Use DeflateStream instead of GZipStream, add basic GZip header reader.

ClassicalSharp.csproj

@@ -127,6 +127,7 @@
     <Compile Include="Network\Enums.cs" />
     <Compile Include="Network\FastNetReader.cs" />
     <Compile Include="Network\FixedBufferStream.cs" />
+    <Compile Include="Network\GZipHeaderReader.cs" />
     <Compile Include="Network\NetworkProcessor.cs" />
     <Compile Include="Network\AsyncDownloader.cs" />
     <Compile Include="Network\WomConfigHandler.cs" />

Network/GZipHeaderReader.cs

@@ -0,0 +1,107 @@
+using System;
+using System.IO;
+
+namespace ClassicalSharp {
+	
+	internal class GZipHeaderReader {
+		
+		enum State {
+			Header1,
+			Header2,
+			CompressionMethod,
+			Flags,
+			LastModifiedTime,
+			CompressionFlags,
+			OperatingSystem,
+			HeaderChecksum,
+			Done,
+		}
+		
+		State state = State.Header1;
+		public bool done;
+		int flags;
+		int partsRead;
+		
+		public bool ReadHeader( Stream s ) {		
+			switch( state ) {
+					
+				case State.Header1:
+					if( !ReadAndCheckHeaderByte( s, 0x1F ) )
+						return false;
+					goto case State.Header2;
+					
+				case State.Header2:
+					if( !ReadAndCheckHeaderByte( s, 0x8B ) )
+						return false;
+					goto case State.CompressionMethod;
+					
+				case State.CompressionMethod:
+					if( !ReadAndCheckHeaderByte( s, 0x08 ) )
+						return false;
+					goto case State.Flags;
+					
+				case State.Flags:
+					if( !ReadHeaderByte( s, out flags ) )
+						return false;
+					if( flags >= 0x04 ) // We don't support extra, comment, or original name fields
+						throw new NotSupportedException( "Unsupported gzip flags: " + flags );
+					goto case State.LastModifiedTime;
+					
+				case State.LastModifiedTime:
+					for( ; partsRead < 4; partsRead++ ) {
+						int part = s.ReadByte();
+						if( part == -1 )
+							return false;
+					}
+					partsRead = 0;
+					state = State.CompressionFlags;
+					goto case State.CompressionFlags;
+					
+				case State.CompressionFlags:
+					int comFlags;
+					if( !ReadHeaderByte( s, out comFlags ) )
+						return false;
+					goto case State.OperatingSystem;
+					
+				case State.OperatingSystem:
+					int os;
+					if( !ReadHeaderByte( s, out os ) )
+						return false;
+					goto case State.HeaderChecksum;
+					
+				case State.HeaderChecksum:
+					if( ( flags & 0x02 ) != 0 ) {
+						for( ; partsRead < 2; partsRead++ ) {
+							int part = s.ReadByte();
+							if( part == -1 )
+								return false;
+						}
+					}
+					partsRead = 0;
+					state = State.Done;
+					done = true;
+					return true;
+			}
+			return true;
+		}
+		
+		bool ReadAndCheckHeaderByte( Stream s, byte expected ) {
+			int value;
+			if( !ReadHeaderByte( s, out value ) )
+				return false;
+			
+			if( value != expected )
+				throw new InvalidDataException( "Unepxected constant in GZip header. (" + expected + "-" + value + ")" );
+			return true;
+		}
+		
+		bool ReadHeaderByte( Stream s, out int value ) {
+			value = s.ReadByte();
+			if( value == -1 )
+				return false;
+			
+			state++;
+			return true;
+		}
+	}
+}

Network/NetworkProcessor.cs

@@ -120,7 +120,7 @@ namespace ClassicalSharp {
 			"EmoteFix", "ClickDistance", "HeldBlock", "BlockPermissions",
 			"SelectionCuboid", "MessageTypes", "CustomBlocks", "EnvColors",
 			"HackControl", "EnvMapAppearance", "ExtPlayerList", "ChangeModel",
-			"EnvWeatherType", 
+			"EnvWeatherType",
 		};
 		
 		
@@ -236,7 +236,8 @@ namespace ClassicalSharp {
 		FastNetReader reader;
 		int cpeServerExtensionsCount;
 		DateTime receiveStart;
-		GZipStream gzipStream;
+		DeflateStream gzipStream;
+		GZipHeaderReader gzipHeader;
 		int mapSizeIndex;
 		byte[] mapSize = new byte[4];
 		byte[] map;
@@ -286,7 +287,8 @@ namespace ClassicalSharp {
 							sendWomId = true;
 						}
 						receivedFirstPosition = false;
-						gzipStream = new GZipStream( gzippedMap, CompressionMode.Decompress );
+						gzipHeader = new GZipHeaderReader();
+						gzipStream = new DeflateStream( gzippedMap, CompressionMode.Decompress );
 						mapSizeIndex = 0;
 						mapIndex = 0;
 						receiveStart = DateTime.UtcNow;
@@ -298,16 +300,18 @@ namespace ClassicalSharp {
 						gzippedMap.Position = 0;
 						gzippedMap.SetLength( usedLength );
 						
-						if( mapSizeIndex < 4 ) {
-							mapSizeIndex += gzipStream.Read( mapSize, 0, 4 - mapSizeIndex );
-						}
-
-						if( mapSizeIndex == 4 ) {
-							if( map == null ) {
-								int size = mapSize[0] << 24 | mapSize[1] << 16 | mapSize[2] << 8 | mapSize[3];
-								map = new byte[size];
+						if( gzipHeader.done || gzipHeader.ReadHeader( gzippedMap ) ) {
+							if( mapSizeIndex < 4 ) {
+								mapSizeIndex += gzipStream.Read( mapSize, 0, 4 - mapSizeIndex );
+							}
+
+							if( mapSizeIndex == 4 ) {
+								if( map == null ) {
+									int size = mapSize[0] << 24 | mapSize[1] << 16 | mapSize[2] << 8 | mapSize[3];
+									map = new byte[size];
+								}
+								mapIndex += gzipStream.Read( map, mapIndex, map.Length - mapIndex );
 							}
-							mapIndex += gzipStream.Read( map, mapIndex, map.Length - mapIndex );
 						}
 						reader.Remove( 1024 );
 						byte progress = reader.ReadUInt8();