perf: Reduce enum bandwidth (#794)

enums are serialized according to their size.
if enum extend byte,  they use 1 byte
if enum extend short, they use 2 bytes
if enum extend int,  they are varinted
if enum extend long, they are varinted

So on average,  most enums will take 1 byte.   Previously they always required 4 bytes

Assets/Mirror/Editor/Weaver/Extensions.cs

@@ -1,3 +1,4 @@
+using System;
 using Mono.Cecil;
 
 namespace Mirror.Weaver
@@ -40,6 +41,16 @@ public static bool IsDerivedFrom(this TypeDefinition td, TypeReference baseClass
             return false;
         }
 
+        public static TypeReference GetEnumUnderlyingType(this TypeDefinition td)
+        {
+            foreach (FieldDefinition field in td.Fields)
+            {
+                if (!field.IsStatic)
+                    return field.FieldType;
+            }
+            throw new ArgumentException($"Invalid enum {td.FullName}");
+        }
+
         public static bool ImplementsInterface(this TypeDefinition td, TypeReference baseInterface)
         {
             TypeDefinition typedef = td;

Assets/Mirror/Editor/Weaver/Readers.cs

@@ -96,7 +96,7 @@ public static MethodReference GetReadFunc(TypeReference variable, int recursionC
             }
             else if (td.IsEnum)
             {
-                return Weaver.NetworkReaderReadInt32;
+                return GetReadFunc(td.GetEnumUnderlyingType(), recursionCount);
             }
             else
             {

Assets/Mirror/Editor/Weaver/Weaver.cs

@@ -83,9 +83,6 @@ class Weaver
         public static TypeReference CmdDelegateReference;
         public static MethodReference CmdDelegateConstructor;
 
-        public static MethodReference NetworkReaderReadInt32;
-
-        public static MethodReference NetworkWriterWriteInt32;
         public static MethodReference NetworkWriterWriteInt16;
 
         public static MethodReference NetworkServerGetActive;
@@ -307,9 +304,6 @@ static void SetupTargetTypes()
             NetworkServerGetLocalClientActive = Resolvers.ResolveMethod(NetworkServerType, CurrentAssembly, "get_localClientActive");
             NetworkClientGetActive = Resolvers.ResolveMethod(NetworkClientType, CurrentAssembly, "get_active");
 
-            NetworkReaderReadInt32 = Resolvers.ResolveMethod(NetworkReaderType, CurrentAssembly, "ReadInt32");
-
-            NetworkWriterWriteInt32 = Resolvers.ResolveMethodWithArg(NetworkWriterType, CurrentAssembly, "Write", int32Type);
             NetworkWriterWriteInt16 = Resolvers.ResolveMethodWithArg(NetworkWriterType, CurrentAssembly, "Write", int16Type);
 
             NetworkReaderReadPackedUInt32 = Resolvers.ResolveMethod(NetworkReaderType, CurrentAssembly, "ReadPackedUInt32");

Assets/Mirror/Editor/Weaver/Writers.cs

@@ -90,7 +90,7 @@ public static MethodReference GetWriteFunc(TypeReference variable, int recursion
             }
             else if (variable.Resolve().IsEnum)
             {
-                return Weaver.NetworkWriterWriteInt32;
+                return GetWriteFunc(variable.Resolve().GetEnumUnderlyingType(), recursionCount);
             }
             else
             {