Merge PR #316: Throw exception when attempting to read a zero code length symbol

* Add test for zip file containing 0 code length entries
* Modify GetSymbol to throw on 0 code length symbols

Author: piksel

src/ICSharpCode.SharpZipLib/Zip/Compression/InflaterHuffmanTree.cs

@@ -183,13 +183,18 @@ public int GetSymbol(StreamManipulator input)
 			int lookahead, symbol;
 			if ((lookahead = input.PeekBits(9)) >= 0)
 			{
-				if ((symbol = tree[lookahead]) >= 0)
+                symbol = tree[lookahead];
+				int bitlen = symbol & 15;
+
+				if (symbol >= 0)
 				{
-					input.DropBits(symbol & 15);
+                    if(bitlen == 0){
+                        throw new SharpZipBaseException("Encountered invalid codelength 0");
+                    } 
+					input.DropBits(bitlen);
 					return symbol >> 4;
 				}
 				int subtree = -(symbol >> 4);
-				int bitlen = symbol & 15;
 				if ((lookahead = input.PeekBits(bitlen)) >= 0)
 				{
 					symbol = tree[subtree | (lookahead >> 9)];

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

@@ -0,0 +1,20 @@
+using System;
+using System.Threading;
+using System.Reflection;
+
+public class ThreadEx
+{
+	public static void Abort(Thread thread)
+	{
+		MethodInfo abort = null;
+		foreach(MethodInfo m in thread.GetType().GetMethods(BindingFlags.NonPublic | BindingFlags.Instance))
+		{
+			if (m.Name.Equals("AbortInternal") && m.GetParameters().Length == 0) abort = m;
+		}
+		if (abort == null)
+		{
+			throw new Exception("Failed to get Thread.Abort method");
+		}
+		abort.Invoke(thread, new object[0]);
+	}
+}

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

@@ -0,0 +1,57 @@
+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
+    {
+
+        const string TestFileZeroCodeLength = "UEsDBBQA+AAIANwyZ0U5T8HwjQAAAL8AAAAIABUAbGltZXJpY2t" +
+            "VVAkAAzBXXFR6LmBUVXgEAPQB9AEFjTEOwjAQBHu/YkVDg3gHoUaivjgHtmKfI5+D5d9zbndHM6/AldFJQTIJ" +
+            "PrVkPOkgce9QlJFi5hr9rhD+cUUvZ9qgnuRuBAtId97Qw0AL1Kbw5h6MykeKdlyWdlWs7OlUdgsodRqKVo0v8" +
+            "JWyGWZ6mLpuiii2t2Bl0mZ54QksOIpqXNPATF/eH1BLAQIXAxQAAgAIANxQZ0U5T8HwjQAAAL8AAAAIAA0AAA" +
+            "AAAAEAAACggQAAAABsaW1lcgEAQwAAAMgAAAAAAA==";
+		
+        [Test]
+		[Category("Zip")]
+        public void ZeroCodeLengthZipFile()
+        {
+            Assert.Throws<SharpZipBaseException>(() => {
+                Exception threadException = null;
+                var testThread = new Thread(() => {
+                    try {
+                        var fileBytes = Convert.FromBase64String(TestFileZeroCodeLength);
+                        using (var ms = new MemoryStream(fileBytes))
+                        using (var zip = new ZipInputStream(ms))
+                        {
+                            while (zip.GetNextEntry() != null) { }
+                        }
+                    }
+                    catch (Exception x) {
+                        threadException = x;
+                    }
+                });
+
+                testThread.Start();
+
+                if(!testThread.Join(5000)){
+                    // Aborting threads is deprecated in .NET Core, but if we don't do this,
+                    // the poor CI will hang for 2 hours upon running this test
+                    ThreadEx.Abort(testThread);
+                    throw new TimeoutException("Timed out waiting for GetNextEntry() to return");
+                }
+                else  if(threadException != null){
+                    throw threadException;
+                }
+            });
+        }
+
+    }
+
+}