Initial commit.

App.config

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+<?xml version="1.0"?>
+<configuration>
+    <startup> 
+
+    <supportedRuntime version="v2.0.50727" sku="Client"/></startup>
+</configuration>

Unzip.cs

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+// Unzip class for .NET 3.5
+// Written by Alexey Yakovlev <[email protected]>
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.IO;
+using System.IO.Compression;
+using System.Linq;
+
+namespace Internals
+{
+	public class Unzip : IDisposable
+	{
+		private const int EntrySignature = 0x02014B50;
+
+		private const int FileSignature = 0x04034b50;
+
+		private const int DirectorySignature = 0x06054B50;
+
+		private const int BufferSize = 16 * 1024;
+
+		public Unzip(string fileName)
+			: this(File.OpenRead(fileName))
+		{
+		}
+
+		public Unzip(Stream stream)
+		{
+			Stream = stream;
+			Reader = new BinaryReader(Stream);
+		}
+
+		private Stream Stream { get; set; }
+
+		private BinaryReader Reader { get; set; }
+
+		public void Dispose()
+		{
+			if (Stream != null)
+			{
+				Stream.Dispose();
+				Stream = null;
+			}
+
+			if (Reader != null)
+			{
+				Reader.Close();
+				Reader = null;
+			}
+		}
+
+		public void Decompress(string fileName, Stream outputStream)
+		{
+			var entry = Entries.Where(e => e.FileName == fileName).First();
+			Decompress(entry, outputStream);
+		}
+
+		public void Decompress(ZipEntry entry, Stream outputStream)
+		{
+			// check file signature
+			Stream.Seek(entry.FileHeaderOffset, SeekOrigin.Begin);
+			if (Reader.ReadInt32() != FileSignature)
+			{
+				throw new InvalidOperationException("File signature don't match.");
+			}
+
+			// move to file data
+			Stream.Seek(entry.FileDataOffset, SeekOrigin.Begin);
+			var inputStream = Stream;
+			if (entry.Deflated)
+			{
+				Console.WriteLine("entry: {0} is deflated.", entry.FileName);
+				inputStream = new DeflateStream(Stream, CompressionMode.Decompress, true);
+			}
+
+			// allocate buffer
+			var count = entry.FileSize;
+			var bufferSize = Math.Min(BufferSize, entry.FileSize);
+			var buffer = new byte[bufferSize];
+
+			while (count > 0)
+			{
+				// decompress data
+				var read = inputStream.Read(buffer, 0, bufferSize);
+				if (read == 0)
+				{
+					break;
+				}
+
+				// copy to the output stream
+				outputStream.Write(buffer, 0, read);
+				count -= read;
+			}
+		}
+
+		public IEnumerable<string> FileNames
+		{
+			get
+			{
+				return Entries.Select(e => e.FileName).Where(f => !f.EndsWith("/"));
+			}
+		}
+
+		private ZipEntry[] entries;
+
+		public IEnumerable<ZipEntry> Entries
+		{
+			get
+			{
+				if (entries == null)
+				{
+					entries = ReadZipEntries().ToArray();
+				}
+
+				return entries;
+			}
+		}
+
+		private IEnumerable<ZipEntry> ReadZipEntries()
+		{
+			if (Stream.Length < 22)
+			{
+				yield break;
+			}
+
+			Stream.Seek(-22, SeekOrigin.End);
+
+			// find directory signature
+			while (Reader.ReadInt32() != DirectorySignature)
+			{
+				if (Stream.Position <= 5)
+				{
+					yield break;
+				}
+
+				// move 1 byte back
+				Stream.Seek(-5, SeekOrigin.Current);
+			}
+
+			// read directory properties
+			Stream.Seek(6, SeekOrigin.Current);
+			var entries = Reader.ReadUInt16();
+			var difSize = Reader.ReadInt32();
+			var dirOffset = Reader.ReadUInt32();
+			Stream.Seek(dirOffset, SeekOrigin.Begin);
+
+			// read directory entries
+			for (int i = 0; i < entries; i++)
+			{
+				if (Reader.ReadInt32() != EntrySignature)
+				{
+					continue;
+				}
+
+				// read file properties
+				Reader.ReadInt32();
+				bool utf8 = (Reader.ReadInt16() & 0x0800) != 0;
+				short method = Reader.ReadInt16();
+				int timestamp = Reader.ReadInt32();
+				int crc32 = Reader.ReadInt32();
+				int compressedSize = Reader.ReadInt32();
+				int fileSize = Reader.ReadInt32();
+				short fileNameSize = Reader.ReadInt16();
+				short extraSize = Reader.ReadInt16();
+				short commentSize = Reader.ReadInt16();
+				int headerOffset = Reader.ReadInt32();
+				Reader.ReadInt32();
+				int fileHeaderOffset = Reader.ReadInt32();
+				var fileNameBytes = Reader.ReadBytes(fileNameSize);
+				Stream.Seek(extraSize, SeekOrigin.Current);
+				var fileCommentBytes = Reader.ReadBytes(commentSize);
+				var fileDataOffset = CalculateFileDataOffset(fileHeaderOffset);
+
+				// decode zip file entry
+				var encoder = utf8 ? Encoding.UTF8 : Encoding.Default;
+				yield return new ZipEntry
+				{
+					FileName = encoder.GetString(fileNameBytes),
+					FileComment = encoder.GetString(fileCommentBytes),
+					Crc32 = crc32,
+					CompressedSize = compressedSize,
+					FileSize = fileSize,
+					FileHeaderOffset = fileHeaderOffset,
+					FileDataOffset = fileDataOffset,
+					Deflated = method == 8
+				};
+			}
+		}
+
+		private int CalculateFileDataOffset(int fileHeaderOffset)
+		{
+			var position = Stream.Position;
+			Stream.Seek(fileHeaderOffset + 26, SeekOrigin.Begin);
+			var fileNameSize = Reader.ReadInt16();
+			var extraSize = Reader.ReadInt16();
+
+			var fileOffset = (int)Stream.Position + fileNameSize + extraSize;
+			Stream.Seek(position, SeekOrigin.Begin);
+			return fileOffset;
+		}
+	}
+
+	public class ZipEntry
+	{
+		public string FileName { get; set; }
+
+		public string FileComment { get; set; }
+
+		public int Crc32 { get; set; }
+
+		public int CompressedSize { get; set; }
+
+		public int FileSize { get; set; }
+
+		public int FileHeaderOffset { get; set; }
+
+		public int FileDataOffset { get; set; }
+
+		public bool Deflated { get; set; }
+
+		public bool IsDirectory { get { return FileName.EndsWith("/"); } }
+	}
+}

Unzip.csproj

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+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
+  <PropertyGroup>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <ProjectGuid>{219BB6A2-8DF5-4A85-BD38-EA09293FDDEE}</ProjectGuid>
+    <OutputType>Exe</OutputType>
+    <AppDesignerFolder>Properties</AppDesignerFolder>
+    <RootNamespace>Internals</RootNamespace>
+    <AssemblyName>Unzip</AssemblyName>
+    <TargetFrameworkVersion>v3.5</TargetFrameworkVersion>
+    <FileAlignment>512</FileAlignment>
+    <TargetFrameworkProfile>Client</TargetFrameworkProfile>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
+    <PlatformTarget>AnyCPU</PlatformTarget>
+    <DebugSymbols>true</DebugSymbols>
+    <DebugType>full</DebugType>
+    <Optimize>false</Optimize>
+    <OutputPath>bin\Debug\</OutputPath>
+    <DefineConstants>DEBUG;TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
+    <PlatformTarget>AnyCPU</PlatformTarget>
+    <DebugType>pdbonly</DebugType>
+    <Optimize>true</Optimize>
+    <OutputPath>bin\Release\</OutputPath>
+    <DefineConstants>TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <ItemGroup>
+    <Reference Include="System" />
+    <Reference Include="System.Core" />
+    <Reference Include="System.Xml.Linq" />
+    <Reference Include="System.Data.DataSetExtensions" />
+    <Reference Include="Microsoft.CSharp" />
+    <Reference Include="System.Data" />
+    <Reference Include="System.Xml" />
+  </ItemGroup>
+  <ItemGroup>
+    <Compile Include="Unzip.cs" />
+    <Compile Include="UsageExample.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="App.config" />
+  </ItemGroup>
+  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
+       Other similar extension points exist, see Microsoft.Common.targets.
+  <Target Name="BeforeBuild">
+  </Target>
+  <Target Name="AfterBuild">
+  </Target>
+  -->
+</Project>

Unzip.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio 2012
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Unzip", "Unzip.csproj", "{219BB6A2-8DF5-4A85-BD38-EA09293FDDEE}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{219BB6A2-8DF5-4A85-BD38-EA09293FDDEE}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{219BB6A2-8DF5-4A85-BD38-EA09293FDDEE}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{219BB6A2-8DF5-4A85-BD38-EA09293FDDEE}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{219BB6A2-8DF5-4A85-BD38-EA09293FDDEE}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+EndGlobal

UsageExample.cs

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+// Unzip class usage example
+// Written by Alexey Yakovlev <[email protected]>
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+
+namespace Internals
+{
+	struct Program
+	{
+		static void Main()
+		{
+			using (var unzip = new Unzip("zssample.zip"))
+			{
+				Console.WriteLine("Files: {0}", string.Join(", ", unzip.FileNames.ToArray()));
+
+				foreach (var entry in unzip.Entries.Where(e => !e.IsDirectory))
+				{
+					Console.WriteLine("{0}: {1} -> {2}", entry.FileName, entry.FileSize, entry.CompressedSize);
+
+					var fileName = Path.Combine("Unzipped", entry.FileName);
+					var dirName = Path.GetDirectoryName(fileName);
+					Directory.CreateDirectory(dirName);
+
+					using (var outStream = File.Create(fileName))
+					{
+						unzip.Decompress(entry.FileName, outStream);
+					}
+				}
+			}
+		}
+	}
+}