From 64d594cc0cfbfb747468dc9ce219028fcf846ce5 Mon Sep 17 00:00:00 2001
From: Ogoun <ogoun@users.noreply.github.com>
Date: Wed, 18 Dec 2019 16:32:22 +0300
Subject: [PATCH] Fixes

---
 ZeroLevel/Services/Config/Configuration.cs    | 13 +++-
 ZeroLevel/Services/Network/BaseSocket.cs      |  2 +-
 .../Reflection/EntryAssebmlyAttribute.cs      | 71 +++++++++++++++++++
 3 files changed, 82 insertions(+), 4 deletions(-)
 create mode 100644 ZeroLevel/Services/Reflection/EntryAssebmlyAttribute.cs

diff --git a/ZeroLevel/Services/Config/Configuration.cs b/ZeroLevel/Services/Config/Configuration.cs
index 385b3b0..efb4e54 100644
--- a/ZeroLevel/Services/Config/Configuration.cs
+++ b/ZeroLevel/Services/Config/Configuration.cs
@@ -2,9 +2,11 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Reflection;
 using ZeroLevel.Services.Config;
 using ZeroLevel.Services.Config.Implementation;
+using ZeroLevel.Services.Reflection;
 using ZeroLevel.Services.Serialization;
 
 namespace ZeroLevel
@@ -14,14 +16,13 @@ namespace ZeroLevel
         /// <summary>
         /// Application folder path
         /// </summary>
-        public static string BaseDirectory = Path.GetDirectoryName(Assembly.GetEntryAssembly().Location);
+        public static readonly string BaseDirectory;
 
-        public static string AppLocation = Assembly.GetEntryAssembly()?.Location;
+        public static readonly string AppLocation;
 
         public const string DEFAULT_SECTION_NAME = "_defaultsection";
 
         #region Ctor
-
         static Configuration()
         {
             _empty = new BaseConfiguration();
@@ -29,6 +30,12 @@ namespace ZeroLevel
             _empty.Freeze(true);
             _emptySet.FreezeConfiguration(true);
             DefaultSet = Configuration.CreateSet();
+            var assembly = EntryAssemblyAttribute.GetEntryAssembly();
+            if (assembly != null)
+            {
+                BaseDirectory = Path.GetDirectoryName(assembly.Location);
+                AppLocation = assembly.Location;
+            }
         }
 
         #endregion Ctor
diff --git a/ZeroLevel/Services/Network/BaseSocket.cs b/ZeroLevel/Services/Network/BaseSocket.cs
index de24b00..e1f04b2 100644
--- a/ZeroLevel/Services/Network/BaseSocket.cs
+++ b/ZeroLevel/Services/Network/BaseSocket.cs
@@ -6,7 +6,7 @@ namespace ZeroLevel.Network
     {
         static BaseSocket()
         {
-            MAX_FRAME_PAYLOAD_SIZE = Configuration.Default.FirstOrDefault<int>("MAX_FRAME_PAYLOAD_SIZE", DEFAULT_MAX_FRAME_PAYLOAD_SIZE);
+            MAX_FRAME_PAYLOAD_SIZE = Configuration.Default?.FirstOrDefault<int>("MAX_FRAME_PAYLOAD_SIZE", DEFAULT_MAX_FRAME_PAYLOAD_SIZE) ?? DEFAULT_MAX_FRAME_PAYLOAD_SIZE;
         }
 
         public static readonly IRouter NullRouter = new NullRouter();
diff --git a/ZeroLevel/Services/Reflection/EntryAssebmlyAttribute.cs b/ZeroLevel/Services/Reflection/EntryAssebmlyAttribute.cs
new file mode 100644
index 0000000..372b4b4
--- /dev/null
+++ b/ZeroLevel/Services/Reflection/EntryAssebmlyAttribute.cs
@@ -0,0 +1,71 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+
+namespace ZeroLevel.Services.Reflection
+{
+    /// <summary>
+    /// For certain types of apps, such as web apps, <see cref="Assembly.GetEntryAssembly"/> 
+    /// returns null.  With the <see cref="EntryAssemblyAttribute"/>, we can designate 
+    /// an assembly as the entry assembly by creating an instance of this attribute, 
+    /// typically in the AssemblyInfo.cs file.
+    /// <example>
+    /// [assembly: EntryAssembly]
+    /// </example>
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Assembly)]
+    public sealed class EntryAssemblyAttribute : Attribute
+    {
+        /// <summary>
+        /// Lazily find the entry assembly.
+        /// </summary>
+        private static readonly Lazy<Assembly> EntryAssemblyLazy = new Lazy<Assembly>(GetEntryAssemblyLazily);
+
+        /// <summary>
+        /// Gets the entry assembly.
+        /// </summary>
+        /// <returns>The entry assembly.</returns>
+        public static Assembly GetEntryAssembly()
+        {
+            return EntryAssemblyLazy.Value;
+        }
+
+        /// <summary>
+        /// Invoked lazily to find the entry assembly.  We want to cache this value as it may 
+        /// be expensive to find.
+        /// </summary>
+        /// <returns>The entry assembly.</returns>
+        private static Assembly GetEntryAssemblyLazily()
+        {
+            return Assembly.GetEntryAssembly() ?? FindEntryAssemblyInCurrentAppDomain();
+        }
+
+        /// <summary>
+        /// Finds the entry assembly in the current app domain.
+        /// </summary>
+        /// <returns>The entry assembly.</returns>
+        private static Assembly FindEntryAssemblyInCurrentAppDomain()
+        {
+            var assemblies = AppDomain.CurrentDomain.GetAssemblies();
+            var entryAssemblies = new List<Assembly>();
+            foreach (var assembly in assemblies)
+            {
+                // Note the usage of LINQ SingleOrDefault.  The EntryAssemblyAttribute's AttrinuteUsage 
+                // only allows it to occur once per assembly; declaring it more than once results in 
+                // a compiler error.
+                var attribute =
+                    assembly.GetCustomAttributes().OfType<EntryAssemblyAttribute>().SingleOrDefault();
+                if (attribute != null)
+                {
+                    entryAssemblies.Add(assembly);
+                }
+            }
+
+            // Note that we use LINQ Single to ensure we found one and only one assembly with the 
+            // EntryAssemblyAttribute.  The EntryAssemblyAttribute should only be put on one assembly 
+            // per application.
+            return entryAssemblies.SingleOrDefault();
+        }
+    }
+}