SEBWIN-296: Implemented unit tests for GZip compressor.

SafeExamBrowser.Configuration.UnitTests/DataCompression/GZipCompressorTests.cs

@@ -0,0 +1,90 @@
+/*
+ * Copyright (c) 2019 ETH Zürich, Educational Development and Technology (LET)
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+using System;
+using System.IO;
+using System.Linq;
+using System.Text;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Moq;
+using SafeExamBrowser.Configuration.DataCompression;
+using SafeExamBrowser.Contracts.Logging;
+
+namespace SafeExamBrowser.Configuration.UnitTests.DataCompression
+{
+	[TestClass]
+	public class GZipCompressorTests
+	{
+		private const int ID1 = 0x1F;
+		private const int ID2 = 0x8B;
+		private const int CM = 8;
+		private const int FOOTER_LENGTH = 8;
+		private const int HEADER_LENGTH = 10;
+
+		private Mock<ILogger> logger;
+		private GZipCompressor sut;
+
+		[TestInitialize]
+		public void Initialize()
+		{
+			logger = new Mock<ILogger>();
+			sut = new GZipCompressor(logger.Object);
+		}
+
+		[TestMethod]
+		public void MustCorrectlyDetectGZipStream()
+		{
+			var randomBytes = new byte[123];
+
+			new Random().NextBytes(randomBytes);
+
+			Assert.IsFalse(sut.IsCompressed(null));
+			Assert.IsFalse(sut.IsCompressed(new MemoryStream()));
+			Assert.IsFalse(sut.IsCompressed(new MemoryStream(randomBytes)));
+
+			Assert.IsTrue(sut.IsCompressed(new MemoryStream(new byte[] { ID1, ID2, CM }.Concat(randomBytes).ToArray())));
+		}
+
+		[TestMethod]
+		public void MustPerformCorrectly()
+		{
+			var data = Encoding.UTF8.GetBytes(String.Join(" ", Enumerable.Repeat("A comparatively easy text to compress.", 100)));
+			var compressed = sut.Compress(new MemoryStream(data));
+
+			compressed.Seek(0, SeekOrigin.Begin);
+
+			Assert.AreEqual(ID1, compressed.ReadByte());
+			Assert.AreEqual(ID2, compressed.ReadByte());
+			Assert.AreEqual(CM, compressed.ReadByte());
+			Assert.IsTrue(compressed.Length < data.Length);
+
+			var decompressed = sut.Decompress(compressed);
+
+			decompressed.Seek(0, SeekOrigin.Begin);
+
+			foreach (var item in data)
+			{
+				Assert.AreEqual(item, decompressed.ReadByte());
+			}
+
+			Assert.IsTrue(decompressed.Length == data.Length);
+		}
+
+		[TestMethod]
+		public void MustPreviewDataCorrectly()
+		{
+			var data = Encoding.UTF8.GetBytes("A comparatively easy text to compress.");
+			var compressed = sut.Compress(new MemoryStream(data));
+
+			var preview = sut.Peek(compressed, 5);
+
+			Assert.AreEqual(5, preview.Length);
+			Assert.IsTrue(Encoding.UTF8.GetBytes("A com").SequenceEqual(preview));
+		}
+	}
+}

SafeExamBrowser.Configuration.UnitTests/SafeExamBrowser.Configuration.UnitTests.csproj

@@ -88,6 +88,7 @@
     <Compile Include="Cryptography\PasswordEncryptionTests.cs" />
     <Compile Include="Cryptography\PublicKeyHashEncryptionTests.cs" />
     <Compile Include="Cryptography\PublicKeyHashWithSymmetricKeyEncryptionTests.cs" />
+    <Compile Include="DataCompression\GZipCompressorTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
   </ItemGroup>
   <ItemGroup>

SafeExamBrowser.Configuration/DataCompression/GZipCompressor.cs

@@ -95,7 +95,7 @@ namespace SafeExamBrowser.Configuration.DataCompression
 			}
 			catch (Exception e)
 			{
-				logger.Error($"Failed to check whether '{data}' with {data.Length / 1000.0} KB data is a gzip-compressed stream!", e);
+				logger.Error($"Failed to check whether '{data}' with {data?.Length / 1000.0} KB data is a gzip-compressed stream!", e);
 			}
 
 			return false;