Merge PR #363: Change ZipFile.ReadEntries to always look for the Zip64 central directory

* Change ZipFile.ReadEntries to always look for the Zip64 central directory
* Add test for Zip64 preference

Author: Numpsy

src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs

@@ -3408,6 +3408,7 @@ private void ReadEntries()
 			}
 
 			bool isZip64 = false;
+			bool requireZip64 = false;
 
 			// Check if zip64 header information is required.
 			if ((thisDiskNumber == 0xffff) ||
@@ -3417,13 +3418,22 @@ private void ReadEntries()
 				(centralDirSize == 0xffffffff) ||
 				(offsetOfCentralDir == 0xffffffff))
 			{
-				isZip64 = true;
+				requireZip64 = true;
+			}
 
-				long offset = LocateBlockWithSignature(ZipConstants.Zip64CentralDirLocatorSignature, locatedEndOfCentralDir, 0, 0x1000);
-				if (offset < 0)
+			// #357 - always check for the existance of the Zip64 central directory.
+			long locatedZip64EndOfCentralDir = LocateBlockWithSignature(ZipConstants.Zip64CentralDirLocatorSignature, locatedEndOfCentralDir, 0, 0x1000);
+			if (locatedZip64EndOfCentralDir < 0)
+			{
+				if (requireZip64)
 				{
+					// This is only an error in cases where the Zip64 directory is required.
 					throw new ZipException("Cannot find Zip64 locator");
 				}
+			}
+			else
+			{
+				isZip64 = true;
 
 				// number of the disk with the start of the zip64 end of central directory 4 bytes
 				// relative offset of the zip64 end of central directory record 8 bytes

test/ICSharpCode.SharpZipLib.Tests/Zip/ZipCorruptionHandling.cs

@@ -1,15 +1,12 @@
 using System;
 using System.IO;
-using System.Runtime.InteropServices;
-using System.Text;
 using System.Threading;
-using ICSharpCode.SharpZipLib;
 using ICSharpCode.SharpZipLib.Zip;
 using NUnit.Framework;
 
 namespace ICSharpCode.SharpZipLib.Tests.Zip
 {
-    public class ZipCorruptionHandling
+	public class ZipCorruptionHandling
     {
 
         const string TestFileZeroCodeLength = "UEsDBBQA+AAIANwyZ0U5T8HwjQAAAL8AAAAIABUAbGltZXJpY2t" +
@@ -52,6 +49,23 @@ public void ZeroCodeLengthZipFile()
             });
         }
 
-    }
+		const string TestFileBadCDGoodCD64 = @"UEsDBC0AAAAIANhy+k4cj+r8//////////8IABQAdGVzdGZpbGUBABAAAAA
+			AAAAAAAAUAAAAAAAAACtJLS5Jy8xJVUjOzytJzSsp5gIAUEsBAjMALQAAAAgA2HL6ThyP6vz//////////wgAFAAAAAAAA
+			AAAAAAAAAAAAHRlc3RmaWxlAQAQABIAAAAAAAAAFAAAAAAAAABQSwUGAAAAAAEAAQBKAAAATgAAAAAA";
+
+		[Test]
+		[Category("Zip")]
+		public void CorruptCentralDirWithCorrectZip64CD()
+		{
+			var fileBytes = Convert.FromBase64String(TestFileBadCDGoodCD64);
+			using (var ms = new MemoryStream(fileBytes))
+			using (var zip = new ZipFile(ms))
+			{
+				Assert.AreEqual(1, zip.Count);
+				Assert.AreNotEqual(0, zip[0].Size, "Uncompressed file size read from corrupt CentralDir instead of CD64");
+			}
+		}
+
+	}
 
 }