZip/GZipWriter.Factory.cs b/src/SharpCompress/Writers/GZip/GZipWriter.Factory.cs
index f4f2b902..cae0b91d 100644
--- a/src/SharpCompress/Writers/GZip/GZipWriter.Factory.cs
+++ b/src/SharpCompress/Writers/GZip/GZipWriter.Factory.cs
@@ -22,7 +22,7 @@ public partial class GZipWriter : IWriterOpenable<GZipWriterOptions>
 
     public static IWriter OpenWriter(Stream stream, GZipWriterOptions writerOptions)
     {
-        stream.NotNull(nameof(stream));
+        stream.RequireWritable();
         return new GZipWriter(stream, writerOptions);
     }
 
diff --git a/src/SharpCompress/Writers/SevenZip/SevenZipWriter.Factory.cs b/src/SharpCompress/Writers/SevenZip/SevenZipWriter.Factory.cs
index e84d7401..1191a83a 100644
--- a/src/SharpCompress/Writers/SevenZip/SevenZipWriter.Factory.cs
+++ b/src/SharpCompress/Writers/SevenZip/SevenZipWriter.Factory.cs
@@ -36,7 +36,7 @@ public partial class SevenZipWriter : IWriterOpenable<SevenZipWriterOptions>
     /// </summary>
     public static IWriter OpenWriter(Stream stream, SevenZipWriterOptions writerOptions)
     {
-        stream.NotNull(nameof(stream));
+        stream.RequireWritable();
         return new SevenZipWriter(stream, writerOptions);
     }
 
diff --git a/src/SharpCompress/Writers/Tar/TarWriter.Factory.cs b/src/SharpCompress/Writers/Tar/TarWriter.Factory.cs
index b00ed13e..7613374b 100644
--- a/src/SharpCompress/Writers/Tar/TarWriter.Factory.cs
+++ b/src/SharpCompress/Writers/Tar/TarWriter.Factory.cs
@@ -22,7 +22,7 @@ public partial class TarWriter : IWriterOpenable<TarWriterOptions>
 
     public static IWriter OpenWriter(Stream stream, TarWriterOptions writerOptions)
     {
-        stream.NotNull(nameof(stream));
+        stream.RequireWritable();
         return new TarWriter(stream, writerOptions);
     }
 
diff --git a/src/SharpCompress/Writers/WriterFactory.cs b/src/SharpCompress/Writers/WriterFactory.cs
index 48ef1d47..847766f9 100644
--- a/src/SharpCompress/Writers/WriterFactory.cs
+++ b/src/SharpCompress/Writers/WriterFactory.cs
@@ -75,6 +75,8 @@ public static class WriterFactory
         IWriterOptions writerOptions
     )
     {
+        stream.RequireWritable();
+
         var factory = Factories
             .Factory.Factories.OfType<IWriterFactory>()
             .FirstOrDefault(item => item.KnownArchiveType == archiveType);
@@ -102,6 +104,8 @@ public static class WriterFactory
         CancellationToken cancellationToken = default
     )
     {
+        stream.RequireWritable();
+
         var factory = Factories
             .Factory.Factories.OfType<IWriterFactory>()
             .FirstOrDefault(item => item.KnownArchiveType == archiveType);
diff --git a/src/SharpCompress/Writers/Zip/ZipWriter.Factory.cs b/src/SharpCompress/Writers/Zip/ZipWriter.Factory.cs
index b6667842..825de870 100644
--- a/src/SharpCompress/Writers/Zip/ZipWriter.Factory.cs
+++ b/src/SharpCompress/Writers/Zip/ZipWriter.Factory.cs
@@ -22,7 +22,7 @@ public partial class ZipWriter : IWriterOpenable<ZipWriterOptions>
 
     public static IWriter OpenWriter(Stream stream, ZipWriterOptions writerOptions)
     {
-        stream.NotNull(nameof(stream));
+        stream.RequireWritable();
         return new ZipWriter(stream, writerOptions);
     }
 
diff --git a/tests/SharpCompress.Test/WriterFactoryTests.cs b/tests/SharpCompress.Test/WriterFactoryTests.cs
new file mode 100644
index 00000000..ca7a45a5
--- /dev/null
+++ b/tests/SharpCompress.Test/WriterFactoryTests.cs
@@ -0,0 +1,34 @@
+using System;
+using System.IO;
+using System.Threading.Tasks;
+using SharpCompress.Common;
+using SharpCompress.Test.Mocks;
+using SharpCompress.Writers;
+using Xunit;
+
+namespace SharpCompress.Test;
+
+public class WriterFactoryTests
+{
+    [Fact]
+    public void OpenWriter_Stream_Throws_On_Unwritable_Stream()
+    {
+        using var unwritable = new TestStream(new MemoryStream(), true, false, true);
+
+        Assert.Throws<ArgumentException>(() =>
+            WriterFactory.OpenWriter(unwritable, ArchiveType.Zip, WriterOptions.ForZip())
+        );
+    }
+
+    [Fact]
+    public async ValueTask OpenAsyncWriter_Stream_Throws_On_Unwritable_Stream()
+    {
+        using var unwritable = new TestStream(new MemoryStream(), true, false, true);
+
+        await Assert.ThrowsAsync<ArgumentException>(() =>
+            WriterFactory
+                .OpenAsyncWriter(unwritable, ArchiveType.Zip, WriterOptions.ForZip())
+                .AsTask()
+        );
+    }
+}