Eliminate allocations in EnumExtensions and make public again

Author: iamcarbon

Src/Fido2.Models/Converters/EnumNameMapper.cs

@@ -0,0 +1,80 @@
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using System.Runtime.Serialization;
+
+namespace Fido2NetLib
+{
+    public static class EnumNameMapper<TEnum>
+        where TEnum: struct, Enum
+    {
+        private static readonly Dictionary<TEnum, string> valueToNames = GetIdToNameMap();
+        private static readonly Dictionary<string, TEnum> namesToValues = Invert(valueToNames);
+
+        private static Dictionary<string, TEnum> Invert(Dictionary<TEnum, string> map)
+        {
+            var result = new Dictionary<string, TEnum>(map.Count, StringComparer.OrdinalIgnoreCase);
+
+            foreach (var item in map)
+            {
+                result[item.Value] = item.Key;
+            }
+
+            return result;
+        }
+
+        public static bool TryGetValue(string name, bool ignoreCase, out TEnum value)
+        {
+            if (namesToValues.TryGetValue(name, out value))
+            {
+                if (!ignoreCase && !valueToNames[value].Equals(name, StringComparison.Ordinal))
+                {
+                    value = default;
+
+                    return false;
+                }
+                else
+                {
+                    return true;
+                }
+            }
+            else
+            {
+                value = default;
+
+                return false;
+            }
+        }
+
+        public static bool TryGetValue(string name, out TEnum value)
+        {
+            return namesToValues.TryGetValue(name, out value);
+        }
+
+        public static string GetName(TEnum value)
+        {
+            return valueToNames[value];
+        }
+
+        public static IEnumerable<string> GetNames()
+        {
+            return namesToValues.Keys;
+        }
+
+        private static Dictionary<TEnum, string> GetIdToNameMap()
+        {
+            var dic = new Dictionary<TEnum, string>();
+
+            foreach (var field in typeof(TEnum).GetFields(BindingFlags.Public | BindingFlags.Static))
+            {
+                var description = field.GetCustomAttribute<EnumMemberAttribute>(false);
+
+                var value = (TEnum)field.GetValue(null);
+
+                dic[value] = description is not null ? description.Value : value.ToString();
+            }
+
+            return dic;
+        }
+    }
+}

Src/Fido2.Models/Converters/FidoEnumConverter.cs

@@ -1,23 +1,18 @@
 using System;
-using System.Collections.Generic;
-using System.Reflection;
-using System.Runtime.Serialization;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 
 namespace Fido2NetLib
 {
+
     public sealed class FidoEnumConverter<T> : JsonConverter<T>
         where T: struct, Enum
     {
-        private static readonly Dictionary<T, string> valueToNames = GetIdToNameMap();
-        private static readonly Dictionary<string, T> namesToValues = Invert(valueToNames);
-
         public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {
             string text = reader.GetString();
 
-            if (namesToValues.TryGetValue(reader.GetString(), out T value))
+            if (EnumNameMapper<T>.TryGetValue(reader.GetString(), out T value))
             {
                 return value;
             }
@@ -29,35 +24,7 @@ public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerial
 
         public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
         {
-            writer.WriteStringValue(valueToNames[value]);
-        }
-
-        private static Dictionary<string, T> Invert(Dictionary<T, string> map)
-        {
-            var result = new Dictionary<string, T>(map.Count, StringComparer.OrdinalIgnoreCase);
-
-            foreach (var item in map)
-            {
-                result[item.Value] = item.Key;
-            }
-
-            return result;
-        }
-
-        private static Dictionary<T, string> GetIdToNameMap()
-        {
-            var dic = new Dictionary<T, string>();
-
-            foreach (var field in typeof(T).GetFields(BindingFlags.Public | BindingFlags.Static))
-            {
-                var description = field.GetCustomAttribute<EnumMemberAttribute>(false);
-
-                var value = (T)field.GetValue(null);
-
-                dic[value] = description is not null ? description.Value : value.ToString();
-            }
-
-            return dic;
+            writer.WriteStringValue(EnumNameMapper<T>.GetName(value));
         }
     }
 }

Src/Fido2/Extensions/EnumExtensions.cs

@@ -1,11 +1,8 @@
 using System;
-using System.Linq;
-using System.Reflection;
-using System.Runtime.Serialization;
 
 namespace Fido2NetLib
 {
-    internal static class EnumExtensions
+    public static class EnumExtensions
     {
         /// <summary>
         /// Gets the enum value from EnumMemberAttribute's value.
@@ -14,22 +11,20 @@ internal static class EnumExtensions
         /// <param name="value">The EnumMemberAttribute's value.</param>
         /// <param name="ignoreCase">ignores the case when comparing values.</param>
         /// <returns>TEnum.</returns>
-        /// <exception cref="System.ArgumentException">No XmlEnumAttribute code exists for type " + typeof(TEnum).ToString() + " corresponding to value of " + value</exception>
+        /// <exception cref="ArgumentException">No XmlEnumAttribute code exists for type " + typeof(TEnum).ToString() + " corresponding to value of " + value</exception>
         public static TEnum ToEnum<TEnum>(this string value, bool ignoreCase = true) where TEnum : struct, Enum
         {
             // Try to parse it normally on the first try
             if (Enum.TryParse<TEnum>(value, ignoreCase, out var result))
                 return result;
 
             // Try with value from EnumMemberAttribute
-            var values = Enum.GetValues(typeof(TEnum)).OfType<TEnum>().ToArray();
-            foreach (var val in values)
+            if (EnumNameMapper<TEnum>.TryGetValue(value, ignoreCase, out result))
             {
-                if (ToEnumMemberValue(val)!.Equals(value, ignoreCase ? StringComparison.OrdinalIgnoreCase : StringComparison.Ordinal))
-                    return val;
+                return result;
             }
 
-            throw new ArgumentException($"Value '{value}' is not a valid enum name of '{typeof(TEnum)}' ({nameof(ignoreCase)}={ignoreCase}). Valid values are: {string.Join(", ", values.Select(v => v.ToEnumMemberValue()))}.");
+            throw new ArgumentException($"Value '{value}' is not a valid enum name of '{typeof(TEnum)}' ({nameof(ignoreCase)}={ignoreCase}). Valid values are: {string.Join(", ", EnumNameMapper<TEnum>.GetNames())}.");
         }
 
         /// <summary>
@@ -38,13 +33,10 @@ public static TEnum ToEnum<TEnum>(this string value, bool ignoreCase = true) whe
         /// <typeparam name="TEnum">The type of enum.</typeparam>
         /// <param name="value">The enum's value.</param>
         /// <returns>string.</returns>
-        public static string? ToEnumMemberValue<TEnum>(this TEnum value) where TEnum : struct, Enum
+        public static string ToEnumMemberValue<TEnum>(this TEnum value) where TEnum : struct, Enum
         {
-            return typeof(TEnum).GetTypeInfo()
-                                .DeclaredMembers
-                                .SingleOrDefault(x => x.Name == value.ToString())
-                                ?.GetCustomAttribute<EnumMemberAttribute>(false)
-                                ?.Value;
+            return EnumNameMapper<TEnum>.GetName(value);
         }
+
     }
 }