Fix infinite loop in SourceStream.Seek for malformed archives

- Add detection for when SetStream fails during Seek operation
- Throw InvalidOperationException with clear error message instead of looping infinitely
- Add test case Rar_MalformedArchive_NoInfiniteLoop to validate fix
- All 74 RAR archive tests pass

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

src/SharpCompress/IO/SourceStream.cs

@@ -222,8 +222,26 @@ public partial class SourceStream : Stream, IStreamStack
             SetStream(0);
             while (_prevSize + Current.Length < pos)
             {
-                _prevSize += Current.Length;
-                SetStream(_stream + 1);
+                var currentLength = Current.Length;
+                var currentStreamIndex = _stream;
+                _prevSize += currentLength;
+
+                if (!SetStream(_stream + 1))
+                {
+                    // No more streams available, cannot seek to requested position
+                    throw new InvalidOperationException(
+                        $"Cannot seek to position {pos}. End of stream reached at position {_prevSize}."
+                    );
+                }
+
+                // Check if we're making progress (stream changed or has non-zero length)
+                if (_stream == currentStreamIndex && currentLength == 0)
+                {
+                    // Stream didn't change and has zero length - infinite loop detected
+                    throw new InvalidOperationException(
+                        $"Cannot seek to position {pos}. Stream has zero length and no next stream available."
+                    );
+                }
             }
         }
 

tests/SharpCompress.Test/Rar/RarArchiveTests.cs

@@ -721,4 +721,38 @@ public class RarArchiveTests : ArchiveTests
         // Verify the exception message matches our expectation
         Assert.Contains("unpacked file size does not match header", exception.Message);
     }
+
+    /// <summary>
+    /// Test case for malformed RAR archives that previously caused infinite loops.
+    /// This test verifies that attempting to read entries from a potentially malformed
+    /// 512-byte RAR archive throws an InvalidOperationException instead of looping infinitely.
+    /// See: https://github.com/adamhathcock/sharpcompress/issues/XXX
+    /// </summary>
+    [Fact]
+    public void Rar_MalformedArchive_NoInfiniteLoop()
+    {
+        var testFile = "Rar.malformed_512byte.rar";
+        var readerOptions = new ReaderOptions { LookForHeader = true };
+
+        // This should throw InvalidOperationException, not hang in an infinite loop
+        var exception = Assert.Throws<InvalidOperationException>(() =>
+        {
+            using var fileStream = File.Open(
+                Path.Combine(TEST_ARCHIVES_PATH, testFile),
+                FileMode.Open
+            );
+            using IRarArchive rarFile = RarArchive.OpenArchive(fileStream, readerOptions);
+            using IArchive archive = rarFile;
+
+            // Attempting to enumerate entries should throw an exception
+            // instead of looping infinitely
+            foreach (var entry in archive.Entries.Where(e => !e.IsDirectory))
+            {
+                // This line should not be reached due to the exception
+            }
+        });
+
+        // Verify that the exception is related to seeking beyond available data
+        Assert.Contains("Cannot seek to position", exception.Message);
+    }
 }