Fix win_indicator parser to accept zero (compressed by itself) (#7)

Author: ytoku

src/VCDiff.Tests/WindowDecoderTests.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Security.Cryptography;
+using System.Text;
+using VCDiff.Decoders;
+using VCDiff.Includes;
+using Xunit;
+
+namespace VCDiff.Tests
+{
+    public class WindowDecoderTests
+    {
+        [Fact]
+        public void WinIndicator_Zero()
+        {
+            var inputStream = File.OpenRead($"patches{Path.DirectorySeparatorChar}empty.test");
+            var targetStream = File.OpenRead($"patches{Path.DirectorySeparatorChar}win_indicator_zero.test");
+            var deltaStream = File.OpenRead($"patches{Path.DirectorySeparatorChar}win_indicator_zero.xdelta");
+            using var md5 = MD5.Create();
+            targetStream.Position = 0;
+            var originalHash = md5.ComputeHash(targetStream);
+
+            using var outputStream = new MemoryStream();
+
+            var decoder = new VcDecoder(inputStream, deltaStream, outputStream);
+            Assert.Equal(VCDiffResult.SUCCESS, decoder.Decode(out long bytesWritten));
+            outputStream.Position = 0;
+            var outputHash = md5.ComputeHash(outputStream);
+            Assert.Equal(originalHash, outputHash);
+        }
+    }
+}

src/VCDiff.Tests/patches/win_indicator_zero.test

@@ -0,0 +1 @@
+ABCDABCDABCDDDDDDDDDD

src/VCDiff.Tests/patches/win_indicator_zero.xdelta

@@ -286,6 +286,11 @@ private bool ParseWindowIndicatorAndSegment(long dictionarySize, long decodedTar
 
             switch (sourceFlags)
             {
+                case 0:
+                    sourceSegmentPosition = 0;
+                    sourceSegmentLength = 0;
+                    return true;
+
                 case (int)VCDiffWindowFlags.VCDSOURCE:
                     return ParseSourceSegmentLengthAndPosition(dictionarySize, out sourceSegmentLength, out sourceSegmentPosition);