Allow for programmatic configuration of protocol settings in master-2…

….x branch (#959)

neo.UnitTests/UT_ProtocolSettings.cs

@@ -0,0 +1,96 @@
+using FluentAssertions;
+using Microsoft.Extensions.Configuration;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using System.Text;
+
+namespace Neo.UnitTests
+{
+    [TestClass]
+    public class UT_ProtocolSettings
+    {
+        const uint mainNetMagic = 0x746E41u;
+
+        // since ProtocolSettings.Default is designed to be writable only once, use reflection to 
+        // reset the underlying _default field to null before and after running tests in this class.
+        static void ResetProtocolSettings()
+        {
+            var defaultField = typeof(ProtocolSettings)
+                .GetField("_default", BindingFlags.Static | BindingFlags.NonPublic);
+            defaultField.SetValue(null, null);
+        }
+
+        [TestInitialize]
+        public void Initialize()
+        {
+            ResetProtocolSettings();
+        }
+
+        [TestCleanup]
+        public void Cleanup()
+        {
+            ResetProtocolSettings();
+        }
+
+        [TestMethod]
+        public void Default_Magic_should_be_mainnet_Magic_value()
+        {
+            ProtocolSettings.Default.Magic.Should().Be(mainNetMagic);
+        }
+
+        [TestMethod]
+        public void Can_initialize_ProtocolSettings()
+        {
+            var expectedMagic = 12345u;
+
+            var dict = new Dictionary<string, string>()
+            {
+                { "ProtocolConfiguration:Magic", $"{expectedMagic}" }
+            };
+
+            var config = new ConfigurationBuilder().AddInMemoryCollection(dict).Build();
+            ProtocolSettings.Initialize(config).Should().BeTrue();
+            ProtocolSettings.Default.Magic.Should().Be(expectedMagic);
+        }
+
+        [TestMethod]
+        public void Cant_initialize_ProtocolSettings_after_default_settings_used()
+        {
+            ProtocolSettings.Default.Magic.Should().Be(mainNetMagic);
+
+            var updatedMagic = 54321u;
+            var dict = new Dictionary<string, string>()
+            {
+                { "ProtocolConfiguration:Magic", $"{updatedMagic}" }
+            };
+
+            var config = new ConfigurationBuilder().AddInMemoryCollection(dict).Build();
+            ProtocolSettings.Initialize(config).Should().BeFalse();
+            ProtocolSettings.Default.Magic.Should().Be(mainNetMagic);
+        }
+
+        [TestMethod]
+        public void Cant_initialize_ProtocolSettings_twice()
+        {
+            var expectedMagic = 12345u;
+            var dict = new Dictionary<string, string>()
+            {
+                { "ProtocolConfiguration:Magic", $"{expectedMagic}" }
+            };
+
+            var config = new ConfigurationBuilder().AddInMemoryCollection(dict).Build();
+            ProtocolSettings.Initialize(config).Should().BeTrue();
+
+            var updatedMagic = 54321u;
+            dict = new Dictionary<string, string>()
+            {
+                { "ProtocolConfiguration:Magic", $"{updatedMagic}" }
+            };
+            config = new ConfigurationBuilder().AddInMemoryCollection(dict).Build();
+            ProtocolSettings.Initialize(config).Should().BeFalse();
+            ProtocolSettings.Default.Magic.Should().Be(expectedMagic);
+        }
+    }
+}

neo/ProtocolSettings.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 
 namespace Neo
 {
@@ -16,12 +17,31 @@ public class ProtocolSettings
         public Fixed8 LowPriorityThreshold { get; }
         public uint SecondsPerBlock { get; }
 
-        public static ProtocolSettings Default { get; }
+        static ProtocolSettings _default;
 
-        static ProtocolSettings()
+        static bool UpdateDefault(IConfiguration configuration)
         {
-            IConfigurationSection section = new ConfigurationBuilder().AddJsonFile("protocol.json", true).Build().GetSection("ProtocolConfiguration");
-            Default = new ProtocolSettings(section);
+            var settings = new ProtocolSettings(configuration.GetSection("ProtocolConfiguration"));
+            return null == Interlocked.CompareExchange(ref _default, settings, null);
+        }
+
+        public static bool Initialize(IConfiguration configuration)
+        {
+            return UpdateDefault(configuration);
+        }
+
+        public static ProtocolSettings Default
+        {
+            get
+            {
+                if (_default == null)
+                {
+                    var configuration = new ConfigurationBuilder().AddJsonFile("protocol.json", true).Build();
+                    UpdateDefault(configuration);
+                }
+
+                return _default;
+            }
         }
 
         private ProtocolSettings(IConfigurationSection section)