Presize MemoryStream when possible.

Also use GetBuffer when we know we have presized the stream to the exact required size to prevent a needless copy.

OpenRA.Game/FileSystem/ZipFile.cs

@@ -44,7 +44,7 @@ public Stream GetStream(string filename)
 
 				using (var z = pkg.GetInputStream(entry))
 				{
-					var ms = new MemoryStream();
+					var ms = new MemoryStream((int)entry.Size);
 					z.CopyTo(ms);
 					ms.Seek(0, SeekOrigin.Begin);
 					return ms;
@@ -104,7 +104,13 @@ public ReadWriteZipFile(string filename, bool create = false)
 				// SharpZipLib breaks when asked to update archives loaded from outside streams or files
 				// We can work around this by creating a clean in-memory-only file, cutting all outside references
 				if (!create)
-					new MemoryStream(File.ReadAllBytes(filename)).CopyTo(pkgStream);
+				{
+					using (var copy = new MemoryStream(File.ReadAllBytes(filename)))
+					{
+						pkgStream.Capacity = (int)copy.Length;
+						copy.CopyTo(pkgStream);
+					}
+				}
 
 				pkgStream.Position = 0;
 				pkg = ZipFileHelper.Create(pkgStream);

OpenRA.Game/Network/Connection.cs

@@ -77,10 +77,10 @@ public virtual void SendImmediate(List<byte[]> orders)
 
 		public virtual void SendSync(int frame, byte[] syncData)
 		{
-			var ms = new MemoryStream();
+			var ms = new MemoryStream(4 + syncData.Length);
 			ms.Write(BitConverter.GetBytes(frame));
 			ms.Write(syncData);
-			Send(ms.ToArray());
+			Send(ms.GetBuffer());
 		}
 
 		protected virtual void Send(byte[] packet)
@@ -197,10 +197,10 @@ void NetworkConnectionReceive(object networkStreamObject)
 
 		public override void SendSync(int frame, byte[] syncData)
 		{
-			var ms = new MemoryStream();
+			var ms = new MemoryStream(4 + syncData.Length);
 			ms.Write(BitConverter.GetBytes(frame));
 			ms.Write(syncData);
-			queuedSyncPackets.Add(ms.ToArray());
+			queuedSyncPackets.Add(ms.GetBuffer());
 		}
 
 		protected override void Send(byte[] packet)

OpenRA.Game/Network/Order.cs

@@ -240,7 +240,7 @@ public byte[] Serialize()
 		{
 			if (IsImmediate)
 			{
-				var ret = new MemoryStream();
+				var ret = new MemoryStream(1 + OrderString.Length + TargetString.Length);
 				var w = new BinaryWriter(ret);
 				w.Write((byte)0xfe);
 				w.Write(OrderString);

OpenRA.Game/Network/OrderIO.cs

@@ -38,14 +38,14 @@ public static List<Order> ToOrderList(this byte[] bytes, World world)
 
 		public static byte[] SerializeSync(int sync)
 		{
-			var ms = new MemoryStream();
+			var ms = new MemoryStream(1 + 4);
 			using (var writer = new BinaryWriter(ms))
 			{
 				writer.Write((byte)0x65);
 				writer.Write(sync);
 			}
 
-			return ms.ToArray();
+			return ms.GetBuffer();
 		}
 
 		public static int2 ReadInt2(this BinaryReader r)

OpenRA.Game/Network/ReplayConnection.cs

@@ -127,10 +127,10 @@ public ReplayConnection(string replayFilename)
 
 		public void SendSync(int frame, byte[] syncData)
 		{
-			var ms = new MemoryStream();
+			var ms = new MemoryStream(4 + syncData.Length);
 			ms.Write(BitConverter.GetBytes(frame));
 			ms.Write(syncData);
-			sync.Add(ms.ToArray());
+			sync.Add(ms.GetBuffer());
 
 			// Store the current frame so Receive() can return the next chunk of orders.
 			ordersFrame = frame + LobbyInfo.GlobalSettings.OrderLatency;

OpenRA.Game/Server/ServerOrder.cs

@@ -49,7 +49,7 @@ public static ServerOrder Deserialize(BinaryReader r)
 
 		public byte[] Serialize()
 		{
-			var ms = new MemoryStream();
+			var ms = new MemoryStream(1 + Name.Length + Data.Length);
 			var bw = new BinaryWriter(ms);
 
 			bw.Write((byte)0xfe);

OpenRA.Mods.Cnc/FileSystem/MixFile.cs

@@ -150,7 +150,7 @@ static MemoryStream Decrypt(uint[] h, Blowfish fish)
 			{
 				var decrypted = fish.Decrypt(h);
 
-				var ms = new MemoryStream();
+				var ms = new MemoryStream(decrypted.Length * 4);
 				var writer = new BinaryWriter(ms);
 				foreach (var t in decrypted)
 					writer.Write(t);