fix(tar): clear rest of buffer when eof is reached (#789)

Author: piksel

src/ICSharpCode.SharpZipLib/Tar/TarBuffer.cs

@@ -402,6 +402,11 @@ private async ValueTask<bool> ReadRecordAsync(CancellationToken ct, bool isAsync
 				//
 				if (numBytes <= 0)
 				{
+					// Fill the rest of the buffer with 0 to clear any left over data in the shared buffer
+					for (; offset < RecordSize; offset++)
+					{
+						recordBuffer[offset] = 0;
+					}
 					break;
 				}
 

test/ICSharpCode.SharpZipLib.Tests/Tar/TarInputStreamTests.cs

@@ -1,9 +1,11 @@
 using System;
+using System.Buffers;
 using System.IO;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using ICSharpCode.SharpZipLib.Tar;
+using ICSharpCode.SharpZipLib.Tests.TestSupport;
 using NUnit.Framework;
 
 namespace ICSharpCode.SharpZipLib.Tests.Tar
@@ -87,5 +89,27 @@ public async Task TestReadAsync()
 			Assert.AreEqual(975, read3);
 			Assert.AreEqual(entryBytes.AsSpan(1025, 975).ToArray(), buffer.AsSpan().Slice(0, 975).ToArray());
 		}
+
+		[Test]
+		public void ReadEmptyStreamWhenArrayPoolIsDirty()
+		{
+			// Rent an array with the same size as the tar buffer from the array pool
+			var buffer = ArrayPool<byte>.Shared.Rent(TarBuffer.DefaultRecordSize);
+
+			// Fill the array with anything but 0
+			Utils.FillArray(buffer, 0x8b);
+
+			// Return the now dirty buffer to the array pool
+			ArrayPool<byte>.Shared.Return(buffer);
+
+			Assert.DoesNotThrow(() =>
+			{
+				using var emptyStream = new MemoryStream(Array.Empty<byte>());
+				using var tarInputStream = new TarInputStream(emptyStream, Encoding.UTF8);
+				while (tarInputStream.GetNextEntry() is { } tarEntry)
+				{
+				}
+			}, "reading from an empty input stream should not cause an error");
+		}
 	}
 }

test/ICSharpCode.SharpZipLib.Tests/TestSupport/Utils.cs

@@ -133,6 +133,15 @@ public static void PatchFirstEntrySize(Stream stream, int newSize)
 				stream.Write(sizeBytes, 0, 4);
 			}
 		}
+
+		public static void FillArray(byte[] buffer, byte value)
+		{
+#if NET6_0_OR_GREATER
+			Array.Fill(buffer, value);
+#else
+			for(var i = 0; i < buffer.Length; i++) buffer[i] = value;
+#endif
+		}
 	}
 
 	public class TestTraceListener : TraceListener
@@ -185,7 +194,7 @@ internal TempFile(string dirPath = null, string filename = null)
 		    _fileInfo = new FileInfo(Path.Combine(dirPath, filename));
 	    }
 
-    	#region IDisposable Support
+#region IDisposable Support
 
     	private bool _disposed; // To detect redundant calls
 
@@ -213,7 +222,7 @@ public void Dispose()
     		GC.SuppressFinalize(this);
     	}
 
-    	#endregion IDisposable Support
+#endregion IDisposable Support
 	}
 
 
@@ -245,7 +254,7 @@ public TempFile CreateDummyFile(string name, int size = 16, int seed = Utils.Def
 
         public TempFile GetFile(string fileName) => new TempFile(FullPath, fileName);
 
-    	#region IDisposable Support
+#region IDisposable Support
 
     	private bool _disposed; // To detect redundant calls
 
@@ -272,6 +281,6 @@ public void Dispose()
     		GC.SuppressFinalize(this);
     	}
 
-        #endregion IDisposable Support
+#endregion IDisposable Support
     }
 }