Minor reduction in memory allocations

SteamKit2/SteamKit2/Steam/CMClient.cs

@@ -529,7 +529,7 @@ void HandleMulti( IPacketMsg packetMsg )
                 {
                     using var compressedStream = new MemoryStream( payload );
                     using var gzipStream = new GZipStream( compressedStream, CompressionMode.Decompress );
-                    using var decompressedStream = new MemoryStream();
+                    using var decompressedStream = new MemoryStream( capacity: ( int )msgMulti.Body.size_unzipped );
                     gzipStream.CopyTo( decompressedStream );
                     payload = decompressedStream.ToArray();
                 }

SteamKit2/SteamKit2/Steam/SteamClient/CallbackMgr/CallbackMgr.cs

@@ -129,9 +129,14 @@ void ICallbackMgrInternals.Register( CallbackBase call )
 
         void Handle( ICallbackMsg call )
         {
-            registeredCallbacks
-                .FindAll( callback => callback.CallbackType.IsAssignableFrom( call.GetType() ) ) // find handlers interested in this callback
-                .ForEach( callback => callback.Run( call ) ); // run them
+            // find handlers interested in this callback
+            foreach ( var callback in registeredCallbacks )
+            {
+                if ( callback.CallbackType.IsAssignableFrom( call.GetType() ) )
+                {
+                    callback.Run( call );
+                }
+            }
         }
 
         void ICallbackMgrInternals.Unregister( CallbackBase call )

SteamKit2/SteamKit2/Util/StreamHelpers.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Buffers;
 using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Text;
@@ -74,6 +75,11 @@ public static float ReadFloat( this Stream stream )
 
         public static string ReadNullTermString( this Stream stream, Encoding encoding )
         {
+            if ( encoding == Encoding.UTF8 )
+            {
+                return ReadNullTermUtf8String( stream );
+            }
+
             int characterSize = encoding.GetByteCount( "e" );
 
             using MemoryStream ms = new MemoryStream();
@@ -94,6 +100,43 @@ public static string ReadNullTermString( this Stream stream, Encoding encoding )
             return encoding.GetString( ms.GetBuffer(), 0, ( int )ms.Length );
         }
 
+        private static string ReadNullTermUtf8String( Stream stream )
+        {
+            var buffer = ArrayPool<byte>.Shared.Rent( 32 );
+
+            try
+            {
+                var position = 0;
+
+                do
+                {
+                    var b = stream.ReadByte();
+
+                    if ( b <= 0 ) // null byte or stream ended
+                    {
+                        break;
+                    }
+
+                    if ( position >= buffer.Length )
+                    {
+                        var newBuffer = ArrayPool<byte>.Shared.Rent( buffer.Length * 2 );
+                        Buffer.BlockCopy( buffer, 0, newBuffer, 0, buffer.Length );
+                        ArrayPool<byte>.Shared.Return( buffer );
+                        buffer = newBuffer;
+                    }
+
+                    buffer[ position++ ] = (byte)b;
+                }
+                while ( true );
+
+                return Encoding.UTF8.GetString( buffer[ ..position ] );
+            }
+            finally
+            {
+                ArrayPool<byte>.Shared.Return( buffer );
+            }
+        }
+
         public static void WriteNullTermString( this Stream stream, string value, Encoding encoding )
         {
             var dataLength = encoding.GetByteCount( value );