From 2a68ec725704ca82a491d12a1fa4f79c23628ea6 Mon Sep 17 00:00:00 2001
From: Adam Hathcock <adam@hathcock.uk>
Date: Sat, 10 Oct 2026 15:40:35 +0100
Subject: [PATCH] Read ARC entry headers fully on fragmented streams

---
 .../Common/Arc/ArcEntryHeader.cs              |  8 ++----
 .../Arc/ArcHeaderReadTests.cs                 | 26 +++++++++++++++++++
 2 files changed, 28 insertions(+), 6 deletions(-)
 create mode 100644 tests/SharpCompress.Test/Arc/ArcHeaderReadTests.cs

diff --git a/src/SharpCompress/Common/Arc/ArcEntryHeader.cs b/src/SharpCompress/Common/Arc/ArcEntryHeader.cs
index 983b1b78..1fb91983 100644
--- a/src/SharpCompress/Common/Arc/ArcEntryHeader.cs
+++ b/src/SharpCompress/Common/Arc/ArcEntryHeader.cs
@@ -26,7 +26,7 @@ public class ArcEntryHeader
     public ArcEntryHeader? ReadHeader(Stream stream)
     {
         byte[] headerBytes = new byte[29];
-        if (stream.Read(headerBytes, 0, headerBytes.Length) != headerBytes.Length)
+        if (!stream.ReadFully(headerBytes))
         {
             return null;
         }
@@ -40,11 +40,7 @@ public class ArcEntryHeader
     )
     {
         byte[] headerBytes = new byte[29];
-        if (
-            await stream
-                .ReadAsync(headerBytes, 0, headerBytes.Length, cancellationToken)
-                .ConfigureAwait(false) != headerBytes.Length
-        )
+        if (!await stream.ReadFullyAsync(headerBytes, cancellationToken).ConfigureAwait(false))
         {
             return null;
         }
diff --git a/tests/SharpCompress.Test/Arc/ArcHeaderReadTests.cs b/tests/SharpCompress.Test/Arc/ArcHeaderReadTests.cs
new file mode 100644
index 00000000..147ebc42
--- /dev/null
+++ b/tests/SharpCompress.Test/Arc/ArcHeaderReadTests.cs
@@ -0,0 +1,26 @@
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using SharpCompress.Common;
+using SharpCompress.Common.Arc;
+using SharpCompress.Test.Mocks;
+using Xunit;
+
+namespace SharpCompress.Test.Arc;
+
+public class ArcHeaderReadTests
+{
+    [Fact]
+    public async Task Arc_Header_Allows_Partial_Reads()
+    {
+        var header = new byte[29];
+        header[0] = 0x1A;
+        header[1] = 2;
+        header[2] = (byte)'x';
+        using var sync = new ShortReadStream(new MemoryStream(header));
+        using var asyncInput = new ShortReadStream(new MemoryStream(header));
+        var parser = new ArcEntryHeader(new ArchiveEncoding());
+        Assert.Equal("x", parser.ReadHeader(sync)!.Name);
+        Assert.Equal("x", (await parser.ReadHeaderAsync(asyncInput, CancellationToken.None))!.Name);
+    }
+}