Activate ChangeToken when Ocelot's configuration changes #1037

* Add configuration change token (#1036)

* Add IOptionsMonitor<IInternalConfiguration>

* Activate change token from *ConfigurationRepository instead of FileAndInternalConfigurationSetter; add acceptance & integration tests

* Update documentation

* Use IWebHostEnvironment as IHostingEnvironment deprecated

Co-authored-by: Chris Swinchatt <chrisswinchatt@gmail.com>

src/Ocelot/Configuration/ChangeTracking/IOcelotConfigurationChangeTokenSource.cs

@@ -0,0 +1,14 @@
+namespace Ocelot.Configuration.ChangeTracking
+{
+    using Microsoft.Extensions.Primitives;
+
+    /// <summary>
+    /// <see cref="IChangeToken" /> source which is activated when Ocelot's configuration is changed.
+    /// </summary>
+    public interface IOcelotConfigurationChangeTokenSource
+    {
+        IChangeToken ChangeToken { get; }
+
+        void Activate();
+    }
+}

src/Ocelot/Configuration/ChangeTracking/OcelotConfigurationChangeToken.cs

@@ -0,0 +1,74 @@
+namespace Ocelot.Configuration.ChangeTracking
+{
+    using System;
+    using System.Collections.Generic;
+    using Microsoft.Extensions.Primitives;
+
+    public class OcelotConfigurationChangeToken : IChangeToken
+    {
+        public const double PollingIntervalSeconds = 1;
+
+        private readonly ICollection<CallbackWrapper> _callbacks = new List<CallbackWrapper>();
+        private readonly object _lock = new object();
+        private DateTime? _timeChanged;
+
+        public IDisposable RegisterChangeCallback(Action<object> callback, object state)
+        {
+            lock (_lock)
+            {
+                var wrapper = new CallbackWrapper(callback, state, _callbacks, _lock);
+                _callbacks.Add(wrapper);
+                return wrapper;
+            }
+        }
+
+        public void Activate()
+        {
+            lock (_lock)
+            {
+                _timeChanged = DateTime.UtcNow;
+                foreach (var wrapper in _callbacks)
+                {
+                    wrapper.Invoke();
+                }
+            }
+        }
+
+        // Token stays active for PollingIntervalSeconds after a change (could be parameterised) - otherwise HasChanged would be true forever.
+        // Taking suggestions for better ways to reset HasChanged back to false.
+        public bool HasChanged => _timeChanged.HasValue && (DateTime.UtcNow - _timeChanged.Value).TotalSeconds < PollingIntervalSeconds;
+
+        public bool ActiveChangeCallbacks => true;
+
+        private class CallbackWrapper : IDisposable
+        {
+            private readonly ICollection<CallbackWrapper> _callbacks;
+            private readonly object _lock;
+
+            public CallbackWrapper(Action<object> callback, object state, ICollection<CallbackWrapper> callbacks, object @lock)
+            {
+                _callbacks = callbacks;
+                _lock = @lock;
+                Callback = callback;
+                State = state;
+            }
+
+            public void Invoke()
+            {
+                Callback.Invoke(State);
+            }
+
+            public void Dispose()
+            {
+                lock (_lock)
+                {
+                    _callbacks.Remove(this);
+                }
+            }
+
+            public Action<object> Callback { get; }
+
+            public object State { get; }
+        }
+    }
+}

src/Ocelot/Configuration/ChangeTracking/OcelotConfigurationChangeTokenSource.cs

@@ -0,0 +1,16 @@
+namespace Ocelot.Configuration.ChangeTracking
+{
+    using Microsoft.Extensions.Primitives;
+
+    public class OcelotConfigurationChangeTokenSource : IOcelotConfigurationChangeTokenSource
+    {
+        private readonly OcelotConfigurationChangeToken _changeToken = new OcelotConfigurationChangeToken();
+
+        public IChangeToken ChangeToken => _changeToken;
+
+        public void Activate()
+        {
+            _changeToken.Activate();
+        }
+    }
+}

src/Ocelot/Configuration/ChangeTracking/OcelotConfigurationMonitor.cs

@@ -0,0 +1,30 @@
+namespace Ocelot.Configuration.ChangeTracking
+{
+    using System;
+    using Microsoft.Extensions.Options;
+    using Ocelot.Configuration.Repository;
+
+    public class OcelotConfigurationMonitor : IOptionsMonitor<IInternalConfiguration>
+    {
+        private readonly IOcelotConfigurationChangeTokenSource _changeTokenSource;
+        private readonly IInternalConfigurationRepository _repo;
+
+        public OcelotConfigurationMonitor(IInternalConfigurationRepository repo, IOcelotConfigurationChangeTokenSource changeTokenSource)
+        {
+            _changeTokenSource = changeTokenSource;
+            _repo = repo;
+        }
+
+        public IInternalConfiguration Get(string name)
+        {
+            return _repo.Get().Data;
+        }
+
+        public IDisposable OnChange(Action<IInternalConfiguration, string> listener)
+        {
+            return _changeTokenSource.ChangeToken.RegisterChangeCallback(_ => listener(CurrentValue, ""), null);
+        }
+
+        public IInternalConfiguration CurrentValue => _repo.Get().Data;
+    }
+}

src/Ocelot/Configuration/Repository/DiskFileConfigurationRepository.cs

@@ -4,18 +4,21 @@ using Ocelot.Configuration.File;
 using Ocelot.Responses;
 using System;
 using System.Threading.Tasks;
+using Ocelot.Configuration.ChangeTracking;
 
 namespace Ocelot.Configuration.Repository
 {
     public class DiskFileConfigurationRepository : IFileConfigurationRepository
     {
+        private readonly IOcelotConfigurationChangeTokenSource _changeTokenSource;
         private readonly string _environmentFilePath;
         private readonly string _ocelotFilePath;
         private static readonly object _lock = new object();
         private const string ConfigurationFileName = "ocelot";
 
-        public DiskFileConfigurationRepository(IWebHostEnvironment hostingEnvironment)
+        public DiskFileConfigurationRepository(IWebHostEnvironment hostingEnvironment, IOcelotConfigurationChangeTokenSource changeTokenSource)
         {
+            _changeTokenSource = changeTokenSource;
             _environmentFilePath = $"{AppContext.BaseDirectory}{ConfigurationFileName}{(string.IsNullOrEmpty(hostingEnvironment.EnvironmentName) ? string.Empty : ".")}{hostingEnvironment.EnvironmentName}.json";
 
             _ocelotFilePath = $"{AppContext.BaseDirectory}{ConfigurationFileName}.json";
@@ -56,6 +59,7 @@ namespace Ocelot.Configuration.Repository
                 System.IO.File.WriteAllText(_ocelotFilePath, jsonConfiguration);
             }
 
+            _changeTokenSource.Activate();
             return Task.FromResult<Response>(new OkResponse());
         }
     }

src/Ocelot/Configuration/Repository/InMemoryInternalConfigurationRepository.cs

@@ -1,4 +1,5 @@
-using Ocelot.Responses;
+using Ocelot.Configuration.ChangeTracking;
+using Ocelot.Responses;
 
 namespace Ocelot.Configuration.Repository
 {
@@ -10,6 +11,12 @@ namespace Ocelot.Configuration.Repository
         private static readonly object LockObject = new object();
 
         private IInternalConfiguration _internalConfiguration;
+        private readonly IOcelotConfigurationChangeTokenSource _changeTokenSource;
+
+        public InMemoryInternalConfigurationRepository(IOcelotConfigurationChangeTokenSource changeTokenSource)
+        {
+            _changeTokenSource = changeTokenSource;
+        }
 
         public Response<IInternalConfiguration> Get()
         {
@@ -23,6 +30,7 @@ namespace Ocelot.Configuration.Repository
                 _internalConfiguration = internalConfiguration;
             }
 
+            _changeTokenSource.Activate();
             return new OkResponse();
         }
     }

src/Ocelot/DependencyInjection/OcelotBuilder.cs

@@ -1,9 +1,12 @@
+using Ocelot.Configuration.ChangeTracking;
+
 namespace Ocelot.DependencyInjection
 {
     using Microsoft.AspNetCore.Http;
     using Microsoft.Extensions.Configuration;
     using Microsoft.Extensions.DependencyInjection;
     using Microsoft.Extensions.DependencyInjection.Extensions;
+    using Microsoft.Extensions.Options;
     using Ocelot.Authorisation;
     using Ocelot.Cache;
     using Ocelot.Claims;
@@ -112,6 +115,8 @@ namespace Ocelot.DependencyInjection
             Services.TryAddSingleton<IDownstreamAddressesCreator, DownstreamAddressesCreator>();
             Services.TryAddSingleton<IDelegatingHandlerHandlerFactory, DelegatingHandlerHandlerFactory>();
             Services.TryAddSingleton<ICacheKeyGenerator, CacheKeyGenerator>();
+            Services.TryAddSingleton<IOcelotConfigurationChangeTokenSource, OcelotConfigurationChangeTokenSource>();
+            Services.TryAddSingleton<IOptionsMonitor<IInternalConfiguration>, OcelotConfigurationMonitor>();
 
             // see this for why we register this as singleton http://stackoverflow.com/questions/37371264/invalidoperationexception-unable-to-resolve-service-for-type-microsoft-aspnetc
             // could maybe use a scoped data repository
@@ -215,7 +220,7 @@ namespace Ocelot.DependencyInjection
         {
             // see: https://greatrexpectations.com/2018/10/25/decorators-in-net-core-with-dependency-injection
             var wrappedDescriptor = Services.First(x => x.ServiceType == typeof(IPlaceholders));
-            
+
             var objectFactory = ActivatorUtilities.CreateFactory(
                 typeof(ConfigAwarePlaceholders),
                 new[] { typeof(IPlaceholders) });
@@ -229,7 +234,7 @@ namespace Ocelot.DependencyInjection
 
             return this;
         }
-        
+
         private static object CreateInstance(IServiceProvider services, ServiceDescriptor descriptor)
         {
             if (descriptor.ImplementationInstance != null)

src/Ocelot/Properties/AssemblyInfo.cs

@@ -15,4 +15,4 @@ using System.Runtime.InteropServices;
 [assembly: ComVisible(false)]
 
 // The following GUID is for the ID of the typelib if this project is exposed to COM
-[assembly: Guid("d6df4206-0dba-41d8-884d-c3e08290fdbb")]
+[assembly: Guid("d6df4206-0dba-41d8-884d-c3e08290fdbb")]