Fix InvalidOperationException when RAR uncompressed size exceeds header value

src/SharpCompress/Compressors/Rar/RarStream.cs

@@ -134,7 +134,7 @@ public override int Read(byte[] buffer, int offset, int count)
             fetch = false;
         }
         _position += outTotal;
-        if (count > 0 && outTotal == 0 && _position != Length)
+        if (count > 0 && outTotal == 0 && _position < Length)
         {
             // sanity check, eg if we try to decompress a redir entry
             throw new InvalidOperationException(
@@ -179,7 +179,7 @@ System.Threading.CancellationToken cancellationToken
             fetch = false;
         }
         _position += outTotal;
-        if (count > 0 && outTotal == 0 && _position != Length)
+        if (count > 0 && outTotal == 0 && _position < Length)
         {
             // sanity check, eg if we try to decompress a redir entry
             throw new InvalidOperationException(

tests/SharpCompress.Test/Mocks/TruncatedStream.cs

@@ -0,0 +1,65 @@
+using System;
+using System.IO;
+
+namespace SharpCompress.Test.Mocks;
+
+/// <summary>
+/// A stream wrapper that truncates the underlying stream after reading a specified number of bytes.
+/// Used for testing error handling when streams end prematurely.
+/// </summary>
+public class TruncatedStream : Stream
+{
+    private readonly Stream baseStream;
+    private readonly long truncateAfterBytes;
+    private long bytesRead;
+
+    public TruncatedStream(Stream baseStream, long truncateAfterBytes)
+    {
+        this.baseStream = baseStream ?? throw new ArgumentNullException(nameof(baseStream));
+        this.truncateAfterBytes = truncateAfterBytes;
+        bytesRead = 0;
+    }
+
+    public override bool CanRead => baseStream.CanRead;
+    public override bool CanSeek => baseStream.CanSeek;
+    public override bool CanWrite => false;
+    public override long Length => baseStream.Length;
+
+    public override long Position
+    {
+        get => baseStream.Position;
+        set => baseStream.Position = value;
+    }
+
+    public override int Read(byte[] buffer, int offset, int count)
+    {
+        if (bytesRead >= truncateAfterBytes)
+        {
+            // Simulate premature end of stream
+            return 0;
+        }
+
+        var maxBytesToRead = (int)Math.Min(count, truncateAfterBytes - bytesRead);
+        var actualBytesRead = baseStream.Read(buffer, offset, maxBytesToRead);
+        bytesRead += actualBytesRead;
+        return actualBytesRead;
+    }
+
+    public override long Seek(long offset, SeekOrigin origin) => baseStream.Seek(offset, origin);
+
+    public override void SetLength(long value) => throw new NotSupportedException();
+
+    public override void Write(byte[] buffer, int offset, int count) =>
+        throw new NotSupportedException();
+
+    public override void Flush() => baseStream.Flush();
+
+    protected override void Dispose(bool disposing)
+    {
+        if (disposing)
+        {
+            baseStream?.Dispose();
+        }
+        base.Dispose(disposing);
+    }
+}

tests/SharpCompress.Test/Rar/RarArchiveTests.cs

@@ -1,10 +1,12 @@
+using System;
 using System.IO;
 using System.Linq;
 using SharpCompress.Archives;
 using SharpCompress.Archives.Rar;
 using SharpCompress.Common;
 using SharpCompress.Compressors.LZMA.Utilites;
 using SharpCompress.Readers;
+using SharpCompress.Test.Mocks;
 using Xunit;
 
 namespace SharpCompress.Test.Rar;
@@ -642,4 +644,77 @@ public void Rar_TestEncryptedDetection()
         );
         Assert.True(passwordProtectedFilesArchive.IsEncrypted);
     }
+
+    /// <summary>
+    /// Test for issue: InvalidOperationException when extracting RAR files.
+    /// This test verifies the fix for the validation logic that was changed from
+    /// (_position != Length) to (_position &lt; Length).
+    /// The old logic would throw an exception when position exceeded expected length,
+    /// but the new logic only throws when decompression ends prematurely (position &lt; expected).
+    /// </summary>
+    [Fact]
+    public void Rar_StreamValidation_OnlyThrowsOnPrematureEnd()
+    {
+        // Test normal extraction - should NOT throw InvalidOperationException
+        // even if actual decompressed size differs from header
+        var testFiles = new[] { "Rar.rar", "Rar5.rar", "Rar4.rar", "Rar2.rar" };
+
+        foreach (var testFile in testFiles)
+        {
+            using var stream = File.OpenRead(Path.Combine(TEST_ARCHIVES_PATH, testFile));
+            using var archive = RarArchive.Open(stream);
+
+            // Extract all entries and read them completely
+            foreach (var entry in archive.Entries.Where(e => !e.IsDirectory))
+            {
+                using var entryStream = entry.OpenEntryStream();
+                using var ms = new MemoryStream();
+
+                // This should complete without throwing InvalidOperationException
+                // The fix ensures we only throw when position &lt; expected length, not when position >= expected
+                entryStream.CopyTo(ms);
+
+                // Verify we read some data
+                Assert.True(
+                    ms.Length > 0,
+                    $"Failed to extract data from {entry.Key} in {testFile}"
+                );
+            }
+        }
+    }
+
+    /// <summary>
+    /// Negative test case: Verifies that InvalidOperationException IS thrown when
+    /// a RAR stream ends prematurely (position &lt; expected length).
+    /// This tests the validation condition (_position &lt; Length) works correctly.
+    /// </summary>
+    [Fact]
+    public void Rar_StreamValidation_ThrowsOnTruncatedStream()
+    {
+        // This test verifies the exception is thrown when decompression ends prematurely
+        // by using a truncated stream that stops reading after a small number of bytes
+        var testFile = "Rar.rar";
+        using var fileStream = File.OpenRead(Path.Combine(TEST_ARCHIVES_PATH, testFile));
+
+        // Wrap the file stream with a truncated stream that will stop reading early
+        // This simulates a corrupted or truncated RAR file
+        using var truncatedStream = new TruncatedStream(fileStream, 1000);
+
+        // Opening the archive should work, but extracting should throw
+        // when we try to read beyond the truncated data
+        var exception = Assert.Throws<InvalidOperationException>(() =>
+        {
+            using var archive = RarArchive.Open(truncatedStream);
+            foreach (var entry in archive.Entries.Where(e => !e.IsDirectory))
+            {
+                using var entryStream = entry.OpenEntryStream();
+                using var ms = new MemoryStream();
+                // This should throw InvalidOperationException when it can't read all expected bytes
+                entryStream.CopyTo(ms);
+            }
+        });
+
+        // Verify the exception message matches our expectation
+        Assert.Contains("unpacked file size does not match header", exception.Message);
+    }
 }